Lineage-restricted expression of protein kinase C isoforms in hematopoiesis

The pattern of expression of several protein kinase C (PKC) isoforms (α, βI, δ, ε, η, and ζ) 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-ε 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 ε and η PKC isoforms, and showed a weak or absent upregulation of the remaining isoforms, except βI, 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 e isoform only when cultured with IL-3. On the other hand, when cultured in Epo, 32D Epo1.1 cells lacked the expression of both ε and η PKC isoforms, similarly to 32D Epo1. (5) All 32D cell lines expressed the mRNA for PKC-ε, indicating that the downmodulation of the ε isoform occurred at a posttranscriptional level. In conclusion, the PKC isoform expression during hematepoiesis appears to be lineage-specific and, at least partially, related to the growth factor response.