IL-6 activates serum and glucocorticoid kinase via p38alpha mitogen-activated protein kinase pathway

• Published in: American Journal of Physiology: Cell Physiology Vol. 58; no. 4; p. C971
• Main Authors: Meng, Fanyin, Yamagiwa, Yoko, Taffetani, Silvia, Han, Jiahuai, Patel, Tushar
• Format: Journal Article
• Language: English
• Published: Bethesda American Physiological Society 01.10.2005
• Subjects: Cancer; Cytokines; Enzymes; Inhibitor drugs; Proteins; Signal transduction
• ISSN: 0363-6143; 1522-1563

Interleukin-6 (IL-6) has been implicated as an autocrine factor involved in growth of several human cancers, such as tumors arising from the biliary tract or cholangiocarcinoma. In malignant biliary tract epithelia, IL-6 activates the p38 MAPK pathway, which mediates a dominant survival signaling pathway. Serum and glucocorticoid-stimulated kinase (SGK) has been implicated as a survival kinase, but its role in survival signaling by IL-6 is unknown. After IL-6 stimulation, p38 MAPK activation preceded phosphorylation of SGK at Ser78. Pretreatment with the pharmacological inhibitors of p38 MAPK SB-203580 or SB-202190 blocked IL-6-induced SGK phosphorylation at Ser78 and SGK activation. Overexpression of p38{alpha} increased constitutive SGK phosphorylation at Ser78, whereas dominant negative p38{alpha} MAPK blocked IL-6-induced SGK phosphorylation and nuclear translocation. Interestingly, in addition to stimulating SGK phosphorylation, both IL-6 stimulation and p38{alpha} MAPK overexpression increased SGK mRNA and protein expression. An increase in p38 MAPK and SGK occurred following enforced expression of IL-6 in vivo. Furthermore, inhibition of SGK expression by siRNA increased toxicity due to chemotherapeutic drugs. Taken together, these data identify SGK as both a downstream kinase substrate as well as a transcriptionally regulated gene target of p38 MAPK in response to IL-6 and support a role of SGK during survival signaling by IL-6 in human cancers, such as cholangiocarcinoma. [PUBLICATION ABSTRACT]