Functional interaction between co-expressed MAGE-A proteins.

Julieta E Laiseca,Javier Cotignola,Martin Monte,Leticia Y Peche,Bryan A Castaño,Mario D Galigniana,Claudio Schneider,Franco A Pascucci,María F Ladelfa

doi:10.1371/journal.pone.0178370

Abstract

MAGE-A (Melanoma Antigen Genes-A) are tumor-associated proteins with expression in a broad spectrum of human tumors and normal germ cells. MAGE-A gene expression and function are being increasingly investigated to better understand the mechanisms by which MAGE proteins collaborate in tumorigenesis and whether their detection could be useful for disease prognosis purposes. Alterations in epigenetic mechanisms involved in MAGE gene silencing cause their frequent co-expression in tumor cells. Here, we have analyzed the effect of MAGE-A gene co-expression and our results suggest that MageA6 can potentiate the androgen receptor (AR) co-activation function of MageA11. Database search confirmed that MageA11 and MageA6 are co-expressed in human prostate cancer samples. We demonstrate that MageA6 and MageA11 form a protein complex resulting in the stabilization of MageA11 and consequently the enhancement of AR activity. The mechanism involves association of the Mage A6-MHD domain to MageA11, prevention of MageA11 ubiquitinylation on lysines 240 and 245 and decreased proteasome-dependent degradation. We experimentally demonstrate here for the first time that two MAGE-A proteins can act together in a non-redundant way to potentiate a specific oncogenic function. Overall, our results highlight the complexity of the MAGE gene networking in regulating cancer cell behavior.

Highlights

Proteins of the MAGE-A (Melanoma Antigen GEnes-A) family belong to the Cancer Testis Antigens (CTA) group and are expressed in normal testis and a broad spectrum of human tumors [1]
While the expression of most tested MAGE-A genes affected in some way the activity of p53, we observed an interesting degree of specificity of MAGE-A expression on the regulation of androgen receptor (AR) activity
Recent unpublished studies form our laboratory evidenced that MageA6 is able to regulate transcription factors of the nuclear receptor (NR) family such as the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR), but no significant regulation was observed for AR

Summary

Introduction

Proteins of the MAGE-A (Melanoma Antigen GEnes-A) family belong to the Cancer Testis Antigens (CTA) group and are expressed in normal testis and a broad spectrum of human tumors [1]. We approached this topic by using specific reporter-gene assay in HEK293T cells, since these cells do not express MAGE genes and do not display significant NRs activity. To address whether endogenous MageA6 could regulate AR activation in human prostate cancer cells (LNCaP) expressing MageA11, we silenced MageA6 expression through siRNA-mediated knock-down (KD) and AR function was determined by measuring PSA gene expression levels in DHT treated cells.

Results

Conclusion