Immunoexpression patterns for Hypoxia-inducible Factor-1α and von Hippel-Lindau protein, in relation to Hsp90, of human brain tumors

Abstract

The pathogenesis of many tumors, including brain tumors, has been associated with hypoxia, which induces the transcriptional activity of Ηypoxia-inducible Factor-1α (HIF-1α). HIF-1α is normally degradated by the von Hippel-Lindau protein (pVHL) but, in hypoxia, pVHL/HIF-1α interaction is inhibited resulting in the nuclear accumulation of HIF-1α. Hsp90 (Heat shock protein 90), as a chaperone protein, plays a critical role for both stabilization of HIF-1α and degradation of pVHL. The aim of this study was to estimate immunohistochemically the expression levels of HIF-1α and pVHL, in relation to Hsp90, in different types of human brain tumors (42 gliomas, 9 medulloblastomas, and 38 meningiomas) using specific antibodies. The tumors were further divided into two groups according to the age of patients (≥19 years old or <19 years old). Nuclear, for HIF-1α, and cytoplasmic, for pVHL and Hsp90, localization was detected in a high percentage of tumor cells in the majority of tumors. In astrocytomas, a significant, grade-dependent relationship for HIF-1α immunoexpression was observed (p<0.05). Furthermore, there was a significant correlation between pVHL and Hsp90 immunoexpression (p<0.01). The group of ≥19 years old patients with glioblastomas (WHO grade IV) demonstrated significantly increased immunoexpression for HIF-1α compared to pVHL (p<0.0001) and Hsp90 expression (p<0.01). In medulloblastomas, a significant correlation of HIF-1α with Hsp90 immunoexpression (p<0.05) was found. In meningiomas, no significant correlation for the expression of the three proteins was detected (p≥0.05). These results indicate that HIF1α/pVHL/Hsp90 interactions may be implicated in biology of different types of brain tumors through different signaling mechanisms.