Kinome siRNA screen identifies regulators of ciliogenesis and hedgehog signal transduction

Disruption or improper activation of the Hedgehog (Hh) pathway is associated with developmental abnormalities and cancer. Although characterized in Drosophila, the mechanisms that mediate the Hh signal downstream of the Smoothened (Smo) seven-transmembrane protein in vertebrates remain poorly understood. In particular, the Fused (Fu) kinase, which mediates Hh signaling in flies, is dispensable in mammals. To identify kinases that positively regulate the Hh pathway in mammals, we screened a mouse kinome small interfering RNA library and validated nine candidates that modulate Hh signaling. Among these candidates, Nek1 and Prkra did not directly function in the Hh pathway but exerted their effects on Hh signaling indirectly through a primary role in ciliogenesis. In contrast, another kinase, Cdc2l1, directly participated in the Hh pathway. Cdc2l1 was necessary and sufficient for activation of the Hh pathway, functioning downstream of Smo and upstream of the Glioma-associated (Gli) transcription factors. More specifically, Cdc2l1 interacted with the negative regulator Suppressor of Fused (Sufu) and relieved its inhibition on Gli, thus providing a mechanism for how Cdc2l1 might play a role in Hh signaling. Finally, with zebrafish as model organism, we showed that Cdc2l1 activated the Hh pathway in vivo. We propose that Cdc2l1 is a previously unrecognized member of the Hh signal transduction cascade.