The pattern of expression of several protein kinase C (PKC) isoforms (alpha, betaI, delta, epsilon, eta, and zeta) during the course of hematopoietic development was investigated using primary human CD34(+) hematopoietic cells and stable cell lines subcloned from the growth factor-dependent 32D murine hematopoietic cell line. Each 32D cell clone shows the phenotype and growth factor dependence characteristics of the corresponding hematopoietic lineage. Clear-cut differences were noticed between erythroid and nonerythroid lineages. (1) The functional inhibition of PKC-epsilon in primary human CD34(+) hematopoietic cells resulted in a twofold increase in the number of erythroid colonies. (2) Erythroid 32D Epo1 cells showed a lower level of bulk PKC catalytic activity, lacked the expression of epsilon and eta PKC isoforms, and showed a weak or absent upregulation of the remaining isoforms, except betaI, upon readdition of Epo to growth factor-starved cells. (3) 32D, 32D GM1, and 32D G1 cell lines with mast cell, granulo-macrophagic, and granulocytic phenotype, respectively, expressed all the PKC isoforms investigated, but showed distinct responses to growth factor readdition. (4) 32D Epo 1.1, a clone selected for interleukin-3 (IL-3) responsiveness from 32D Epo1, expressed the epsilon isoform only when cultured with IL-3. On the other hand, when cultured in Epo, 32D Epo1.1 cells lacked the expression of both epsilon and eta PKC isoforms, similarly to 32D Epo1. (5) All 32D cell lines expressed the mRNA for PKC-epsilon, indicating that the downmodulation of the epsilon isoform occurred at a posttranscriptional level. In conclusion, the PKC isoform expression during hematopoiesis appears to be lineage-specific and, at least partially, related to the growth factor response.
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