Transforming Growth Factor-β-independent Regulation of Myogenesis by SnoN Sumoylation

Mingyao Liu,Min Liang,Brad Bryan,Xia Lin,Kunxin Luo,Xin-Hua Feng,Katharine H Wrighton

doi:10.1074/jbc.m610206200

Abstract

Recent progress has been made on the role of oncoproteins c-Ski and related SnoN in the control of cellular transformation. c-Ski/SnoN potently repress transforming growth factor-beta (TGF-beta) antiproliferative signaling through physical interaction with signal transducers called Smads. Overexpression of c-Ski/SnoN also induces skeletal muscle differentiation, but how c-Ski/SnoN function in myogenesis is largely unknown. During our investigation on the role of sumoylation in TGF-beta signaling, we inadvertently found that SnoN is modified by small ubiquitin-like modifier-1 (SUMO-1). Here, we biochemically characterize SnoN sumoylation in detail and report the physiological function of the modification. Sumoylation occurs primarily at lysine 50 (Lys-50). PIAS1 and PIASx proteins physically interact with SnoN to stimulate its sumoylation, thus serving as SUMO-protein isopeptide ligases (E3) for SnoN sumoylation. SnoN sumoylation does not alter its metabolic stability or its ability to repress TGF-beta signaling. Notably, loss of sumoylation in the Lys-50 site (via a Lys-to-Arg point mutation) potently activates muscle-specific gene expression and enhances myotube formation. Our study suggests a novel role for SUMO modification in the regulation of myogenic differentiation.

Highlights

Ski and SnoN are structurally and functionally related nuclear proto-oncoproteins implicated in the control of cell proliferation and differentiation
During our investigation on the role of sumoylation in TGF-␤ signaling, we inadvertently found that SnoN is modified by small ubiquitin-like modifier-1 (SUMO-1)
Loss of Ski leads to reduced skeletal muscle mass [4, 5], whereas Ski overexpression in mice produces muscle hypertrophy [6]

Summary

Introduction

Ski and SnoN are structurally and functionally related nuclear proto-oncoproteins implicated in the control of cell proliferation and differentiation. Plasmid 4R-TK-luc, containing 4xE-boxes activated by Cells—To determine whether SnoN is SUMO-1 modified, myogenic transcription factors, was used to assay the myo- HEK293T cells were transfected with His-SnoN and FLAG- Anti-SnoN Western blotting addition, His-SnoN transfected in the absence of SUMO-1 detected free SnoN and ϳ100-kDa SUMO-conjugated SnoN in appears to be modified by endogenous SUMO, as judged by the presence of PIAS1, x␣, and x␤ (Fig. 2A, lanes 4, 6, and 7).

Results

Conclusion