Methionine adenosyltransferase α2 sumoylation positively regulate Bcl-2 expression in human colon and liver cancer cells

Abstract

Ubiquitin-conjugating enzyme 9 (Ubc9) is required for sumoylation and inhibits apoptosis via Bcl-2 by unknown mechanism. Methionine adenosyltransferase 2A (MAT2A) encodes for MATα2, the catalytic subunit of the MATII isoenzyme that synthesizes S-adenosylmethionine (SAMe). Ubc9, Bcl-2 and MAT2A expression are up-regulated in several malignancies. Exogenous SAMe decreases Ubc9 and MAT2A expression and is pro-apoptotic in liver and colon cancer cells. Here we investigated whether there is interplay between Ubc9, MAT2A and Bcl-2. We used human colon and liver cancer cell lines RKO and HepG2, respectively, and confirmed key finding in colon cancer specimens. We found MATα2 can regulate Bcl-2 expression at multiple levels. MATα2 binds to Bcl-2 promoter to activate its transcription. This effect is independent of SAMe as MATα2 catalytic mutant was also effective. MATα2 also directly interacts with Bcl-2 to enhance its protein stability. MATα2's effect on Bcl-2 requires Ubc9 as MATα2's stability is influenced by sumoylation at K340, K372 and K394. Overexpressing wild type (but not less stable MATα2 sumoylation mutants) protected from 5-fluorouracil-induced apoptosis in both colon and liver cancer cells. Colon cancer have higher levels of sumoylated MATα2, total MATα2, Ubc9 and Bcl-2 and higher MATα2 binding to the Bcl-2 P2 promoter. Taken together, Ubc9's protective effect on apoptosis may be mediated at least in part by sumoylating and stabilizing MATα2 protein, which in turn positively maintains Bcl-2 expression. These interactions feed forward to further enhance growth and survival of the cancer cell.

Role of S-adenosylmethionine cycle in carcinogenesis

“…1). While the expression of MAT1A (Cai et al 1996) is downregulated the levels of both, MAT2A (Cai et al 1996;Liu et al 2011;Tomasi et al 2015;Yang et al 2015) and MAT2B (Martínez-Chantar et al 2003a), gene products are increased. This relates with isozyme switch of MAT I/III to MAT II that leads to lowering of SAM concentration Frau et al 2013) with subsequent dysregulation in methylation of DNA (Frau et al 2012;Tomasi et al 2012) and histones with impact on the gene expression (Mentch et al 2015).…”

“…Since, α2 subunit of MAT II in addition to its enzymatic role in process of SAM synthesis possesses also several signaling functions. Increased acetylation (Yang et al 2015) or suppressed sumoylation (Tomasi et al 2015) of α2 subunit exerts anti-proliferative effect on cancer cells. While an acetylation of α2 subunit promotes its ubiquitination and subsequent proteasomal degradation and represses the tumor growth (Yang et al 2015), sumoylation of α2 subunit is linked with its increased stability and enhanced expression of Bcl-2 protein leading to cancer cell survival and growth (Tomasi et al 2015).…”

“…Increased acetylation (Yang et al 2015) or suppressed sumoylation (Tomasi et al 2015) of α2 subunit exerts anti-proliferative effect on cancer cells. While an acetylation of α2 subunit promotes its ubiquitination and subsequent proteasomal degradation and represses the tumor growth (Yang et al 2015), sumoylation of α2 subunit is linked with its increased stability and enhanced expression of Bcl-2 protein leading to cancer cell survival and growth (Tomasi et al 2015). The regulatory role of MAT α2 subunit on the expression could be mediated by its interaction with several transcription factors and capability to function as a transcriptional co-repressor (Katoh et al 2011;Kera et al 2013;Tomasi et al 2015).…”

“…While an acetylation of α2 subunit promotes its ubiquitination and subsequent proteasomal degradation and represses the tumor growth (Yang et al 2015), sumoylation of α2 subunit is linked with its increased stability and enhanced expression of Bcl-2 protein leading to cancer cell survival and growth (Tomasi et al 2015). The regulatory role of MAT α2 subunit on the expression could be mediated by its interaction with several transcription factors and capability to function as a transcriptional co-repressor (Katoh et al 2011;Kera et al 2013;Tomasi et al 2015). In colon and hepatic cancer cells, also the expression of β subunit of MAT II positively correlates with their survival, due to a capability of β subunit to assembly with GIT1 protein (G protein coupled receptor kinase interacting ArfGAP 1) to a complex that activates ERK and MEK signaling pathways those are subsequently promoting the cancer cell growth (Peng et al 2013).…”

Methionine adenosyltransferases in liver health and diseases

“…42 Three SUMO-1 modifications of MATα2 at K340, K372, and K394 were recently shown to enhance its stability and its interactions with oncoproteins such as B-Cell CLL/lymphoma 2 (BCL-2). 43 …”