An additional region of coactivator GRIP1 required for interaction with the hormone-binding domains of a subset of nuclear receptors

Transcriptional coactivators of the p160 family (SRC-1, GRIP1, and p/CIP) a ssociate with DNA-bound nuclear receptors (NRs) and help the NRs to recruit an active transcription initiation complex to the promoters of target gene s. Previous studies have demonstrated the importance of the NR interaction domain (NID) of p160 proteins containing three NR box motifs (LXXLL) for th e interaction with the hormone-binding domains of NRs, Here we report that, in addition to NID, another region of coactivator GRIP1 (amino acids 1011- 1121), called the auxiliary NID (NIDaux), is required in vitro and in vivo for efficient interaction with a subset of NRs, including the glucocorticoi d receptor (GR), androgen receptor, and retinoic acid receptor cu, A second group of NRs, which includes the progesterone receptor, retinoid X recepto r alpha, thyroid hormone receptor beta 1, and vitamin D receptor, required only NID for efficient interaction. For binding to GR, the MD and NIDaux of GRIP1 must act in cis, but deletion of up to 144 amino acids between the t wo regions did not reduce binding efficiency. Amino acids 1011-1121 of GRIP 1 also contain a p300 interaction domain, but mutational analysis indicated that the p300 interaction function within this region is separable from th e ability to contribute to GR hormone-binding domain binding. SRC-1 lacks a n NIDaux activity equivalent to that in GRIP1.