TGFB1 and neoplasm: In PSPC1-deficient cells, TGF-β could act as a tumor suppressor by activating cell-cycle arrest genes like p15, p21, p57 and DAPK1. Besides RUNX3 and PSPC1, there are reports of other factors that could modulate this dichotomous TGF-β signaling; these are listed in Figure 1.