Expression of laminin beta2: a novel marker of hypoxia in pituitary adenomas

Some studies indicate that pituitary adenoma tissues are hypovascular and have lower oxygen saturation relative to the normal pituitary gland and suggest that this may induce hypoxia. Our previous study showed that laminin beta2 mRNA is upregulated under hypoxic conditions (1% oxygen) but not under normoxic conditions (21% oxygen) in the HP-75 cell line. In the present study, we further investigated the expression of laminin beta1, 2, or 3 chain, under hypoxic and normoxic conditions in HP-75 cells using Western blotting. We found that only laminin beta2 had a significantly higher expression under hypoxia than under normoxia in the HP-75 cell line. The expression of laminin beta chains was investigated by fluorescent immunohistochemistry of paraffin-embedded sections of tissue from pituitary adenomas of 42 cases (30 cases without apoplexy and 12 with apoplexy) categorized according to Knosp grading and tumor size. We found that only laminin beta2 expression correlated significantly with tumor size, but did not correlate with apoplexy and invasiveness. In conclusion, laminin beta2 can be regarded as a surrogate marker of hypoxia as its level is significantly elevated under hypoxic conditions, and it is predominantly expressed in pituitary macroadenomas.