Characterization of MTAP Gene Expression in Breast Cancer Patients and Cell Lines

Abstract

MTAP is a ubiquitously expressed gene important for adenine and methionine salvage. The gene is located at 9p21, a chromosome region often deleted in breast carcinomas, similar to CDKN2A, a recognized tumor suppressor gene. Several research groups have shown that MTAP acts as a tumor suppressor, and some therapeutic approaches were proposed based on a tumors´ MTAP status. We analyzed MTAP and CDKN2A gene (RT-qPCR) and protein (western-blotting) expression in seven breast cancer cell lines and evaluated their promoter methylation patterns to better characterize the contribution of these genes to breast cancer. Cytotoxicity assays with inhibitors of de novo adenine synthesis (5-FU, AZA and MTX) after MTAP gene knockdown showed an increased sensitivity, mainly to 5-FU. MTAP expression was also evaluated in two groups of samples from breast cancer patients, fresh tumors and paired normal breast tissue, and from formalin-fixed paraffin embedded (FFPE) core breast cancer samples diagnosed as Luminal-A tumors and triple negative breast tumors (TNBC). The difference of MTAP expression between fresh tumors and normal tissues was not statistically significant. However, MTAP expression was significantly higher in Luminal-A breast tumors than in TNBC, suggesting the lack of expression in more aggressive breast tumors and the possibility of using the new approaches based on MTAP status in TNBC.

MTAP-deficiency could predict better treatment response in advanced lung adenocarcinoma patients initially treated with pemetrexed-platinum chemotherapy and bevacizumab

“…www.nature.com/scientificreports www.nature.com/scientificreports/ Based on the metabolic difference, blockade of de novo purine synthesis in MTAP-deficient tumors, in theory, might be a potent strategy to inhibit tumors without affecting normal cells. Several studies demonstrated MTAP-deficient tumor cells are more sensitive than MTAP-positive cells to purine synthesis inhibitors 7,14,15 . In breast cancer cell lines, the cytotoxic activity of 5-fluorouracil and methotrexate were increased after MTAP knockdown 15 .…”

“…Several studies demonstrated MTAP-deficient tumor cells are more sensitive than MTAP-positive cells to purine synthesis inhibitors 7,14,15 . In breast cancer cell lines, the cytotoxic activity of 5-fluorouracil and methotrexate were increased after MTAP knockdown 15 . MTAP was often used to predict outcomes in clinical practice.…”

Environmental factors shape methionine metabolism in p16/MTAP deleted cells

“…For example, approximately 15% of cancers exhibit homozygous deletions of the CDKN2a locus, which encodes for the tumor suppressor p16, with 80-90% of these tumors also exhibiting concurrent deletion of a proximal gene, MTAP, that encodes for the methionine salvage enzyme methylthioadenosine phosphorylase (1,2). A number of studies have investigated MTAP deletion as a possible collateral lethality and have identified vulnerabilities in this subset of cancers (3)(4)(5)(6)(7), with several investigating some of the effects of MTAP deletion on metabolism (8)(9)(10). However, a systematic comparison of the relative effects of MTAP deletion as it relates to other variables that shape metabolism is lacking.…”

Loss of MTAP Expression is a Negative Prognostic Marker in Ewing Sarcoma Family of Tumors

“…Deficiency of this enzyme has been recently found in different types of neoplasms, mainly due to deletion of the 9p21 locus, and associated with increased tumor aggressiveness [1,[3][4][5]. Su et al (2014), in an immunohistochemistry (IHC) study of 99 lung cancer samples, demonstrated that MTAP was an independent marker of prognosis in patients with non-small-cell lung cancer [3].…”