Fibroblast growth factor receptor influences primary cilium length through an interaction with intestinal cell kinase

Significance A properly functioning primary cilium is prerequisite for both normal development and aging of all ciliated organisms, including humans. In vertebrates, the signaling of Hedgehog family morphogens depends entirely on primary cilium. Recently, we reported that fibroblast growth factors (FGF) signaling interacts with that of Hedgehog, and that this is a consequence of FGF regulating length of the cilium and speed of processes that happen therein. In this report, we provide a molecular mechanism of such interaction, identifying intestinal cell kinase as a mediator of the FGF-induced changes in the ciliary morphology and function. This expands our understanding how FGF signaling regulates intracellular processes, and how aberrant FGF signaling contributes to diseases, such as achondroplasia and cancer.
Vertebrate primary cilium is a Hedgehog signaling center but the extent of its involvement in other signaling systems is less well understood. This report delineates a mechanism by which fibroblast growth factor (FGF) controls primary cilia. Employing proteomic approaches to characterize proteins associated with the FGF-receptor, FGFR3, we identified the serine/threonine kinase intestinal cell kinase (ICK) as an FGFR interactor. ICK is involved in ciliogenesis and participates in control of ciliary length. FGF signaling partially abolished ICK’s kinase activity, through FGFR-mediated ICK phosphorylation at conserved residue Tyr15, which interfered with optimal ATP binding. Activation of the FGF signaling pathway affected both primary cilia length and function in a manner consistent with cilia effects caused by inhibition of ICK activity. Moreover, knockdown and knockout of ICK rescued the FGF-mediated effect on cilia. We provide conclusive evidence that FGF signaling controls cilia via interaction with ICK.