Interaction of hyaluronan and CD44 promotes topoisomerase II-mediated regulation of DNA topology and function in head and neck cancer Free

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BACKGROUND AND OBJECTIVE: Hyaluronan (HA) is a ligand for the CD44 receptor, which interacts with multiple signaling pathways to influence cellular behavior. We recently determined that HA-CD44 promotes phospholipase C (PLC)-mediated Ca²⁺ signaling and cisplatin resistance in head and neck squamous cell carcinoma (HNSCC). The objective of this study was to investigate the downstream molecular targets of HA-CD44 and PLC-mediated Ca²⁺ signaling in HNSCC. DESIGN: HNSCC tumor cell proliferation 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 Ca²⁺-calmodulin kinase II (CaMKII) signaling. RESULTS: HA treatment promoted Topo II phosphorylation, suggesting that HA can modulate Topo II activity. Topo II-mediated DNA cleavable complex formation was increased by VP-16, and this increase was significantly enhanced by non-cytotoxic 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. PLC and CaMKII inhibitors also enhanced VP-16 inhibition of Topo II-mediated DNA decatenation. HA treatment reduced VP-16 cytotoxicity. On the other hand, U73122 and KN-62 enhanced VP-16 cytotoxicity and reduced the ability of HA to promote VP-16 resistance. CONCLUSION: Our results suggest that HA, PLC, and CaMKII are upstream regulators of Topo II-mediated DNA metabolism in HNSCC and suggest that this signaling pathway could be a promising target for development of novel therapies against HNSCC.