Hypoxia and MITF control metastatic behaviour in mouse and human melanoma cells

Abstract

Melanomas are very aggressive neoplasms with notorious resistance to therapeutics. It was recently proposed that the remarkable phenotypic plasticity of melanoma cells allows for the rapid development of both resistance to chemotherapeutic drugs and invasive properties. Indeed, the capacity of melanoma cells to form distant metastases is the main cause of mortality in melanoma patients. Therefore, the identification of the mechanism controlling melanoma phenotype is of paramount importance. In the present report, we show that deletion of microphthalmiaassociated transcription factor (MITF), the master gene in melanocyte differentiation, is sufficient to increase the metastatic potential of mouse and human melanoma cells. MITF silencing also increases fibronectin and Snail, two mesenchymal markers that might explain the increased invasiveness in vitro and in vivo. Furthermore, ablation of this population by Forskolin-induced differentiation or MITF-forced expression significantly decreases tumour and metastasis formation, suggesting that eradication of low-MITF cells might improve melanoma treatment. Moreover, we demonstrate that a hypoxic microenvironment decreases MITF expression through an indirect, hypoxia-inducible factor 1 (HIF1)a-dependant transcriptional mechanism, and increases the tumourigenic and metastatic properties of melanoma cells. We identified Bhlhb2, a new factor in melanoma biology, as the mediator of hypoxia/HIF1a inhibitory effect on MITF expression. Our results reveal a hypoxia-HIF1a-BHLHB2-MITF cascade controlling the phenotypic plasticity in melanoma cells and favouring metastasis development. Targeting this pathway might be helpful in the design of new anti-melanoma therapies.

miR-33a functions as a tumor suppressor in melanoma by targeting HIF-1α

“…28,29 It is reported that HIF-1a can activate CXCR4, PDK1 to promote the invasion and metastasis of melanoma cells. 30,31 In addition, bcl -2 plays an important role in promotion of melanoma angiogenesis. 31,32 After overexpression or inhibition of miR-33a, we tested HIF-1a expression and found it had an opposite trend of miR-33a, which highly suggested it may be a target gene of miR-33a.…”

“…30,31 In addition, bcl -2 plays an important role in promotion of melanoma angiogenesis. 31,32 After overexpression or inhibition of miR-33a, we tested HIF-1a expression and found it had an opposite trend of miR-33a, which highly suggested it may be a target gene of miR-33a. To further confirm that HIF-1a is the direct target of miR-33a, we performed dual luciferase reporter assay which testify that miR-33a has a direct binding at HIF-1a 3'-UTR.…”

Distinctive properties of metastasis-initiating cells

“…Two other lung alveolar differentiation transcription factors (GATA6 and HOPX) also cooperatively limit the metastatic competence of lung adenocarcinoma (Cheung et al 2013). Similarly, the loss of MITF, a melanocyte differentiation factor, is sufficient to increase metastasis of melanoma (Cheli et al 2012).…”

BDNF rs6265 methylation and genotype interact on risk for schizophrenia

“…For example, binding of CREB 51 and GADD45B 52 in the BDNF region upstream of the rs6265 SNP has been detected. Moreover, BHLHB2 and GADD45B are regulated by hypoxia, since they have a highstringency HIF1 binding site, 53,54 and BHLHB2 represses expression of MITF, 53 a TF stimulating HIF1a expression. 55 Studies in mice have also proved how the basic helix-loop-helix protein BHLHB2 is regulated by neurotrophins and modulate BDNF transcription.…”