Elevated cell invasion is induced by hypoxia in a human pituitary adenoma cell line

Pituitary adenoma tissues are hypovascular, and have a lower partial oxygen pressure compared with neighboring normal organs. In this study, we investigated whether hypoxia influences the cell invasiveness of the human pituitary adenoma cell line, HP-75. HP-75 cells were exposed to hypoxic (1-10% oxygen) or normoxic (21% oxygen) conditions for 24 hours. Gelatin and reverse zymogram assays were used to determine the enzyme activities of matrix metalloproteinases (MMP) and tissue inhibitor of metalloproteinases (TIMP). Cell adhesion and Matrigel cell invasion were examined with a Boiden chamber. Finally, the mRNA gene expression profiles of cells exposed to hypoxia or normoxia were examined by cDNA microarray and confirmed with real-time RT-PCR and flow cytometry. The gelatin and reverse zymograms revealed that the activities of MMP and TIMP were not significantly altered by hypoxia. Matrigel cell invasion and cell adhesion to Matrigel or collagen type IV were increased by hypoxia (3.8- and 4.8-fold, respectively). The cDNA microarray analysis revealed that laminin beta2 chain mRNA was specifically up-regulated under hypoxic conditions (4.96-fold). Finally, real-time RT-PCR and flow cytometry verified the elevated expression of laminin beta2 chain at the mRNA and protein levels under hypoxic conditions. RNA interference with siRNA targeting laminin beta2 inhibited Matrigel invasion and adhesion to collagen type IV in a dose-dependent manner. Collectively, these results suggested that hypoxia (1% oxygen) enhanced the cell invasion properties of a pituitary adenoma cell line in association with elevated expression of laminin beta2 and enhanced binding to collagen type IV.