title: Targeting PKC delta-mediated topoisomerase II beta overexpression subverts the differentiation block in a retinoic acid-resistant APL cell line.
abstract: 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.
authors.affiliation: Division of Experimental Medicine, Department of Oncology, Segal Cancer Comprehensive Centre, Lady Davis Institute for Medical Research, Sir Mortimer B Davis Jewish General Hospital, McGill University, Montréal, Quebec, Canada.
authors.forename: S
authors.initials: S
authors.lastname: McNamara
authors.forename: J N
authors.initials: JN
authors.lastname: Nichol
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.forename: W H
authors.initials: WH
authors.lastname: Miller
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D002454:Cell Differentiation / Q000187:drug effects*; D045744:Cell Line, Tumor; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D005455:Fluorescent Antibody Technique; D015973:Gene Expression Regulation, Leukemic; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology*; D010766:Phosphorylation; D000075223:Poly-ADP-Ribose Binding Proteins; D051745:Protein Kinase C-delta / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D000075223:Poly-ADP-Ribose Binding Proteins; D012333:RNA, Messenger; D014212:Tretinoin; D051745:Protein Kinase C-delta; D004250:DNA Topoisomerases, Type II; C000618814:TOP2B protein, human