Inhibits estrogen-induced cell proliferation by competing with PLCG for binding to ESR1, blocking the effect of estrogen on PLCG and repressing estrogen-induced proliferation. May play a role in T- cell development and function. {ECO:0000269|PubMed:18641339, ECO:0000269|PubMed:19712589}. This is the function of Ensembl gene identifier ENSG00000104611 (SH2D4A, SH2 domain containing 4A).