The function of IER5 (immediate early response 5, ENSG00000162783) is as follows. Plays a role as a transcription factor (PubMed:22132193, PubMed:25355627). Mediates positive transcriptional regulation of several chaperone genes during the heat shock response in a HSF1- dependent manner (PubMed:25355627, PubMed:25816751). Mediates negative transcriptional regulation of CDC25B expression (PubMed:22132193). Plays a role in the dephosphorylation of the heat shock factor HSF1 and ribosomal protein S6 kinase (S6K) by the protein phosphatase PP2A (PubMed:25816751, PubMed:26496226). Involved in the regulation of cell proliferation and resistance to thermal stress (PubMed:22132193, PubMed:25355627, PubMed:26496226). Involved in the cell cycle checkpoint and survival in response to ionizing radiation (PubMed:19238419, PubMed:22132193). Associates with chromatin to the CDC25B promoter (PubMed:22132193). {ECO:0000269|PubMed:19238419, ECO:0000269|PubMed:22132193, ECO:0000269|PubMed:25355627, ECO:0000269|PubMed:25816751, ECO:0000269|PubMed:26496226}.