Abstract
Transcriptional coactivators of the p160 family (SRC-1, GRIP1, and p/CIP) associate with DNA-bound nuclear receptors (NRs) and help the NRs to recruit an active transcription initiation complex to the promoters of target genes. Previous studies have demonstrated the importance of the NR interaction domain (NID) of p160 proteins containing three NR box motifs (LXXLL) for the 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 glucocorticoid receptor (GR), androgen receptor, and retinoic acid receptor alpha. A second group of NRs, which includes the progesterone receptor, retinoid X receptor alpha, thyroid hormone receptor beta1, and vitamin D receptor, required only NID for efficient interaction. For binding to GR, the NID and NIDaux of GRIP1 must act in cis, but deletion of up to 144 amino acids between the two regions did not reduce binding efficiency. Amino acids 1011-1121 of GRIP1 also contain a p300 interaction domain, but mutational analysis indicated that the p300 interaction function within this region is separable from the ability to contribute to GR hormone-binding domain binding. SRC-1 lacks an NIDaux activity equivalent to that in GRIP1.
Highlights
The nuclear receptor (NR)1 superfamily is a large group of structurally homologous transcription factors that includes the receptors for the five steroid hormones (Class I receptors); receptors for thyroid hormone, vitamin D, and retinoic acid
Short polypeptides containing one or more of the NR box motifs are sufficient for binding some NR hormone-binding domain (HBD) [32], our preliminary experiments had indicated that the requirements for glucocorticoid receptor (GR) HBD binding to GRIP1 were more complex
GR HBD was expressed as a fusion protein with Gal4 DNA-binding domain (DBD), and GRIP1 fragments were fused with Gal4 activation domain (AD)
Summary
The nuclear receptor (NR)1 superfamily is a large group of structurally homologous transcription factors that includes the receptors for the five steroid hormones (Class I receptors); receptors for thyroid hormone, vitamin D, and retinoic acid. The Minimum Fragment of GRIP1 Required to Bind GR HBD—The importance of the three clustered NR box or LXXLL motifs in the NID of the p160 coactivator family for binding to the HBDs of all NRs has been established [13, 29, 32].
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