Tumor suppressor which functions to suppress MRTFA-induced SRF transcriptional activity. May function in the RHOA-DIAPH1 signal transduction pathway and regulate cell migration through transcriptional regulation of ITGB1. Interacts with DIAPH1 (By similarity). Forms a nuclear ternary complex with MRTFA and SRF. Nuclear localization is required for inhibition of MRTFA. Belongs to the SCAI family.