title: The influence of hyaluronan-CD44 interaction on topoisomerase II activity and etoposide cytotoxicity in head and neck cancer.
abstract: OBJECTIVE
  To investigate the downstream molecular targets of hyaluronan (HA)-CD44 and phospholipase C (PLC)-mediated calcium ion (Ca(2+)) signaling in head and neck squamous cell carcinoma (HNSCC). Hyaluronan is a ligand for the CD44 receptor, which interacts with multiple signaling pathways to influence cellular behavior. We recently determined that HA-CD44 interaction promotes PLC-mediated Ca(2+) signaling and cisplatin resistance in HNSCC.
  
  
  METHODS
  Proliferation of HNSCC tumor cells and topoisomerase (Topo) II enzymatic activity, including DNA-cleavable complex formation and DNA decatenation, were analyzed in the presence or absence of HA, the Topo II poison etoposide (VP-16), and various inhibitors of PLC and Ca(2+)-calmodulin kinase II (CaMKII) signaling.
  
  
  RESULTS
  Treatment with HA promoted Topo II phosphorylation, suggesting that HA can modulate Topo II activity. Topoisomerase II-mediated DNA cleavable complex formation was increased by VP-16, and this increase was significantly enhanced by noncytotoxic doses of the PLC inhibitor U73122 and the CaMKII inhibitor KN-62, implicating PLC and CaMKII in Topo II regulation. However, the drug- and inhibitor-mediated increase in DNA cleavable complex formation was reduced with HA pretreatment. Inhibitors of PLC and CaMKII also enhanced VP-16 inhibition of Topo II-mediated DNA decatenation. Treatment with HA reduced VP-16 cytotoxic activity. On the other hand, U73122 and KN-62 enhanced VP-16 cytotoxic activity and reduced the ability of HA to promote VP-16 resistance.
  
  
  CONCLUSIONS
  Our results suggest that HA, PLC, and CaMKII are upstream regulators of Topo II-mediated DNA metabolism in HNSCC and that this signaling pathway could be a promising target for the development of novel therapies against HNSCC.
authors: Department of Otolaryngology-Head and Neck Surgery and Endocrine Unit, Department of Medicine, Veterans Affairs Medical Center, University of California, San Francisco, USA. swang@ohns.ucsf.edu
authors: Steven J
authors: SJ
authors: Wang
authors: Karine
authors: K
authors: Peyrollier
authors: Lilly Y
authors: LY
authors: Bourguignon
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000009:adverse effects* / Q000627:therapeutic use; D020013:Calcium Signaling / Q000187:drug effects; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000378:metabolism*; D045744:Cell Line, Tumor; D004250:DNA Topoisomerases, Type II / Q000187:drug effects* / Q000378:metabolism; D005047:Etoposide / Q000009:adverse effects* / Q000627:therapeutic use; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism*; D006820:Hyaluronic Acid / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D010766:Phosphorylation; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000494:pharmacology
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D018960:Hyaluronan Receptors; D005047:Etoposide; D006820:Hyaluronic Acid; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010738:Type C Phospholipases; D004250:DNA Topoisomerases, Type II