αB-crystallin stimulates VEGF secretion and tumor cell migration and correlates with enhanced distant metastasis in head and neck squamous cell carcinoma

Background: alpha B-crystallin is able to modulate vascular endothelial growth factor (VEGF) secretion. In many solid tumors VEGF is associated with angiogenesis, metastasis formation and poor prognosis. We set out to assess whether alpha B-crystallin expression is correlated with worse prognosis and whether this is related to VEGF secretion and cell motility in head and neck squamous cell carcinoma (HNSCC). Methods: alpha B-crystallin expression was determined immunohistochemically in tumor biopsies of 38 HNSCC patients. Locoregional control (LRC) and metastasis-free survival (MFS) of the patients were analyzed in relation to alpha B-crystallin expression. Additionally, the effects of alpha B-crystallin knockdown on VEGF secretion and cell motility were studied in vitro. Results: Patients with higher staining fractions of alpha B-crystallin exhibited a significantly shorter MFS (Log-Rank test, p < 0.005). Under normoxic conditions alpha B-crystallin knockdown with two different siRNAs in a HNSCC cell line reduced VEGF secretion 1.9-fold and 2.1-fold, respectively. Under hypoxic conditions, a similar reduction of VEGF secretion was observed, 1.9-fold and 2.2-fold, respectively. The effect on cell motility was assessed by a gap closure assay, which showed that alpha B-crystallin knockdown decreased the rate by which HNSCC cells were able to close a gap by 1.5- to 2.0-fold. Conclusions: Our data suggest that alpha B-crystallin expression is associated with distant metastases formation in HNSCC patients. This association might relate to the chaperone function of alpha B-crystallin in mediating folding and secretion of VEGF and stimulating cell migration.