Regulation of Jak2 tyrosine kinase by protein kinase C during macrophage differentiation of IL-3-dependent myeloid progenitor cells

Differentiation of macrophages from myeloid progenitor cells depends on a d iscrete balance between cell growth, survival, and differentiation signals. Interleukin-8 (IL-3) supports the growth and survival of myeloid progenito r cells through the activation of Jak2 tyrosine kinase, and macrophage diff erentiation has been shown to be regulated by protein kinase C (PKC). Durin g terminal differentiation of macrophages, the cells lose their mitogenic r esponse to IL-3 and undergo growth arrest, but the underlying signaling mec hanisms have remained elusive. Here we show that in IL-3-dependent 32D myel oid progenitor cells, the differentiation-inducing PKC isoforms PKC-(C) 200 0 by The American Society of Hematology alpha and PKC-delta specifically ca used rapid inhibition of IL-3-induced tyrosine phosphorylation. The target for this inhibition was Jak2, and the activation of PKC by 12-O-tetradecano yl-phorbol-13-acetate treatment also abrogated Ii-a-induced tyrosine phosph orylation of Jak2 in Ba/F3 cells, The mechanism of this regulation was inve stigated in 32D and COS7 cells, and the inhibition of Jak2 required catalyt ic activity of PKC-delta and involved the phosphorylation of Jak2 on serine and threonine residues by the associated PKC-delta, Furthermore, PKC-delta inhibited the in vitro catalytic activity of Jak2, indicating that Jak2 wa s a direct target for PKC-delta In 32D cells, the inhibition of Jak2 either by PKC-delta, tyrosine kinase inhibitor AG490, or IL-3 deprivation caused a similar growth arrest. Reversal of PKC-delta-mediated inhibition by the o verexpression of Jak2 promoted apoptosis in differentiating 32D cells. Thes e results demonstrate a PKC-mediated negative regulatory mechanism of cytok ine signaling and Jak2, and they suggest that it serves to integrate growth -promoting and differentiation signals during macrophage differentiation. ( C) 2000 by The American Society of Hematology.