title: STAT3-mediated transcription of Bcl-2, Mcl-1 and c-IAP2 prevents apoptosis in polyamine-depleted cells.
abstract: Activation of STAT3 (signal transducer and activator of transcription 3) plays a crucial role in cell survival and proliferation. The aim of the present study was to clarify the role of STAT3 signalling in the protection of polyamine-depleted intestinal epithelial cells against TNF-alpha (tumour necrosis factor-alpha)-induced apoptosis. Polyamine depletion by DFMO (alpha-difluoromethylornithine) caused phosphorylation of STAT3 at Tyr-705 and Ser-727. Phospho-Tyr-705 STAT3 was immunolocalized at the cell periphery and nucleus, whereas phospho-Ser-727 STAT3 was predominantly detected in the nucleus of polyamine-depleted cells. Sustained phosphorylation of STAT3 at tyrosine residues was observed in polyamine-depleted cells after exposure to TNF-alpha. Inhibition of STAT3 activation by AG490 or cell-membrane-permeant inhibitory peptide (PpYLKTK; where pY represents phospho-Tyr) increased the sensitivity of polyamine-depleted cells to apoptosis. Expression of DN-STAT3 (dominant negative-STAT3) completely eliminated the protective effect of DFMO against TNF-alpha-induced apoptosis. Polyamine depletion increased mRNA and protein levels for Bcl-2, Mcl-1 (myeloid cell leukaemia-1) and c-IAP2 (inhibitor of apoptosis protein-2). Significantly higher levels of Bcl-2 and c-IAP2 proteins were observed in polyamine-depleted cells before and after 9 h of TNF-alpha treatment. Inhibition of STAT3 by AG490 and DN-STAT3 decreased Bcl-2 promoter activity. DN-STAT3 decreased mRNA and protein levels for Bcl-2, Mcl-1 and c-IAP2 in polyamine-depleted cells. siRNA (small interfering RNA)-mediated inhibition of Bcl-2, Mcl-1 and c-IAP2 protein levels increased TNF-alpha-induced apoptosis. DN-STAT3 induced the activation of caspase-3 and PARP [poly(ADP-ribose) polymerase] cleavage in polyamine-depleted cells. These results suggest that activation of STAT3 in response to polyamine depletion increases the transcription and subsequent expression of anti-apoptotic Bcl-2 and IAP family proteins and thereby promotes survival of cells against TNF-alpha-induced apoptosis.
authors.affiliation: Department of Physiology, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Sujoy
authors.initials: S
authors.lastname: Bhattacharya
authors.forename: Ramesh M
authors.initials: RM
authors.lastname: Ray
authors.forename: Leonard R
authors.initials: LR
authors.lastname: Johnson
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D000518:Eflornithine / Q000494:pharmacology; D004789:Enzyme Activation; D051034:Inhibitor of Apoptosis Proteins / Q000235:genetics* / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism; D011073:Polyamines / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D050796:STAT3 Transcription Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: D051034:Inhibitor of Apoptosis Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D011073:Polyamines; D019253:Proto-Oncogene Proteins c-bcl-2; D050796:STAT3 Transcription Factor; D014409:Tumor Necrosis Factor-alpha; D053148:Caspase 3; D020169:Caspases; D000518:Eflornithine