Nuclear localization of functional FGF receptor 1 in human astrocytes suggests a novel mechanism for growth factor action.

Fractionation of human astrocytes revealed the presence of 103, 118, and 145 kDa forms of FGF receptor 1 (FGFR1) in isolated nuclei. Only trace amounts of FGFR1 proteins were detected in the cell membrane or cytoplasmic fractions. Nuclear FGFR1 is found in the nucleoplasm and nuclear matrix but not in chromatin. Immuno-confocal microscopy further demonstrates the intranuclear presence of FGFR1 and its colocalization with FGF-2. Nuclear FGFR1 binds to FGF-2 and has tyrosine kinase activity. Translocation of functional growth factor receptors into the cell nucleus offers a novel mechanism for growth factor action.