Abstract
The MC1R/cAMP/MITF pathway is a key determinant for growth, differentiation, and survival of melanocytes and melanoma. MITF-M is the melanocyte-specific isoform of Microphthalmia-associated Transcription Factor (MITF) in human melanoma. Here we use two melanocyte cell lines to show that forced expression of hemagglutinin (HA) -tagged MITF-M through lentiviral transduction represents an oncogenic insult leading to consistent cell transformation of the immortalized melanocyte cell line Hermes 4C, being a melanocortin-1 receptor (MC1R) compound heterozygote, while not causing transformation of the MC1R wild type cell line Hermes 3C. The transformed HA-tagged MITF-M transduced Hermes 4C cells form colonies in soft agar and tumors in mice. Further, Hermes 4C cells display increased MITF chromatin binding, and transcriptional reprogramming consistent with an invasive melanoma phenotype. Mechanistically, forced expression of MITF-M drives the upregulation of the AXL tyrosine receptor kinase (AXL), with concomitant downregulation of phosphatase and tensin homolog (PTEN), leading to increased activation of the PI3K/AKT pathway. Treatment with AXL inhibitors reduces growth of the transformed cells by reverting AKT activation. In conclusion, we present a model system of melanoma development, driven by MITF-M in the context of MC1R loss of function, and independent of UV exposure. This model provides a basis for further studies of critical changes in the melanocyte transformation process.
Highlights
The melanocortin-1 receptor (MC1R) has been found to be a low-risk melanoma susceptibility gene [1,2]
We found that endogenous Microphthalmia-associated Transcription Factor (MITF) was downregulated to undetectable levels in 4C-HA-MITF, indicating MITF expression autoregulation, while to a lesser degree in 3C-HA-MITF, when compared to their respective control transduced lines, hereafter referred as 3C
We found that SOX10, a transcriptional activator of MITF transcription and a major cofactor of MITF in the pigmentation process was concomitantly suppressed in 4C-HA-MITF
Summary
The melanocortin-1 receptor (MC1R) has been found to be a low-risk melanoma susceptibility gene [1,2]. MC1R variants have been shown to increase the melanoma risk in families possessing cyclin-dependent kinase inhibitor 2A (CDKN2A) mutations [3]. CDKN2A was identified as the first melanoma susceptibility gene more than 20 years ago, and germline CDKN2A mutations have been found in up to 20–40% of the melanoma-prone families worldwide [4]. Cancers 2020, 12, 1719 of the RB1 protein, with subsequent impact on the G1-S control of the cell cycle. This signaling is altered in 90–100% of melanomas [5,6]. The MC1R gene locus is highly polymorphic in populations of European ancestry, and more than 200 coding region variants have been identified to date, with a combined prevalence of any MC1R variant being present in
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