Impairing hydrolase transport machinery prevents human melanoma metastasis.

Metastases are the major cause of cancer-related death, yet, molecular weaknesses that could be exploited to prevent tumor cells spreading are poorly known. Here, we found that perturbing hydrolase transport to lysosomes by blocking either the expression of IGF2R, the main receptor responsible for their trafficking, or GNPT, a transferase involved in the addition of the specific tag recognized by IGF2R, reduces melanoma invasiveness potential. Mechanistically, we demonstrate that the perturbation of this traffic, leads to a compensatory lysosome neo-biogenesis devoided of degradative enzymes. This regulatory loop relies on the stimulation of TFEB transcription factor expression. Interestingly, the inhibition of this transcription factor playing a key role of lysosome production, restores melanomas' invasive potential in the absence of hydrolase transport. These data implicate that targeting hydrolase transport in melanoma could serve to develop new therapies aiming to prevent metastasis by triggering a physiological response stimulating TFEB expression in melanoma.

Mutated MITF-E87R in Melanoma Enhances Tumor Progression via S100A4.

Melanoma, a melanocyte origin neoplasm, is the most lethal type of skin cancer, and incidence is increasing. Several familial and somatic mutations have been identified in the gene encoding the melanocyte lineage master regulator, MITF; however, the neoplastic mechanisms of these mutant MITF variants are mostly unknown. Here, by performing unbiased analysis of the transcriptomes in cells expressing mutant MITF, we identified calcium-binding protein S100A4 as a downstream target of MITF-E87R. By using wild-type and mutant MITF melanoma lines, we found that both endogenous wild-type and MITF-E87R variants occupy the S100A4 promoter. Remarkably, whereas wild-type MITF represses S100A4 expression, MITF-E87R activates its transcription. The opposite effects of wild-type and mutant MITF result in opposing cellular phenotypes, because MITF-E87R via S100A4 enhanced invasion and reduced adhesion in contrast to wild-type MITF activity. Finally, we found that melanoma patients with altered S100A4 expression have poor prognosis. These data show that a change in MITF transcriptional activity from repression to activation of S100A4 that results from a point mutation in MITF alters melanoma invasive ability. These data suggest new opportunities for diagnosis and treatment of metastatic melanoma.