- Email: [email protected]
New Insights into the Molecular Distinction of Dysplastic Nevi and Common Melanocytic Nevi—Highlighting the Keratinocyte-Melanocyte Relationship
COMMENTARY active promotion of public involvement in research (www.invo.org.uk). However, such efforts will only bear fruit if they are adopted elsewhere, and concerted international effort will still be required to reduce waste in dermatology research, ultimately for the benefit of our patients. Disclaimer The content of this commentary was inspired by a lecture delivered by Professor Hywel Williams at the British Society for Investigative Dermatology Annual Meeting in Dundee on April 4th 2016. CF holds a personal UK National Institute for Health Research (NIHR) Career Development Award. The views expressed in this publication are those of the authors and not necessarily those of the UK National Health Service (NHS), the NIHR, or the UK Department of Health.
CONFLICT OF INTEREST The authors state no conflict of interest.
REFERENCES Chalmers I, Glasziou P. Avoidable waste in the production and reporting of research evidence. Lancet 2009;374:86e9. Chalmers I, Bracken MB, Djulbegovic B, Garattini S, Grant J, Gu¨lmezoglu AM, et al. How to increase value and reduce waste when
research priorities are set. Lancet 2014;383: 156e65. Collins FS. NIH basics. Science 2012;337:503. Cooper NJ, Jones DR, Sutton AJ. The use of systematic reviews when designing studies. Clin Trials 2005;2:260e4. European Medicines Agency. External guidance on the implementation of the European Medicines Agency policy on the publication of clinical data for medicinal products for human use. London: EMA; 2016. Ker K, Edwards P, Perel P, Shakur H, Roberts I. Effect of tranexamic acid on surgical bleeding: systematic review and cumulative metaanalysis. BMJ 2012;344:e3054. Moher D, Avey M, Antes G, Altman DG. The National Institutes of Health and guidance for reporting preclinical research. BMC Med 2015;13:34. Patsopoulos NA, Analatos AA, Ioannidis JP. Relative citation impact of various study designs in the health sciences. JAMA 2005;293:2362e6. Turner EH. How to access and process FDA drug approval packages for use in research. BMJ 2013;347:f5992. Wilkes SR, Nankervis H, Tavernier E, Maruani A, Williams HC. How clinically relevant are treatment comparisons of topical calcineurin inhibitor trials for atopic eczema? J Invest Dermatol 2016;136:1944e9.
See related article on pg 2030
New Insights into the Molecular Distinction of Dysplastic Nevi and Common Melanocytic Nevi—Highlighting the Keratinocyte-Melanocyte Relationship Philip Eliades1,2 and Hensin Tsao1 Mitsui et al. approach the problem of differentiating dysplastic nevi from common melanocytic nevi through a molecular lens. Whereas most of the literature on this topic shines the spotlight toward melanocytes, the focus of this paper is shifted to the tumor microenvironment. Using microarrays, reverse transcriptase-PCR, and immunohistochemistry, their results emphasize the role of keratinocyte dysplasia within dysplastic nevi. Journal of Investigative Dermatology (2016) 136, 1933e1935. doi:10.1016/j.jid.2016.01.008
1
Wellman Center for Photomedicine and Department of Dermatology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA; and 2Tufts University School of Medicine, Boston, Massachusetts, USA Correspondence: Hensin Tsao, Wellman Center for Photomedicine, Department of Dermatology, Massachusetts General Hospital, 50 Blossom St, Boston, Massachusetts 02114, USA. E-mail: htsao@mgh. harvard.edu ª 2016 The Authors. Published by Elsevier, Inc. on behalf of the Society for Investigative Dermatology.
The concept that dysplastic nevi (DN) are at an intermediate step between common melanocytic nevi (CMN) and melanoma was first put forth by Clark et al. (1978), a concept that has been fraught with contention ever since. The uncertainty regarding DN is twofold. First, ambiguity surrounding the hierarchy of melanocytic tumors results, at least in part, from the histological challenge of differentiating DN from CMN. Second, disagreement exists over the inherent risk of DN to progress to melanoma and how this relates to their role as a risk factor for melanoma. In 2016, nearly four decades later, the field of dermatology still lacks a clear consensus on these matters. Mitsui et al. (2016) in a paper titled “Discrimination of dysplastic nevi from common melanocytic nevi by cellular and molecular criteria” describe differences between DN and CMN, thereby shedding new light on the mechanistic etiology of DN. The clinical relevance of DN relates to their proposed characterization as premalignant melanocytic lesions that are associated with increased lifetime risk of becoming melanomas. Their clinical significance is variable, depending on the ability of physicians to distinguish DN from CMN. Historically, DN have been identified by a constellation of clinical and histological features, although several studies have demonstrated low correlations between clinical atypia and histologic dysplasia with respect to the identity of melanocytic lesions (Duffy and Grossman, 2012a). The World Health Organization weighed in on this question in 1991, when it defined DN solely on their histologic features, whereas the National Institutes of Health defined them clinically in 1992 (Rosendahl et al., 2015). Although consensus has not been reached on methods of separating DN and CMN into distinct entities, studies of the molecular and genetic differences between the two suggest DN do, indeed, have distinguishing features. Mitsui et al. (2016) provide further insight into this question, insight that helps to define molecular features of DN. The current literature is divided when it comes to distinguishing histologically diagnosed DN from CMN using molecular and genetic characteristics; www.jidonline.org 1933
COMMENTARY
Clinical Implications Controversy remains concerning whether dysplastic nevi are a distinct entity, representing an intermediate between common melanocytic nevi and melanoma, rather than a variant of common nevi. The immune microenvironment of dysplastic nevi and the follicular differentiation of keratinocytes within them are distinct from common melanocytic nevi. Mitsui et al. (2016) hypothesize that dysplastic nevi may be more appropriately defined as a dysplastic keratinocyte-melanocyte unit.
depending on the molecular feature under consideration, the conclusions are sometimes similar and at other times different. The evidence that supports distinctions between these two entities includes increased markers of proliferation in DN compared with CMN, the presence of microsatellite instability in DN, but not in CMN, and elevated levels of reactive oxygen species in melanocytes from DN (Duffy and Grossman, 2012b; Rosendahl et al., 2015). Opposing these data are studies that have reported DN and CMN both to be clonal in nature, harbor similar rates of B-Raf proto-oncogene serine/threonine kinase (BRAF) mutations, have similar patterns of phosphatase and tensin homolog (PTEN) expression, and have comparable expression of IGFBP7, a senescence marker induced by mutant BRAF (Duffy and Grossman, 2012b; Mitsui et al., 2016; Rosendahl et al., 2015). In addition, an investigation of whole genome expression of DN, CMN, and melanomas through microarray analyses found that DN and CMN shared overlapping molecular profiles. Importantly, they were similar with respect to the expression of genes involved in the regulation of transcription, mitosis, and apoptosis (Scatolini et al., 2010). Mitsui et al. (2016) contribute valuable data to this discussion, and they support the concept that DN are not only histologically distinct from CMN but also genetically and molecularly distinct. The authors took a unique approach by investigating the tumor microenvironment of DN, which revealed dysplasia at the level of the keratinocyte-melanocyte unit. What was previously reported by Scatolini et al. regarding whole genome expression profiles was expanded upon, the immune microenvironments and melanocyte-activating factors of DN
and CMN were analyzed for the first time, and another marker of senescence was explored as a discrete molecular classifier. The microarray analysis revealed surprisingly different results from what is presented above, suggesting a gene expression profile for DN that is distinct from that of CMN. Specifically, they found that genes related to follicular keratinocytes (TCHH, KRT25, and KRT71) and inflammation (S100A7 and S100A8) were expressed at significantly higher levels in DN compared with CMN (Mitsui et al., 2016). RT-PCR and immunohistochemistry confirmed the differences in the expression profiles of these genes; the epidermis of CMN and normal skin strongly expressed KRT25 in hair bulbs, whereas the epidermis of DN stained strongly throughout. The authors noted that their results may differ from the study by Scatolini et al. because of their more stringent inclusion criteria for DN. Only compound nevi with moderate-to-severe atypia were analyzed, whereas Scatolini et al. included lesions with varying degrees of pathological atypia (Mitsui et al., 2016). An area of differentiation between DN and CMN that has not been explored previously is the immune microenvironment. The increased density of CD3þ T cells and CD11cþ dendritic cells in DN prompted the authors to examine the landscape of immune system-related markers via RT-PCR. In doing so, they uncovered several characteristics of this immune microenvironment that separate DN from CMN. Many immune activators (IFNG, IL10, IL12B, and IL13) and immune suppressors (CTLA4, PDCD1, PDCD1LG2, and FOXP3) had significantly upregulated expressions in DN compared with
1934 Journal of Investigative Dermatology (2016), Volume 136
CMN (Mitsui et al., 2016). IL22 and IL24, two cytokines involved in driving pathologic epidermal hyperplasia, were not expressed at higher levels in DN, even though all the DN in the study were confirmed to be hyperplastic by histology and had increased levels of Ki67þ cells compared with CMN. This latter point corroborated a previous study that reported that DN are more proliferative than CMN based on levels of Ki67 positivity (Lebe et al., 2007). Although the investigators failed to link the immune microenvironment of DN to epidermal thickness through specific interleukin secretion, they turned their focus back to keratinocytes in an interesting way. As mentioned, the microarray analysis comparing the global gene expression of DN and CMN, which was substantiated through immunohistochemistry, indicated that the epidermis of DN likely harbors keratinocytes that have undergone aberrant follicular differentiation. In that respect, it has been known that hair follicles serve as melanocyte reservoirs, propagating new melanocytes to colonize and pigment the hair matrix with each hair cycle. Patients with vitiligo have taught us that epidermal repigmentation also begins at hair follicles (Mort et al., 2015; Nishimura, 2011). If folliculardifferentiated keratinocytes do indeed exist within DN, as Mitsui et al. (2016) hypothesize, they may establish a milieu that promotes the pathologic proliferation of melanocytes. In an attempt to support this possibility, they provided additional evidence that DN and CMN are molecularly distinct entities. The expression of CXCL1, a melanocyte stimulating cytokine secreted by keratinocytes, and its receptor, CXCR2, were higher in DN compared with CMN. Furthermore, oncostatin M (OSM), a cytokine known to stimulate keratinocytes to produce CXCL1 in vitro, was found at higher levels in DN, and its receptor (OSMR) stained strongly in epidermal, and especially follicular keratinocytes, in DN (Mitsui et al., 2016). The identification of OSMR on follicular keratinocytes in DN ties in nicely to the idea that the hyperproliferative state of DN is possibly driven by dysplastic keratinocytes that have undergone follicular differentiation.
COMMENTARY Lastly, this paper provides an updated examination of senescence markers as a point of comparison between DN and CMN; the authors arrived at these findings unsuspectingly. Oncogene-induced senescence, or rather escape therefrom, is commonly implicated in discussions of why some BRAF-mutant melanocytes become melanomas, whereas others remain benign nevi (Roh et al., 2015). One way in which constitutively activated mutant BRAF can induce senescence is by upregulating a tumor suppressor protein, IGFBP7; it has been demonstrated that this mechanism is frequently lacking in BRAF-mutant melanomas (Wajapeyee et al., 2008). However, studies investigating the differential expression of IGFBP7 between DN and CMN have been equivocal (Duffy and Grossman, 2012b). Studies comparing the altered expression of the tumor suppressor genes CDKN2A and TP53 in DN and CMN are also inconclusive, with some, but not all, studies suggesting that they differ (Duffy and Grossman, 2012b). Mitsui et al. (2016) were able to fill some of this knowledge gap by identifying DUSP3 as a potential molecular marker for the classification of DN and CMN. Loss of DUSP3, a mitogen-activated protein kinase phosphatase, results in cellular senescence (Rahmouni et al., 2006). In their analyses, the authors used three independent algorithms to differentiate DN from CMN on the basis of their microarray data. DUSP3 was one of eight genes common among the three best algorithms. Immunohistochemistry supported this finding by revealing that there was less DUSP3 expression in CMN compared with DN (Mitsui et al., 2016). This suggests that CMN and DN can be discriminated at a molecular level and that DUSP3 may play an
important role in the regulation of melanocytic tumor proliferation. Through the use of microarray analyses, RT-PCR, and immunohistochemistry, the investigators have made valuable contributions to the discussion of how DN and CMN differ, going so far as to propose that DN are best distinguished from the hierarchy of melanocytic tumors by treating them as dysplastic keratinocyte-melanocyte units. What this paper does not address is the long-disputed question about the risk inherent in DN to transform to melanomas and their relationship as a risk factor for the development of melanomas. To that end, several epidemiologic studies have revealed an increased risk of melanoma in patients with DN, although many of the earlier studies were based solely on clinical morphology, which has attracted criticism because clinical and histologic diagnoses often fail to correlate (Rosendahl et al., 2015). Likewise, many studies of nevus-associated melanomas failed to find a higher incidence of melanomas arising from DN compared with CMN (Duffy and Grossman, 2012a). Mitsui et al. (2016) demonstrate through their studies that the discussion of DN within the larger context of the hierarchy of melanocytic tumors is evolving, and as more is revealed about their pathophysiology at molecular and genetic levels, we will be able to advance our understanding of their relationships with CMN and with melanomas. CONFLICT OF INTEREST The authors state no conflict of interest.
ACKNOWLEDGMENT Mentorship and supervision during the writing of this manuscript was supported by a grant from the National Institutes of Health (to HT; K24 CA149202).
REFERENCES Clark WH Jr, Reimer RR, Greene M, Ainsworth AM, Mastrangelo MJ. Origin of familial malignant melanomas from heritable melanocytic lesions. ‘The B-K mole syndrome’. Arch Dermatol 1978;114:732e8. Duffy K, Grossman D. The dysplastic nevus: from historical perspective to management in the modern era: part I. Historical, histologic, and clinical aspects. J Am Acad Dermatol 2012a;67:1.e1e1.e16; quiz 7e8. Duffy K, Grossman D. The dysplastic nevus: from historical perspective to management in the modern era: part II. Molecular aspects and clinical management. J Am Acad Dermatol 2012b;67:19.e1e2; quiz 31e2. Lebe B, Pabuccuoglu U, Ozer E. The significance of Ki-67 proliferative index and cyclin D1 expression of dysplastic nevi in the biologic spectrum of melanocytic lesions. Appl Immunohistochem Mol Morphol 2007;15: 160e4. Mitsui H, Kiecker F, Shemer A, Cannizzaro MV, Wang CQF, Gulati N, et al. Discrimination of dysplastic nevi from common melanocytic nevi by cellular and molecular criteria. J Invest Dermatol 2016;136:2030e40. Mort RL, Jackson IJ, Patton EE. The melanocyte lineage in development and disease. Development 2015;142:1387. Nishimura EK. Melanocyte stem cells: a melanocyte reservoir in hair follicles for hair and skin pigmentation. Pigment Cell Melanoma Res 2011;24:401e10. Rahmouni S, Cerignoli F, Alonso A, Tsutji T, Henkens R, Zhu C, et al. Loss of the VHR dualspecific phosphatase causes cell-cycle arrest and senescence. Nat Cell Biol 2006;8: 524e31. Roh MR, Eliades P, Gupta S, Tsao H. Genetics of melanocytic nevi. Pigment Cell Melanoma Res 2015;28:661e72. Rosendahl CO, Grant-Kels JM, Que SK. Dysplastic nevus: fact and fiction. J Am Acad Dermatol 2015;73:507e12. Scatolini M, Grand MM, Grosso E, Venesio T, Pisacane A, Balsamo A, et al. Altered molecular pathways in melanocytic lesions. Int J Cancer 2010;126:1869e81. Wajapeyee N, Serra RW, Zhu X, Mahalingam M, Green MR. Oncogenic BRAF induces senescence and apoptosis through pathways mediated by the secreted progtein. Cell 2008;132: 363e74.
www.jidonline.org 1935
CONFLICT OF INTEREST The authors state no conflict of interest.
REFERENCES Chalmers I, Glasziou P. Avoidable waste in the production and reporting of research evidence. Lancet 2009;374:86e9. Chalmers I, Bracken MB, Djulbegovic B, Garattini S, Grant J, Gu¨lmezoglu AM, et al. How to increase value and reduce waste when
research priorities are set. Lancet 2014;383: 156e65. Collins FS. NIH basics. Science 2012;337:503. Cooper NJ, Jones DR, Sutton AJ. The use of systematic reviews when designing studies. Clin Trials 2005;2:260e4. European Medicines Agency. External guidance on the implementation of the European Medicines Agency policy on the publication of clinical data for medicinal products for human use. London: EMA; 2016. Ker K, Edwards P, Perel P, Shakur H, Roberts I. Effect of tranexamic acid on surgical bleeding: systematic review and cumulative metaanalysis. BMJ 2012;344:e3054. Moher D, Avey M, Antes G, Altman DG. The National Institutes of Health and guidance for reporting preclinical research. BMC Med 2015;13:34. Patsopoulos NA, Analatos AA, Ioannidis JP. Relative citation impact of various study designs in the health sciences. JAMA 2005;293:2362e6. Turner EH. How to access and process FDA drug approval packages for use in research. BMJ 2013;347:f5992. Wilkes SR, Nankervis H, Tavernier E, Maruani A, Williams HC. How clinically relevant are treatment comparisons of topical calcineurin inhibitor trials for atopic eczema? J Invest Dermatol 2016;136:1944e9.
See related article on pg 2030
New Insights into the Molecular Distinction of Dysplastic Nevi and Common Melanocytic Nevi—Highlighting the Keratinocyte-Melanocyte Relationship Philip Eliades1,2 and Hensin Tsao1 Mitsui et al. approach the problem of differentiating dysplastic nevi from common melanocytic nevi through a molecular lens. Whereas most of the literature on this topic shines the spotlight toward melanocytes, the focus of this paper is shifted to the tumor microenvironment. Using microarrays, reverse transcriptase-PCR, and immunohistochemistry, their results emphasize the role of keratinocyte dysplasia within dysplastic nevi. Journal of Investigative Dermatology (2016) 136, 1933e1935. doi:10.1016/j.jid.2016.01.008
1
Wellman Center for Photomedicine and Department of Dermatology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA; and 2Tufts University School of Medicine, Boston, Massachusetts, USA Correspondence: Hensin Tsao, Wellman Center for Photomedicine, Department of Dermatology, Massachusetts General Hospital, 50 Blossom St, Boston, Massachusetts 02114, USA. E-mail: htsao@mgh. harvard.edu ª 2016 The Authors. Published by Elsevier, Inc. on behalf of the Society for Investigative Dermatology.
The concept that dysplastic nevi (DN) are at an intermediate step between common melanocytic nevi (CMN) and melanoma was first put forth by Clark et al. (1978), a concept that has been fraught with contention ever since. The uncertainty regarding DN is twofold. First, ambiguity surrounding the hierarchy of melanocytic tumors results, at least in part, from the histological challenge of differentiating DN from CMN. Second, disagreement exists over the inherent risk of DN to progress to melanoma and how this relates to their role as a risk factor for melanoma. In 2016, nearly four decades later, the field of dermatology still lacks a clear consensus on these matters. Mitsui et al. (2016) in a paper titled “Discrimination of dysplastic nevi from common melanocytic nevi by cellular and molecular criteria” describe differences between DN and CMN, thereby shedding new light on the mechanistic etiology of DN. The clinical relevance of DN relates to their proposed characterization as premalignant melanocytic lesions that are associated with increased lifetime risk of becoming melanomas. Their clinical significance is variable, depending on the ability of physicians to distinguish DN from CMN. Historically, DN have been identified by a constellation of clinical and histological features, although several studies have demonstrated low correlations between clinical atypia and histologic dysplasia with respect to the identity of melanocytic lesions (Duffy and Grossman, 2012a). The World Health Organization weighed in on this question in 1991, when it defined DN solely on their histologic features, whereas the National Institutes of Health defined them clinically in 1992 (Rosendahl et al., 2015). Although consensus has not been reached on methods of separating DN and CMN into distinct entities, studies of the molecular and genetic differences between the two suggest DN do, indeed, have distinguishing features. Mitsui et al. (2016) provide further insight into this question, insight that helps to define molecular features of DN. The current literature is divided when it comes to distinguishing histologically diagnosed DN from CMN using molecular and genetic characteristics; www.jidonline.org 1933
COMMENTARY
Clinical Implications Controversy remains concerning whether dysplastic nevi are a distinct entity, representing an intermediate between common melanocytic nevi and melanoma, rather than a variant of common nevi. The immune microenvironment of dysplastic nevi and the follicular differentiation of keratinocytes within them are distinct from common melanocytic nevi. Mitsui et al. (2016) hypothesize that dysplastic nevi may be more appropriately defined as a dysplastic keratinocyte-melanocyte unit.
depending on the molecular feature under consideration, the conclusions are sometimes similar and at other times different. The evidence that supports distinctions between these two entities includes increased markers of proliferation in DN compared with CMN, the presence of microsatellite instability in DN, but not in CMN, and elevated levels of reactive oxygen species in melanocytes from DN (Duffy and Grossman, 2012b; Rosendahl et al., 2015). Opposing these data are studies that have reported DN and CMN both to be clonal in nature, harbor similar rates of B-Raf proto-oncogene serine/threonine kinase (BRAF) mutations, have similar patterns of phosphatase and tensin homolog (PTEN) expression, and have comparable expression of IGFBP7, a senescence marker induced by mutant BRAF (Duffy and Grossman, 2012b; Mitsui et al., 2016; Rosendahl et al., 2015). In addition, an investigation of whole genome expression of DN, CMN, and melanomas through microarray analyses found that DN and CMN shared overlapping molecular profiles. Importantly, they were similar with respect to the expression of genes involved in the regulation of transcription, mitosis, and apoptosis (Scatolini et al., 2010). Mitsui et al. (2016) contribute valuable data to this discussion, and they support the concept that DN are not only histologically distinct from CMN but also genetically and molecularly distinct. The authors took a unique approach by investigating the tumor microenvironment of DN, which revealed dysplasia at the level of the keratinocyte-melanocyte unit. What was previously reported by Scatolini et al. regarding whole genome expression profiles was expanded upon, the immune microenvironments and melanocyte-activating factors of DN
and CMN were analyzed for the first time, and another marker of senescence was explored as a discrete molecular classifier. The microarray analysis revealed surprisingly different results from what is presented above, suggesting a gene expression profile for DN that is distinct from that of CMN. Specifically, they found that genes related to follicular keratinocytes (TCHH, KRT25, and KRT71) and inflammation (S100A7 and S100A8) were expressed at significantly higher levels in DN compared with CMN (Mitsui et al., 2016). RT-PCR and immunohistochemistry confirmed the differences in the expression profiles of these genes; the epidermis of CMN and normal skin strongly expressed KRT25 in hair bulbs, whereas the epidermis of DN stained strongly throughout. The authors noted that their results may differ from the study by Scatolini et al. because of their more stringent inclusion criteria for DN. Only compound nevi with moderate-to-severe atypia were analyzed, whereas Scatolini et al. included lesions with varying degrees of pathological atypia (Mitsui et al., 2016). An area of differentiation between DN and CMN that has not been explored previously is the immune microenvironment. The increased density of CD3þ T cells and CD11cþ dendritic cells in DN prompted the authors to examine the landscape of immune system-related markers via RT-PCR. In doing so, they uncovered several characteristics of this immune microenvironment that separate DN from CMN. Many immune activators (IFNG, IL10, IL12B, and IL13) and immune suppressors (CTLA4, PDCD1, PDCD1LG2, and FOXP3) had significantly upregulated expressions in DN compared with
1934 Journal of Investigative Dermatology (2016), Volume 136
CMN (Mitsui et al., 2016). IL22 and IL24, two cytokines involved in driving pathologic epidermal hyperplasia, were not expressed at higher levels in DN, even though all the DN in the study were confirmed to be hyperplastic by histology and had increased levels of Ki67þ cells compared with CMN. This latter point corroborated a previous study that reported that DN are more proliferative than CMN based on levels of Ki67 positivity (Lebe et al., 2007). Although the investigators failed to link the immune microenvironment of DN to epidermal thickness through specific interleukin secretion, they turned their focus back to keratinocytes in an interesting way. As mentioned, the microarray analysis comparing the global gene expression of DN and CMN, which was substantiated through immunohistochemistry, indicated that the epidermis of DN likely harbors keratinocytes that have undergone aberrant follicular differentiation. In that respect, it has been known that hair follicles serve as melanocyte reservoirs, propagating new melanocytes to colonize and pigment the hair matrix with each hair cycle. Patients with vitiligo have taught us that epidermal repigmentation also begins at hair follicles (Mort et al., 2015; Nishimura, 2011). If folliculardifferentiated keratinocytes do indeed exist within DN, as Mitsui et al. (2016) hypothesize, they may establish a milieu that promotes the pathologic proliferation of melanocytes. In an attempt to support this possibility, they provided additional evidence that DN and CMN are molecularly distinct entities. The expression of CXCL1, a melanocyte stimulating cytokine secreted by keratinocytes, and its receptor, CXCR2, were higher in DN compared with CMN. Furthermore, oncostatin M (OSM), a cytokine known to stimulate keratinocytes to produce CXCL1 in vitro, was found at higher levels in DN, and its receptor (OSMR) stained strongly in epidermal, and especially follicular keratinocytes, in DN (Mitsui et al., 2016). The identification of OSMR on follicular keratinocytes in DN ties in nicely to the idea that the hyperproliferative state of DN is possibly driven by dysplastic keratinocytes that have undergone follicular differentiation.
COMMENTARY Lastly, this paper provides an updated examination of senescence markers as a point of comparison between DN and CMN; the authors arrived at these findings unsuspectingly. Oncogene-induced senescence, or rather escape therefrom, is commonly implicated in discussions of why some BRAF-mutant melanocytes become melanomas, whereas others remain benign nevi (Roh et al., 2015). One way in which constitutively activated mutant BRAF can induce senescence is by upregulating a tumor suppressor protein, IGFBP7; it has been demonstrated that this mechanism is frequently lacking in BRAF-mutant melanomas (Wajapeyee et al., 2008). However, studies investigating the differential expression of IGFBP7 between DN and CMN have been equivocal (Duffy and Grossman, 2012b). Studies comparing the altered expression of the tumor suppressor genes CDKN2A and TP53 in DN and CMN are also inconclusive, with some, but not all, studies suggesting that they differ (Duffy and Grossman, 2012b). Mitsui et al. (2016) were able to fill some of this knowledge gap by identifying DUSP3 as a potential molecular marker for the classification of DN and CMN. Loss of DUSP3, a mitogen-activated protein kinase phosphatase, results in cellular senescence (Rahmouni et al., 2006). In their analyses, the authors used three independent algorithms to differentiate DN from CMN on the basis of their microarray data. DUSP3 was one of eight genes common among the three best algorithms. Immunohistochemistry supported this finding by revealing that there was less DUSP3 expression in CMN compared with DN (Mitsui et al., 2016). This suggests that CMN and DN can be discriminated at a molecular level and that DUSP3 may play an
important role in the regulation of melanocytic tumor proliferation. Through the use of microarray analyses, RT-PCR, and immunohistochemistry, the investigators have made valuable contributions to the discussion of how DN and CMN differ, going so far as to propose that DN are best distinguished from the hierarchy of melanocytic tumors by treating them as dysplastic keratinocyte-melanocyte units. What this paper does not address is the long-disputed question about the risk inherent in DN to transform to melanomas and their relationship as a risk factor for the development of melanomas. To that end, several epidemiologic studies have revealed an increased risk of melanoma in patients with DN, although many of the earlier studies were based solely on clinical morphology, which has attracted criticism because clinical and histologic diagnoses often fail to correlate (Rosendahl et al., 2015). Likewise, many studies of nevus-associated melanomas failed to find a higher incidence of melanomas arising from DN compared with CMN (Duffy and Grossman, 2012a). Mitsui et al. (2016) demonstrate through their studies that the discussion of DN within the larger context of the hierarchy of melanocytic tumors is evolving, and as more is revealed about their pathophysiology at molecular and genetic levels, we will be able to advance our understanding of their relationships with CMN and with melanomas. CONFLICT OF INTEREST The authors state no conflict of interest.
ACKNOWLEDGMENT Mentorship and supervision during the writing of this manuscript was supported by a grant from the National Institutes of Health (to HT; K24 CA149202).
REFERENCES Clark WH Jr, Reimer RR, Greene M, Ainsworth AM, Mastrangelo MJ. Origin of familial malignant melanomas from heritable melanocytic lesions. ‘The B-K mole syndrome’. Arch Dermatol 1978;114:732e8. Duffy K, Grossman D. The dysplastic nevus: from historical perspective to management in the modern era: part I. Historical, histologic, and clinical aspects. J Am Acad Dermatol 2012a;67:1.e1e1.e16; quiz 7e8. Duffy K, Grossman D. The dysplastic nevus: from historical perspective to management in the modern era: part II. Molecular aspects and clinical management. J Am Acad Dermatol 2012b;67:19.e1e2; quiz 31e2. Lebe B, Pabuccuoglu U, Ozer E. The significance of Ki-67 proliferative index and cyclin D1 expression of dysplastic nevi in the biologic spectrum of melanocytic lesions. Appl Immunohistochem Mol Morphol 2007;15: 160e4. Mitsui H, Kiecker F, Shemer A, Cannizzaro MV, Wang CQF, Gulati N, et al. Discrimination of dysplastic nevi from common melanocytic nevi by cellular and molecular criteria. J Invest Dermatol 2016;136:2030e40. Mort RL, Jackson IJ, Patton EE. The melanocyte lineage in development and disease. Development 2015;142:1387. Nishimura EK. Melanocyte stem cells: a melanocyte reservoir in hair follicles for hair and skin pigmentation. Pigment Cell Melanoma Res 2011;24:401e10. Rahmouni S, Cerignoli F, Alonso A, Tsutji T, Henkens R, Zhu C, et al. Loss of the VHR dualspecific phosphatase causes cell-cycle arrest and senescence. Nat Cell Biol 2006;8: 524e31. Roh MR, Eliades P, Gupta S, Tsao H. Genetics of melanocytic nevi. Pigment Cell Melanoma Res 2015;28:661e72. Rosendahl CO, Grant-Kels JM, Que SK. Dysplastic nevus: fact and fiction. J Am Acad Dermatol 2015;73:507e12. Scatolini M, Grand MM, Grosso E, Venesio T, Pisacane A, Balsamo A, et al. Altered molecular pathways in melanocytic lesions. Int J Cancer 2010;126:1869e81. Wajapeyee N, Serra RW, Zhu X, Mahalingam M, Green MR. Oncogenic BRAF induces senescence and apoptosis through pathways mediated by the secreted progtein. Cell 2008;132: 363e74.
www.jidonline.org 1935