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Apoptosis and Benign Prostatic Hypertrophy
Vol. 158,2-3, July 1997 Printed in U . S A
This Month in Investigative Urology APOPTOSIS AND BENIGN PROSTATIC HYPERTROPHY Two papers in this month’s Investigative Urology Section discuss the regulation of cell growth in benign prostatic hypertrophy. These articles both discuss the important biologic phenomenon of apoptosis, also known as programmed cell death. Apoptosis is now recognized as a critical biologic process not only in the physiology of normal cells, but in various disease states, both benign and malignant. While once thought of as a topic to be discussed only among basic scientists, understanding how to trigger apoptosis is now the basis for many clinical therapeutic strategies. Inducing a cancer or hyperplastic cell to undergo programmed cell death through a clinical intervention necessitates an understanding of the unique pathways by which cells govern both apoptosis and proliferation. The development and maintenance of any human organ relies upon the balance of cell proliferation and cell death. If there is any alteration in this process, the organ will not be able to maintain homeostasis, resulting in growth or involution. Alterations in the balance of apoptosis and proliferation are readily apparent in cancer, but are more subtle in common diseases such as benign prostatic hyperplasia. Apoptosis was first described in the 1970’s and is derived from the Greek “apo” for apart and “ptosis” for fallen. Apoptosis is an energy dependent, orderly, irreversible cellular process that leads to cell death and is distinct from necrosis.’ A cell undergoing necrosis will undergo swelling, membrane rupture and cellular bursting. The sine qua non of apoptosis is a dramatic change in the structure of the nucleus. The nucleus will condense upon itself and become pyknotic. Apoptosis is characterized by DNA fragmentation, intracellular autolysis, cellular lysis and ultimately by phagocytosis of the cellular debris.’ While cell death caused by necrosis is not a precisely controlled event, apoptosis can be precisely controlled on a cell by cell basis. As an example of this precision, apoptosis is important in limb bud development during embryogenesis. The tissues between the digits undergo highly selective cell death (apoptosis), resulting in the formation of functional digits. Apoptosis can oRen be identified histologically on routine samples by a highly trained pathologist. However, newer molecular techniques have allowed a more accurate assessment of apoptosis. One commonly used approach is the TUNEL assay (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling) that allows the identification of specific cells undergoing apoptosis. Likewise, identification of proliferating cells using immunohistochemical staining for proliferation markers such as Ki-67 allows these cells to be more clearly identified. These basic techniques allow assessment of both proliferation and apoptotic indices in a given tissue sample and hence allow the identification of any imbalance between cell proliferation and cell death. These techniques are described in this month’s articles by Cardillo et al. and Claus et al. How is apoptosis triggered? What are the mechanisms that will cause a cell to undergo this selective involution? Many cells have preprogrammed intrinsic “time clocks” that trigger cell death. Exogenous factors such as ionizing radiation, viral infection, chemicals, growth factors and hormones to name a few have been identified as apoptotic triggers in various cells. For common diseases of the prostate, the hormonal pathways that regulate cell growth and involution are key in the pathophysiology of both prostate cancer and benign prostatic hyperplasia.2 Studies have shown that androgens are capable of both stimulating cellular proliferation and inhibiting the rate of glandular epithelial cell death.2 The withdrawal of androgens triggers apoptotic cell death in normal prostate epithelium and in androgen sensitive prostate cancer cells. One theory is that androgen independent prostate cells have lost the mechanism to undergo apoptosis with androgen withdrawal. While an understanding of the triggers of apoptosis is a logical step in developing novel therapies for diseases such as benign prostatic hypertrophy and prostate cancer, identifying the factors that block apoptosis are equally important. BCL-Z is an oncoprotein that is unique in its ability to suppress apoptosis in a variety of cells including prostate.3 It has been postulated that BCL-Z expression may be increased after androgen ablation of prostate cancer and BCL-Z may be related to the progression of prostate cancer to the androgen independent state.3 Many of the genes involved in prostate cancer, such as p53, myc and the androgen receptor gene also appear to be involved in the regulation of apoptosis.3 Growth factors such as TGF-beta-1 can induce prostatic apoptosis under physiologic conditions, and in a sense TGF-beta-1 can be viewed as a ”negative growth factoF.4 Apoptotic mechanisms have received much attention in the management of prostate cancer, but there is limited data on the apoptotic mechanisms that may govern benign prostatic hypertrophy. The precise mechanism of the characteristic glandular and stromal hyperplasia seen in BPH remains an area of ongoing clinical and basic science research. As this month’s papers by Claus et al. and Cardillo et al. both suggest, alterations in apoptotic regulation are operational in benign prostatic hypertrophy. Cardillo et al. studied 26 men who underwent hormonal ablation with LH-RH analogues one month before radical prostatectomy. They compared the apoptosis in the pre-treatment biopsy with the radical prostatectomy specimen. With androgen withdrawal, the normal prostatic epithelial cells and the prostate cancer cells demonstrated apoptosis, but in 1 % ~ specimens of benign prostatic hyperplasia these was no identifiable apoptosis. The BCL-2 oncoprotein was upregulated in all of the areas of BPH. They suggest that the BCL-2 expression after androgen deprivation may render the hyperplastic epithelium relatively resistant to apoptosis. In the study by Claus et al., 17 men with BPH treated by open prostatectomy were studied to determine the mean apoptotic and proliferative indices of both the stromal and epithelial cells. Their findings suggest that while the epithelial cells appear to be in a steady state of apoptosis and proliferation, the stromal hyperplasia may be due to cellular proliferation in the absence of cell death. 2
APOPTOSIS AND BENIGN PROSTATIC HYPERTROPHY
3
Understanding t h e mechanisms that regulate cell death and proliferation i n t h e normal, hypertrophied a n d cancerous prostate will allow the development of new therapies, beyond simple androgen ablation, that could induce apoptosis in t h e abnormal prostate tissues.
Leonard G. Gomella and Bernard W. Godwin, Jr. Urologic Oncology, Kimmel Cancer Center, Thomas Jefferson University Philadelphia, Pennsylvania REFERENCES
1. Gupta, S.: Apoptosis/programmed cell death. A historical perspective, Advances in Experimental Medicine and Biology, 406: 1. 1996. 2. Denmeade, S . R., Lin, X. S., Isaacs, J. T.: Role of programmed (apoptotic cell death during the progression and therapy for prostate cancer. Prostate, 28: 251, 1996. 3. Shi, X. B., Gumerlock, P. H. and deVere White, R. W.: Molecular biology of prostate cancer. World J. Urol., 14: 318, 1996. 4. Kyprianou, N., Tu, H. and Jacobs, S. C.: Apoptotic versus proliferative activities in human benign prostatic hyperplasia. Human Pathology, 27: 668, 1996.
This Month in Investigative Urology APOPTOSIS AND BENIGN PROSTATIC HYPERTROPHY Two papers in this month’s Investigative Urology Section discuss the regulation of cell growth in benign prostatic hypertrophy. These articles both discuss the important biologic phenomenon of apoptosis, also known as programmed cell death. Apoptosis is now recognized as a critical biologic process not only in the physiology of normal cells, but in various disease states, both benign and malignant. While once thought of as a topic to be discussed only among basic scientists, understanding how to trigger apoptosis is now the basis for many clinical therapeutic strategies. Inducing a cancer or hyperplastic cell to undergo programmed cell death through a clinical intervention necessitates an understanding of the unique pathways by which cells govern both apoptosis and proliferation. The development and maintenance of any human organ relies upon the balance of cell proliferation and cell death. If there is any alteration in this process, the organ will not be able to maintain homeostasis, resulting in growth or involution. Alterations in the balance of apoptosis and proliferation are readily apparent in cancer, but are more subtle in common diseases such as benign prostatic hyperplasia. Apoptosis was first described in the 1970’s and is derived from the Greek “apo” for apart and “ptosis” for fallen. Apoptosis is an energy dependent, orderly, irreversible cellular process that leads to cell death and is distinct from necrosis.’ A cell undergoing necrosis will undergo swelling, membrane rupture and cellular bursting. The sine qua non of apoptosis is a dramatic change in the structure of the nucleus. The nucleus will condense upon itself and become pyknotic. Apoptosis is characterized by DNA fragmentation, intracellular autolysis, cellular lysis and ultimately by phagocytosis of the cellular debris.’ While cell death caused by necrosis is not a precisely controlled event, apoptosis can be precisely controlled on a cell by cell basis. As an example of this precision, apoptosis is important in limb bud development during embryogenesis. The tissues between the digits undergo highly selective cell death (apoptosis), resulting in the formation of functional digits. Apoptosis can oRen be identified histologically on routine samples by a highly trained pathologist. However, newer molecular techniques have allowed a more accurate assessment of apoptosis. One commonly used approach is the TUNEL assay (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling) that allows the identification of specific cells undergoing apoptosis. Likewise, identification of proliferating cells using immunohistochemical staining for proliferation markers such as Ki-67 allows these cells to be more clearly identified. These basic techniques allow assessment of both proliferation and apoptotic indices in a given tissue sample and hence allow the identification of any imbalance between cell proliferation and cell death. These techniques are described in this month’s articles by Cardillo et al. and Claus et al. How is apoptosis triggered? What are the mechanisms that will cause a cell to undergo this selective involution? Many cells have preprogrammed intrinsic “time clocks” that trigger cell death. Exogenous factors such as ionizing radiation, viral infection, chemicals, growth factors and hormones to name a few have been identified as apoptotic triggers in various cells. For common diseases of the prostate, the hormonal pathways that regulate cell growth and involution are key in the pathophysiology of both prostate cancer and benign prostatic hyperplasia.2 Studies have shown that androgens are capable of both stimulating cellular proliferation and inhibiting the rate of glandular epithelial cell death.2 The withdrawal of androgens triggers apoptotic cell death in normal prostate epithelium and in androgen sensitive prostate cancer cells. One theory is that androgen independent prostate cells have lost the mechanism to undergo apoptosis with androgen withdrawal. While an understanding of the triggers of apoptosis is a logical step in developing novel therapies for diseases such as benign prostatic hypertrophy and prostate cancer, identifying the factors that block apoptosis are equally important. BCL-Z is an oncoprotein that is unique in its ability to suppress apoptosis in a variety of cells including prostate.3 It has been postulated that BCL-Z expression may be increased after androgen ablation of prostate cancer and BCL-Z may be related to the progression of prostate cancer to the androgen independent state.3 Many of the genes involved in prostate cancer, such as p53, myc and the androgen receptor gene also appear to be involved in the regulation of apoptosis.3 Growth factors such as TGF-beta-1 can induce prostatic apoptosis under physiologic conditions, and in a sense TGF-beta-1 can be viewed as a ”negative growth factoF.4 Apoptotic mechanisms have received much attention in the management of prostate cancer, but there is limited data on the apoptotic mechanisms that may govern benign prostatic hypertrophy. The precise mechanism of the characteristic glandular and stromal hyperplasia seen in BPH remains an area of ongoing clinical and basic science research. As this month’s papers by Claus et al. and Cardillo et al. both suggest, alterations in apoptotic regulation are operational in benign prostatic hypertrophy. Cardillo et al. studied 26 men who underwent hormonal ablation with LH-RH analogues one month before radical prostatectomy. They compared the apoptosis in the pre-treatment biopsy with the radical prostatectomy specimen. With androgen withdrawal, the normal prostatic epithelial cells and the prostate cancer cells demonstrated apoptosis, but in 1 % ~ specimens of benign prostatic hyperplasia these was no identifiable apoptosis. The BCL-2 oncoprotein was upregulated in all of the areas of BPH. They suggest that the BCL-2 expression after androgen deprivation may render the hyperplastic epithelium relatively resistant to apoptosis. In the study by Claus et al., 17 men with BPH treated by open prostatectomy were studied to determine the mean apoptotic and proliferative indices of both the stromal and epithelial cells. Their findings suggest that while the epithelial cells appear to be in a steady state of apoptosis and proliferation, the stromal hyperplasia may be due to cellular proliferation in the absence of cell death. 2
APOPTOSIS AND BENIGN PROSTATIC HYPERTROPHY
3
Understanding t h e mechanisms that regulate cell death and proliferation i n t h e normal, hypertrophied a n d cancerous prostate will allow the development of new therapies, beyond simple androgen ablation, that could induce apoptosis in t h e abnormal prostate tissues.
Leonard G. Gomella and Bernard W. Godwin, Jr. Urologic Oncology, Kimmel Cancer Center, Thomas Jefferson University Philadelphia, Pennsylvania REFERENCES
1. Gupta, S.: Apoptosis/programmed cell death. A historical perspective, Advances in Experimental Medicine and Biology, 406: 1. 1996. 2. Denmeade, S . R., Lin, X. S., Isaacs, J. T.: Role of programmed (apoptotic cell death during the progression and therapy for prostate cancer. Prostate, 28: 251, 1996. 3. Shi, X. B., Gumerlock, P. H. and deVere White, R. W.: Molecular biology of prostate cancer. World J. Urol., 14: 318, 1996. 4. Kyprianou, N., Tu, H. and Jacobs, S. C.: Apoptotic versus proliferative activities in human benign prostatic hyperplasia. Human Pathology, 27: 668, 1996.