In terms of growth, differentiation, and signaling pathways of hematopoietic factors, the effects of protein kinase C (PKC) activator, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and protein kinase A(PKA) activator, dibutyryl cyclic adenosine monophosphate (dbcAMP) were examined in vitro using three factor-responsive myeloid leukemia cell lines. TPA suppressed the growth of OCI/AML-1 and OCI/AML-5 cells but stimulated the proliferation of OCI/AML-4 cells. TPA differentiated OCI/AML-4 and OCI/AML-5 cells to macrophage-like cells. dbcAMP suppressed the growth of the three without differentiation. The stimulation of TPA induced tyrosine phosphorylation of some proteins in OCI/AML-4 and OCI/AML-5 cells. Their molecular weights were the same as those phosphorylated by hematopoietic factors. The patterns of phosphorylated proteins were different between the two. TPA induced the phosphorylation of MAP kinase, but not that of JAK2 protein in three cell lines. The stimulation of dbcAMP did not induce tyrosine phosphorylation in three cell lines. Overnight exposure of TPA inhibited the tyrosine phosphorylation induced by hematopoietic factors, although that of dbcAMP did not. We suggest a close relation of PKC to signaling pathways of hematopoietic factors, however, the ways of relation were diverse among the cell lines and the clear mechanism explaining its effects on growth and differentiation was not elucidated.

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