A novel role of CKIP-1 in promoting megakaryocytic differentiation.

Casein kinase 2-interacting protein-1 (CKIP-1) is a known regulator of cardiomyocytes and macrophage proliferation. In this study, we showed that CKIP-1 was involved in the process of megakaryocytic differentiation. During megakaryocytic differentiation of K562 cells, CKIP-1 was dramatically upregulated and this upregulation induced by PMA was mediated through downregulation of transcription factor GATA-1. By transient transfection, oligonucleotide-directed mutagenesis and chromatin immunoprecipitation assays, we identified the transcriptional regulation of CKIP-1 by GATA-1. Overexpression of CKIP-1 initiated events of spontaneous megakaryocytic differentiation in K562 cells. Conversely, knockdown of CKIP-1 in cell lines suppressed megakaryocytic differentiation. Mechanistically, overexpression of CKIP-1 changed the expression levels of transcription factors that have been shown to be critical in erythro-megakaryocytic differentiation such as Fli-1, c-Myb and c-Myc. In vivo analysis confirmed that CKIP-1-/- mice had decreased number of CD41+ cells harvested from bone marrow, and lower platelet levels when compared to wild-type littermates. This is the first direct evidence suggesting that CKIP-1 is a novel regulator of megakaryocytic differentiation.