MAPK1 and cancer: However, MAPK1+MITF (S73A)-overexpressing cultures presented highly dampened proliferative and metastatic capacities relative to MAPK1 + MITF co-expressing cultures, which indicated that MAPK1 overexpression notably enhances the cancer-promoting characteristics of MITF but not of the MITF (S73A) mutant (Figure 8D).