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 October 1, 2019; First 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 6

Expression of degradation-resistant SRSF3-K11R reduced liver steatosis, fibrosis, and inflammation in mice on a NASH diet.

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Expression of degradation-resistant SRSF3-K11R reduced liver steatosis, ...
(A) Liver sections from lean mice on normal chow (Lean) or mice on a NASH diet for 7 weeks infected with AAV8 expressing GFP (NASH-GFP), wild-type SRSF3 (NASH-WT), or the degradation-resistant K11R-mutant SRSF3 (NASH-K11R). Green arrowheads indicate steatotic hepatocytes and yellow arrowheads indicate ballooned hepatocytes on H&E-stained sections. White and black arrowheads indicate fibrosis on Masson’s trichrome– and Sirius red–stained sections. Red arrowheads indicate inflammatory cell infiltrates on H&E sections. Original magnification ×40. (B) Quantification of steatosis. Histological scoring was performed by a pathologist blinded to the identity of the samples. Lipid droplet number and area were measured using ImageJ (NIH). Lean mice shown in white, GFP-expressing mice in red, WT SRSF3–expressing mice in blue, and SRSF3-K11R–expressing mice in cyan. (C) Histological scoring of hepatocyte ballooning, fibrosis, and inflammation. Results are presented as mean ± SEM (n = 6–8 mice/group). *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001 by 1-way ANOVA with Tukey’s post hoc testing.