Degradation of splicing factor SRSF3 contributes to progressive liver disease
Deepak Kumar, … , Olivia Osborn, Nicholas J.G. Webster
Deepak Kumar, … , Olivia Osborn, Nicholas J.G. Webster
Published August 8, 2019
Citation Information: J Clin Invest. 2019;129(10):4477-4491. https://doi.org/10.1172/JCI127374.
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Research Article Endocrinology Hepatology

Degradation of splicing factor SRSF3 contributes to progressive liver disease

Abstract

Serine-rich splicing factor 3 (SRSF3) plays a critical role in liver function and its loss promotes chronic liver damage and regeneration. As a consequence, genetic deletion of SRSF3 in hepatocytes caused progressive liver disease and ultimately led to hepatocellular carcinoma. Here we show that SRSF3 is decreased in human liver samples with nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH), or cirrhosis that was associated with alterations in RNA splicing of known SRSF3 target genes. Hepatic SRSF3 expression was similarly decreased and RNA splicing dysregulated in mouse models of NAFLD and NASH. We showed that palmitic acid–induced oxidative stress caused conjugation of the ubiquitin-like NEDD8 protein to SRSF3 and proteasome-mediated degradation. SRSF3 was selectively neddylated at lysine 11 and mutation of this residue (SRSF3-K11R) was sufficient to prevent both SRSF3 degradation and alterations in RNA splicing. Lastly, prevention of SRSF3 degradation in vivo partially protected mice from hepatic steatosis, fibrosis, and inflammation. These results highlight a neddylation-dependent mechanism regulating gene expression in the liver that is disrupted in early metabolic liver disease and may contribute to the progression to NASH, cirrhosis, and ultimately hepatocellular carcinoma.

Authors

Deepak Kumar, Manasi Das, Consuelo Sauceda, Lesley G. Ellies, Karina Kuo, Purva Parwal, Mehak Kaur, Lily Jih, Gautam K. Bandyopadhyay, Douglas Burton, Rohit Loomba, Olivia Osborn, Nicholas J.G. Webster

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Figure 1

Loss of SRSF3 expression in NAFLD, NASH, and cirrhosis.

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Loss of SRSF3 expression in NAFLD, NASH, and cirrhosis. (A) Immunoblotti...
(A) Immunoblotting of SRSF3 in extracts from 4 representative human liver samples from normal individuals and individuals with NASH, NAFL, or cirrhosis. Graph shows quantification of SRSF3 protein level in human liver samples normalized to β-actin (n = 9, 21, 11, and 20 for normal [white], NAFL [orange], NASH [red], and cirrhosis [cyan], respectively). (B) Immunohistochemical staining for SRSF3 on FFPE sections from normal, NAFL, NASH, and cirrhotic livers. Graph shows quantification of SRSF3-positive nuclei per field (brown stain) (n = 4/group). Colors are as in panel A. Scale bars: 50 μm. (C) Immunoblotting of SRSF3 from hepatocytes from obese mice on high-fat diet (HFD) or lean mice on normal chow (Lean). Graph shows quantification of SRSF3 protein levels normalized to β-actin (n = 4/group). Lean mice shown in white, obese mice (HFD) shown in orange. (D) Immunoblotting of SRSF3 from hepatocytes from obese mice on NASH diet (NASH) or lean mice on normal chow (Lean). Graph shows quantification of SRSF3 protein levels normalized to β-actin (n = 4/group). Lean mice shown in white, NASH mice shown in red. (E) Immunohistochemical staining for SRSF3 on FFPE liver sections from lean, obese HFD, or obese NASH diet mice. Graph shows quantification of SRSF3-positive nuclei/field (brown stain) (n = 4/group). Colors are as in panel A. Scale bars: 50 μm. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001 by 1-way ANOVA with Tukey’s post hoc testing. All quantified results are presented as mean ± SEM.