Pyrrolidine dithiocarbamate inhibits interleukin-6 signaling through impaired STAT3 activation and association with transcriptional coactivators in hepatocytes.
Interleukin (IL)-6 is a proinflammatory cytokine that has been implicated in the expression of acute phase plasma proteins and hepatic insulin resistance through activation of the JAK/STAT3 pathway. Although previous studies have demonstrated that pyrrolidine dithiocarbamate (PDTC) exerts protection against inflammatory responses, its role in the regulation of IL-6 receptor signaling remains unclear. Here we show that treatment of cultured HepG2 hepatoma cells with PDTC inhibits IL-6-stimulated tyrosine phosphorylation and subsequent nuclear translocation of STAT3 in a dose- and time-dependent fashion. No inhibition of JAK-1 activity was observed. To provide insight into PDTC signaling, we constructed a conditionally active STAT3 by fusing it with the ligand binding domain of the estrogen receptor (STAT3-ER). In the presence of 4-hydroxytamoxifen STAT3-ER was translocated in the nucleus of HepG2 cells in a phosphorylation-independent manner, and treatment with PDTC mitigated the response. Although STAT3 coprecipitated with heat-shock protein 90 (Hsp90) in control cells, coprecipitation of the two proteins was greatly reduced after PDTC treatment or after exposure to geldanamycin, an Hsp90 inhibitor. As a result there was a decrease in IL-6-induced association of STAT3 with the transcriptional coactivators FOXO1a and C/EBPbeta together with significant reduction in the expression of SOCS-3 protein and that of two major acute phase plasma proteins. Importantly, treatment of HepG2 cells and a primary culture of rat hepatocytes with PDTC restored insulin responsiveness that was abrogated by IL-6. These studies are consistent with the ability of PDTC to down-regulate IL-6-induced STAT3 activation by altering the stability of STAT3-Hsp90 complex.
He
Hua-Jun
HJ
Diabetes Section, Laboratory of Clinical Investigation, National Institutes of Health, Baltimore, Maryland 21224, USA.
Zhu
Tie-Nian
TN
Xie
Yi
Y
Fan
Jinshui
J
Kole
Sutapa
S
Saxena
Satya
S
Bernier
Michel
M
D021581:Active Transport, Cell Nucleus; D000975:Antioxidants / Q000494:pharmacology; D002467:Cell Nucleus / Q000378:metabolism; D015500:Chloramphenicol O-Acetyltransferase / Q000378:metabolism; D015536:Down-Regulation; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D011759:Pyrrolidines / Q000494:pharmacology*; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction; D013629:Tamoxifen / Q000031:analogs & derivatives / Q000494:pharmacology; D013859:Thiocarbamates / Q000494:pharmacology*; D015533:Transcriptional Activation
D000975:Antioxidants; D018841:HSP90 Heat-Shock Proteins; D015850:Interleukin-6; D011759:Pyrrolidines; D050796:STAT3 Transcription Factor; D013859:Thiocarbamates; D013629:Tamoxifen; C016601:afimoxifene; C020972:pyrrolidine dithiocarbamic acid; D015500:Chloramphenicol O-Acetyltransferase