MX 2 is a novel regulator of cell cycle in melanoma cells

Abstract

MX2 protein is a dynamin‐like GTPase2 that has recently been identified as an interferon‐induced restriction factor of HIV‐1 and other primate lentiviruses. A single nucleotide polymorphism (SNP), rs45430, in an intron of the MX2 gene, was previously reported as a novel melanoma susceptibility locus in genome‐wide association studies. Functionally, however, it is still unclear whether and how MX2 contributes to melanoma susceptibility and tumorigenesis. Here, we show that MX2 is differentially expressed in melanoma tumors and cell lines, with most metastatic cell lines showing lower MX2 expression than primary melanoma cell lines and melanocytes. Furthermore, high expression of MX2 RNA in primary melanoma tumors is associated with better patient survival. Overexpression of MX2 reduces in vivo proliferation partially through inhibition of AKT activation, suggesting that it can act as a tumor suppressor in melanoma. However, we have also identified a subset of melanoma cell lines with high endogenous MX2 expression where downregulation of MX2 leads to reduced proliferation. In these cells, MX2 downregulation interfered with DNA replication and cell cycle processes. Collectively, our data for the first time show that MX2 is functionally involved in the regulation of melanoma proliferation but that its function is context‐dependent.

MX2 mediates establishment of interferon response profile, regulates XAF1, and can sensitize melanoma cells to targeted therapy

“…Interestingly, low XAF1 expression was seen in normal human melanocytes, while it was present in two primary and four metastatic lines. Variable expression of XAF1 RNA was also observed in our panel of 45 patient‐derived lymph node MM samples (Figure 3D) that significantly correlated with previously reported MX2 RNA expression 5 (Figure ). The correlation between XAF1 and MX2 mRNA was also high in cell lines ( R = 0.47, p = 0.06, and data not shown), but sample size was too small to achieve statistical significance.…”

“…Of note, previously we have demonstrated that MX2 knockdown downregulates expression of multiple nuclear genes, 5 including Lamin B1 and α‐tubulin, which are commonly used as loading controls for nuclear proteins in fractionation experiments. Therefore, in our study, we chose c‐MYC as a loading control for nuclear fraction of proteins, since it shows nuclear distribution and is not affected by MX2 downregulation in melanoma cells.…”

“…Cell lines were established using the same vectors and reagents and following procedures as described in a publication 5 . Briefly, expression constructs were generated by recombining entry clones pENTR1A containing MX2 or GFP cDNA into the destination vectors.…”

“…We have reported that MX2 has tumor‐suppressive activity and is downregulated during the progression of melanoma. Its expression is also a predictor of better patient survival 5 . It is possible that MX2 downregulation is a result of frequently observed downregulation of interferon signaling in melanoma that ultimately can result in reduced immune cell recruitment and immune recognition of tumor cells 6,7 .…”

Massively parallel reporter assays of melanoma risk variants identify MX2 as a gene promoting melanoma

“…Our single cell-type growth assays for MX2 also show growth effects for MX2 in melanocytic-lineage in the absence of neighboring cell types from the skin, albeit in the opposite direction. A recent study also reported that MX2 over-expression resulted in decreased growth in primary melanocytes and melanoma cells, while the effect could be the opposite in a subset of melanoma cells 53 . Our zebrafish tumor proliferation assay also suggested that accelerated melanoma formation by MX2 might not be due to increased proliferation per se.…”