Poster Presentation 25th Lorne Cancer Conference 2013

Targeted deletion of ILK in tumour-initiating cells improves survival of mice with highly aggressive Hedgehog-driven medulloblastoma. (#196)

Gregory E Hannigan 1 , Badia Barakat 1 , Jason Cain 1 , Adrian Dubuc 2 , David Neil Watkins 1 , Michael D Taylor 2
  1. Monash Institute of Medical Research, Clayton, VIC, Australia
  2. Program in Stem Cell and Developmental Biology, The Hospital for Sick Children, Toronto, Ontario, Canada

Aberrant activation of Hedgehog (Hh) signaling causes about 25% of medulloblastomas (MB), the most common solid malignancy of childhood. Expression analyses of Hh MB cohorts (n=85) revealed overexpression of ILK) in 12% of cases. SmoM2 is an activated mutant of the Hh effector, Smoothened (Smo), originally identified in human Hh-initiated cancers. Math1 is selectively expressed in cerebellar granule cell precursors, MB cells of origin. We crossed Math1-Cre mice with mice carrying a floxed, SmoM2[fl/fl] allele, a well-characterized model of Hh-initiated MB. These mice developed MB with 100% penetrance and mean survival of 42 days after birth (8% surviving at d42, n=12). Targeted ablation of ilk[fl/fl] in Math1-Cre;SmoM2 cerebellae increased the survival time of tumour-bearing mice to 47 days after birth (70% surviving at d42, n=10, P=0.013). Math1-Cre-mediated ILK knockout phenocopied Smo knockout in the embryonic cerebellum (E18.5), and both these knockouts inhibited activation of Hh signalling in GCPs. The primary cilium is a cellular signalling organelle required for normal Hh signalling and for growth of Smo-driven MB. ILK has been identified as a ciliary protein, and we confirmed localization of endogenous ILK in primary cilia by immunocytochemistry. In ciliated cell models siRNA-mediated silencing, or a selective small molecule ILK inhibitor, blocked Hh-stimulated transport of Smo into primary cilia, required for signalling. Bimolecular fluorescence complementation demonstrated close specific (< 30nm) association of ILK and Smo in the primary cilium, suggesting that ILK mediates signalling via direct interaction with Smo.  We are currently evaluating the effect of ILK knockout in a second model of MB caused by activation of normal Smo signalling. Our data identify ILK as a mediator of developmental Hh signalling, contributing to MB pathogenesis and representing a novel therapeutic target in Hh cancers.