Abstract 5249: Butterfly effect in cancer: How a single base mutation of PIK3CA remodels multiple pathways

PI 3-kinase is a frequently mutated oncogene. Along with the phosphatase PTEN, numerous receptor tyrosine kinases, and Akt, the PI 3-kinase pathway is among the most frequently activated in cancer. The H1047R mutation of PIK3CA is a representative gain-of-function mutation in the PI 3-kinase pathway and is transforming in both chicken fibroblasts and mouse embryonic fibroblasts. Recently, a knock-in of this mutation has been made in the normal human mammary epithelial cell line, MCF-10A. Here, H1047R confers growth factor independence, but does enable the knock-in cells to grow in soft agar or to form xenografts in mice. We have investigated this knock-in cell line and the parental MCF-10A by both deep sequencing and proteomics to determine the transcriptional and translational changes induced by PIK3CA-H1047R. We can confirm that the only coding mutation introduced into the MCF-10A cell line is PIK3CA-H1047R. Surprisingly, this single base mutation induces changes in the expression of thousands of transcripts and proteins. Despite rapid proliferation and growth factor independence, H1047R also induces a decrease in cell cycle genes including Cyclin A2 and Cyclin D2. The decrease in these genes may be the cause of an observed decrease in S and G2 phase cells as compared with the parental MCF-10A cell line. The parental cells overexpress MYC, however this overexpression is lost upon H1047R expression. Inhibition of PI 3-kinase with small molecule compounds that are selective for p110α or affect all isoforms of p110 as well as inhibition of mTOR do not restore the expression of c-MYC. This suggests that long-term activation of the PI 3-kinase pathway can result in changes to the gene expression landscape which no longer depend upon the PI 3-kinase pathway. Finally, H1047R causes changes in 3D cell culture morphology. Both MCF-10A and the H1047R knock-in form acinar structures with hollow lumen when grown on reduced growth factor Matrigel substrates. However, if these cultures are treated with IGF1, the MCF-10A cells retain their acinar structures while, H1047R form branching tube-like structures which invade into Matrigel. The formation of these structures can be inhibited by the introduction of GDC-0941, a pan-PI3K inhibitor. IGF1 has no effect upon cell proliferation or migration in 2D cell culture systems. In summary, the H1047R mutation of PIK3CA while possessing a single catalytic activity can lead to a diverse range of phenotypes beyond growth factor independence. This work was supported by the National Institutes of Health under award numbers R01 CA078230 and R21 AG039716 (JRH and PKV), P30 NS057096 and P41 RR011823 (YZ, LL and JRY). This is abstract 24060 of The Scripps Research Institute. Citation Format: Jonathan R. Hart, Yaoyang Zhang, Lujian Liao, Lisa Du, John R. Yates, Peter K. Vogt. Butterfly effect in cancer: How a single base mutation of PIK3CA remodels multiple pathways. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5249. doi:10.1158/1538-7445.AM2014-5249