HNF4A and neoplasm: Rap1GAP has been reported to as a negative regulator of Rap1 activity and serves an important role in tumor cell proliferation.[16] The results demonstrated that silencing Id1 expression could increase HNF‐4α and Rap1GAP protein levels, and overexpression of Id1 could suppress the level of HNF‐4α and Rap1GAP (Figure 6L).