Binding of FGF-1 variants to protein kinase CK2 correlates with mitogenicity

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Abstract
Fibroblast growth factor‐1 (FGF‐1) has both extra‐ and intracellular functions. To identify intracellular binding partners for FGF‐1, we isolated proteins from U2OS human osteosarcoma cells interacting specifically with FGF‐1. One of the isolated proteins was identified as protein kinase CK2 (CK2). We here provide evidence that FGF‐1 binds to both the catalytic α‐subunit and to the regulatory β‐subunit of CK2. The interaction between FGF‐1 and CK2α and β was characterized by surface plasmon resonance, giving KD values of 0.4 ± 0.3 and 1.2 ± 0.2 μM, respectively. By using a novel assay for intracellular protein interaction, FGF‐1 and CK2α are shown to interact in vivo. In vitro, FGF‐1 and FGF‐2 are phosphorylated by CK2, and the presence of FGF‐1 or FGF‐2 was found to enhance the autophosphorylation of CK2β. A correlation between the mitogenic potential of FGF‐1 mutants and their ability to bind to CK2α was observed. The possible involvement of CK2 in the FGF‐induced stimulation of DNA synthesis is discussed.