Research Articles: Therapeutics, Targets, and Development

Inhibition of Src family kinases enhances retinoic acid–induced gene expression and myeloid differentiation

¹ Departments of ¹Medicine and ²Pharmacology, University of Pittsburgh and the University of Pittsburgh Cancer Institute, Pittsburgh, Pennsylvania

^* To whom correspondence should be addressed. E-mail: johnsond{at}pitt.edu.

	Abstract

Treatment of acute promyelocytic leukemia with retinoic acid (RA) results in differentiation of the leukemic cells and clinical remission. However, the cellular factors that regulate RA-induced myeloid differentiation are largely unknown, and other forms of acute myelogenous leukemia (AML) do not respond to this differentiation therapy. A greater understanding of the molecules that positively or negatively regulate RA-induced differentiation should facilitate the development of more effective differentiation therapies. In this study, we investigated the potential role of Src family kinases (SFK) in the regulation of RA-induced gene expression and myeloid differentiation. We report that inhibition of SFKs markedly enhanced RA-induced differentiation in myeloid cell lines and primary AML cells, as assessed by flow-cytometric analysis of cell surface markers, morphologic analysis, and nitroblue tetrazolium reduction. In addition, inhibition of SFKs enhanced expression from retinoic acid receptor (RAR) target genes encoding CCAAT/enhancer binding protein (C/EBP), PU.1, intercellular adhesion molecule-1 (ICAM-1), and cathepsin D. Moreover, a constitutively active Src inhibited RAR-dependent transcription, whereas a kinase-dead Src exerted little effect. These studies provide the first demonstration that SFKs act to negatively regulate RA-induced gene expression and myeloid differentiation and suggest that the combination of SFK inhibition and RA treatment may be therapeutically beneficial in AML. [Mol Cancer Ther 2007;6(12):OF1–10]

Key Words: Src, myeloid differentiation, retinoic acid, PP1, PP2