Fig. 5.

HNF4α is a target for ubiquitin-mediated degradation. (A) Because RNF4 plays an important role in modulating HNF4α stability in vitro, we monitored its expression during human embryonic stem cell differentiation. RNF4 expression was observed and increased during hepatic differentiation and maturation. (B,C) To assess whether ubiquitin-mediated proteolysis played a central role in the stability of HNF4α, we inhibited the 26S proteasome using MG132. hESC-derived hepatocytes were incubated with or without MG132 for 4 hours and cell extracts were collected, separated, western blotted and probed for HNF4α. HNF4α levels increased ∼fourfold in the presence of MG132, as determined by actin-controlled densitometry.