Cancer-specific mutations in PIK3CA are oncogenic in vivo

Abstract

The PIK3CA gene, coding for the catalytic subunit p110␣ of class IA phosphatidylinositol 3-kinases (PI3Ks), is frequently mutated in human cancer. Mutated p110␣ proteins show a gain of enzymatic function in vitro and are oncogenic in cell culture. Here, we show that three prevalent mutants of p110␣, E542K, E545K, and H1047R, are oncogenic in vivo. They induce tumors in the chorioallantoic membrane of the chicken embryo and cause hemangiosarcomas in the animal. These tumors are marked by increased angiogenesis and an activation of the Akt pathway. The target of rapamycin inhibitor RAD001 blocks tumor growth induced by the H1047R p110␣ mutant. The in vivo oncogenicity of PIK3CA mutants in an avian species strongly suggests a critical role for these mutated proteins in human malignancies.T he PIK3CA gene codes for the catalytic subunit p110␣ of class IA phosphatidylinositol 3-kinases (PI3Ks) (reviewed in refs. 1-3). PIK3CA is the cellular homolog of the retroviral v-p3k oncogene and is amplified in ovarian and cervical cancer (4-6). Genomic profiling of human cancers revealed the presence of somatic, heterozygous point mutations in PIK3CA (7-16). These mutations occur in Ϸ30% of all breast and colon cancers and are less frequent in cancers of the brain, stomach, liver, and ovary. The mutations are nonrandomly distributed over the primary structure of p110␣ and cluster to regions in the p85-binding domain, the C2 domain, the helical domain, and the C terminus of the catalytic domain. The sites most frequently affected by mutation are the residues E542 and E545 in the helical domain and H1047 in the catalytic domain. The glutamates at position 542 and 545 are commonly changed to lysines, and H1047 is often replaced by arginine. The cancer-specific point mutations of p110␣ confer a gain of function resulting in increased lipid kinase activity (15,(17)(18)(19). Expression of p110␣ mutants activates the Akt-signaling pathway in the absence of growth factors and induces oncogenic cellular transformation of chicken embryo fibroblasts (CEFs) and of NIH 3T3 cells (17, 18). The transformation by p110␣ mutants is sensitive to rapamycin, suggesting that the target of rapamycin (TOR) and downstream effector molecules of TOR are crucial components of the oncogenic process (18).Here, we provide evidence for the oncogenicity of p110␣ E542K, E545K, and H1047R in vivo and identify the PIK3CA mutants as oncoproteins. These mutants induce angiogenesis and malignant cell growth in the chorioallantoic membrane (CAM) of the chicken embryo and cause hemangiosarcomas in young chickens. The rapamycin derivative RAD001 interferes with H1047R-induced tumor formation, in agreement with observations made in cell culture and in murine tumor systems that depend on increased PI3K function (18,20,21).

Concomitant PI3K–AKT and p53 alterations in endometrial carcinomas are associated with poor prognosis

“…[26][27][28][29] However, it has been reported that chickens injected with exon 20 PIK3CA mutants developed larger tumors than those injected with exon 9 PIK3CA mutants. 30 The distinct associations of the different PIK3CA mutations with histologic type, grade, and depth of myometrial invasion in endometrial carcinomas is consistent with the idea that different categories of mutants, defined by their structural and functional domains, would increase PI3K function by diverse mechanisms. Mutations in the kinase domain of exon 20 alter the catalytic loop and increase the specific activity of the enzyme, thus enhancing pathway activation.…”

PIK3CA Gene Mutations in Pediatric and Adult Glioblastoma Multiforme

“…Another mutation that has been studied functionally (H1047R; refs. [16][17][18][19][20] was not found in our study; however, we found a mutation that changed the amino acid at the same position (H1047Y). Thus, for many mutations in the current study, there are data supporting a functional role in oncogenesis.…”

“…Several of the mutations found in our study (E542K, E545K, and M1043I) are oncogenic or increase kinase activity, albeit in nongliomatous systems (16)(17)(18)(19)(20). Another mutation that has been studied functionally (H1047R; refs.…”

The transcriptional induction of PIK3CA in tumor cells is dependent on the oncoprotein Y-box binding protein-1

“…Moreover, expression of the mutant PIK3CA increases PI3K activity and has been shown to be transforming (Bader et al, 2006;Horn et al, 2008;Zhang et al, 2008). Therefore, it is important to elucidate mechanisms that lead to expression of these activating mutants.…”

“…In addition, gene deletion studies in mice have shown that p110a is essential for growth factor signaling as well as for oncogenic transformation (Zhao et al, 2006), whereas direct interaction of Ras with p110a is required for oncogenic Ras-induced tumorigenesis (Gupta et al, 2007). Moreover, activating PIK3CA mutations, observed in many different cancers, are also shown to be transforming (Bader et al, 2006;Horn et al, 2008;Zhang et al, 2008) and increased expression of mutant PIK3CA further induces PI3K activity . All these studies indicate the importance of p110a in cancer and the significance of understanding the mechanisms that lead to its expression.…”