Tomasi Maria Lauda, Ryoo Minjung, Ramani Komal, Tomasi Ivan, Giordano Pasquale, Mato José M, Lu Shelly C
Division of Gastroenterology, Cedars-Sinai Medical Center, Los Angeles, CA 90048, USA.
USC Research Center for Liver Diseases, Keck School of Medicine of University of Southern California, Los Angeles, CA 90033, USA.
Oncotarget. 2015 Nov 10;6(35):37706-23. doi: 10.18632/oncotarget.5342.
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.
泛素结合酶9（Ubc9）是SUMO化所必需的，并通过未知机制经由Bcl-2抑制细胞凋亡。甲硫氨酸腺苷转移酶2A（MAT2A）编码MATα2，MATII同工酶的催化亚基，其合成S-腺苷甲硫氨酸（SAMe）。Ubc9、Bcl-2和MAT2A的表达在几种恶性肿瘤中上调。外源性SAMe降低Ubc9和MAT2A的表达，并在肝癌和结肠癌细胞中具有促凋亡作用。在这里，我们研究了Ubc9、MAT2A和Bcl-2之间是否存在相互作用。我们分别使用人结肠癌细胞系RKO和肝癌细胞系HepG2，并在结肠癌标本中证实了关键发现。我们发现MATα2可以在多个水平上调节Bcl-2的表达。MATα2与Bcl-2启动子结合以激活其转录。这种作用独立于SAMe，因为MATα2催化突变体也有效。MATα2还直接与Bcl-2相互作用以增强其蛋白质稳定性。MATα2对Bcl-2的作用需要Ubc9，因为MATα2的稳定性受K340、K372和K394处的SUMO化影响。过表达野生型（但不是稳定性较低的MATα2 SUMO化突变体）可保护结肠和肝癌细胞免受5-氟尿嘧啶诱导的细胞凋亡。结肠癌中SUMO化的MATα2、总MATα2、Ubc9和Bcl-2水平较高，且MATα2与Bcl-2 P2启动子的结合更高。综上所述，Ubc9对细胞凋亡的保护作用可能至少部分是通过SUMO化和稳定MATα2蛋白来介导的，而MATα2蛋白又反过来正向维持Bcl-2的表达。这些相互作用会进一步促进癌细胞的生长和存活。
