title: Proteasome- and p53-dependent masking of signal transducer and activator of transcription (STAT) factors.
abstract: Hepatoma Hep3B cell lines stably expressing a temperature-sensitive p53 species (p53-Val-135) displayed a reduced response to interleukin-6 (IL-6) when cultured at the wild-type (wt) p53 temperature (Wang, L., Rayanade, R., Garcia, D., Patel, K., Pan, H., and Sehgal, P. B. (1995) J. Biol. Chem. 270, 23159-23165). We now report that in such cultures IL-6 caused a rapid (20-30 min) and marked loss of cellular immunostaining for STAT3 and STAT5, but not for STAT1. The loss of STAT3 and STAT5 immunostaining was transient (lasted 120 min) and tyrosine kinase-dependent, and even though the loss was blocked by the proteasome inhibitors MG132 and lactacystin it was not accompanied by changes in cellular levels of STAT3 and STAT5 proteins suggesting that IL-6 triggered a rapid masking but not degradation of these transcription factors. STAT3 and STAT5 masking was accompanied by a reduction in IL-6-induced nuclear DNA-binding activity. The data suggest that p53 may influence Jak-STAT signaling through a novel indirect mechanism involving a wt p53-dependent gene product which upon cytokine addition is activated into a "STAT-masking factor" in a proteasome-dependent step.
authors.affiliation: Department of Cell Biology & Anatomy, New York Medical College, Valhalla, New York 10595, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Rayanade
authors.forename: K
authors.initials: K
authors.lastname: Patel
authors.forename: M
authors.initials: M
authors.lastname: Ndubuisi
authors.forename: S
authors.initials: S
authors.lastname: Sharma
authors.forename: S
authors.initials: S
authors.lastname: Omura
authors.forename: J D
authors.initials: JD
authors.lastname: Etlinger
authors.forename: R
authors.initials: R
authors.lastname: Pine
authors.forename: P B
authors.initials: PB
authors.lastname: Sehgal
mesh_terms: D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008894:Milk Proteins; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D008894:Milk Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D016159:Tumor Suppressor Protein p53