MAPK14 and breast cancer: However, our studies show that the anti-invasive action of melatonin is mediated through the p38 MAPK pathway and not the ERK1/2 pathway since melatonin treatment (10-9 M) repressed p38 phosphorylation in both MCF-7/6 (Figure 5a) and MCF-7/Her2.1 (data not shown) breast cancer cells but had no effect on ERK1/2 phosphorylation (data not shown).