Overexpression of vascular endothelial growth factor(164) and its co-receptor neuropilin-1 in estrogen-induced rat pituitary tumors and GH3 rat pituitary tumor cells

We have shown previously that the VEGF system plays a crucial role in regul ation of tumor angiogenesis during the development of estrogen-induced prol actin-secreting pituitary tumors in Fisher 344 rats. Studies also suggested that both endothelial and non-endothelial cells expressed VEGF. However, s everal questions concerning the VEGF signals in regulation of estrogen-indu ced angiogenesis in rat pituitary remained unanswered. VEGF exists in a num ber of isoforms in human and rodent tissue (i.e., VEGF(206h/205r), VEGF(189 h/188r), VEGF(165h/164r), VEGF(145h/144r) and VEGF(121)) that differ in the ir molecular masses and biological activities. The VEGF isoforms bind with two tyrosine-kinase receptors, KDR/flk-1 and flt-1. In addition, VEGF(165) binds with a newly identified co-receptor, neuropilin-1, which is expressed in human endothelial cells and several types of non-endothelial cells incl uding tumor cells. The present study was undertaken to elucidate which isof orms of VEGF are predominantly expressed in normal Fisher 344 rat pituitari es, estrogen-induced prolactin secreting rat pituitary tumors and in prolac tin secreting rat pituitary tumor cell line (GH3 cell line). To identify th e isoform, RT-PCR with primer pairs derived from exon 1 and exon 8 of the V EGF gene, cloning, sequencing and Western blot analysis were performed. The status of neuropilin-1 in the rat pituitaries (normal and transformed) and GH3 pituitary tumor cell line has also been investigated using RT-PCR and Western blot analysis. These studies demonstrate that normal rat pituitarie s, estrogen-induced rat pituitary tumors and GH3 pituitary tumor cells expr essed VEGF(164) and co-receptor, neuropilin-1. The VFGF(164) was the predom inant form in all of these cells. The VEGF(164) and neuropilin-1 mRNA and p rotein levels were significantly higher in the estrogen-induced pituitary t umors and GH3 tumor cell line, as compared to normal pituitary. The data su ggest that both VEGF(164) and neuropilin-1 may actively participate in modu lation of tumor angiogenesis and the development of pituitary tumors in Fis her 344 rats.