- Email: [email protected]
Lessons from anticancer research might provide new insights into mechanisms of hormone action
Research Update
TRENDS in Endocrinology & Metabolism Vol.12 No.3 April 2001
87
Research News
Lessons from anticancer research might provide new insights into mechanisms of hormone action Arthur R. Buckley The extent to which specific anticancer drugs induce apoptosis in tumors frequently predicts the success of chemotherapy for a particular type of cancer. Recent results from experiments designed to evaluate drug-induced apoptosis in colon cancer cells revealed that the levels of BCL-2-related apoptotic suppressor proteins were dramatically reduced compared with those of pro-apoptotic proteins. In the case of nonsteroidal anti-inflammatory drugs, this might be a consequence of inhibition of the cyclooxygenase-mediated production of prostaglandins.
Apoptosis plays a crucial role in tissue development and remodeling, immune function and numerous endocrinological processes, as well as in pathological situations such as cancer. This type of cell death is characterized by activation of a genetic program that includes pro- and anti-apoptotic proteins. Members of the BCL2 gene family are widely recognized as positive and negative regulators of cell death. The founding member of this family, BCL-2, is the prototypic suppressor of apoptosis, whereas an analog, BAX, promotes cell death1. Notably, a variety of hormones have been shown to regulate levels of these proteins, depending upon physiological circumstances, in various target tissues. Much of the evidence accumulated to date suggests that the BCL-2:BAX ratio functions as a rheostat to modulate cellular fate. Thus, if the ratio is low, apoptosis is favored; if BCL-2 predominates, cells survive. However, because most studies have relied upon using overexpression or gene disruption as experimental approaches, which might not accurately mimic physiological situations, conflicting results concerning the roles of death regulators have been reported. Moreover, variations between mice and humans with respect to transcriptional regulation of these genes have also contributed to the confusion2.
Using the colorectal cancer HCT116 cell line as a model, Zhang et al.1 evaluated the apoptotic effects of the chemotherapeutic agent 5-fluorouracil (5-FU), and the nonsteroidal antiinflammatory drugs (NSAIDs) indomethacin and sulindac, in isogenic cells solely differing in BAX levels. In cells lacking functional BAX genes, apoptosis induced by 5-FU, which uses a p53-dependent process, was reduced but not eliminated, indicating that BAX-independent mechanisms contribute to the action of this compound. By contrast, the apoptotic effect of the NSAIDs was completely abrogated by loss of BAX, suggesting that the functional BAX protein is required for cell death induced by these drugs. Not only did NSAID-induced apoptosis require BAX, but it was also independent of p53 status. Other experiments were conducted to determine whether anti-apoptotic BCL-2 family members contributed to the results observed. Although BCL-2 itself was not detected in HCT116 cells, BCL-XL, another anti-apoptotic family member, was reduced at both the mRNA and protein levels following exposure to NSAIDs. In addition to HCT116 cells, treatment with NSAIDs also reduced BCL-XL levels in the majority of colorectal cancer cell lines investigated, whereas BAX levels remained unchanged. These observations, together with those from other experiments, convincingly demonstrated that the ratio of antiapoptotic BCL-2 family proteins to BAX plays a key role in the susceptibility of cells to apoptosis induced by NSAIDs. NSAIDs have also been shown to be chemopreventative against additional tumor types, including cancers of the lung and breast3, and to induce apoptosis in human myeloid leukemias in vitro4. The mechanism by which these drugs exert these effects reflects their capacity to inhibit cyclooxygenase (COX). COX is the rate-limiting enzyme in the pathway that catalyzes the conversion of arachidonic acid to prostaglandin H, the precursor
molecule in the synthesis of prostacyclin, thromboxane and prostaglandins D, E and F. The enzyme exists as two isoforms, COX-1 and COX-2, which exhibit 61% homology in humans. These isoforms are products of different genes. The two proteins are structurally and enzymatically similar, and have nearly identical molecular weights. COX-1 is constitutively expressed in many tissues, whereas COX-2 is highly induced by inflammatory stimuli and blastocyst implantation, and during cell growth and apoptosis. Additionally, COX-2, but not COX-1, levels are elevated in several cancer types. These observations have given rise to the hypothesis that COX-2 might be central to carcinogenesis. The widely recognized ability of NSAIDs to inhibit COX, together with the observation that these drugs downregulated BCL-XL in HCT116 cells, suggests that one or more prostaglandins could be responsible for maintaining sufficient levels of apoptosis suppressor proteins to insure cell survival. Prostanoids, produced as a consequence of COX catalytic activity, are examples of ‘local’ hormones that primarily affect cellular targets through paracrine or autocrine mechanisms. Signals are transduced by these fatty acid derivatives subsequent to their interaction with seven transmembrane receptors which, by coupling to various guanine nucleotidebinding proteins, signal to distinct downstream pathways. As indicated, elevated levels of COX-2, as observed in several tumor models, are associated with increased cellular proliferation and resistance to apoptosis. In both human intestinal epithelial cells5 and transformed mammary epithelial cells6, overexpression of COX-2 inhibits apoptotic cell death. In addition, growth of human HCA-7 colon cancer cell xenografts, which express COX-2, was blocked by treatment with a highly selective inhibitor (SC-58125) of this enzyme. In culture, colony formation by HCA-7 cells was inhibited and apoptosis
http://tem.trends.com 1043-2760/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S1043-2760(01)00380-0
Research Update
88
TRENDS in Endocrinology & Metabolism Vol.12 No.3 April 2001
Estrogens Progesterone α
AA
PGs
PGs
COX-1 COX-2
β
γ
BCL-2 BCL-XL Survivin
Blastocyst implantation
COX mRNA
TRENDS in Endocrinology & Metabolism
Fig. 1. Schematic representation of the proposed role of prostanoids in the regulation of endometrial sensitivity to apoptosis. Abbreviations: AA, arachidonic acid; COX, cyclooxygenase; PGs, prostaglandins.
expression of apoptosis-regulatory genes. It is tempting to speculate that prostanoids produced in response to hormone-activated COX, regulate the downstream expression of apoptosisassociated genes (Fig. 1). Thus, during the proliferative and secretory phases of the endometrium, stimulation by estrogens and progesterone might lead to increased expression of apoptosis suppression genes such as those encoding BCL-2, BCL-XL or survivin, via a COX-dependent mechanism. The decrease in progesterone levels, in turn, might reduce COX levels or activity, with concurrent parallel decreases in the levels of apoptosis suppressor proteins relative to those of proapoptotic proteins. Acknowledgements
was increased by SC-58125. However, treatment with prostaglandin E2 increased clonogenicity, augmented BCL-2 protein levels, and reversed the effects of the COX-2 inhibitor7. Thus, it appears that COX-2-mediated prostanoid synthesis is required both for growth and for suppression of apoptosis mediated by BCL-2 analogs. Whereas proliferation and suppression of apoptosis appear to be coupled in a number of hormone target tissues, a role for COX-generated prostanoids in these processes has not been fully evaluated. For example, prolactin is mitogenic in rat Nb2 lymphoma cells, a paradigm in which it also blocks apoptosis, presumably by induction of BCL-2 and other apoptotic suppressors8. Whether these effects of the hormone reflect activation of COX and subsequent prostanoid production has not been assessed. However, the uterus is an example of a hormone-responsive tissue in which COX-1 and COX-2 are expressed and prostanoids are known to be crucially important. In this organ, estrogen and progesterone control growth, differentiation and apoptosis of endometrial epithelium. Prostanoids are thought to provoke uterine contraction and relaxation during parturition, and are also required for ovulation, fertilization, embryo implantation and maintenance of patency of the fetal ductus arteriosus. Although both COX1 and COX2 are expressed in the uterine endometrium, the two genes appear to be differentially regulated. Estrogens and progesterone stimulate COX1, but not COX2, expression. By http://tem.trends.com
contrast, COX2 is regulated by the implanting blastocyst9. In the myometrium, COX2 expression is induced by inflammatory cytokines such as interleukin-1β (Ref. 10). Studies using targeted disruption of the COX genes have provided important insights into the roles of uterine prostanoids. COX1−/− mice exhibit delayed parturition and reduced pup survival, whereas COX2 −/− mice are infertile11. Apoptosis, an important process in the uterine endometrium, takes place in the glandular epithelium, primarily during the late secretory and menstrual phases. Estrogens stimulate proliferation of endometrial cells and progesterone ultimately induces differentiation. Here, the steroids are required for normal growth and differentiation. Elimination of steroidal action, by ovariectomy or administration of antiprogestin drugs, profoundly induces endometrial apoptosis12, indicating that the hormones are necessary for cell survival. In addition, progestins have been shown to facilitate survival in vitro. In this setting, the addition of progesterone also increased the expression of BCL-2-related apoptosis suppressor genes relative to those that activate cell death13. Results from other studies showed that progesterone also induced expression of survivin, a novel inhibitor of apoptosis, in the endometrium during the secretory phase of the human menstrual cycle14. Therefore, just as with COX expression, the hormonal environment determines whether cells proliferate, differentiate or are removed, as a consequence of altered
Work in the author’s laboratory is supported by DK53452 from the National Institutes of Health and by the American Institute for Cancer Research. References 1 Zhang, L. et al. (2000) Role of BAX in the apoptotic response to anticancer agents. Science 290, 989–992 2 Schmidt, T. et al. (1999) The activity of the murine BAX promoter is regulated by Sp1/3 and E-box binding proteins but not by p53. Cell Death Differ. 6, 873–882 3 Fosslein, E. (2000) Biochemistry of cyclooxygenase (COX)-2 inhibitors and molecular pathology of COX-2 in neoplasia. Crit. Rev. Clin. Lab. Sci. 37, 431–502 4 Klampfer, L. et al. (1999) Sodium salicylate activates caspases and induces apoptosis of myeloid leukemia cell lines. Blood 93, 2386–2394 5 Battu, S. et al. (1998) Resistance to apoptosis and cyclooxygenase-2 gene expression in a human adenocarcinoma cell line HT29 Cl.19A. Anticancer Res. 18, 3579–3583 6 Subbaramaiah, K. et al. (1997) Cyclooxygenase-2 gene expression is upregulated in transformed mammary epithelial cells. Ann. New York Acad. Sci. 833, 179–185 7 Sheng, H. et al. (1998) Modulation of apoptosis and BCL2 expression by prostaglandin E2 in human colon cancer cells. Cancer Res. 58, 362–366 8 Leff, M.A. et al. (1996) Rapid modulation of the apoptosis regulatory genes, BCL2 and BAX by prolactin in rat Nb2 lymphoma cells. Endocrinology 137, 5456–5462 9 Chakraborty, I. et al. (1996) Developmental expression of the cyclo-oxygenase-1 and cyclooxygenase-2 genes in the peri-implantation mouse uterus and their differential regulation by the blastocyst and ovarian steroids. J. Mol. Endocrinol. 16, 107–122 10 Erkinheimo, T-L. et al. (2000) Expression of cyclooxygenase-2 and prostanoid receptors by human myometrium. J. Clin. Endocrinol. Metab. 85, 3468–3475
Research Update
11 Reese, J. et al. (2000) Coordinated regulation of fetal and maternal prostaglandins directs successful birth and postnatal adaptation in the mouse. Proc. Natl. Acad. Sci. U. S. A. 97, 9759–9764 12 Rotello, R.J. et al. (1992) Characterization of uterine epithelium apoptotic cell death kinetics and regulation by progesterone and RU 486.
TRENDS in Endocrinology & Metabolism Vol.12 No.3 April 2001
Am. J. Pathol. 140, 449–456 13 Pecci, A. et al. (1997) Progestins prevent apoptosis in a rat endometrial cell line and increase the ratio of bcl-XL to bcl-XS. J. Biol. Chem. 272, 11791–11798 14 Konno, R. et al. (2000) Expression of survivin and BCL2 in the normal human endometrium. Mol. Hum. Reprod. 6, 529–534
89
Arthur R. Buckley College of Pharmacy and Dept of Molecular and Cellular Physiology, University of Cincinnati Medical Center, 3223 Eden Ave, PO Box 670004, Cincinnati, OH 45267-0004, USA. e-mail: [email protected]
Meeting Report
Relaxin on the beach Richard Ivell The Relaxin 2000: 3rd International Conference on Relaxin and Related Peptides meeting was held on 22–27 October 2000 in Broome, Australia.
In October 2000, relaxinologists from around the world met at Broome to discuss the latest findings about the relaxin family of peptide hormones. This was the third in a series of international conferences on this theme, each held at roughly five-year intervals. The meeting began with a broad discussion on the better-known functions of relaxin in the context of the reproductive system. David Sherwood and Shangping Zhao (University of Illinois, Urbana-Champaign, IL, USA) discussed the remodeling associated with pregnancy and parturition, particularly the influence of relaxin on apoptosis in the rat cervix. By describing studies of relaxin knockout mice, Ling Zhao (Howard Florey Institute, University of Melbourne, VIC, Australia) showed that, in female rodents, the major roles for relaxin are in the preparation of the uterus and cervix for parturition and in the development of the nipples before suckling. These appear to be primitive traits because a similar relaxin-dependent physiology was also described for a marsupial, the tammar wallaby [Laura Parry and Ross Bathgate (Howard Florey Institute)]. In primates, including the human, the situation appears to be somewhat different. Relaxin still aids the birth process by encouraging cervical softening and pubic widening; indeed, Ida Vogel (Skejby Hospital, Aarhus, Denmark) showed that serum relaxin levels can be a good predictor for preterm delivery. However, in primates, circulating levels of the hormone are much lower than those seen in many non-primate
mammals, and are generally maximal in the first half of pregnancy, in particular around the time of implantation. One of the most elegant presentations at the meeting was that by Almuth Einspanier (German Primate Centre, Göttingen, Germany), who described how he used the marmoset monkey to study relaxin expression in the ovary and uterus through the cycle and pregnancy, and the effects of relaxin, in combination with steroids, on implantation, pregnancy success and birth parameters. Because the function of relaxin in this model is very similar to that seen in the human, it will probably be of great value in relaxin research with relevance for the human. Many of the presentations [Gerson Weiss (New Jersey Medical School, Newark, NJ, USA), Elaine Unamori (Connetics Corporation, Palo Alto, CA, USA), Carol Bagnell (Rutgers University, New Brunswick, NJ, USA) and Suresh Pillai (University of Maryland School of Medicine, Baltimore, MD, USA)] discussed the role of relaxin in inducing vascular endothelial growth factor (VEGF) expression and hence angiogenesis. It is well known that relaxin is very important in inducing the differentiation of endometrial stromal cells (ESCs) in a process known as decidualization in primates. This differentiation step is a prerequisite for successful implantation, which largely depends on the stimulation of VEGFinduced uterine angiogenesis. In addition, Robert Koos (University of Maryland School of Medicine) showed how relaxin interacts with estradiol, possibly involving the vascular permeability properties of VEGF, to cause the uterine edema associated with estradiol application. His experiments very nicely supported the
in vivo observations in the marmoset model shown by Einspanier. These experiments point to a role for relaxin in uterine responsiveness and implantation, and also potentially in later stages of placental development and trophoblast invasion. Peter Ryan (Mississippi State University, MS, USA) presented data suggesting a relationship between circulating relaxin and placental dysfunction, whereas Thomas Klonisch (Martin-Luther University Faculty of Medicine, Halle, Germany) identified local relaxin production in placental tissues that are involved in establishing and maintaining maternal–fetal exchange. An important take-home from the meeting was that relaxin is not restricted to a single organ, neither in its biosynthesis nor its effects. In addition to the uterus, relaxin is synthesized in the ovary, in both the follicular theca cells and the corpus luteum (indeed, the latter is the major source of circulating relaxin in most mammals). Evidence for a role of intraovarian relaxin in luteinization (a differentiation process in which the corpus luteum upregulates progesterone production under the influence of gonadotropins) was presented by Einspanier. A similar role for relaxin as a paracrine mediator of differentiation in the thyroid gland and the breast was also suggested by Klonisch. Relaxin has recently been linked with the remodeling of connective tissue. Earlier studies showed that relaxin inhibited the formation of fibrotic lesions in rats, and had a beneficial influence on the phenotype of scleroderma fibroblasts in vitro. Furthermore, early clinical trials suggested that relaxin was effective in ameliorating the symptoms of scleroderma in severely handicapped patients.
http://tem.trends.com 1043-2760/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S1043-2760(00)00371-4
TRENDS in Endocrinology & Metabolism Vol.12 No.3 April 2001
87
Research News
Lessons from anticancer research might provide new insights into mechanisms of hormone action Arthur R. Buckley The extent to which specific anticancer drugs induce apoptosis in tumors frequently predicts the success of chemotherapy for a particular type of cancer. Recent results from experiments designed to evaluate drug-induced apoptosis in colon cancer cells revealed that the levels of BCL-2-related apoptotic suppressor proteins were dramatically reduced compared with those of pro-apoptotic proteins. In the case of nonsteroidal anti-inflammatory drugs, this might be a consequence of inhibition of the cyclooxygenase-mediated production of prostaglandins.
Apoptosis plays a crucial role in tissue development and remodeling, immune function and numerous endocrinological processes, as well as in pathological situations such as cancer. This type of cell death is characterized by activation of a genetic program that includes pro- and anti-apoptotic proteins. Members of the BCL2 gene family are widely recognized as positive and negative regulators of cell death. The founding member of this family, BCL-2, is the prototypic suppressor of apoptosis, whereas an analog, BAX, promotes cell death1. Notably, a variety of hormones have been shown to regulate levels of these proteins, depending upon physiological circumstances, in various target tissues. Much of the evidence accumulated to date suggests that the BCL-2:BAX ratio functions as a rheostat to modulate cellular fate. Thus, if the ratio is low, apoptosis is favored; if BCL-2 predominates, cells survive. However, because most studies have relied upon using overexpression or gene disruption as experimental approaches, which might not accurately mimic physiological situations, conflicting results concerning the roles of death regulators have been reported. Moreover, variations between mice and humans with respect to transcriptional regulation of these genes have also contributed to the confusion2.
Using the colorectal cancer HCT116 cell line as a model, Zhang et al.1 evaluated the apoptotic effects of the chemotherapeutic agent 5-fluorouracil (5-FU), and the nonsteroidal antiinflammatory drugs (NSAIDs) indomethacin and sulindac, in isogenic cells solely differing in BAX levels. In cells lacking functional BAX genes, apoptosis induced by 5-FU, which uses a p53-dependent process, was reduced but not eliminated, indicating that BAX-independent mechanisms contribute to the action of this compound. By contrast, the apoptotic effect of the NSAIDs was completely abrogated by loss of BAX, suggesting that the functional BAX protein is required for cell death induced by these drugs. Not only did NSAID-induced apoptosis require BAX, but it was also independent of p53 status. Other experiments were conducted to determine whether anti-apoptotic BCL-2 family members contributed to the results observed. Although BCL-2 itself was not detected in HCT116 cells, BCL-XL, another anti-apoptotic family member, was reduced at both the mRNA and protein levels following exposure to NSAIDs. In addition to HCT116 cells, treatment with NSAIDs also reduced BCL-XL levels in the majority of colorectal cancer cell lines investigated, whereas BAX levels remained unchanged. These observations, together with those from other experiments, convincingly demonstrated that the ratio of antiapoptotic BCL-2 family proteins to BAX plays a key role in the susceptibility of cells to apoptosis induced by NSAIDs. NSAIDs have also been shown to be chemopreventative against additional tumor types, including cancers of the lung and breast3, and to induce apoptosis in human myeloid leukemias in vitro4. The mechanism by which these drugs exert these effects reflects their capacity to inhibit cyclooxygenase (COX). COX is the rate-limiting enzyme in the pathway that catalyzes the conversion of arachidonic acid to prostaglandin H, the precursor
molecule in the synthesis of prostacyclin, thromboxane and prostaglandins D, E and F. The enzyme exists as two isoforms, COX-1 and COX-2, which exhibit 61% homology in humans. These isoforms are products of different genes. The two proteins are structurally and enzymatically similar, and have nearly identical molecular weights. COX-1 is constitutively expressed in many tissues, whereas COX-2 is highly induced by inflammatory stimuli and blastocyst implantation, and during cell growth and apoptosis. Additionally, COX-2, but not COX-1, levels are elevated in several cancer types. These observations have given rise to the hypothesis that COX-2 might be central to carcinogenesis. The widely recognized ability of NSAIDs to inhibit COX, together with the observation that these drugs downregulated BCL-XL in HCT116 cells, suggests that one or more prostaglandins could be responsible for maintaining sufficient levels of apoptosis suppressor proteins to insure cell survival. Prostanoids, produced as a consequence of COX catalytic activity, are examples of ‘local’ hormones that primarily affect cellular targets through paracrine or autocrine mechanisms. Signals are transduced by these fatty acid derivatives subsequent to their interaction with seven transmembrane receptors which, by coupling to various guanine nucleotidebinding proteins, signal to distinct downstream pathways. As indicated, elevated levels of COX-2, as observed in several tumor models, are associated with increased cellular proliferation and resistance to apoptosis. In both human intestinal epithelial cells5 and transformed mammary epithelial cells6, overexpression of COX-2 inhibits apoptotic cell death. In addition, growth of human HCA-7 colon cancer cell xenografts, which express COX-2, was blocked by treatment with a highly selective inhibitor (SC-58125) of this enzyme. In culture, colony formation by HCA-7 cells was inhibited and apoptosis
http://tem.trends.com 1043-2760/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S1043-2760(01)00380-0
Research Update
88
TRENDS in Endocrinology & Metabolism Vol.12 No.3 April 2001
Estrogens Progesterone α
AA
PGs
PGs
COX-1 COX-2
β
γ
BCL-2 BCL-XL Survivin
Blastocyst implantation
COX mRNA
TRENDS in Endocrinology & Metabolism
Fig. 1. Schematic representation of the proposed role of prostanoids in the regulation of endometrial sensitivity to apoptosis. Abbreviations: AA, arachidonic acid; COX, cyclooxygenase; PGs, prostaglandins.
expression of apoptosis-regulatory genes. It is tempting to speculate that prostanoids produced in response to hormone-activated COX, regulate the downstream expression of apoptosisassociated genes (Fig. 1). Thus, during the proliferative and secretory phases of the endometrium, stimulation by estrogens and progesterone might lead to increased expression of apoptosis suppression genes such as those encoding BCL-2, BCL-XL or survivin, via a COX-dependent mechanism. The decrease in progesterone levels, in turn, might reduce COX levels or activity, with concurrent parallel decreases in the levels of apoptosis suppressor proteins relative to those of proapoptotic proteins. Acknowledgements
was increased by SC-58125. However, treatment with prostaglandin E2 increased clonogenicity, augmented BCL-2 protein levels, and reversed the effects of the COX-2 inhibitor7. Thus, it appears that COX-2-mediated prostanoid synthesis is required both for growth and for suppression of apoptosis mediated by BCL-2 analogs. Whereas proliferation and suppression of apoptosis appear to be coupled in a number of hormone target tissues, a role for COX-generated prostanoids in these processes has not been fully evaluated. For example, prolactin is mitogenic in rat Nb2 lymphoma cells, a paradigm in which it also blocks apoptosis, presumably by induction of BCL-2 and other apoptotic suppressors8. Whether these effects of the hormone reflect activation of COX and subsequent prostanoid production has not been assessed. However, the uterus is an example of a hormone-responsive tissue in which COX-1 and COX-2 are expressed and prostanoids are known to be crucially important. In this organ, estrogen and progesterone control growth, differentiation and apoptosis of endometrial epithelium. Prostanoids are thought to provoke uterine contraction and relaxation during parturition, and are also required for ovulation, fertilization, embryo implantation and maintenance of patency of the fetal ductus arteriosus. Although both COX1 and COX2 are expressed in the uterine endometrium, the two genes appear to be differentially regulated. Estrogens and progesterone stimulate COX1, but not COX2, expression. By http://tem.trends.com
contrast, COX2 is regulated by the implanting blastocyst9. In the myometrium, COX2 expression is induced by inflammatory cytokines such as interleukin-1β (Ref. 10). Studies using targeted disruption of the COX genes have provided important insights into the roles of uterine prostanoids. COX1−/− mice exhibit delayed parturition and reduced pup survival, whereas COX2 −/− mice are infertile11. Apoptosis, an important process in the uterine endometrium, takes place in the glandular epithelium, primarily during the late secretory and menstrual phases. Estrogens stimulate proliferation of endometrial cells and progesterone ultimately induces differentiation. Here, the steroids are required for normal growth and differentiation. Elimination of steroidal action, by ovariectomy or administration of antiprogestin drugs, profoundly induces endometrial apoptosis12, indicating that the hormones are necessary for cell survival. In addition, progestins have been shown to facilitate survival in vitro. In this setting, the addition of progesterone also increased the expression of BCL-2-related apoptosis suppressor genes relative to those that activate cell death13. Results from other studies showed that progesterone also induced expression of survivin, a novel inhibitor of apoptosis, in the endometrium during the secretory phase of the human menstrual cycle14. Therefore, just as with COX expression, the hormonal environment determines whether cells proliferate, differentiate or are removed, as a consequence of altered
Work in the author’s laboratory is supported by DK53452 from the National Institutes of Health and by the American Institute for Cancer Research. References 1 Zhang, L. et al. (2000) Role of BAX in the apoptotic response to anticancer agents. Science 290, 989–992 2 Schmidt, T. et al. (1999) The activity of the murine BAX promoter is regulated by Sp1/3 and E-box binding proteins but not by p53. Cell Death Differ. 6, 873–882 3 Fosslein, E. (2000) Biochemistry of cyclooxygenase (COX)-2 inhibitors and molecular pathology of COX-2 in neoplasia. Crit. Rev. Clin. Lab. Sci. 37, 431–502 4 Klampfer, L. et al. (1999) Sodium salicylate activates caspases and induces apoptosis of myeloid leukemia cell lines. Blood 93, 2386–2394 5 Battu, S. et al. (1998) Resistance to apoptosis and cyclooxygenase-2 gene expression in a human adenocarcinoma cell line HT29 Cl.19A. Anticancer Res. 18, 3579–3583 6 Subbaramaiah, K. et al. (1997) Cyclooxygenase-2 gene expression is upregulated in transformed mammary epithelial cells. Ann. New York Acad. Sci. 833, 179–185 7 Sheng, H. et al. (1998) Modulation of apoptosis and BCL2 expression by prostaglandin E2 in human colon cancer cells. Cancer Res. 58, 362–366 8 Leff, M.A. et al. (1996) Rapid modulation of the apoptosis regulatory genes, BCL2 and BAX by prolactin in rat Nb2 lymphoma cells. Endocrinology 137, 5456–5462 9 Chakraborty, I. et al. (1996) Developmental expression of the cyclo-oxygenase-1 and cyclooxygenase-2 genes in the peri-implantation mouse uterus and their differential regulation by the blastocyst and ovarian steroids. J. Mol. Endocrinol. 16, 107–122 10 Erkinheimo, T-L. et al. (2000) Expression of cyclooxygenase-2 and prostanoid receptors by human myometrium. J. Clin. Endocrinol. Metab. 85, 3468–3475
Research Update
11 Reese, J. et al. (2000) Coordinated regulation of fetal and maternal prostaglandins directs successful birth and postnatal adaptation in the mouse. Proc. Natl. Acad. Sci. U. S. A. 97, 9759–9764 12 Rotello, R.J. et al. (1992) Characterization of uterine epithelium apoptotic cell death kinetics and regulation by progesterone and RU 486.
TRENDS in Endocrinology & Metabolism Vol.12 No.3 April 2001
Am. J. Pathol. 140, 449–456 13 Pecci, A. et al. (1997) Progestins prevent apoptosis in a rat endometrial cell line and increase the ratio of bcl-XL to bcl-XS. J. Biol. Chem. 272, 11791–11798 14 Konno, R. et al. (2000) Expression of survivin and BCL2 in the normal human endometrium. Mol. Hum. Reprod. 6, 529–534
89
Arthur R. Buckley College of Pharmacy and Dept of Molecular and Cellular Physiology, University of Cincinnati Medical Center, 3223 Eden Ave, PO Box 670004, Cincinnati, OH 45267-0004, USA. e-mail: [email protected]
Meeting Report
Relaxin on the beach Richard Ivell The Relaxin 2000: 3rd International Conference on Relaxin and Related Peptides meeting was held on 22–27 October 2000 in Broome, Australia.
In October 2000, relaxinologists from around the world met at Broome to discuss the latest findings about the relaxin family of peptide hormones. This was the third in a series of international conferences on this theme, each held at roughly five-year intervals. The meeting began with a broad discussion on the better-known functions of relaxin in the context of the reproductive system. David Sherwood and Shangping Zhao (University of Illinois, Urbana-Champaign, IL, USA) discussed the remodeling associated with pregnancy and parturition, particularly the influence of relaxin on apoptosis in the rat cervix. By describing studies of relaxin knockout mice, Ling Zhao (Howard Florey Institute, University of Melbourne, VIC, Australia) showed that, in female rodents, the major roles for relaxin are in the preparation of the uterus and cervix for parturition and in the development of the nipples before suckling. These appear to be primitive traits because a similar relaxin-dependent physiology was also described for a marsupial, the tammar wallaby [Laura Parry and Ross Bathgate (Howard Florey Institute)]. In primates, including the human, the situation appears to be somewhat different. Relaxin still aids the birth process by encouraging cervical softening and pubic widening; indeed, Ida Vogel (Skejby Hospital, Aarhus, Denmark) showed that serum relaxin levels can be a good predictor for preterm delivery. However, in primates, circulating levels of the hormone are much lower than those seen in many non-primate
mammals, and are generally maximal in the first half of pregnancy, in particular around the time of implantation. One of the most elegant presentations at the meeting was that by Almuth Einspanier (German Primate Centre, Göttingen, Germany), who described how he used the marmoset monkey to study relaxin expression in the ovary and uterus through the cycle and pregnancy, and the effects of relaxin, in combination with steroids, on implantation, pregnancy success and birth parameters. Because the function of relaxin in this model is very similar to that seen in the human, it will probably be of great value in relaxin research with relevance for the human. Many of the presentations [Gerson Weiss (New Jersey Medical School, Newark, NJ, USA), Elaine Unamori (Connetics Corporation, Palo Alto, CA, USA), Carol Bagnell (Rutgers University, New Brunswick, NJ, USA) and Suresh Pillai (University of Maryland School of Medicine, Baltimore, MD, USA)] discussed the role of relaxin in inducing vascular endothelial growth factor (VEGF) expression and hence angiogenesis. It is well known that relaxin is very important in inducing the differentiation of endometrial stromal cells (ESCs) in a process known as decidualization in primates. This differentiation step is a prerequisite for successful implantation, which largely depends on the stimulation of VEGFinduced uterine angiogenesis. In addition, Robert Koos (University of Maryland School of Medicine) showed how relaxin interacts with estradiol, possibly involving the vascular permeability properties of VEGF, to cause the uterine edema associated with estradiol application. His experiments very nicely supported the
in vivo observations in the marmoset model shown by Einspanier. These experiments point to a role for relaxin in uterine responsiveness and implantation, and also potentially in later stages of placental development and trophoblast invasion. Peter Ryan (Mississippi State University, MS, USA) presented data suggesting a relationship between circulating relaxin and placental dysfunction, whereas Thomas Klonisch (Martin-Luther University Faculty of Medicine, Halle, Germany) identified local relaxin production in placental tissues that are involved in establishing and maintaining maternal–fetal exchange. An important take-home from the meeting was that relaxin is not restricted to a single organ, neither in its biosynthesis nor its effects. In addition to the uterus, relaxin is synthesized in the ovary, in both the follicular theca cells and the corpus luteum (indeed, the latter is the major source of circulating relaxin in most mammals). Evidence for a role of intraovarian relaxin in luteinization (a differentiation process in which the corpus luteum upregulates progesterone production under the influence of gonadotropins) was presented by Einspanier. A similar role for relaxin as a paracrine mediator of differentiation in the thyroid gland and the breast was also suggested by Klonisch. Relaxin has recently been linked with the remodeling of connective tissue. Earlier studies showed that relaxin inhibited the formation of fibrotic lesions in rats, and had a beneficial influence on the phenotype of scleroderma fibroblasts in vitro. Furthermore, early clinical trials suggested that relaxin was effective in ameliorating the symptoms of scleroderma in severely handicapped patients.
http://tem.trends.com 1043-2760/01/$ – see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S1043-2760(00)00371-4