Breast carcinoma amplified sequence 3, also known as BCAS3, is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 which in humans is encoded by the BCAS3 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

. BCAS3 is a gene that is amplified and overexpressed in breast cancer cells.

Function

The BCAS3 gene is regulated by estrogen receptor alpha

Estrogen receptor alpha

Estrogen receptor alpha , also known as NR3A1 , is a nuclear receptor that is activated by the sex hormone estrogen...

 (ER-α). The PELP1

PELP-1

PELP-1 is a transcriptional corepressor for nuclear receptors such as glucocorticoid receptors and a coactivator for estrogen receptors.-Activation of protein kinases:...

 protein acts as a transcriptional coactivator

Coactivator (genetics)

A coactivator is a protein that increases gene expression by binding to an activator which contains a DNA binding domain. The coactivator is unable to bind DNA by itself....

 of estrogen receptor induced BCAS3 gene expression. In addition BCAS3 possesses histone acetyltransferase

Histone acetyltransferase

Histone acetyltransferases are enzymes that acetylate conserved lysine amino acids on histone proteins by transferring an acetyl group from acetyl CoA to form ε-N-acetyl lysine....

activity and itself appears to act as a coactivator of ER-α. Furthermore BCAS3 requires PELP1 to function as a coactivator in ER-α. Hence BCAS3 apparently is involved in a positive feedback loop leading to ER-α mediated signal amplification.

Further reading