We analyzed these proteins because (i) SOX2’s proliferative function in cancer cells is exerted, at least in part, through direct repression of p21CIP1 and p27KIP1 expression [27,28]; (ii) there is an interaction between SOX2 and p27KIP1 in mice, in which we have just demonstrated that Srr2 plays a role [20,29]. This evidence concerns the gene CDKN1B and cancer.