Here, we show that αB-crystallin expression in HNSCC tumors correlates with MFS, but not with LRC. Clues for the mechanism by which αB-crystallin might affect distant metastasis formation in patients were obtained by the depletion of αB-crystallin in HNSCC cell lines, which showed that both VEGF secretion and cell motility were decreased when αB-crystallin expression was reduced.
Previously, two studies have addressed the prognostic value of αB-crystallin in HNSCC. Chin and coworkers have shown that αB-crystallin is a marker for poor prognosis , which is substantiated by our data. However, they noted that none of the patients lacking αB-crystallin had LRR, while 37% of the patients with tumors stained positive for αB-crystallin had LRR. In the current study, the difference in prognosis was mainly caused by a higher rate of distant metastasis in the high αB-crystallin group and not by a difference in LRR. Boslooper and colleagues did not find αB-crystallin to be a prognostic marker for HNSCC . These researchers observed the highest concentrations of αB-crystallin in the centre of tumor cell nests and not the more diffuse localization observed in this study and the study of Chin and coworkers . This difference in αB-crystallin localization may have been caused by a difference in staining procedure and could be the reason why this study led to a different conclusion.
αB-crystallin was also found to be associated with a poor prognosis in several other types of cancers, such as breast cancer [3–5, 25, 26] and was downregulated in a breast cancer cell line by breast cancer metastasis suppressor 1, which specifically suppresses metastasis . αB-crystallin is a molecular chaperone able to prevent protein aggregation and can confer protection to cells under stress conditions. αB-crystallin inhibits apoptosis in response to different anti-cancer agents, such as DNA-damaging drugs, TNFα and Fas ligand  and has been shown to be a predictor of resistance to chemotherapy . However, since our data do not support an association of αB-crystallin expression with local recurrence after treatment of the patients, the cytoprotective activity is likely not the sole reason why αB-crystallin is associated with poor prognosis.
Metastasis formation occurs via a series of steps, also known as the “metastatic cascade” . One of the factors associated with metastatic spread is VEGF [30, 31]. Several studies have demonstrated roles for αB-crystallin in VEGF-dependent angiogenesis . Tumor vasculature in αB-crystallin-deficient mice displays high levels of endothelial apoptosis and decreased vessel formation. αB-crystallin has been shown to associate with VEGF-A (the most well-known member of the VEGF protein family) [8, 33] and colocalizes with VEGF at the endoplasmic reticulum . Furthermore, VEGF-A expression remained low in αB-crystallin-deficient mice during retinal revascularization after artificially-induced retinopathy . Here we have shown that in a HNSCC cell line αB-crystallin is also involved in secretion of VEGF and in this way may influence tumorigenic blood vessel formation and metastasis formation in HNSCC. For the growth of metastatic tumors in lymph nodes neoangiogenesis is not absolutely needed [34, 35], which might explain why no correlation was found between αB-crystallin expression and LRC.
Migration-associated proteins may also correlate with worse outcome, as has been shown for patients with squamous cell carcinoma of the tongue . αB-crystallin can affect cell migration as well. Overexpression of αB-crystallin led to higher cell motility in several studies [3, 25, 37]. Here we have shown that depletion of αB-crystallin decreased the motility of UT-SCC cells, indicating also in these types of cells αB-crystallin may affect cell migration. VEGF also plays a role in cell migration , potentially by enhancing invadopodia formation . The effect of αB-crystallin on cell migration may thus be mediated by VEGF, although other mechanisms are also possible, as for example by the influence of αB-crystallin on actin filaments dynamics [39, 40]. Further research is needed to reveal the molecular mechanisms by which αB-crystallin affects cell migration.