Question

An inactivating mutation of the transactivating domain of a transcription factor in the presence of coactivator results in binding to DNA but not transcription. Why? (I don't really understand what a transactivating domain or coactivators are)

Answer 1

With the example of CITED1, a CBP/p300-binding nuclear protein that does not bind directly to DNA, is a transcriptional coregulator.

Here, evidence that CITED1 functions as a selective coactivator for estrogen-dependent transcription.

When transfected, CITED1 enhanced transcriptional activation by the ligand-binding/AF2 domain of both estrogen receptor-? (ER?) and ER? in an estrogen-dependent manner, but it affected transcriptional activities of other nuclear receptors only marginally.

CITED1 bound directly to ER? in an estrogen-dependent manner through its transactivating domain, and this binding activity was separable from its p300-binding activity.

CITED1 was strongly expressed in nulliparous mouse mammary epithelial cells and, when expressed in ER-positive MCF-7 breast cancer cells by transduction, exogenous CITED1 enhanced sensitivity of MCF-7 cells to estrogen, stabilizing the estrogen-dependent interaction between p300 and ER?.

The estrogen-induced expression of the transforming growth factor-? (TGF-?) mRNA transcript was enhanced in the CITED1-expressing MCF-7 cells, whereas estrogen-induced expression of the mRNA transcripts for progesterone receptor or pS2 was not affected.

Chromatin immunoprecipitation assay revealed that endogenous CITED1 is recruited to the chromosomal TGF-? promoter in MCF-7 cells in an estrogen-dependent manner but not to the pS2 promoter.

These results suggest that CITED1 may play roles in regulation of estrogen sensitivity in a gene-specific manner.