Fig. 5
From: The Id-protein family in developmental and cancer-associated pathways
The Id proteins promote cell-cycle progression. Cyclin/Cdk-mediated cell-cycle progression is supported by the Id-protein-induced inactivation of the Cdk inhibitors p15/16/21 and Ets, or by the direct interaction of Id2 with hypophosphorylated pRb. In addition, a cross talk between Id1 and the p53 pathway involving the cell-cycle blocker p21 and the Id1 transcriptional repressor DEC1 has been proposed. Also, Id1 may activate the MAPK pathway by promoting the phosphorylation of Raf and MEK1/2, which results in the induction of the transcription factor Egr1, a positive regulator of Id1 and Id3 gene expression