Flash Talk & Poster Presentation 31st Lorne Cancer Conference 2019

p53 and Rb Regulate Autophagy, Primary Cilia Formation and Hedgehog Signalling  (#305)

Catherine R Cochrane 1 2 , Anette Szczepny 1 2 , Vijesh Vaghjiani 1 2 , Samantha N Jayasekara 1 2 , Neil Watkins 3 , Jason E Cain 1 2
  1. Centre for Cancer Research, Hudson Institute of Medical Research, Clayton, VIC, Australia
  2. Molecular and Translational Sciences, Monash University, Clayton, VIC, Australia
  3. The Kinghorn Cancer Centre , Garvan Institute of Medical Research, Darlinghurst, New South Wales, Australia

The evolutionary conserved Hedgehog (Hh) signalling pathway plays fundamental roles in development and homeostasis, as well as in the initiation and progression of various cancers. Signalling is driven by the binding of Sonic hedgehog (Shh) ligand to the receptor Patched to initiate primary cilia-dependent Smoothened–Gli activation. Although mutations in Hh pathway components are described in some cancers, the majority of Hh tumours exhibit ligand-dependent Hh signalling, where Hh ligand is produced by the stroma and/or tumour cells to maintain pathway activation and self-renewal. However, the mechanistic basis of Hh ligand-dependency still remains unknown. Our data suggests that p53 and Rb, tumour suppressors commonly mutated in Hh-cancers, are strongly implicated in regulating ligand-dependent Hh signalling in development and cancer. We show that genetic inactivation of Trp53 and/or Rb1 in the developing mouse neural tube enhanced ciliogenesis and expanded the Nkx2.2 Hh-dependent ventral domain at embryonic day 10.5, consistent with a Hh gain-of-function phenotype. Moreover, deletion of Trp53 and/or Rb1 in mouse embryonic fibroblasts (MEFs) also increased primary cilia frequency and cell responsiveness to Shh ligand. Interestingly, this response is associated with diminished autophagic flux and reduced expression of autophagy-related genes in Trp53;Rb1 KO MEFs, supporting an interaction between autophagy and ciliogenesis (1). Furthermore, siRNA knockdown of Atg5 and Atg9b in C57Bl/6 wildtype MEFs resulted in increased Hh ligand responsiveness linking autophagy-mediated ciliogenesis to Hh ligand response. This mechanism was also observed in murine Trp53 and Rb1-deficient cancer models of osteosarcoma (OS) and small cell lung cancer (SCLC), which displayed enhanced Gli1 mRNA expression in response to Shh, increased primary cilia frequency and reduced autophagic flux. These affects were not observed in Trp53 and Rb1 wildtype OS and lung adenocarcinoma models. These data suggest that p53 and Rb control the genes required for autophagy, which regulates ciliogenesis and ultimately Hh pathway responsiveness to ligand, implicating p53 and Rb mutation status and primary cilia frequency as biomarkers for Hh ligand-dependency

  1. Pampliega O, Orhon I, Patel B, Sridhar S, Díaz-Carretero A, Beau I, Codogno P, Satir BH, Satir P, Cuervo AM. Functional interaction between autophagy and ciliogenesis. Nature. 2013 Oct;502(7470):194.