Novel mechanism by which histone deacetylase inhibitors facilitate topoisomerase IIα degradation in hepatocellular carcinoma cells.
Histone deacetylase (HDAC) inhibitors exhibit a unique ability to degrade topoisomerase (topo)IIα in hepatocellular carcinoma (HCC) cells, which contrasts with the effect of topoII-targeted drugs on topoIIβ degradation. This selective degradation might foster novel strategies for HCC treatment in light of the correlation of topoIIα overexpression with the aggressive tumor phenotype and chemoresistance. Here we report a novel pathway by which HDAC inhibitors mediate topoIIα proteolysis in HCC cells. Our data indicate that HDAC inhibitors transcriptionally activated casein kinase (CK)2α expression through increased association of acetylated histone H3 with the CK2α gene promoter. In turn, CK2 facilitated the binding of topoIIα to COP9 signalosome subunit (Csn)5 by way of topoIIα phosphorylation. Furthermore, we identified Fbw7, a Csn5-interacting F-box protein, as the E3 ligase that targeted topoIIα for degradation. Moreover, knockdown of CK2α, Csn5, or Fbw7 reversed HDAC inhibitor-induced topoIIα degradation. Mutational analysis indicates that the (1361) SPKLSNKE(1368) motif plays a crucial role in regulating topoIIα protein stability. This motif contains the consensus recognition sites for CK2 (SXXE), glycogen synthase kinase (GSK)3β (SXXXS), and Fbw7 (SPXXS). This study also reports the novel finding that topoIIα may be a target of GSK3β phosphorylation. Evidence suggests that CK2 serves as a priming kinase, through phosphorylation at Ser1365, for GSK3β-mediated phosphorylation at Ser1361. This double phosphorylation facilitated the recruitment of Fbw7 to the phospho-degron (1361) pSPKLpS(1365) of topoIIα, leading to its ubiquitin-dependent degradation.


CONCLUSIONS
This study shows a novel pathway by which HDAC inhibitors facilitate the selective degradation of topoIIα, which underlies the complexity of the functional role of HDAC in regulating tumorigenesis and aggressive phenotype in HCC cells.
Division of Medicinal Chemistry, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA.
Mei-Chuan
MC
Chen
Chun-Han
CH
Chen
Hsiao-Ching
HC
Chuang
Samuel K
SK
Kulp
Che-Ming
CM
Teng
Ching-Shih
CS
Chen
D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D000075686:COP9 Signalosome Complex; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D047390:Casein Kinase II / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D044783:F-Box Proteins / Q000378:metabolism; D000073979:F-Box-WD Repeat-Containing Protein 7; D005260:Female; D055785:Gene Knockdown Techniques; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology; D008113:Liver Neoplasms / Q000378:metabolism*; D051379:Mice; D008819:Mice, Nude; D010447:Peptide Hydrolases / Q000502:physiology; D010654:Phenylbutyrates / Q000494:pharmacology; D010766:Phosphorylation; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
D000951:Antigens, Neoplasm; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D044783:F-Box Proteins; D000073979:F-Box-WD Repeat-Containing Protein 7; C513273:FBXW7 protein, human; D056572:Histone Deacetylase Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; C529674:OSU-HDAC42 compound; D010654:Phenylbutyrates; D044767:Ubiquitin-Protein Ligases; D047390:Casein Kinase II; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D010447:Peptide Hydrolases; C501488:COPS5 protein, human; D000075686:COP9 Signalosome Complex; D004250:DNA Topoisomerases, Type II
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