S-adenosylmethionine and its metabolite induce apoptosis in HepG2 cells: Role of protein phosphatase 1 and Bcl-x(S).
S-adenosylmethionine (SAMe) and its metabolite 5'-methylthioadenosine (MTA) are proapoptotic in HepG2 cells. In microarray studies, we found SAMe treatment induced Bcl-x expression. Bcl-x is alternatively spliced to produce two distinct mRNAs and proteins, Bcl-x(L) and Bcl-x(S). Bcl-x(L) is antiapoptotic, while Bcl-x(S) is proapoptotic. In this study we showed that SAMe and MTA selectively induced Bcl-x(S) in a time- and dose-dependent manner in HepG2 cells. There are three transcription start sites in the human Bcl-x gene which yield only Bcl-x(L) in control HepG2 cells. SAMe and MTA treatment did not affect promoter usage, but while one promoter yielded only Bcl-x(L), the other two yielded both Bcl-x(L) and Bcl-x(S), with Bcl-x(S) as the predominant messenger RNA (mRNA) species. Trichostatin A, 3-deaza-adenosine, cycloleucine, and okadaic acid had no effect on Bcl-x(S) induction by SAMe or MTA. Calyculin A and tautomycin, on the other hand, blocked SAMe and MTA-mediated Bcl-x(S) induction and apoptosis in a dose-dependent manner. SAMe and MTA increased protein phosphatase 1 (PP1) catalytic subunit mRNA and protein levels and dephosphorylation of serine-arginine proteins, with the latter blocked by calyculin A. The effects of SAMe and MTA on Bcl-x(S), PP1 expression, and apoptosis were also seen in 293 cells, but not in primary hepatocytes. Induction of Bcl-x(S) by ceramide in HepG2 cells also resulted in apoptosis. In conclusion, we have uncovered a highly novel action of SAMe and MTA, namely the ability to affect the cellular phosphorylation state and alternative splicing of genes, in this case resulting in the induction of Bcl-x(S) leading to apoptosis.
Yang
Heping
H
Division of Gastroenterology and Liver Diseases, University of Southern California Research Center for Liver Diseases, USC-UCLA Research Center for Alcoholic Liver and Pancreatic Diseases, Keck School of Medicine, Los Angeles, 90033, USA.
Sadda
Mamatha R
MR
Li
Mei
M
Zeng
Ying
Y
Chen
Lixin
L
Bae
Wanjun
W
Ou
Xiaopeng
X
Runnegar
Maria T
MT
Mato
José M
JM
Lu
Shelly C
SC
D000107:Acetylation / Q000187:drug effects; D000818:Animals; D017209:Apoptosis; D006528:Carcinoma, Hepatocellular / Q000473:pathology / Q000503:physiopathology*; D002478:Cells, Cultured; D003839:Deoxyadenosines / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006657:Histones / Q000378:metabolism; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009124:Muscle Proteins / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000235:genetics; D020033:Protein Isoforms / Q000378:metabolism; D054645:Protein Phosphatase 1; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000008:administration & dosage*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013872:Thionucleosides / Q000008:administration & dosage*; D014372:Tubercidin / Q000494:pharmacology; D051020:bcl-X Protein
C494811:BCL2L1 protein, human; C494812:Bcl2l1 protein, mouse; D003839:Deoxyadenosines; D004791:Enzyme Inhibitors; D006657:Histones; D009124:Muscle Proteins; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2; D013872:Thionucleosides; D051020:bcl-X Protein; C008500:5'-methylthioadenosine; D012436:S-Adenosylmethionine; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D014372:Tubercidin