The nuclear receptor coactivator 3 also known as NCOA3 is a protein that, in humans, is encoded by the NCOA3 gene. [5] [6] NCOA3 is also frequently called 'amplified in breast 1' (AIB1), steroid receptor coactivator-3 (SRC-3), or thyroid hormone receptor activator molecule 1 (TRAM-1).
NCOA3 is a transcriptional coactivator protein that contains several nuclear receptor interacting domains and an intrinsic histone acetyltransferase activity. NCOA3 is recruited to DNA promotion sites by ligand-activated nuclear receptors. NCOA3, in turn, acylates histones, which makes downstream DNA more accessible to transcription. Hence, NCOA3 assists nuclear receptors in the upregulation of gene expression. [7] [8]
The ratio of PAX2 to AIB-1 protein expression may be predictive of the effectiveness of tamoxifen in breast cancer treatment. [9] [10]
Several molecular mechanisms implicate NCOA3 (AIB1) in the endocrine therapy resistance (depicted in the figure). Signaling pathways or mutations (i.e. HER2/neu overexpression, activating mutations in PIK3CA (PI3K), activating mutations in the proto-oncogene tyrosine-protein kinase Src, etc.) that lead to persistent activation of ERK and/or PIK3CA/AKT kinase pathways result, in one hand in an enhanced AIB1 transcriptional coactivation capacity, [11] and in the other hand in the inhibition of the proteasome-dependent AIB1 turn-over and therefore, in AIB1 overexpression. [12] In both conditions, the equilibrium of estrogen receptor (ER) complex formation is displaced towards a transcriptionally active complex and thus, counteracting the inhibition caused by anti-estrogenic drugs such as tamoxifen or fulvestrant (selective estrogen receptor modulators). The result is the restoration of estrogen-sensitive gene transcription and the promotion of cancer progression and/or relapse.
Notably, tumors diagnosed with concomitant overexpression of AIB1 and HER2/neu have worse outcome with tamoxifen therapy than all other patients combined. [13] In addition, dormant tumor cells of luminal breast cancers treated with endocrine therapy may acquire with time, mutations that alter kinase signalling pathways and ultimately enhance AIB1 oncogenic functions. Also, estrogen receptor-PAX2 complexes repress HER2/neu expression, but loss of PAX2 expression may result in de novo HER2/neu expression and initiate endocrine therapy resistance and relapse. [14]
Nuclear receptor coactivator 3 has been shown to interact with:
Estrogen receptors (ERs) are a group of proteins found inside cells. They are receptors that are activated by the hormone estrogen (17β-estradiol). Two classes of ER exist: nuclear estrogen receptors, which are members of the nuclear receptor family of intracellular receptors, and membrane estrogen receptors (mERs), which are mostly G protein-coupled receptors. This article refers to the former (ER).
Histone acetyltransferase p300 also known as p300 HAT or E1A-associated protein p300 also known as EP300 or p300 is an enzyme that, in humans, is encoded by the EP300 gene. It functions as histone acetyltransferase that regulates transcription of genes via chromatin remodeling by allowing histone proteins to wrap DNA less tightly. This enzyme plays an essential role in regulating cell growth and division, prompting cells to mature and assume specialized functions (differentiate), and preventing the growth of cancerous tumors. The p300 protein appears to be critical for normal development before and after birth.
Proline-, glutamic acid- and leucine-rich protein 1 (PELP1) also known as modulator of non-genomic activity of estrogen receptor (MNAR) and transcription factor HMX3 is a protein that in humans is encoded by the PELP1 gene. is a transcriptional corepressor for nuclear receptors such as glucocorticoid receptors and a coactivator for estrogen receptors.
In molecular biology and genetics, transcription coregulators are proteins that interact with transcription factors to either activate or repress the transcription of specific genes. Transcription coregulators that activate gene transcription are referred to as coactivators while those that repress are known as corepressors. The mechanism of action of transcription coregulators is to modify chromatin structure and thereby make the associated DNA more or less accessible to transcription. In humans several dozen to several hundred coregulators are known, depending on the level of confidence with which the characterisation of a protein as a coregulator can be made. One class of transcription coregulators modifies chromatin structure through covalent modification of histones. A second ATP dependent class modifies the conformation of chromatin.
Estrogen receptor alpha (ERα), also known as NR3A1, is one of two main types of estrogen receptor, a nuclear receptor that is activated by the sex hormone estrogen. In humans, ERα is encoded by the gene ESR1.
The nuclear receptor coactivator 1 (NCOA1) is a transcriptional coregulatory protein that contains several nuclear receptor interacting domains and an intrinsic histone acetyltransferase activity. NCOA1 is recruited to DNA promotion sites by ligand-activated nuclear receptors. NCOA1, in turn, acylates histones, which makes downstream DNA more accessible to transcription. Hence, NCOA1 assists nuclear receptors in the upregulation of DNA expression.
The nuclear receptor coactivator 2 also known as NCoA-2 is a protein that in humans is encoded by the NCOA2 gene. NCoA-2 is also frequently called glucocorticoid receptor-interacting protein 1 (GRIP1), steroid receptor coactivator-2 (SRC-2), or transcriptional mediators/intermediary factor 2 (TIF2).
Retinoid X receptor alpha (RXR-alpha), also known as NR2B1 is a nuclear receptor that in humans is encoded by the RXRA gene.
AKT2, also known as RAC-beta serine/threonine-protein kinase, is an enzyme that in humans is encoded by the AKT2 gene. It influences metabolite storage as part of the insulin signal transduction pathway.
Signal transducer and activator of transcription 5A is a protein that in humans is encoded by the STAT5A gene. STAT5A orthologs have been identified in several placentals for which complete genome data are available.
Nuclear receptor-interacting protein 1 (NRIP1) also known as receptor-interacting protein 140 (RIP140) is a protein that in humans is encoded by the NRIP1 gene.
Mediator of RNA polymerase II transcription subunit 1 also known as DRIP205 or Trap220 is a subunit of the Mediator complex and is a protein that in humans is encoded by the MED1 gene. MED1 functions as a nuclear receptor coactivator.
Probable ATP-dependent RNA helicase DDX5 also known as DEAD box protein 5 or RNA helicase p68 is an enzyme that in humans is encoded by the DDX5 gene.
Scaffold attachment factor B, also known as SAFB, is a gene with homologs that have been studied in humans and mice.
Nuclear receptor coactivator 6 is a protein that in humans is encoded by the NCOA6 gene.
Steroid receptor RNA activator 1 also known as steroid receptor RNA activator protein (SRAP) is a protein that in humans is encoded by the SRA1 gene. The mRNA transcribed from the SRA1 gene is a component of the ribonucleoprotein complex containing NCOA1. This functional RNA also encodes a protein.
Tripartite motif-containing 24 (TRIM24) also known as transcriptional intermediary factor 1α (TIF1α) is a protein that, in humans, is encoded by the TRIM24 gene.
Peroxisome proliferator-activated receptor gamma coactivator 1-beta is a protein that in humans is encoded by the PPARGC1B gene.
Mediator of RNA polymerase II transcription subunit 16 is an enzyme that in humans is encoded by the MED16 gene.
Nuclear receptor coregulators are a class of transcription coregulators that have been shown to be involved in any aspect of signaling by any member of the nuclear receptor superfamily. A comprehensive database of coregulators for nuclear receptors and other transcription factors was previously maintained at the Nuclear Receptor Signaling Atlas website which has since been replaced by the Signaling Pathways Project website.
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