Nuclear oncogene products have the potential to induce alterations in gene regulation leading to the genesis of cancer. The biochemical mechanisms by which nuclear oncoproteins act remain unknown. Recently, an oncogene, v-jun, was found to share homology with the DNA binding domain of a yeast transcription factor, GCN4. Furthermore, GCN4 and the phorbol ester-inducible enhancer binding protein, AP-1, recognize very similar DNA sequences. The human proto-oncogene c-jun has now been isolated, and the deduced amino acid sequence indicates more than 80 percent identity with v-jun. Expression of cloned c-jun in bacteria produced a protein with sequence-specific DNA binding properties identical to AP-1. Antibodies raised against two distinct peptides derived from v-jun reacted specifically with human AP-1. In addition, partial amino acid sequence of purified AP-1 revealed tryptic peptides in common with the c-jun protein. The structural and functional similarities between the c-jun product and the enhancer binding protein suggest that AP-1 may be encoded by c-jun. These findings demonstrate that the proto-oncogene product of c-jun interacts directly with specific target DNA sequences to regulate gene expression, and therefore it may now be possible to identify genes under the control of c-jun that affect cell growth and neoplasia.

Akt ͉ oncogenic transformation ͉ p110␣ ͉ PIK3CA

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 p110alpha of PI3K, have heightened the interest in the oncogenic potential of this lipid kinase and have made p110alpha an ideal drug target.

No abstract

Class I phosphoinositide 3-kinase (PI3K) is a dimeric enzyme, consisting of a catalytic and a regulatory subunit. The catalytic subunit occurs in four isoforms designated as p110a, p110b, p110c and p110d. These isoforms combine with several regulatory subunits; for p110a, b and d, the standard regulatory subunit is p85, for p110c, it is p101. PI3Ks play important roles in human cancer. PIK3CA, the gene encoding p110a, is mutated frequently in common cancers, including carcinoma of the breast, prostate, colon and endometrium. Eighty percent of these mutations are represented by one of the three amino-acid substitutions in the helical or kinase domains of the enzyme. The mutant p110a shows a gain of function in enzymatic and signaling activity and is oncogenic in cell culture and in animal model systems. Structural and genetic data suggest that the mutations affect regulatory inter-and intramolecular interactions and support the conclusion that there are at least two molecular mechanisms for the gain of function in p110a. One of these mechanisms operates largely independently of binding to p85, the other abolishes the requirement for an interaction with Ras. The non-a isoforms of p110 do not show cancerspecific mutations. However, they are often differentially expressed in cancer and, in contrast to p110a, wild-type non-a isoforms of p110 are oncogenic when overexpressed in cell culture. The isoforms of p110 have become promising drug targets. Isoform-selective inhibitors have been identified. Inhibitors that target exclusively the cancer-specific mutants of p110a constitute an important goal and challenge for current drug development.

No abstract

The phosphatidylinositol 3-kinase (PI3K) signaling pathway is upregulated in cancer. PIK3CA, the gene coding for the catalytic subunit p110␣ of PI3K, is mutated in Ϸ30% of tumors of the prostate, breast, cervix, and endometrium. The most prominent of these mutants, represented by single amino acid substitutions in the helical or kinase domain, show a gain of enzymatic function, activate AKT signaling, and induce oncogenic transformation. We have carried out a genetic and biochemical analysis of these hot-spot mutations in PIK3CA. The results of this study suggest that the helical and kinase domain mutations trigger gain of function through different mechanisms. They show different requirements for interaction with the PI3K regulatory subunit p85 and with RAS-GTP. The gain of function induced by helical domain mutations is independent of binding to p85 but requires interaction with RAS-GTP. In contrast, the kinase domain mutation is active in the absence of RAS-GTP binding but is highly dependent on the interaction with p85. We speculate that the contrasting roles of p85 and RAS-GTP in helical and kinase domain mutations reflect two distinct states of mutated p110␣. These two states differ in mutation-induced surface charges and also may differ in conformational properties that are controlled by interactions with p85 and RAS-GTP. The two states do not appear mutually exclusive because the helical and kinase domain mutations act synergistically when present in the same p110␣ molecule. This synergism also supports the conclusion that the helical and kinase domain mutations operate by two different and independent mechanisms.cancer ͉ molecular mechanisms ͉ p85 ͉ RAS ͉ AKT P hosphatidylinositol 3-kinases (PI3Ks) phosphorylate phosphatidylinositols at the 3Ј position of the inositol ring, generating second messengers that control cellular activities and properties, including proliferation, survival, motility, and cell shape. Mutations that block PI3K function disrupt these processes (1-12). PI3Ks form a family that is divided into three classes, differing in structure, substrate preference, tissue distribution, mechanism of activation, and, ultimately, function (12-16). For the regulation of cell proliferation and in tumorigenesis, the most important PI3K proteins are those of class IA, notably the catalytic subunit p110␣ and its associated regulatory subunits (p85␣, p55␣, p50␣, p85␤, and p55␥).p110␣ contains an N-terminal p85-binding domain (p85BD), a Ras-binding domain (RBD), a protein-kinase-C homology-2 (C2) domain, a helical domain, and a C-terminal kinase domain (17). p110␣ is constitutively associated with regulatory subunits, of which p85␣ is the best studied (herein referred to as p85). p110␣ and p85 exist in the cell as a heterodimeric complex. In quiescent cells, p85 stabilizes p110␣ and inactivates PI3K activity (18). Upon growth factor stimulation, receptor tyrosine kinases (RTKs) undergo autophosphorylation, creating binding sites for Src homology 2 (SH2) domain-containing proteins. The SH2 domains of p8...

Glycomics is emerging as a new field for the biology of complex glycoproteins and glycoconjugates. The lack of versatile glycanlabeling methods has presented a major obstacle to visualizing at the cellular level and studying glycoconjugates.