Transforming Growth Factor-ß (TGF-ß) Directly Activates the JAK1-STAT3 Axis to Induce Hepatic Fibrosis in Coordination with the SMAD Pathway.

Transforming growth factor-ß (TGF-ß) signals through both SMAD and non-SMAD pathways to elicit a wide array of biological effects. Existing data have shown the association and coordination between STATs and SMADs in mediating TGF-ß functions in hepatic cells, but it is not clear how STATs are activated under these circumstances. Here, we report that JAK1 is a constitutive TGFßRI binding protein and is absolutely required for phosphorylation of STATs in a SMAD-independent manner within minutes of TGF-ß stimulation. Following the activation of SMADs, TGF-ß also induces a second phase of STAT phosphorylation that requires SMADs, de novo protein synthesis, and contribution from JAK1. Our global gene expression profiling indicates that the non-SMAD JAK1/STAT pathway is essential for the expression of a subset of TGF-ß target genes in hepatic stellate cells, and the cooperation between the JAK1-STAT3 and SMAD pathways is critical to the roles of TGF-ß in liver fibrosis. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

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