Melanomas require HEDGEHOG-GLI signaling regulated by interactions between GLI1 and the RAS-MEK/AKT pathways

Abstract

Melanoma is one of the most aggressive cancers, and its incidence is increasing. These tumors derive from the melanocyte lineage and remain incurable after metastasis. Here we report that SONIC HEDGEHOG (SHH)-GLI signaling is active in the matrix of human hair follicles, and that it is required for the normal proliferation of human melanocytes in culture. SHH-GLI signaling also regulates the proliferation and survival of human melanomas: the growth, recurrence, and metastasis of melanoma xenografts in mice are prevented by local or systemic interference of HH-GLI function. Moreover, we show that oncogenic RAS-induced melanomas in transgenic mice express Gli1 and require Hh-Gli signaling in vitro and in vivo. Finally, we provide evidence that endogenous RAS-MEK and AKT signaling regulate the nuclear localization and transcriptional activity of GLI1 in melanoma and other cancer cells. Our data uncover an unsuspected role of HH-GLI signaling in melanocytes and melanomas, demonstrate a role for this pathway in RAS-induced tumors, suggest a general integration of the RAS/AKT and HH-GLI pathways, and open a therapeutic approach for human melanomas.cancer ͉ melanocyte ͉ hair follicle ͉ metastasis ͉ skin

Activation of the hedgehog-signaling pathway in human cancer and the clinical implications

“…Cyclopamine administration reduced BCCs, but not SCCs or fibrosarcomas in these mice, highlighting the specificity of cyclopamine for the hedgehog pathway (Athar et al, 2004). Similarly, cyclopamine is effective in reducing medulloblastoma development in Ptch1 þ /À mice (Sanchez and Ruiz i Altaba, 2005) as well as tumor growth of many cancer cell lines in nu/nu mice (Berman et al, 2002;Thayer et al, 2003;Karhadkar et al, 2004;Stecca et al, 2007 Table 2). Another clinical trial of GDC-0449 on a medulloblastoma patient also resulted in a rapid reduction of tumor (although transiently) but the drug resistance occurred because of SMO mutation Rudin et al, 2009).…”

“…There are several ways to regulate the activity of Gli transcription factors. First, nuclear-cytoplasmic shuttling of Gli molecules is tightly regulated (Kogerman et al, 1999;Barnfield et al, 2005;Sheng et al, 2006;Stecca et al, 2007). For example, protein kinase A is shown to retain Gli1 proteins in the cytoplasm (through a PKA site in the nuclear localization signal peptide) whereas active Ras signaling promotes Gli nuclear localization (Stecca et al, 2007).…”

“…First, nuclear-cytoplasmic shuttling of Gli molecules is tightly regulated (Kogerman et al, 1999;Barnfield et al, 2005;Sheng et al, 2006;Stecca et al, 2007). For example, protein kinase A is shown to retain Gli1 proteins in the cytoplasm (through a PKA site in the nuclear localization signal peptide) whereas active Ras signaling promotes Gli nuclear localization (Stecca et al, 2007). Second, ubiquitination and protein degradation of Gli molecules is also regulated by several distinct mechanisms, including b-TRCP-, cul3/BTBand numb/Itch-mediated Gli ubiquitination (Di Marcotullio et al, 2006;Huntzicker et al, 2006;Jiang, 2006;Pan et al, 2006;Wang and Li, 2006).…”

“…Third, different standards have been used to define Hh signaling activation. Some groups use elevated expression of Gli1 as the read-out of Hhsignaling activation (Stecca et al, 2007;Bhattacharya et al, 2008) whereas others assess expression of several Hh target genes, such as Gli1, PTCH1, sFRP1 and HIP (Thayer et al, 2003;Karhadkar et al, 2004;Ma et al, 2005;Huang et al, 2006;Lee et al, 2007). Similarly, some groups use only immunohistochemistry to detect Hh-signaling activation (Kubo et al, 2004;Liao et al, 2009) whereas most studies use multiple approaches.…”

Cooperation between GLI and JUN enhances transcription of JUN and selected GLI target genes

“…GLI target gene activation and specificity was shown to be affected by PKCd (Riobo et al, 2006a;Lauth et al, 2007), Akt/ PI3K (Riobo et al, 2006b), RAS/MEK/ERK (Pasca di Magliano et al, 2006;Stecca et al, 2007;Neill et al, 2008) and EGF signaling (Bigelow et al, 2005;Kasper et al, 2006b;Mimeault et al, 2007). However, the integration of different upstream signals by co-activators and other modulators on GLI target gene promoters is still far from clear.…”