KLF4 is regulated by RAS/RAF/MEK/ERK signaling through E2F1 and promotes melanoma cell growth
Melanoma is the most lethal form of skin cancer and treatment of metastatic melanoma remains challenging. BRAF/MEK inhibitors show only temporary benefit due the occurrence of resistance and immunotherapy is effective only in a subset of patients. To improve patient survival, there is a need to better understand molecular mechanisms that drive melanoma growth and operate downstream of the mitogen activated protein kinase (MAPK) signaling. The Krüppel-like factor 4 (KLF4) is a zinc-finger transcription factor that plays a critical role in embryonic development, stemness and cancer, where it can act either as oncogene or tumor suppressor. KLF4 is highly expressed in post-mitotic epidermal cells, but its role in melanoma remains unknown. Here, we address the function of KLF4 in melanoma and its interaction with the MAPK signaling pathway. We find that KLF4 is highly expressed in a subset of human melanomas. Ectopic expression of KLF4 enhances melanoma cell growth by decreasing apoptosis. Conversely, knock-down of KLF4 reduces melanoma cell proliferation and induces cell death. In addition, depletion of KLF4 reduces melanoma xenograft growth in vivo. We find that the RAS/RAF/MEK/ERK signaling positively modulates KLF4 expression through the transcription factor E2F1, which directly binds to KLF4 promoter. Overall, our data demonstrate the pro-tumorigenic role of KLF4 in melanoma and uncover a novel ERK1/2-E2F1-KLF4 axis. These findings identify KLF4 as a possible new molecular target for designing novel therapeutic treatments to control melanoma growth.