Activation of the HIF1α/TIMP1/MT6-MMP pathway is associated with invasion in pituitary null cell adenomas

Non-functioning pituitary adenomas (NFPAs) are a highly heterogeneous group and often show invasion, but few studies have explored the invasion mechanism and biomarkers for specific subtypes. This study was designed to describe the role of HIF1α and its downstream genes in specific subtypes of NFPAs. Specimens were classified into two subtypes of NFPAs: 46 null cell adenomas (28 invasive and 18 noninvasive) and 46 oncocytomas (11 invasive and 35 noninvasive). HIF1α, TIMP1, MT6-MMP, ECAD and NCAD were detected by qRT-PCR, western blot or immunohistochemistry in tumor tissue. The transwell assay was performed to measure the effects of HIF1α on tumor cell invasion in GH3 and GT1-1 cells. TIMP1, MT6-MMP, ECAD and NCAD were detected by western blot in HIF1α overexpressed GT1-1 cells. HIF1α mRNA and protein level was significantly upregulated in invasive pituitary null cell adenomas but not in invasive pituitary oncocytoma. The TIMP1 mRNA and protein level was significantly downregulated and MT6-MMP mRNA and protein level was significantly upregulated in invasive pituitary null cell adenomas. Meanwhile, there were no significant differences in epithelial-mesenchymal transition (EMT) markers, ECAD and NCAD, between invasive and noninvasive pituitary null cell adenomas. The overexpression of HIF1α promoted the invasive capability of pituitary adenoma cells in vitro. Regarding the molecular mechanism, HIF1α overexpression could downregulate TIMP1 and upregulate MT6-MMP expression levels but did not affect EMT markers' expression. Our results suggested that HIF1α might contribute to the invasion of pituitary null cell adenomas through activating HIF1α/TIMP1/MT6-MMP pathway but not EMT.