RETRACTED: The retinoic acid receptor/CaMKII interaction: Pharmacologic inhibition of CaMKII enhances the differentiation of myeloid leukemia cells (Retracted article. See vol. 42, pg. 300, 2009)

Certain myeloid leukemia cells, particularly the acute promyelocytic leukemia (APL) subset, undergo terminal granulocytic differentiation in response to retinoic acid (RA). RA mediates its biologic effects through specific retinoic acid receptors (RARs) which serve as ligand-activated nuclear transcription factors. The Ca++/calmodulin-dependent protein kinases (CaMKs) are multifunctional serine/threonine kinases that are regulated by Ca++ signaling. We have observed significant cross-talk between these Ca++ and RA signaling pathways that regulates the differentiation of myeloid leukemia cells. We observe that CaMKII gamma is the CaMK that is predominantly expressed in myeloid cells. This enzyme localizes to the promoter of RAR target genes, physically interacts with and phospborylates RAR alpha and inhibits RAR transcriptional activity. KN-62, a pharmacological inhibitor of the CaMKs, enhances both retinoic acid receptor transcriptional activity as well as the terminal in vitro differentiation of certain myeloid leukemia cell lines including HL-60. However, this compound, as well as related synthetic analogs that enhance HL-60 terminal differentiation, fails to inhibit the growth of HL-60 xenografts in NOD-SCID mice likely because of the unfavorable pharmacokinetics displayed by these compounds. Nevertheless, our observations suggest that CaMKII gamma may provide a new therapeutic target for the treatment of the RA-responsive human myeloid leukemias. (C) 2007 Elsevier Inc. All rights reserved.