FOLATE RECEPTOR EXPRESSION IN PITUITARY ADENOMAS: CELLULAR AND MOLECULAR ANALYSIS

Clinically nonfunctional pituitary adenomas cause hypopituitarism or compression of regional structures. Unlike functional tumors, there is no available medical treatment or specific imaging technique for these tumors. We have recently discovered that both folate receptor (FIR)a mRNA and protein are uniquely overexpressed in nonfunctional pituitary tumors, but not in functional adenomas. We hypothesized that FR alpha may hold significant promise for medical treatment by enabling novel molecular imaging and targeted therapy. Here, we used murine pituitary tumor cell line alpha T3-1 as a model to investigate the biological significance of FRa and its mutant FR67. We demonstrate that overexpression of FIR facilitated tumor cell growth and anchorage-independent growth in soft agar. More colonies were observed in FIR overexpressing cells than in mutant FR67 clones in soft agar. Cell proliferation rate was increased, the percentage of cells in S-phase was increased, and high PCNA staining was detected in cells overexpressing the receptor. In aT3-1 cells transfected with mutant FR67, cell proliferation rate was reduced, the percentage of cells residing in S-phase was slightly decreased, and low PCNA staining was observed. By real-time quantitative PCR, the genes involved in NOTCH3 pathway including NOTCH3, HES-1, and TLE2 were altered; the mRNA expression of FGFR1 was upregulated, and ER beta mRNA was downregulated in FIR overexpressing cells. Our findings suggest that FR alpha plays a role in pituitary tumor formation, and this effect may in part be due to its regulation of the NOTCH3 pathway. (C) 2008 Elsevier Inc.