Human cancer cells typically harbour multiple chromosomal aberrations, nucleotide substitutions and epigenetic modifications that drive malignant transformation. The Cancer Genome Atlas ( TCGA) pilot project aims to assess the value of large- scale multi- dimensional analysis of these molecular characteristics in human cancer and to provide the data rapidly to the research community. Here we report the interim integrative analysis of DNA copy number, gene expression and DNA methylation aberrations in 206 glioblastomas - the most common type of primary adult brain cancer - and nucleotide sequence aberrations in 91 of the 206 glioblastomas. This analysis provides new insights into the roles of ERBB2, NF1 and TP53, uncovers frequent mutations of the phosphatidylinositol- 3- OH kinase regulatory subunit gene PIK3R1, and provides a network view of the pathways altered in the development of glioblastoma. Furthermore, integration of mutation, DNA methylation and clinical treatment data reveals a link between MGMT promoter methylation and a hypermutator phenotype consequent to mismatch repair deficiency in treated glioblastomas, an observation with potential clinical implications. Together, these findings establish the feasibility and power of TCGA, demonstrating that it can rapidly expand knowledge of the molecular basis of cancer.

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Comprehensive genomic characterization defines human glioblastoma genes and core pathways

Phosphatidylinositol 3-kinases (PI3Ks) evolved from a single enzyme that regulates vesicle trafficking in unicellular eukaryotes into a family of enzymes that regulate cellular metabolism and growth in multicellular organisms. In this review, we examine how the PI3K pathway has evolved to control these fundamental processes, and how this pathway is in turn regulated by intricate feedback and crosstalk mechanisms. In light of the recent advances in our understanding of the function of PI3Ks in the pathogenesis of diabetes and cancer, we discuss the exciting therapeutic opportunities for targeting this pathway to treat these diseases.

The evolution of phosphatidylinositol 3-kinases as regulators of growth and metabolism

Inositol phospholipids have long been known to have an important regulatory role in cell physiology. The repertoire of cellular processes known to be directly or indirectly controlled by this class of lipids has now dramatically expanded. Through interactions mediated by their headgroups, which can be reversibly phosphorylated to generate seven species, phosphoinositides play a fundamental part in controlling membrane-cytosol interfaces. These lipids mediate acute responses, but also act as constitutive signals that help define organelle identity. Their functions, besides classical signal transduction at the cell surface, include regulation of membrane traffic, the cytoskeleton, nuclear events and the permeability and transport functions of membranes.

Phosphoinositides in cell regulation and membrane dynamics

The phosphoinositide 3-kinase (PI3K) pathway is a key signal transduction system that links oncogenes and multiple receptor classes to many essential cellular functions, and is perhaps the most commonly activated signalling pathway in human cancer. This pathway therefore presents both an opportunity and a challenge for cancer therapy. Even as inhibitors that target PI3K isoforms and other major nodes in the pathway, including AKT and mammalian target of rapamycin (mTOR), reach clinical trials, major issues remain. Here, we highlight recent progress that has been made in our understanding of the PI3K pathway and discuss the potential of and challenges for the development of therapeutic agents that target this pathway in cancer.

/pdf/targeting-the-phosphoinositide-3-kinase-pathway-in-cancer-4zhc81tbx0.pdf

Targeting the phosphoinositide 3-kinase pathway in cancer.

There are ample genetic and laboratory studies that suggest the PI3K-Akt pathway is vital to the growth and survival of cancer cells. Inhibitors targeting this pathway are entering the clinic at a rapid pace. In this Review, the therapeutic potential of drugs targeting PI3K-Akt signalling for the treatment of cancer is discussed. I focus on the advantages and drawbacks of different treatment strategies for targeting this pathway, the cancers that might respond best to these therapies and the challenges and limitations that confront their clinical development.

/pdf/targeting-pi3k-signalling-in-cancer-opportunities-challenges-22a9u88icu.pdf

Targeting PI3K signalling in cancer: opportunities, challenges and limitations.

Mutations in genes that encode components of the phosphatidyl-inositol 3-kinase (PI3-kinase) signaling pathway are common in human cancer. The recent discovery of nonrandom somatic mutations in the PIK3CA gene of many human tumors suggests an oncogenic role for the mutated enzyme. We have determined the growth-regulatory and signaling properties of the three most frequently observed PI3-kinase mutations: E542K, E545K, and H1047R. Expressed in chicken embryo fibroblasts, all three mutants induce oncogenic transformation with high efficiency. This transforming ability is correlated with elevated catalytic activity in in vitro kinase assays. The mutant-transformed cells show constitutive phosphorylation of Akt, of p70 S6 kinase, and of the 4E-binding protein 1. Phosphorylation of S6 kinase and of 4E-binding protein 1 is regulated by the target of rapamycin (TOR) kinase and affects rates of protein synthesis. The inhibitor of TOR, rapamycin, strongly interferes with cellular transformation induced by the PI3-kinase mutants, suggesting that the TOR and its downstream targets are essential components of the transformation process. The oncogenic transforming activity makes the mutated PI3-kinase proteins promising targets for small molecule inhibitors that could be developed into effective and highly specific anticancer drugs.

Phosphatidylinositol 3-kinase mutations identified in human cancer are oncogenic

There have long been indications of a role for PI3K (phosphatidylinositol 3-kinase) in cancer pathogenesis. Experimental data document a requirement for deregulation of both transcription and translation in PI3K-mediated oncogenic transformation. The recent discoveries of cancer-specific mutations in PIK3CA, the gene that encodes the catalytic subunit p110α of PI3K, have heightened the interest in the oncogenic potential of this lipid kinase and have made p110α an ideal drug target.

Oncogenic PI3K deregulates transcription and translation.

The PIK3CA gene, coding for the catalytic subunit p110α of class IA phosphatidylinositol 3-kinases (PI3Ks), is frequently mutated in human cancer. Mutated p110α proteins show a gain of enzymatic function in vitro and are oncogenic in cell culture. Here, we show that three prevalent mutants of p110α, 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 p110α mutant. The in vivo oncogenicity of PIK3CA mutants in an avian species strongly suggests a critical role for these mutated proteins in human malignancies.

https://www.pnas.org/content/pnas/103/5/1475.full.pdf

Cancer-specific mutations in PIK3CA are oncogenic in vivo.

Class I phosphoinositide 3-kinase contains four isoforms of the catalytic subunit, p110α, -β, -γ, and -δ. At physiological levels of expression, the wild-type p110α isoform lacks oncogenic potential, but gain-of-function mutations and overexpression of p110α are correlated with oncogenicity. The p110β, -γ, and -δ isoforms induce transformation of cultured cells as wild-type proteins. This oncogenic potential requires kinase activity and can be suppressed by the target of rapamycin inhibitor rapamycin. The p110δ isoform constitutively activates the Akt signaling pathway; p110γ activates Akt only in the presence of serum. The isoforms differ in their requirements for upstream signaling. The transforming activity of the p110γ isoform depends on rat sarcoma viral oncogene homolog (Ras) binding; preliminary data suggest the same for p110β and indicate Ras-independent oncogenic potential of p110δ. The surprising oncogenic potential of the wild-type non-α isoforms of class I phosphoinositide 3-kinase may explain the dearth of cancer-specific mutations in these proteins, because these non-α isoforms could contribute to the oncogenic phenotype of the cell by differential expression.

https://www.pnas.org/content/pnas/103/5/1289.full.pdf

Oncogenic transformation induced by the p110β, -γ, and -δ isoforms of class I phosphoinositide 3-kinase

https://www.cell.com/trends/biochemical-sciences/pdf/S0968-0004(07)00142-9.pdf

Sohye Kang

Papers

Phosphatidylinositol 3-kinase mutations identified in human cancer are oncogenic

Oncogenic PI3K deregulates transcription and translation.

Cancer-specific mutations in PIK3CA are oncogenic in vivo.

Oncogenic transformation induced by the p110β, -γ, and -δ isoforms of class I phosphoinositide 3-kinase

Cancer-specific mutations in phosphatidylinositol 3-kinase.