Figure 8.

Role of ERK5 and E3 ubiquitin ligases in HNF4α expression by hypoxia. A, MIN6 cells were incubated in either 5 or 20% O₂ for 18 h, and expression of ERK5 or HNF4α protein was examined by Western blot analysis. B, MIN6 cells expressing either control shRNA or Erk5 shRNA were incubated in either 5 or 20% O₂ for 24 h, and HNF4α protein levels were examined by Western blot analysis. C, relative HNF4α protein levels were calculated (n = 3). D–G, effect of overexpression of atrogin-1 shRNA (D and E) or Nedd4l shRNA (F and G) on HNF4α expression was examined. All data are presented as mean ± S.E. (error bars). N.S., not significant; *, p < 0.05; **, p < 0.01; ***, p < 0.001.