Hyaluronan-CD44 promotes phospholipase C-mediated Ca²⁺ signaling and cisplatin resistance in head and neck cancer

Objective: To investigate whether hyaluronan (HA)-CD44 promotes head and neck squamous cell carcinoma (HNSCC) cisplatin resistance and whether HA-CD44 promotes phospholipase C (PLC)-mediated Ca²⁺ signaling to alter cisplatin sensitivity in HNSCC. Design: Cell line study. Main Outcome Measures: Tumor cell growth with the chemotherapeutic drug cisplatin was measured in the presence or absence of HA, anti-CD44 antibody plus HA, and other inhibitors of the PLC-mediated Ca²⁺ signaling pathway. Ca²⁺ mobilization was measured with fluorescence spectrophotometry using the Ca²⁺ binding dye Fura/2AM. Results: In the absence of HA, cisplatin inhibited tumor cell growth. The addition of HA, but not HA plus anti-CD44 antibody, resulted in a 5-fold reduced ability of cisplatin to cause HNSCC cell death, suggesting that HA can promote CD44-dependent cisplatin resistance. Fluorescence spectrophotometry demonstrated that HA can promote CD44-dependent Ca ²⁺ mobilization in HNSCC. On the other hand, the presence of U73122, a PLC inhibitor, and 2-aminoethoxydiphenyl borate, an inositol-1,4,5- triphosphate receptor inhibitor, eliminated HA-mediated Ca²⁺ mobilization and HA-mediated cisplatin resistance in these cell lines. Conclusions: Our results indicate that HA-CD44 signaling influences cisplatin sensitivity in HNSCC cell growth. In particular, HA-CD44 promotion of PLC-mediated Ca²⁺ signaling plays a role in cisplatin resistance in HNSCC cells. Perturbation of this HA-CD44-mediated signaling pathway may be a promising target to overcome cisplatin resistance in HNSCC.