The function of BEX2 (brain expressed X-linked 2, ENSG00000133134) is as follows. Regulator of mitochondrial apoptosis and G1 cell cycle in breast cancer (PubMed:19711341). Protects the breast cancer cells against mitochondrial apoptosis and this effect is mediated through the modulation of BCL2 protein family, which involves the positive regulation of anti-apoptotic member BCL2 and the negative regulation of pro-apoptotic members BAD, BAK1 and PUMA (PubMed:19711341). Required for the normal cell cycle progression during G1 in breast cancer cells through the regulation of CCND1 and CDKN1A (PubMed:19711341). Regulates the level of PP2A regulatory subunit B and PP2A phosphatase activity (PubMed:19711341). In absence of reductive stress, acts as a pseudosubstrate for the CRL2(FEM1B) complex: associates with FEM1B via zinc, thereby preventing association between FEM1B and its substrates (By similarity). {ECO:0000250|UniProtKB:Q9WTZ8, ECO:0000269|PubMed:19711341}.