PHOSPHORYLATION OF BASIC FIBROBLAST GROWTH-FACTOR (FGF-2) IN THE NUCLEI OF SK-HEP-1 CELLS

The subcellular fractions containing protein kinases capable of phosph orylating basic fibroblast growth factor (FGF-2) are unknown, but havi ng previously characterized one that is associated with the plasma mem brane [1991, Mol. Endocrinol, 5, 1003-1012] we evaluated the catalytic properties of another in the nucleus. The reaction is time (linear up to 15 min), enzyme (2,000-25,000 nuclei/ml), and substrate (K(m) 0.18 muM) dependent, and the targets serine. DNase pretreatment of nuclei decreases the incorporation of phosphate into FGF-2 by 50% and the rea ction. It is also inhibited by heparin (EC50 1 mug/ml) and spermidine (EC50 3 muM). Calcium and cAMP have no effect. We conclude that the ki nase is distinct from PKA, and PKC, and suggest that changes in glycos aminoglycan and polyamine concentrations during the cell cycle may mod ulate FGF-2 phosphorylation in the nucleus, or as it is translocated t o the nucleus.