BASIC FIBROBLAST GROWTH-FACTOR (BFGF) REGULATES TYROSINE-HYDROXYLASE AND PROENKEPHALIN MESSENGER-RNA LEVELS IN ADRENAL CHROMAFFIN CELLS

bFGF is a neurotrophic protein expressed in various regions of the adu lt peripheral and central nervous system. The present study was undert aken to examine the role of bFGF in multihormonal, catecholaminergic a nd enkephalinergic cells of the adrenal medulla (AM). Western blot ana lysis revealed the presence of at least three bFGF isoforms (18, 22/23 , and 24 kDa) in cultured bovine AM cells. Incubation of AM cells with the exogenous 18 kDa bFGF produced time-dependent increases in tyrosi ne hydroxylase (TH) and proenkephalin (PEK) mRNA, with maximal changes occurring at 12 h (TH) or 24 h (PEK) of bFGF exposure. Effects of bFG F on TH and PEK mRNA were non-additive with increases induced by expos ure of AM cells to nicotine, the depolarizing agent veratridine, or th e adenylate cyclase activator forskolin. These data indicate that bFGF effects may occur through intracellular pathways accessed during tran ssynaptic induction of TH and PEK genes. The increases in PEK mRNA ind uced by nicotine or bFGF were inhibited by the calcium antagonist TMB- 8. TMB-8 also inhibited bFGF-induced increases in TH mRNA as well. How ever, treatment with TMB-8 increased basal levels of TH mRNA. The addi tion of bFGF increased endogenous levels of c-fos mRNA, c-Fos and c-Fo s-related proteins, suggesting that bFGF may activate TH and PEK gene expression through a calcium-AP1 transcriptional regulatory pathway. I mmunohistochemical analysis revealed the presence of bFGF-immunoreacti vity (bFGF-IR) in the cytoplasm and in the nucleus of AM cells. Incuba tion of cells with exogenous bFGF produced time-dependent increases of nuclear bFGF-IR. The intensity of nuclear bFGF-IR was also enhanced i n cells treated with veratridine, indicating that in both cases nuclea r translocation of bFGF occurs. The present study indicates that bFGF could serve as a paracrine or autocrine factor regulating the expressi on of TH and PEK genes in AM cells. It also suggests that nuclear tran slocation of bFGF in AM cells may play a role in transcriptional effec ts of bFGF in those cells.