Poster Presentation 26th Lorne Cancer Conference 2014

Heterozygous expression of an oncogenic Pik3ca mutation during murine development results in fatal embryonic and extraembryonic defects (#162)

Lauren M Hare 1 2 , Quenten Schwarz 3 , Rajendra Gurung 2 , Karen Montgomery 1 , Christina Mitchell 2 , Wayne A Phillips 1 2
  1. Peter MacCallum Cancer Centre, East Melbourne, VIC, Australia
  2. Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
  3. Department of Human Immunology, Centre of Cancer Biology, Adelaide, South Australia, Australia
The PI3K/Akt signalling pathway regulates many important cellular functions including proliferation, migration, survival and angiogenesis. The PIK3CA gene, encoding the p110α catalytic subunit of the PI3K enzyme, is somatically mutated in a range of human cancers and overgrowth syndromes. We have previously described a novel mouse model with a Cre-recombinase (Cre)-mediated knock-in of the common cancer-associated Pik3caH1047R mutation that can be targeted to selected tissues using various Cre-expressing mouse strains. As the mutation is knocked in to the endogenous gene, the mutant protein is expressed at normal physiological levels.
We have used the Cre-deleter mouse to induce expression of the Pik3caH1047R mutation ubiquitously from the 2-cell stage of development. This results in embryonic lethality by E10.5 with embryos at E9.5 demonstrating stunted growth, failed ‘turning’ and abnormal cardiovascular development in both the embryo proper and extraembryonic yolk sac. These tissues also showed increased expression of vascular endothelial growth factor (VEGF) family proteins. We then selectively targeted the mutation to the endothelial cells of the developing embryo using the Tie2-Cre mouse strain.  No Tie2Cre:Pik3caH1047R mutant embryos survived to E11.5 and at E10.5, while successfully turned, embryos were severely underdeveloped and no longer viable. At E9.5, vascular remodelling was disorganised and truncated in the embryo proper and yolk sacs. Development of the heart was also affected with clear disruption to anterior cardinal vein and dorsal aorta development. Our results demonstrate the importance of PI3K/Akt signalling in embryonic development and cardiovascular formation in the mouse. The observed cell autonomous role in vessel development was further confirmed upon targeted expression to endothelial cells while the increased expression of various VEGF family proteins suggests probable crosstalk between the PI3K/Akt and VEGF signalling pathways during cardiovascular development. The lethality associated with expression of Pik3caH1047R mutation during development likely explains the lack of inherited germline PIK3CA mutations in humans.