In the past few years, many nuclear receptor coactivators have been identified and shown to be an integral part of receptor action. The most frequently studied of these coactivators are members of the steroid receptor coactivator (SRC) family, SRC-1, TIF2/GRIP1/SRC-2, and pCIP/ACTR/AIB-1/RAC-3/TRAM-1/SRC-3. In this report, we describe the biochemical purification of SRC-1 and SRC-3 protein complexes and the subsequent identification of their associated proteins by mass spectrometry. Surprisingly, we found association of SRC-3, but not SRC-1, with the IκB kinase (IKK). IKK is known to be responsible for the degradation of IκB and the subsequent activation of NF-κB. Since NF-κB plays a key role in host immunity and inflammatory responses, we therefore investigated the significance of the SRC-3-IKK complex. We demonstrated that SRC-3 was able to enhance NF-κB-mediated gene expression in concert with IKK. In addition, we showed that SRC-3 was phosphorylated by the IKK complex in vitro. Furthermore, elevated SRC-3 phosphorylation in vivo and translocation of SRC-3 from cytoplasm to nucleus in response to tumor necrosis factor alpha occurred in cells, suggesting control of subcellular localization of SRC-3 by phosphorylation. Finally, the hypothesis that SRC-3 is involved in NF-κB-mediated gene expression is further supported by the reduced expression of interferon regulatory factor 1, a well-known NF-κB target gene, in the spleens of SRC-3 null mutant mice. Taken together, our results not only reveal the IKK-mediated phosphorylation of SRC-3 to be a regulated event that plays an important role but also substantiate the role of SRC-3 in multiple signaling pathways.

Autism, a pervasive neurodevelopmental disorder manifested by deficits in social behavior and interpersonal communication, and by stereotyped, repetitive behaviors, is inexplicably biased towards males by a ratio of ∼4∶1, with no clear understanding of whether or how the sex hormones may play a role in autism susceptibility. Here, we show that male and female hormones differentially regulate the expression of a novel autism candidate gene, retinoic acid-related orphan receptor-alpha (RORA) in a neuronal cell line, SH-SY5Y. In addition, we demonstrate that RORA transcriptionally regulates aromatase, an enzyme that converts testosterone to estrogen. We further show that aromatase protein is significantly reduced in the frontal cortex of autistic subjects relative to sex- and age-matched controls, and is strongly correlated with RORA protein levels in the brain. These results indicate that RORA has the potential to be under both negative and positive feedback regulation by male and female hormones, respectively, through one of its transcriptional targets, aromatase, and further suggest a mechanism for introducing sex bias in autism.

The basic mechanisms underlying ligand-dependent transcriptional activation by nuclear receptors (NRs) require the sequential recruitment of various coactivators. Increasing numbers of coactivators have been identified in recent years, and both biochemical and genetic studies demonstrate that these coactivators are differentially used by transcription factors, including NRs, in a cell/tissue type- and promoter-specific manner. However, the molecular basis underlying this specificity remains largely unknown. Recently, NRs and coregulators were shown to be targets of posttranslational modifications activated by diverse cellular signaling pathways. It is argued that posttranslational modifications of these proteins provide the basis for a combinatorial code required for specific gene activation by NRs and coactivators, and that this code also enables coactivators to efficiently stimulate the activity of other classes of transcription factors. In this review, we will focus on coactivators and discuss the recent progress in understanding the role of phosphorylation of the steroid receptor coactivator family and the potential ramifications of this posttranslational modification for regulation of gene expression.