CHARACTERIZATION OF GH(3) CELLS OVEREXPRESSING BASIC FIBROBLAST GROWTH-FACTOR (FGF-2)

Basic fibroblast growth factor (FGF-2) is not only a potent mitogen fo r various cells but also a multifunctional factor with angiogenic and chemotactic activity, and the capacity to induce the synthesis of vari ous proteinases and to modulate endocrine function, To clarify the rol e played by FGF-2 in the progression of pituitary tumor, we fused rat FGF-2 cDNA to the promoter SR alpha, consisting of the early promoter of SV40 and HTLV(l)-LTR, and we cotransfected GH(3) cells with pSV2-ne o by an electroporation method, After selection by G418, we obtained 7 neomycin-resistant clones. Southern blot analysis of genomic DNA reve aled the presence of transfected rat FGF-2 cDNA in 4 of the 7 clones, To measure FGF-2 molecules, we established a new immuno-fluorometric a ssay system, using 3 monoclonal antibodies against different portions of human FGF-2. This assay had a minimum sensitivity of 10 pg/ml and c ross-reacted neither with acidic fibroblast growth factor (FGF-1) nor insulin-like growth factor 1 (IGF-1), even at a concentration of 100 n g/ml, Although FGF-2 was undetectable in the culture medium of any of the clones, the cell homogenate contained a significant amount of FGF- 2 (7.2 ng/mg protein) in 1 of the 4 FGF-2-transfected clones (GH(3)FGF (+)), whereas FGF-2 was not detected (<5.2 pg/mg protein) in the cell homogenates of either the parent GH(3) cells or the control cells tran sfected with pSV2-neo alone (GH(3)FGF(-)), GH(3)FGF(+) grew as adheren t cells and formed epithelial sheets with a growth rate similar to tha t of control cells. The amount of prolactin (PRL) released by TRH was greater in GH(3)FGF(+) than that in GH(3) or GH(3)FGF(-), On the other hand, the sensitivity to SRIF was increased in GH(3)FGF(+) compared w ith that in other clones. The findings of these in vitro studies indic ate that FGF-2, if it is expressed in pituitary tumor cells, plays lit tle ii any role in cell growth but may modulate certain cell functions such as responsiveness to hormones.