Targeting PKC[delta]-mediated topoisomerase II[beta] overexpression subverts the differentiation block in a retinoic acid-resistant APL cell line.
McNamara, S 1,3; Nichol, J N 1,3; Wang, H 2; Miller, W H Jr 1
[Article] Leukemia. 24(4):729-739, April 2010.

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: Retinoic acid (RA) relieves the maturation block in t(15:17) acute promyelocytic leukemia (APL), leading to granulocytic differentiation. However, RA treatment alone invariably results in RA resistance, both in vivo and in vitro. RA-resistant cell lines have been shown to serve as useful models for elucidation of mechanisms of resistance. Previously, we identified topoisomerase II beta (TOP2B) as a novel mediator of RA-resistance in APL cell lines. In this study, we show that both TOP2B protein stability and activity are regulated by a member of the protein kinase C (PRKC) family, PRKC delta (PRKCD). Co-treatment with a pharmacologic inhibitor of PRKCD and RA resulted in the induction of an RA responsive reporter construct, as well as the endogenous RA target genes, CEBPE, CYP26A1 and RIG-I. Furthermore, the co-treatment overcame the differentiation block in RA-resistant cells, as assessed by morphological analysis, restoration of promyelocytic leukemia nuclear bodies, induction of CD11c cell surface expression and an increase in nitro-blue-tetrazolium reduction. Cumulatively, our data suggest a model whereby inhibition of PRKCD decreases TOP2B protein levels, leading to a loss of TOP2B-mediated repressive effects on RA-induced transcription and granulocytic differentiation.

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