Abstract
Death-associated kinase-1 (DAPK1) is a broadly expressed pro-apoptotic cytoplasmic S/T protein kinase that regulates cell proliferation and survival, modulates a p53 apoptotic checkpoint, and contributes to ALL, AML, and myelodysplastic syndromes. DAPK2, by comparison, is an under-studied (but likewise pro-apoptotic) DAPK1 orthologue that we have discovered to be expressed (via Affymetrix gene profiling) at high-levels in late-stage erythroid progenitor cells. In particular, and as examined in purified and developmentally-staged proerythroblasts, basophillic erythroblasts and orthrochromatic erythroblasts, DAPK2 gene expression was sharply up-modulated as progenitor cells developed to a Ter119(+), CD71-high stage. Using a DAPK2-specific antibody, this was confirmed at the protein level, and initial analyses of expression in cell lines further indicated lineage-restricted DAPK2 expression (e.g. high level in erythroid GIE2 cells but undetectable in pluripotent EML cells). To advance an initial understanding of DAPK2’s role in erythroid cells, its possible regulation via the Epo receptor (EpoR) also was studied. Here, primary erythroid progenitor cells from mice with knocked-in minimal EpoR alleles were used (PY-null and PY343-only EpoR-HM and EpoR-H forms, respectively). Interestingly, the point-mutation of a PY3434/Stat5 specific binding site (to F343) (EpoR-HM allele) resulted in a clear multi-fold de-repression of DAPK2 that also correlated with a decreased survival potential for EpoR-HM erythroblasts. This repressive effect of EpoR/PY343/Stat5 signaling on DAPK2 expression was highly stage-specific, and was exerted distinctly in advance of an observed EpoR/PY343/Stat5-dependent up-modulation of Bcl-xl expression. In addition, in wild-type EpoR pro-erythroblasts, DAPK2 levels increased with decreasing Epo concentrations. Investigations therefore reveal DAPK2 to be a late-stage erythroid- restricted, (and EpoR/PY343/Stat5- modulated) novel candidate regulator of red cell production.
