MAPK8 and Hermansky-Pudlak syndrome: Exposure to HPS for 6 h markedly elevated (p < 0.01) the phosphorylation levels of p38/JNK/ERK (Fig. 4b, d and f), yet the protein levels of JNK, p38 and ERK remained almost unified between the control and HPS groups (Fig. 4a, c and e).