CDKN1B and teratoma: This is in part mediated by the association of p21CIP1 and p27KIP1 to SRR2. Indeed, when p27KIP1 binds to SRR2, together with the p130-E2F4-SIN3A complex, this contributes to the repression of SOX2 and leads to differentiation programs in ESCs, mouse embryonic fibroblasts (MEFs) and teratoma cells [20].