MAP2K7 and hepatocellular carcinoma: Furthermore, pretreatment with PD98059, an inhibitor of MEK, an upstream kinase of Erk, prevents SSa-triggered inhibition of hepatoma cell growth and the accompanying induction of p15 and p16 [16], indicating that activation of Erk and the downstream induction of p16 family proteins are critical for SSa-induced inhibition of hepatoma growth.