Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, The Southern California Research Center for Alcoholic and Pancreatic Diseases & Cirrhosis, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
Hepatology. 2010 Jun;51(6):2152-61. doi: 10.1002/hep.23530.
Increased mitogen-activated protein kinase (MAPK) activity correlates with a more malignant hepatocellular carcinoma (HCC) phenotype. There is a reciprocal regulation between p44/42 MAPK (extracellular signal-regulated kinase [ERK]1/2) and the dual-specificity MAPK phosphatase MKP-1/DUSP1. ERK phosphorylates DUSP1, facilitating its proteasomal degradation, whereas DUSP1 inhibits ERK activity. Methionine adenosyltransferase 1a (Mat1a) knockout (KO) mice express hepatic S-adenosylmethionine (SAM) deficiency and increased ERK activity and develop HCC. The aim of this study was to examine whether DUSP1 expression is regulated by SAM and if so, elucidate the molecular mechanisms. Studies were conducted using Mat1a KO mice livers, cultured mouse and human hepatocytes, and 20S and 26S proteasomes. DUSP1 messenger RNA (mRNA) and protein levels were reduced markedly in livers of Mat1a KO mice and in cultured mouse and human hepatocytes with protein falling to lower levels than mRNA. SAM treatment protected against the fall in DUSP1 mRNA and protein levels in mouse and human hepatocytes. SAM increased DUSP1 transcription, p53 binding to DUSP1 promoter, and stability of its mRNA and protein. Proteasomal chymotrypsin-like and caspase-like activities were increased in Mat1a KO livers and cultured hepatocytes, which was blocked by SAM treatment. SAM inhibited chymotrypsin-like and caspase-like activities by 40% and 70%, respectively, in 20S proteasomes and caused rapid degradation of some of the 26S proteasomal subunits, which was blocked by the proteasome inhibitor MG132. SAM treatment in Mat1a KO mice for 7 days raised SAM, DUSP1, mRNA and protein levels and lowered proteosomal and ERK activities.
DUSP1 mRNA and protein levels are lower in Mat1a KO livers and fall rapidly in cultured hepatocytes. SAM treatment increases DUSP1 expression through multiple mechanisms, and this may suppress ERK activity and malignant degeneration.
丝裂原活化蛋白激酶（MAPK）活性的增加与更恶性的肝细胞癌（HCC）表型相关。p44/42 MAPK（细胞外信号调节激酶[ERK]1/2）和双特异性 MAPK 磷酸酶 MKP-1/DUSP1 之间存在相互调节。ERK 使 DUSP1 磷酸化，促进其蛋白酶体降解，而 DUSP1 抑制 ERK 活性。蛋氨酸腺苷转移酶 1a（Mat1a）敲除（KO）小鼠表达肝 S-腺苷甲硫氨酸（SAM）缺乏和 ERK 活性增加，并发展为 HCC。本研究的目的是检查 SAM 是否调节 DUSP1 的表达，如果是，阐明分子机制。使用 Mat1a KO 小鼠肝脏、培养的小鼠和人肝细胞以及 20S 和 26S 蛋白酶体进行了研究。Mat1a KO 小鼠肝脏和培养的小鼠和人肝细胞中 DUSP1 信使 RNA（mRNA）和蛋白水平明显降低，蛋白水平降至低于 mRNA 的水平。SAM 处理可防止小鼠和人肝细胞中 DUSP1 mRNA 和蛋白水平的下降。SAM 增加了 DUSP1 的转录、p53 与 DUSP1 启动子的结合以及其 mRNA 和蛋白的稳定性。Mat1a KO 肝脏和培养的肝细胞中蛋白酶体糜蛋白酶样和半胱天冬酶样活性增加，SAM 处理可阻断其增加。SAM 分别通过 20S 蛋白酶体抑制糜蛋白酶样和半胱天冬酶样活性 40%和 70%，并导致一些 26S 蛋白酶体亚基迅速降解，MG132 可阻断该降解。Mat1a KO 小鼠用 SAM 处理 7 天可提高 SAM、DUSP1、mRNA 和蛋白水平，并降低蛋白酶体和 ERK 活性。
Mat1a KO 肝脏中的 DUSP1 mRNA 和蛋白水平较低，在培养的肝细胞中迅速下降。SAM 处理通过多种机制增加 DUSP1 的表达，这可能抑制 ERK 活性和恶性转化。
