Fig. 11. A model of PKC-mediated signal transduction pathways in differentiating RD cells. A schematic presentation of PKC-mediated MAPKs cascades induced by TPA and the proposed roles of ERKs, JNKs and p38 in the regulation of growth arrest and myogenic differentiation in RD cells (solid arrows). The MAPK pathways targeted by the agonist, as well as inhibitors and a negative regulator of JNK's effect on p38, are indicated by dashed and dotted lines. PKC-mediated MAPK activation induces growth arrest and myogenic differentiation. When ERK and JNK are downregulated (encircled), by U0126, growth arrest and p38-mediated myogenic differentiation occur. Inhibition of the p38 pathway, by SB203580, prevents myogenic differentiation. Activation of both p38 and JNKs, by anisomycin, induces growth arrest but prevents myogenic process owing to a persistent and highly activated JNK, which negatively regulates the p38 pathway.