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UNLABELLED: Signal transducer and activator of transcription 3 (Stat3) is activated in a variety of malignancies, including hepatocellular carcinoma (HCC). Activation of Ras occurs frequently at advanced stages of HCC by aberrant signaling through growth factor receptors or inactivation of effectors negatively regulating Ras signaling. Here, we addressed the role of Stat3 in Ras-dependent HCC progression in the presence and absence of p19(ARF) /p14(ARF) . We show that constitutive active (ca) Stat3 is tumor suppressive in Ras-transformed p19(ARF-/-) hepatocytes, whereas the expression of Stat3 lacking Tyr(705) phosphorylation (U-Stat3) enhances tumor formation. Accordingly, Ras-transformed Stat3(Δhc) /p19(ARF-/-) hepatocytes (lacking Stat3 and p19(ARF) ) showed increased tumor growth, compared to those expressing Stat3, demonstrating a tumor-suppressor activity of Stat3 in cells lacking p19(ARF) . Notably, endogenous expression of p19(ARF) in Ras-transformed hepatocytes conveyed oncogenic Stat3 functions, resulting in augmented or reduced HCC progression after the expression of caStat3 or U-Stat3, respectively. In accord with these data, the knockdown of p14(ARF) (the human homolog of p19(ARF) ) in Hep3B cells was associated with reduced pY-Stat3 levels during tumor growth to circumvent the tumor-suppressive effect of Stat3. Inhibition of Janus kinases (Jaks) revealed that Jak causes pY-Stat3 activation independently of p14(ARF) levels, indicating that p14(ARF) controls the oncogenic function of pY-Stat3 downstream of Jak. CONCLUSION: These data show evidence that p19(ARF) /p14(ARF) determines the pro- or anti-oncogenic activity of U-Stat3 and pY-Stat3 in Ras-dependent HCC progression.

Original publication

DOI

10.1002/hep.24329

Type

Journal article

Journal

Hepatology

Publication Date

07/2011

Volume

54

Pages

164 - 172

Keywords

Animals, Carcinoma, Hepatocellular, Cell Proliferation, Cells, Cultured, Cyclin-Dependent Kinase Inhibitor p16, Disease Models, Animal, Disease Progression, Hepatocytes, Janus Kinases, Liver Neoplasms, Mice, Mice, Knockout, STAT3 Transcription Factor, Signal Transduction