Insights into Transforming Growth Factor-β Signaling Pathway in Cutaneous Melanoma Ann Dermatol Vol. 25, No. 2, 2013 http://dx.doi.org/10.5021/ad.2013.25.2.135 REVIEW ARTICLE Insights into the Transforming Growth Factor-β Signaling Pathway in Cutaneous Melanoma Carole Yolande Perrot1-3, Delphine Javelaud1-3, Alain Mauviel1-3 1Institut Curie, Team “TGF-β and Oncogenesis”, Equipe Labellisée Ligue Contre le Cancer, 2INSERM U1021, 3CNRS UMR 3347, Orsay, France Transforming growth factor-β (TGF-β) is a pleiotropic gro- oncogenes, including NRAS, BRAF, CKIT and cyclin- wth factor with broad tissue distribution that plays critical dependent kinase (CDK) and tumor suppressors such as roles during embryonic development, normal tissue home- CDKN2A (p16Ink4A) and p53, are linked to melanoma ostasis, and cancer. While its cytostatic activity on normal development3-5. BRAF mutations are found in 70% of all epithelial cells initially defined TGF-β signaling as a tumor melanomas and more than 90% of these mutations carry a suppressor pathway, there is ample evidence indicating that single missense mutation consisting in an activating TGF-β is a potent pro-tumorigenic agent, acting via auto- substitution of glutamate for valine at position 600 crine and paracrine mechanisms to promote peri-tumoral (BRAFV600E) within the kinase domain of this protein6,7. angiogenesis, together with tumor cell migration, immune CDKN2A is a gene involved in familial melanoma escape, and dissemination to metastatic sites. This review pathogenesis and a germline mutation is found among summarizes the current knowledge on the implication of melanoma-prone families8. Additionally, rare germline TGF-β signaling in melanoma. (Ann Dermatol 25(2) 135∼ mutations of CDK4 are exclusively found in individuals 144, 2013) with genetic predisposition to melanoma9. Increased survival of melanoma patients has been obser- -Keywords- ved over the recent decades, which may be due to earlier Melanoma, Metastasis, TGF-beta signaling, Therapeutic- detection (and subsequent surgical resection) of primary targets melanoma lesions. Yet, therapeutic options for unresec- table or metastatic melanoma remain extremely limited. Until recently, dacarbazine and interleukin-2 (IL-2) were INTRODUCTION the only two agents approved by the US Food and Drug Administration (FDA) for the treatment of metastatic mela- Melanoma, a neoplasm of the skin that arises from the noma. In 2011, two additional drugs were approved by the TM transformation of melanocytes, is the most lethal of cu- FDA: Vemurafenib (Plexxikon/Zelboraf ; Roche, Basel, taneous malignancies1. Many factors are now known to Switzerland) and Ipilimumab. Vemurafenib is an oral agent contribute to the formation of melanoma, including expo- that targets mutant BRAF, while Ipilimumab is a fully sure to ultra-violet radiation, skin type, hair/eye color, the human monoclonal antibody against cytotoxic T-lympho- presence of dysplastic nevi and/or increased nevi number, cyte antigen 4 (CTLA-4) that is expressed on the surface of and family history of melanoma2. Mutations of several activated T cells. This novel immunotherapy increases cell-mediated immunity by blocking the key immune che- Corresponding author: Alain Mauviel, Institut Curie, University Center, Bldg ckpoint molecule CTLA-4, thus enhances natural anti- 110, 91400 Orsay, France. Tel: 33-1-69-863043, Fax: 33-1-69-863051, tumor immune response. Despite early therapeutic benefit E-mail: [email protected] of these drugs, materialized by rapid and spectacular This is an Open Access article distributed under the terms of the regression of tumors, resistance rapidly occurs, with brutal Creative Commons Attribution Non-Commercial License (http:// tumor relapse. creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, Melanoma displays multifactorial etiology and its genetic provided the original work is properly cited. and immunological background has not yet been fully Vol. 25, No. 2, 2013 135 CY Perrot, et al elucidated. In vitro studies indicate that cultured melano- regulates the transcription of various target genes. ma cell lines produce excessive levels of cytokines and SMAD7, an inhibitory SMAD, interferes with TGF-β growth factors with pleiotropic biological activities10. signaling by several mechanisms: it can bind TβRI to Among them, Transforming growth factor β (TGF-β) fun- prevent SMAD2/3 phosphorylation and activation, or ctions as an autocrine and paracrine factor that drives recruit the protein phosphatase PP1/GADD34 or the E3 many cellular processes including tumor growth, invasion, ubiquitin ligases SMURF1 and SMURF2 to the receptor escape from immune surveillance, angiogenesis and meta- complex, leading to either receptor dephosphorylation or stasis11. We herein provide in-depth analysis of the rela- proteasomal degradation, respectively11,12. TGF-β path- tionship between melanoma progression and TGF-β way potentially activates other signaling pathways in a signaling. non-canonical manner, including the mitogen-activated protein kinases (MAPKs) and PI3K/AKT pathways11. TGF-β SIGNALING TGF-β IN MELANOCYTES AND MELANOMA The canonical TGF-β signaling cascade is well charac- terized. Briefly, TGF-β ligands bind to the type II trans- In normal epithelial tissues, TGF-β acts as a potent cell membrane receptor serine/threonine kinases (TβRII), whi- growth inhibitor. Thus, it is generally accepted that during ch in turn assembles with, phosphorylates and activates early stages of carcinogenesis, tumor suppressive effects of type I receptor (TβRI; ALK5). Activated TβRI phosphory- TGF-β are mainly driven by the induction of a cytostatic lates the downstream effectors SMAD2 and SMAD3, program. TGF-β upregulates cyclin-dependent kinase which then associate with SMAD4 (Fig. 1). This new (CDK) inhibitors (p21, p15, p27Kip1 and p57Kip2), while complex accumulates in the cell nucleus where it repressing pro-proliferative factors including c-MYC and inhibitor of differentiation (ID) family members11. In addi- tion to its cytostatic effects, the TGF-β/SMAD cascade also regulates the expression of several pro-apoptotic genes13, which also contribute to its tumor suppressor activities. In advanced tumors, TGF-β signaling favors cancer cell proliferation and dissemination, peri-tumoral angiogene- sis, epithelial to mesenchymal transition (EMT) of tumor cells and tumor escape from immune surveillance, thus acting as tumor promoter. In normal melanocytes, TGF-β acts as a potent inhibitor of proliferation and differentiation14. TGF-β1 represses the paired-box transcription factor PAX3, which coopera- tes with the homeobox transcription factor SOX10 to induce melanocyte differentiation15. TGF-β may also in- terfere with melanocyte maturation by inhibiting of microphtalmia transcription factor (M-MITF), a master transcription factor specific of the melanocytic lineage that controls cell survival, migration and differentiation16. Cell autonomous activation of the TGF-β pathway in me- lanoma cell lines has been well documented17,18. While Fig. 1. The transforming growth factor (TGF)-β signaling cascade. TGF-β binds to the type II receptor that recruits, phosphorylates normal melanocytes only express TGF-β1, melanoma cells and activates type I receptor (TβRI). TβRI in turn phosphorylates express and secrete high quantities of the three TGF-β SMAD2/3 which then associate with the co-SMAD SMAD4 to isoforms, TGF-β1, TGF-β2 and TGF-β312. TGF-β ligan- form a heterocomplex that accumulates in the nucleus to regulate ds are able to induce their own expression through a target gene transcription. Inhibitory SMAD7 binds activated TβRI to prevent SMAD2/3 phosphorylation, or recruits E3 ubiquitin positive amplification loop. Furthermore, treatment of me- ligases (SMURF1/2, WW1) or phosphatase GADD34/PP1 to the lanoma cell lines with exogenous TGF-β1 induces the receptor complexes, inducing proteasomal degradation or de- secretion of active TGF-β1 and TGF-β219. Consistently, phosphorylation of the latter, respectively. C-SKI and SNON act β as transcriptional co-repressors to repress TGF-β-induced, plasma levels of TGF- are found elevated in melanoma 20 SMAD-driven, transcription. TβRII: TGF-βreceptor type II. patients, in parallel with metastatic progression . Also, 136 Ann Dermatol Insights into Transforming Growth Factor-β Signaling Pathway in Cutaneous Melanoma TGF-β2 expression was found to correlate with tumor miR-21129. Yet, TGF-β has been implicated in the meta- thickness and invasiveness21. static spread of melanoma12, suggesting that increased Genome-wide expression analysis of nearly one hundred TGF-β signaling through TβRII expression might enhan- human melanoma cell lines identified two groups with ce melanoma invasion and motility when miR-211 levels very distinct gene expression profiles associated with are low. distinct behaviors in vitro: the first group is characterized by high expression of neural crest and melanocytic di- MELANOMA RESPONSIVENESS TO TGF-β fferentiation markers and exhibits a proliferative, poorly Melanoma resistance to TGF-β-mediated growth supp- invasive phenotype, while the other group is charac- ression terized by the expression of a number of genes whose concomitant expression is reminiscent of a TGF-β signa- While normal melanocytes are growth-inhibited by TGF-β, ture, and associated with a highly invasive phenotype and melanoma cells exhibit a variable degree of resistance to its low