Oncogenic activation of glypican-3 by c-Myc in human... : Hepatology (original) (raw)

Hepatobiliary Malignancies

Oncogenic activation of glypican-3 by c-Myc in human hepatocellular carcinoma

Li, Li1,2#†; Jin, Ronghua2†; Zhang, Xiaoli3; Lv, Fudong2; Liu, Lifeng1; Liu, Daojie1; Liu, Kai1; Li, Ning2**; Chen, Dexi1,2*‡

1_Beijing Institute of Liver Disease, Beijing, China_

2_Department of Infectious Medicine, Beijing You'an Hospital, Capital Medical University, Beijing, China_

3_Department of Molecular and Medical Genetics, Oregon Health & Sciences University, Portland, OR_

*Beijing Institute of Liver Disease, Beijing, 100069, China

**Department of Infectious Medicine, Beijing You'an Hospital, Capital Medical University, Beijing, 100069, China

Email:[email protected]

Received 21 December 2011; Accepted 22 May 2012

Grant sponsor: National Natural Science Foundation of China; Grant Number: 30910103915, 81071843; Grant sponsor: Beijing Natural Science Foundation; Grant Number: 7101005;; Grant sponsor: Twelve-fifth Key Science and Technology Five Year Plan of China; Grant Number: 2012ZX10001-003, 2012ZX10001-004.

Potential conflict of interest: Nothing to report.

#These two authors contributed equally to this work.

†These two authors contributed equally to this work.

‡fax: (86) 10-63293371

Additional Supporting Information may be found in the online version of this article.

Abstract

Glypican-3 (GPC3) is a heparan sulfate proteoglycan that has an important role in cell growth and differentiation, and its function in tumorigenesis is tissue-dependent. In hepatocellular carcinoma (HCC), the overexpression of GPC3 has been demonstrated to be a reliable diagnostic indicator. However, the mechanisms that regulate the expression and function of GPC3 remain unclear. The oncoprotein c-Myc is a transcription factor that plays a significant role in more than 50% of human tumors. We report here that GPC3 is a transcriptional target of c-Myc and that the expression of c-Myc is also regulated by GPC3, thus forming a positive feedback signaling loop. We found that the overexpression of c-Myc could induce GPC3 promoter-dependent luciferase activity in luciferase reporter experiments. Furthermore, mutational analysis identified c-Myc-binding sites within the GPC3 promoter. The exogenous overexpression of c-Myc increased the endogenous messenger RNA (mRNA) and protein levels of GPC3. Chromatin immunoprecipitation experiments revealed the binding of c-Myc to the endogenous GPC3 promoter, indicating that c-Myc can directly transcriptionally activate GPC3. Interestingly, GPC3 can also elevate c-Myc expression. Overexpression of GPC3 increased c-Myc protein levels, whereas the knockdown of GPC3 reduced c-Myc expression levels. Lastly, the elevated levels of c-Myc correlate with the overexpression of GPC3 in human HCC samples. Conclusion: These data provide new mechanistic insight into the roles of GPC3 and of c-Myc in the development of HCC.