RB1 and cancer: Since the E7 oncoprotein is known to mediate the inactivation of p53-dependent and pRb-dependent tumor suppression, the finding that TSSK2 was dispensable for cell survival only when expression of the E7 oncoprotein was induced in RKO carcinoma cells is very significant, suggesting that TSSK2 may represent one of the essential regulators of pRb tumor suppression activity in cancer cells.