5290

PIK3CA

PI3K|p110-alpha;phosphoinositide-3-kinase, catalytic, alpha polypeptide;PIK3CA;phosphoinositide-3-kinase, catalytic, alpha polypeptide

PI3-kinase p110 subunit alpha|PI3-kinase subunit alpha|PI3K-alpha|PI3Kalpha|PtdIns-3-kinase p110|p110alpha|phosphatidylinositol 3-kinase, catalytic, 110-KD, alpha|phosphatidylinositol 3-kinase, catalytic, alpha polypeptide|phosphatidylinositol-4,5-bisphos

3q26.3

protein-coding

The phosphatidylinositol 3'-kinase pathway is activated in multiple advanced cancers, including glioblastomas, through inactivation of the PTEN tumor suppressor gene. Recently, mutations in PIK3CA, a member of the family of phosphatidylinositol 3'-kinase catalytic subunits, were identified in a significant fraction (25-30%) of colorectal cancers, gastric cancers, and glioblastomas and in a smaller fraction of breast and lung cancers. These mutations were found to cluster into two major "hot spots" located in the helical and catalytic domains. To determine whether PIK3CA is genetically altered in brain tumors, we performed a large-scale mutational analysis of the helical and catalytic domains. A total of 13 mutations of PIK3CA within these specific domains were identified in anaplastic oligodendrogliomas, anaplastic astrocytomas, glioblastoma multiforme, and medulloblastomas, whereas no mutations were identified in ependymomas or low-grade astrocytomas. These observations implicate PIK3CA as an oncogene in a wider spectrum of adult and pediatric braintumors and suggest that PIK3CA may be a useful diagnostic marker or a therapeutic target in these cancers.

The phosphatidylinositol 3'-kinase pathway is activated in multiple advanced cancers, including glioblastomas, through inactivation of the PTEN tumor suppressor gene. Recently, mutations in PIK3CA, a member of the family of phosphatidylinositol 3'-kinase catalytic subunits, were identified in a significant fraction (25-30%) of colorectal cancers, gastric cancers, and glioblastomas and in a smaller fraction of breast and lung cancers. These mutations were found to cluster into two major "hot spots" located in the helical and catalytic domains. To determine whether PIK3CA is genetically altered in brain tumors, we performed a large-scale mutational analysis of the helical and catalytic domains. A total of 13 mutations of PIK3CA within these specific domains were identified in anaplastic oligodendrogliomas, anaplastic astrocytomas, glioblastoma multiforme, and medulloblastomas, whereas no mutations were identified in ependymomas or low-grade astrocytomas. These observations implicate PIK3CA as an oncogene in a wider spectrum of adult and pediatric braintumors and suggest that PIK3CA may be a useful diagnostic marker or a therapeutic target in these cancers.

The phosphatidylinositol 3'-kinase pathway is activated in multiple advanced cancers, including glioblastomas, through inactivation of the PTEN tumor suppressor gene. Recently, mutations in PIK3CA, a member of the family of phosphatidylinositol 3'-kinase catalytic subunits, were identified in a significant fraction (25-30%) of colorectal cancers, gastric cancers, and glioblastomas and in a smaller fraction of breast and lung cancers. These mutations were found to cluster into two major "hot spots" located in the helical and catalytic domains. To determine whether PIK3CA is genetically altered in brain tumors, we performed a large-scale mutational analysis of the helical and catalytic domains. A total of 13 mutations of PIK3CA within these specific domains were identified in anaplastic oligodendrogliomas, anaplastic astrocytomas, glioblastoma multiforme, and medulloblastomas, whereas no mutations were identified in ependymomas or low-grade astrocytomas. These observations implicate PIK3CA as an oncogene in a wider spectrum of adult and pediatric braintumors and suggest that PIK3CA may be a useful diagnostic marker or a therapeutic target in these cancers.

BACKGROUND: Neuroblastoma is a frequently lethal pediatric cancer in which MYCN genomic amplification is highly correlated with aggressive disease. Deregulated MYC genes require co-operative lesions to foster tumourigenesis and both direct and indirect evidence support activated Ras signaling for this purpose in many cancers. Yet Ras genes and Braf, while often activated in cancer cells, are infrequent targets for activation in neuroblastoma. Recently, the Ras effector PIK3CA was shown to be activated in diverse human cancers. We therefore assessedPIK3CA for mutation in human neuroblastomas, as well as in neuroblastomas arising in transgenic mice with MYCN overexpressed in neural-crest tissues. In this murine model we additionally surveyed for Ras family and Braf mutations as thesehave not been previously reported. METHODS: Sixty-nine human neuroblastomas (42 primary tumors and 27 cell lines) were sequenced for PIK3CA activating mutationswithin the C2, helical and kinase domain "hot spots" where 80% of mutations cluster. Constitutional DNA was sequenced in cases with confirmed alterations toassess for germline or somatic acquisition. Additionally, Ras family members (Hras1, Kras2 and Nras) and the downstream effectors Pik3ca and Braf, were sequenced from twenty-five neuroblastomas arising in neuroblastoma-prone transgenic mice. RESULTS: We identified mutations in the PIK3CA gene in 2 of 69 human neuroblastomas (2.9%). Neither mutation (R524M and E982D) has been studiedto date for effects on lipid kinase activity. Though both occurred in tumors with MYCN amplification the overall rate of PIK3CA mutations in MYCN amplified and single-copy tumors did not differ appreciably (2 of 31 versus 0 of 38, respectively). Further, no activating mutations were identified in a survey of Ras signal transduction genes (including Hras1, Kras2, Nras, Pik3ca, or Braf genes) in twenty-five neuroblastic tumors arising in the MYCN-initiated transgenic mouse model. CONCLUSION: These data suggest that activating mutationsin the Ras/Raf-MAPK/PI3K signaling cascades occur infrequently in neuroblastoma.Further, despite compelling evidence for MYC and RAS cooperation in vitro and invivo to promote tumourigenesis, activation of RAS signal transduction does not constitute a preferred secondary pathway in neuroblastomas with MYCN deregulation in either human tumors or murine models.

The phosphatidylinositol 3-kinases (PI3K) are a family of enzymes that relay important cellular growth control signals. Recently, a large-scale mutational analysis of eight PI3K and eight PI3K-like genes revealed somatic mutations in PIK3CA, which encodes the p110alpha catalytic subunit of class IA PI3K, in several types of cancer, including glioblastoma multiforme. In that report, 4 of15 (27%) glioblastomas contained potentially oncogenic PIK3CA mutations. Subsequent studies, however, showed a significantly lower mutation rate ranging from 0% to 7%. Given this disparity and to address the relation of patient age to mutation frequency, we examined 10 exons of PIK3CA in 73 glioblastoma samples byPCR amplification followed by direct DNA sequencing. Overall, PIK3CA mutations were found in 11 (15%) samples, including several novel mutations. PIK3CA mutations were distributed in ALL sample types, with 18%, 9%, and 13% of primarytumors, xenografts, and cell lines containing mutations, respectively. Of the primary tumors, PIK3CA mutations were identified in 21% and 17% of pediatric andadult samples, respectively. No evidence of PIK3CA gene amplification was detected by quantitative real-time PCR in any of the samples. This study confirms that PIK3CA mutations occur in a significant number of human glioblastomas, further indicating that therapeutic targeting of this pathway in glioblastomas is of value. Moreover, this is the first study showing PIK3CA mutations in pediatric glioblastomas, thus providing a molecular target in this important pediatric malignancy.

PURPOSE: Hepatoblastoma represents the most frequent malignant liver tumor in childhood. The phosphatidylinositol-3'-kinase (PI3K)/AKT pathway is crucial in downstream signaling of multiple receptor tyrosine kinases of pathogenic importance in hepatoblastoma. Increased PI3K/AKT signaling pathway activity and activating mutations of PIK3CA, encoding a PI3K catalytic subunit, have been reported in different childhood tumors. The current study was done to analyze the role of PI3K/AKT signaling in hepatoblastoma. EXPERIMENTAL DESIGN: Immunohistochemical stainings of (Ser473)-phosphorylated (p)-AKT protein, its targets p-(Ser9)-GSK-3beta and p-(Ser2448)-mTOR, as well as the cell cycle regulators Cyclin D1, p27(KIP1), and p21(CIP1) were done and the PIK3CA gene wasscreened for mutations. In vitro, two hepatoblastoma cell lines treated with thePI3K inhibitor LY294002 were analyzed for AKT and GSK-3beta phosphorylation, cell proliferation, and apoptosis. Additionally, simultaneous treatments of hepatoblastoma with LY294002 and cytotoxic drugs were carried out. RESULTS: Mosttumors strongly expressed p-AKT, p-GSK-3beta, and p-mTOR; subgroups showed significant Cyclin D1, p27(KIP1), and p21(CIP1) expression. One hepatoblastoma carried an E545A mutation in the PIK3CA gene. In vitro, PI3K inhibition diminished hepatoblastoma cell growth being accompanied by reduced AKT and GSK-3beta phosphorylation. Flow cytometry and 4', 6-diamidino-2-phenylindole stainings showed that PI3K pathway inhibition leads to a substantial increase inapoptosis and a decrease in cellular proliferation linked to reduced Cyclin D1 and increased p27(KIP1) levels. Simultaneous treatment of hepatoblastoma cell lines with LY294002 and cytotoxic drugs resulted in positive interactions. CONCLUSIONS: Our findings imply that PI3K signaling plays an essential role in growth control of hepatoblastoma and might be successfully targeted in multimodal therapeutic strategies.