Survival of salivary pleomorphic adenoma cells in hypoxic condition

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Salivary pleomorphic adenoma is histopathologically characaterized by its colorful stroma including myxoid one which is poorly vascularized. Pleomorphic adenoma (PA) cells embedded in such poorly-vasculaized stromata are supposed to have their own device to survive in hypoxic conditions. To understand the hypoxia-dependent manner of cellular proliferation, we determined both protein and gene expression levels of hypoxia-inducible factor 1α (HIF-1α), vascular endothelial growth factor (VEGF), and von Hippel-Lindau (vHL) protein which degrades HIF-1α in SM-AP cells originated from a pleomorphic adenoma. They showed more enhanced gene expression levels for VEGF but not for those for HIF-1α under hypoxic conditions. In contrast, HIF-1α and VEGF protein levels were kept higher in hypoxic conditions than in aerobic ones. SM-AP cells had lower expression levels for the vHL gene. On the one hand, their VEGF protein levels were kept lower in hypoxic conditions than in aerobic ones. The results indicate that PA cells are able to proliferate in the hypoxic condition because of the accumulation of HIF-1α probably due to repressed levels of vHL.