Increase of E3 ubiquitin ligase NEDD4 expression leads to degradation of its target proteins PTEN/IGF1R during the formation of goose fatty liver.

Goose fatty liver may have a unique protective mechanism as it does not show a pathological injury even in the case of severe steatosis. Although neural precursor cell-expressed developmentally downregulated gene 4 (NEDD4) participates in repair and regeneration of injured liver through its target proteins, its role in nonalcoholic fatty liver disease remains unknown. Using quantitative polymerase chain reaction (PCR) and immunoblot analyses, here, we found that the messenger RNA (mRNA) and protein expressions of NEDD4 were induced in goose fatty liver compared with normal liver. The mRNA expression of the gene of phosphate and tension homology deleted on chromosome ten (PTEN) and insulin-like growth factor 1 receptor (IGF1R) was also induced in goose fatty liver; however, their protein expression was or tended to be suppressed. Moreover, the co-immunoprecipitation analysis indicated that there was a physical association between NEDD4 and PTEN in goose liver, which was consistent with the ubiquitination of PTEN in goose fatty liver. Furthermore, NEDD4 overexpression in goose primary hepatocytes suppressed the PTEN and IGF1R protein levels without a significant effect on their mRNA expression. In conclusion, the increased expression of NEDD4 leads to the degradation of PTEN and IGF1R proteins through ubiquitination in goose fatty liver, suggesting that NEDD4 may protect goose fatty liver from severe steatosis-associated injury via its target proteins during the development of goose fatty liver.