Phosphatome RNAi Screen Identifies Eya1 as a Positive Regulator of Hedgehog Signal Transduction

The Hedgehog (Hh) signaling pathway is vital for vertebrate embryogenesis and aberrant activation of the pathway can cause tumorigenesis in humans. In this study, we used a phosphatome RNAi screen for regulators of Hh signaling to identify a member of the Eyes Absent protein family, Eya1, as a positive regulator of Hh signal transduction. Eya1 is both a phosphatase and transcriptional regulator. Eya family members have been implicated in tumor biology, and Eya1 is highly expressed in a particular subtype of medulloblastoma (MB). Here we show that RNAi-mediated knock-down of Eya1, as well as knock-down of its co-factor, Six1, blocks Hh signaling as assessed by induction of Hh response genes. Utilizing small molecule agonists, RNAi, and protein overexpression methods, we place the influence of Eya1 and Six1 within the Hh signaling pathway downstream of Smoothened (Smo) and at or above the level of Suppressor of Fused (Sufu). Interestingly, Eya1 appears to be specifically required for Hh-responsive gene activation mediated by Gli transcriptional activators but not for Hh-mediated transcriptional de-repression mediated by the inhibition of Gli transcriptional repressors. Furthermore, we find that Eya1 and Six1 regulate the expression of Neuropilin1 (Nrp1)