Association of protein tyrosine phosphorylation with B cell differentiation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA).

We have assessed whether tyrosine protein kinase (TPK) is involved in B cell differentiation. In vitro phosphorylation of an endogenous substrate in B cell leukemias showed that leukemic B cells at different stages of differentiation had specific endogenous substrates in tyrosine phosphorylation as well as distinct TPK activity. To clarify the relationship between TPK and the process of B cell differentiation, we studied protein tyrosine phosphorylation in two kinds of leukemic B cells, which showed distinct responses to TPA (12-O-tetradecanoylphorbol-13-acetate) in B cell differentiation. TPA-treated leukemic B cells from patients with B cell chronic lymphocytic leukemia (B-CLL) differentiated into cytoplasmic immunoglobulin (clg)+ plasmacytoid cells, while TPA-treated leukemic B cells from patients with hairy cell leukemia (HCL) did not differentiate into clg+ cells, but showed a peculiar morphological change, spreading. Untreated B-CLL cells and HCL cells showed similar TPK activities and tyrosine protein phosphorylation. When treated with TPA, enhanced phosphorylation was seen in B-CLL cells, while a clear reduction in phosphorylation was found in HCL cells. However, using 4-hydroxycinnamide derivatives which reduce TPK activity, we found that only the reduction of TPK activity did not lead HCL cells to spreading. These data suggest that protein tyrosine phosphorylation and/or dephosphorylation might be involved in B cell differentiation, but only the change of TPK activity in HCL cells is not sufficient to induce effects.