Certain phorbol esters, polar solvents and retinoids have been identified as in vitro and in vivo inducers of human myeloid leukemia cell differentiation. These findings have indicated that factor-independent growth of myeloid leukemia cells is reversible. The mechanisms by which these agents induce terminal differentiation, however, are unknown. Our work has focused on induction of the stress activated protein kinase (SAPK/JNK) as a signal that directs cellular differentiation. The results indicate that SAPK activates the c-jun and EGR-1 early response genes and thereby in part the differentiated phenotype. SAPK also targets the release of mitochondrial cytochrome c to integrate apoptosis with terminal differentiation. Our studies have shown that activation of protein kinase C-beta (PKC-beta) in the response to phorbol esters is essential for induction of SAPK and differentiation. PKC-beta-mediated signals induce the production of reactive oxygen species (ROS) and thereby the activation of SAPK. The findings also demonstrate that PKC-beta and the related PKC-beta isoform are each targeted to the nucleus and mitochondria in the phorbol ester response of myeloid leukemia cells. The proposed work will extend these studies by defining the effectors downstream to PKC-beta and PKC-beta that regulate the differentiation program. Our hypothesis is that PKC-beta- and PKC-beta-activated pathways function in concert to integrate nuclear and mitochondrial signals that confer terminal differentiation.
The Specific Aims are: 1) To further define PKC-beta- and ROS-dependent activation of SAPK in TPA-induced nuclear and mitochrondial signaling; 2) To study the functional significance of targeting PKC-beta to the nucleus and mitochrondial in the induction of myeloid leukemia cell differentiation; 3) To define the role of PKC-beta in nuclear and mitochondrial signaling associated with terminal differentiation; and 4) To study integration of the differentiated phenotype with apoptosis in the induction of terminal differentiation.
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