Phospatidylinositol 3-kinase expression in human breast cancer

Phosphorylated Akt1 in Human Breast Cancer Measured by Direct Sandwich Enzyme-Linked Immunosorbent Assay: Correlation with Clinicopathological Features and Tumor VEGF-Signaling System Component Levels

Protein kinase B (Akt) plays a major role in the regulation of breast cancer growth, survival, hormone, drug and radiosensitivity, but the clinical value of its expression and activation in human tumors is unclear. Activated Akt1 (pAkt1) expression was quantified in a series of 46 breast cancer and adjacent mammary gland samples by a direct Path-Scan™ PhosphoAkt1 (Ser473) sandwich ELISA kit. VEGF, sVEGFR1 and sVEGFR2 levels were measured simultaneously by standard ELISA kits. Forty-nine percent of the tumors had an increased pAkt1 level as compared to adjacent tissue. pAkt1 levels were significantly higher in stage IIb than in stage I-IIa tumors. The frequency of pAkt1 elevation was positively associated with tumor size and malignancy grade. pAkt1 was also twice as frequently increased in PgR-negative as in PgR-positive tumors, while its mean level was significantly higher in ER-positive than in ER-negative tumors. VEGF, sVEGFR1 and sVEGFR2 were increased in 73–85% of the tumors, but no associations with most clinicobiological factors and pAkt1 level were found. In conclusion, activation of Akt1 is not associated with VEGF signaling protein expression in breast cancer but is related to tumor size, grade of malignancy, and steroid receptor status.

S137 phosphorylation of profilin 1 is an important signaling event in breast cancer progression

BACKGROUND

Profilins are actin-modulating proteins regulating many intracellular functions based on their multiple and diverse ligand interactions. They have been implicated to play a role in many pathological conditions such as allergies, cardiovascular diseases, muscular atrophy, diabetes, dementia and cancer. Post-translational modifications of profilin 1 can alter its properties and subsequently its function in a cell. In the present study, we identify the importance of phosphorylation of profilin 1 at serine 137 (S137) residue in breast cancer progression.

METHODS/PRINCIPAL FINDINGS

We found elevated profilin 1 (PFN) in human breast cancer tissues when compared to adjacent normal tissues. Overexpression of wild-type profilin 1 (PFN-WT) in breast cancer MCF7 cells made them more migratory, invasive and adherent independent in comparison to empty vector transfected cells. Mutation in serine phosphorylation site (S137) of profilin 1 (PFN-S137A) significantly abrogated these properties. Mutation affecting actin-binding ability (PFN-R74E) of profilin 1 enhanced its tumorigenic function whereas mutation affecting its poly-L-proline binding function (PFN-H133S) alleviated these mechanisms in breast cancer cells. PFN-WT was found to activate matrix metalloproteinases by zymography, MMP2 and MMP9 in presence of PDBu (phorbol 12, 13 dibutyrate, PI3K agonist) to enhance migration and invasion in MCF7 cells while PFN-S137A did not. Phosphorylation increased migration and invasion in other mutants of profilin 1. Nuclear profilin levels also increased in the presence of PDBu.

CONCLUSIONS

Previous studies show that profilin could be executing a dual role in cancer by either suppressing or promoting tumorigenesis in a context dependent manner. In this study we demonstrate for the first time that phosphorylation of profilin 1 at serine 137 enhances oncogenic properties in breast cancer cells. Inhibitors targeting profilin 1 phosphorylation directly or indirectly through inhibition of kinases that phosphorylate profilin could be valuable therapeutic agents that can alter its activity and thereby control the progression of cancer.

Abnormal expression of PI3K isoforms in patients with tobacco-related oral squamous cell carcinoma

BACKGROUND

The phosphatidylinositol 3-kinase (PI3K) signaling regulates several cellular functions such as motility, proliferation, angiogenesis and survival.

METHODS

Since there is no information on expression of PI3K isoforms in oral cancer, we studied the expression of different isoforms of PI3K (p110α, p110γ, PI3K-C2, Vps34p and p85α) in tumor samples and PBMC by RT and q-RTPCR and serum levels of PI3K p110α by SPR and ELISA techniques in 108 patients with tobacco-related oral squamous cell carcinoma (OSCC) and 46 normal subjects.

RESULTS

We observed significantly higher PI3K p110α (p<0.0001) and lower (p<0.0001) vesicular sorting protein 34p (Vps34p) mRNA both in PBMC and tissue samples of oral cancer patients as compared to the normal controls. Other PI3K isoforms did not show such change. Circulating PI3K p110α levels were higher in patients (p<0.0001) as compared to healthy subjects, the SPR data showed direct correlation with advancing stage of the disease. PI3K p110α was overexpressed in tumor samples but not in the normal buccal mucosa.

CONCLUSIONS

Upregulation of circulating PI3K p110α isoform and its direct correlation with increasing tumor load in OSCC patients indicates that it may be a significant prognostic indicator and a suitable target for therapeutic/chemo-preventive strategies for tobacco-related OSCC.

Identification of an mRNP complex regulating tumorigenesis at the translational elongation step

Transcript-selective translational regulation of epithelial-mesenchymal transition (EMT) by transforming growth factor-β (TGF-β) is directed by the hnRNP E1-containing TGF-β-activated-translational (BAT) mRNP complex. Herein, eukaryotic elongation factor-1 A1 (eEF1A1) is identified as an integral component of the BAT complex. Translational silencing of Dab2 and ILEI, two EMT transcripts, is mediated by the binding of hnRNP E1 and eEF1A1 to their 3'UTR BAT element, whereby hnRNP E1 stalls translational elongation by inhibiting the release of eEF1A1 from the ribosomal A site. TGF-β-mediated hnRNP E1 phosphorylation, through Akt2, disrupts the BAT complex, thereby restoring translation of target EMT transcripts. Attenuation of hnRNP E1 expression in two noninvasive breast epithelial cells (NMuMG and MCF-7) not only induced EMT but also enabled cells to form metastatic lesions in vivo. Thus, translational regulation by TGF-β at the elongation stage represents a critical checkpoint coordinating the expression of EMT transcripts required during development and in tumorigenesis and metastatic progression.

Flavonoids as protein kinase inhibitors for cancer chemoprevention: direct binding and molecular modeling

Protein kinases play crucial roles in the regulation of multiple cell signaling pathways and cellular functions. Deregulation of protein kinase function has been implicated in carcinogenesis. The inhibition of protein kinases has emerged as an important target for cancer chemoprevention and therapy. Accumulated data revealed that flavonoids exert chemopreventive effects through acting at protein kinase signaling pathways, more than as conventional hydrogen-donating antioxidants. Recent studies show that flavonoids can bind directly to some protein kinases, including Akt/protein kinase B (Akt/PKB), Fyn, Janus kinase 1 (JAK1), mitogen-activated protein kinase kinase 1 (MEK1), phosphoinositide 3-kinase (PI3K), mitogen-activated protein (MAP) kinase kinase 4 (MKK4), Raf1, and zeta chain-associated 70-kDa protein (ZAP-70) kinase, and then alter their phosphorylation state to regulate multiple cell signaling pathways in carcinogenesis processes. In this review, we report recent results on the interactions of flavonoids and protein kinases, especially their direct binding and molecular modeling. The data suggest that flavonoids act as protein kinase inhibitors for cancer chemoprevention that were thought previously as conventional hydrogen-donating antioxidant. Moreover, the molecular modeling data show some hints for creating natural compound-based protein kinase inhibitors for cancer chemoprevention and therapy.

Molecular markers of tumors

The main biologically significant molecular markers of human tumors are discussed on the basis of modern published data and author's findings of many-year studies: steroid hormone receptors, growth factors and underlying signal proteins, tumor-associated proteases, and angiogenesis markers. Methodological aspects, progress in preclinical studies, international recommendations on the use of these parameters for prediction of the disease course and prescription of effective therapy are analyzed. Latest data on the potentialities and limitations of modern highly productive technologies (microchips) as an alternative to studies of individual molecular markers are presented.

The transforming functions of PI3-kinase-gamma are linked to disruption of intercellular adhesion and promotion of cancer cell invasion

The involvement of phosphoinositide 3-kinases class IA (PI3K-alpha and -beta) in cancer cell proliferation, survival, motility, and invasiveness is now well established. However, the possible contribution of the class IB PI3Kgamma in cancer cell transformation remains to be explored. In this study, we have stably transfected the PI3Kgamma-deficient human colon cancer cell line HCT8/S11 with expression vectors encoding either wild-type PI3Kgamma, its plasma membrane targeted form CAAX-PI3Kgamma, or the PI3Kgamma lipid and protein kinase-dead mutant (CAAX-K832R). We provide evidence that the constitutively active CAAX-PI3Kgamma variant induced collagen type I invasion in HCT8/S11 cells through disruption of cell-cell adhesion, with no apparent impact on cell proliferation and motility. The proinvasive activity of CAAX-PI3K-gamma was abolished by pharmacological inhibitors targeting PI3-K activities (wortmannin), Rho-GTPases, and the Rho-Rho kinase axis (C3T exoenzyme and Y27632, respectively). Conversely, the wild-type PI3Kgamma and its double mutant CAAX-K832R were ineffective on cancer cell invasion measured under control or stimulated conditions operated with the proinvasive agents leptin and intestinal trefoil factor. Taken together, our data indicate that PI3Kgamma exerts transforming functions via several mechanisms in human colon epithelial cancer cells, including alterations of homotypic cell-cell adhesion and induction of collagen type I invasion through canonical proinvasive pathways.

PTHrP increases xenograft growth and promotes integrin alpha6beta4 expression and Akt activation in colon cancer

Parathyroid hormone-related protein (PTHrP) is expressed by human colon cancer tissue and cell lines. Expression of PTHrP and phosphatidylinositol 3-kinase (PI3-K) pathway components correlates with the severity of colon carcinoma. Here we observed a positive effect of endogenous PTHrP on LoVo (human colon cancer) cell proliferation, migration, invasion, integrin alpha6 and beta4 expression, and p-Akt levels. There was a direct correlation between PTHrP expression and anchorage-independent cell growth. PTHrP significantly increased xenograft growth; tumors from PTHrP-overexpressing cells showed increased expression of integrins alpha6 and beta4, and PI3-K pathway components. The higher expression of PTHrP in human colon cancer adenocarcinoma vs. normal colonic mucosa was accompanied by increased integrin alpha6 and beta4 levels. Elevated PTHrP expression in colon cancer may thus upregulate integrin alpha6beta4 expression, with consequent PI3-K activation. Targeting PTHrP might result in effective inhibition of tumor growth, migration, and invasion.

Protein-reactive natural products

Researchers in the post-genome era are confronted with the daunting task of assigning structure and function to tens of thousands of encoded proteins. To realize this goal, new technologies are emerging for the analysis of protein function on a global scale, such as activity-based protein profiling (ABPP), which aims to develop active site-directed chemical probes for enzyme analysis in whole proteomes. For the pursuit of such chemical proteomic technologies, it is helpful to derive inspiration from protein-reactive natural products. Natural products use a remarkably diverse set of mechanisms to covalently modify enzymes from distinct mechanistic classes, thus providing a wellspring of chemical concepts that can be exploited for the design of active-site-directed proteomic probes. Herein, we highlight several examples of protein-reactive natural products and illustrate how their mechanisms of action have influenced and continue to shape the progression of chemical proteomic technologies like ABPP.

Activation of mitogenic pathways and sensitization to estrogen-induced apoptosis: two independent characteristics of tamoxifen-resistant breast cancer cells?

Paradoxical induction of apoptosis by estrogen has been described previously for estrogen-deprived and antiestrogen-resistant breast cancer cells. In this study we analyzed the possible interrelations between cell sensitization to estrogen apoptotic action and cell ability to (anti)estrogen-independent growth. Using tamoxifen-resistant sublines derived from the parent MCF-7 breast cancer cells by long-term tamoxifen treatment we demonstrated that resistant cells are characterized by increased level of EGF receptor and unexpected increase of VEGF receptor 2 (Flk-1/KDR) and its specific ligand, VEGF-A. The importance of the VEGF signaling in the autocrine regulation of cell growth was indicated by the ability of VEGF inhibitor, soluble fragment of Flt-1/Fc chimera, to suppress the phosphorylation of MAP kinases as well as to inhibit the estrogen-independent growth of MCF-7 cells. Sensitization of tamoxifen-resistant cells to estrogen-induced apoptosis required the additional continuous cultivation in steroid-depleted medium and did not depend on the activity of both EGF and VEGF pathways. Finally, we showed that treatment of the cells with 17beta-estradiol (10(-9) M) resulted in a marked increase in p53 level both in the resistant cells undergoing apoptosis and in the parent MCF-7 cells insensitive to apoptotic estrogen action. These data provide an important support for the existence of a disbalance between pro- and anti-apoptotic machinery in the resistant breast cancer cells that forms independently of the acquired ability to estrogen-independent growth.

Targeted molecular therapy of the PI3K pathway: therapeutic significance of PI3K subunit targeting in colorectal carcinoma

OBJECTIVE

The phosphatidylinositol 3-kinase (PI3K) pathway promotes cancer cell proliferation and survival. The authors determined the pattern of distribution of PI3K pathway components (ie, the p85alpha regulatory subunit, p110alpha catalytic subunit, Akt1, Akt2, and the tumor suppressor PTEN) in human colorectal cancer. In addition, inhibition of in vitro proliferation and in vivo liver metastasis by p85alpha or p110alpha siRNA treatment was analyzed.

SUMMARY BACKGROUND DATA

Small interfering RNA (siRNA) molecules suppress expression of target genes and may have therapeutic applications as target-specific therapies for cancer. Therefore, the purpose of this study was 2-fold: 1) to analyze the distribution pattern of PI3K pathway components in human normal colorectal cancers, and 2) to determine whether targeted inhibition of PI3K inhibits colon cancer growth in vitro and suppresses metastatic growth in vivo.

METHODS

Immunohistochemical analysis was performed on colorectal adenocarcinomas and adjacent normal mucosa for PI3K pathway components, including p85alpha, p110alpha, Akt1, Akt2, and the tumor suppressor PTEN, which inhibits PI3K. HT29 and KM20 human colon cancer cells were treated with siRNA directed to p85alpha or p110alpha, and cell viability and apoptosis assessed. HT29 cells, transfected with a plasmid containing green fluorescent protein (GFP), were injected into the spleen of athymic nude mice to establish liver metastases; mice were randomized to receive either nontargeting control (NTC), p85alpha or p110alpha siRNA.

RESULTS

PI3K pathway components p85alpha and Akt2 were highly expressed in glandular elements of colon cancers, with a correlation between staining intensity and clinical stage; PTEN expression was decreased in the colon cancers of all stages. PI3K-specific siRNA treatment decreased cell viability in vitro and suppressed metastatic tumor growth in vivo.

CONCLUSIONS

Selective targeting of PI3K pathway components may enhance the effects of standard chemotherapeutic agents and provide novel adjuvant treatment of selected colorectal cancers.

Action mechanisms and structure-activity relationships of PI3Kgamma inhibitors on the enzyme: a molecular modeling study

Action mechanisms of four types of PI3Kgamma inhibitors were investigated on the ligand-binding pocket (LBP) of PI3Kgamma with molecular modeling method. At first five compounds whose complex structures with PI3Kgamma were available experimentally were used to validate the reliability of docking program Autodock3.0. The results demonstrated that the program could reproduce the bound conformations of those compounds in crystal structures. Then the program was used to dock all the four types of PI3Kgamma inhibitors into the LBP of the enzyme. The predicted activities of these compounds were in agreement with their experimental activities, and a pharmacophore model was hence derived for these compounds, which consisted of one hydrophobic portion flanked by two symmetric hydrophilic portions. Furthermore, the structure-activity relationships of PI3Kgamma inhibitors were elucidated and the activity differences between them were discussed.

Activated proteinkinase B in breast cancer

The content of activated (phosphorylated) form of proteinkinase B in tumors and homologous tissues of 46 patients with breast cancer was measured by enzyme immunoassay. Activity of proteinkinase B was increased in tumors of 48% patients in comparison with homologous histologically unchanged tissue. Activity of proteinkinase B in hormone-dependent mammary tumors was significantly higher than in tumor tissue from patients with negative receptor status.

Study on improving the selectivity of compounds that inhibit two PI3Ks (gamma and delta)

A desirable characteristic of PI3K inhibitors is their selectivity. Up to now, there has been no report that describes the 3 D-structure differences between two PI3Ks (delta and gamma) and applies them to designing selective compounds. In the present study, we used an approach combining protein-structure modeling, GRID/PCA (Principal Component Analysis) and docking methods to investigate the detail interactions of the two PI3Ks with various chemical groups. At first, we constructed a 3 D-model of the PI3Kdelta catalytic subunit with the program Modeller7.0 based on the high resolution X-ray structure of the PI3Kgamma catalytic subunit, and then employed GRID and PCA to reveal the most relevant structural and physicochemical differences between the two PI3Ks related to their selectivity. As a result, the analysis unveiled the most important regions on the two PI3Ks that should be taken into account for the design of selective inhibitors. Finally, based on activity data of 10 PI3Kdelta-selective compounds, a docking study validated the results of the GRID/PCA method, which suggested that the approach could provide clear guidelines for selective drug design.

Polyomavirus middle T–induced mammary intraepithelial neoplasia outgrowths: Single origin, divergent evolution, and multiple outcomes

The development of models to investigate the pathobiology of premalignant breast lesions is a critical prerequisite for development of breast cancer prevention and early intervention strategies. Using tissue transplantation techniques, we modified the widely used polyomavirus middle T (PyV-mT) transgenic mouse model of breast cancer to study the premalignant stages of tumorigenesis. Premalignant atypical lesions were isolated from PyV-mT transgenic mice and used to generate two sets of three mammary intraepithelial neoplasia (MIN) outgrowth lines. Investigation of these six unique lines, each of which fulfills the criteria for MIN, has provided new information regarding the biology of PyV-mT-induced neoplasia. Although expression of the PyV-mT transgene was the primary initiating event for all lines, they exhibited different tumor latencies, metastatic potentials, and morphologies. Six distinguishable morphologic patterns of differentiation were identified within the premalignant outgrowths that are likely to represent several tumorigenic pathways. Further, several tumor phenotypes developed from each line and the tumors developing from the six lines had different metastatic potentials. These observations are consistent with the hypothesis that distinct pathways of PyV-mT-initiated neoplastic progression lead to different outcomes with respect to latency and metastasis. The MIN outgrowth lines share several characteristics with precursors of human breast cancer including the observation that gene expression profiles of tumors are more similar to those of the MIN outgrowth line outgrowth from which they developed than to other tumors. These lines provide an opportunity to study the full range of events occurring secondary to PyV-mT expression in the mammary gland.

Allelic imbalance and altered expression of genes in chromosome 2q11-2q16 from rat mammary gland carcinomas induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a compound found in cooked meat, is a mammary gland carcinogen in rats. Comparative genomic hybridization of PhIP-induced rat mammary gland carcinomas revealed loss in the centromeric region of 2q, a region known to carry the mammary carcinoma susceptibility 1 (Mcs1) gene and several other genes relevant to carcinogenesis. Allelic imbalance, specifically microsatellite instability and loss of heterozygosity, was examined in mammary gland carcinomas induced by PhIP in Sprague-Dawley (SD)xWistar Furth F1 hybrid rats. In a polymerase chain reaction (PCR)-based assay with 34 microsatellite markers coinciding to 2q11-2q16, nine markers revealed allelic imbalance. The frequency of imbalance in the tumors varied from 10 to 100% depending on the specific marker. However, none of the markers coinciding with the Mcs1 gene locus showed allelic imbalance, suggesting that alterations at this locus were not associated with PhIP-induced rat mammary gland cancer. The expression of several genes physically mapped to 2q11-2q16 and potentially involved in carcinogenesis including Ccnb (cyclin B1), Ccnh (cyclin H), Rasa (Ras GAP), Rasgrf2, Pi3kr1 (p85alpha), and Il6st (gp130) was also examined by quantitative real-time PCR and immunohistochemistry (IHC) across a large bank of PhIP-induced SD rat mammary gland carcinomas. By quantitative real-time PCR, the mRNA expression of Rasa, Pi3kr1, Ccnh, and Il6st in carcinomas was, respectively, 22-, 20-, three- and threefold higher in carcinomas than in control mammary gland tissues (P<0.05, Student's t-test). A statistically sixfold lower expression of Rasgrf2 was detected in carcinomas whereas no significant change in Ccnb1 expression was observed. The findings from quantitative real-time PCR were confirmed by IHC for each gene. In addition, the proliferation index in mammary gland carcinomas as assessed by PCNA was found to correlate with the overexpression of Cyclin H by IHC analysis (P<0.05, Spearman Rank Order Correlation). The findings from the current study implicate molecular alterations in the proximal region of 2q in PhIP-induced rat mammary gland carcinomas.

Structural insight into substrate specificity and regulatory mechanisms of phosphoinositide 3-kinases

Phosphoinositide 3-kinases (PI3Ks) are implicated in a variety of fundamental cellular processes. These enzymes catalyse phosphorylation of the 3'-OH position of myo-inositol lipids that serve as secondary messengers. The catalytic subunit for one of the family members, PI3K gamma, has been structurally characterized, independently, in complexes with kinase inhibitors and with the p21(Ras) GTPase. These atomic structures provide a basis for the rationalization of some PI3K substrate specificities and regulatory mechanisms, establishing links to functional and cellular data. Ongoing comprehensive structural and functional studies are essential to realize the promise of PI3K isozyme-specific therapeutic agents.

Dysregulation of phosphatidylinositol 3-kinase and downstream effectors in human breast cancer

Phosphatidylinositol 3-kinase (PI3-K) is a growth factor-activated transforming lipid (and protein) kinase, involved in cell motility and invasion, that has multiple effectors. Relatively little is known about its expression and enzymatic activity in human breast cancer. Since growth factor receptors are amplified in breast cancer, and the tumor suppressor PTEN may be mutated in human breast cancer, it was hypothesized that PI3-K and its downstream effectors would be activated in this disease. In 11 resected tumors analyzed for expression of this kinase, a mean 3-fold increase in protein expression was observed over the corresponding adjacent control tissue. Using an in vitro lipid kinase assay of the immunoprecipitated PI3-K protein, a greater than 2-fold increase in activation was observed. These changes were observed in the absence of an activation of either protein kinase B (PKB, akt1) or p70 S6 kinase (p70 S6K). However, p21-activated kinase (Pak), p38 mitogen-activated protein kinase (p38 MAPK) and mitogen-activated protein kinase-activated protein kinase 2 (MAPKAPK 2) were all overexpressed and demonstrated increased enzyme activity. It may be concluded that aberrant mitogenic signaling in human breast cancer in vivo involves Pak, p38 MAPK and MAPKAPK2 downstream of PI3-K, but neither of PKB or p70 S6K. It is proposed that this pathway may serve as a useful targeting nexus for investigation of small molecule inhibitors in human breast cancer.

Role of phosphoinositide 3OH-kinase in autocrine transformation by PDGF-BB

Phosphoinositide 3OH-kinases (PI3K) are a family of lipid kinases that activates signalling pathways important for migration, cytoskeletal rearrangements, and cell survival. These processes are important hallmarks in transformation. We have evaluated the functional role of PI3K for development of a transformed morphology and migratory responses of murine fibroblasts (NIH/sis and COL1A1/NIH3T3 cell lines) stimulated in an autocrine fashion by constitutive expression of platelet-derived growth factor-BB (PDGF-BB). We show that prolonged treatment with the specific PI3K inhibitor LY294002, induced a reversion of the transformed morphology, and prevented density-independent growth and focus formation. Functional PI3K was also required for development of the transformed morphology of NIH/sis and COL1A1/NIH3T3. Furthermore, treatment with LY294002 completely perturbed random migration of the cells. In addition our data show that, in the signalling pathways downstream of PI3K, activation of the small GTPase Rac was a prerequisite for the transformation signal. Our data also indicate the presence of a suramin-insensitive PI3K activity. Most likely this was due to the presence of a suramin-insensitive intracellular PDGFR pool that allowed activation of PI3K located in intracellular compartments. In conclusion these data show that intact PI3K activity was required for the morphological alterations and the enhanced migratory response that are hallmarks for PDGF induced autocrine transformation.

Phosphoinositide 3-kinase signalling in breast cancer: how big a role might it play?

Phosphoinositide 3-kinase (PI3K) was first identified as a lipid kinase activity associated with the products of viral oncogenes and with activated protein-tyrosine kinases. Since those early studies, the PI3K superfamily has grown to embrace at least 12 structurally and functionally related enzymes present in the human genome, some of which have protein kinase activity but not lipid kinase activity. Evidence is emerging that PI3K superfamily members, and components of PI3K signalling, play a role in the development of many human cancers. In this review, the PI3K family of enzymes and their signalling is reviewed, with particular reference to possible involvement in breast cancer.

Expression of phosphatidylinositol-3 kinase in lung cancer

The expression of phosphatidylinositol-3 kinase in tumors and homologous tissues from 29 patients with lung cancer, 5 patients with lung metastases of various tumors, and some non-tumorous pulmonary diseases was studied by Western blot analysis. The expression of phosphatidylinositol-3 kinase was increased in these tumors in comparison with histologically intact lung tissue in 5 patients with non-small-cell cancer. In 20 patients expression of phosphatidylinositol-3 kinase was the same as in homologous tissue and in 4 patients it was decreased. No relationship between phosphatidylinositol-3 kinase expression and clinical and morphological characteristics of lung cancer was revealed.

A specific function for phosphatidylinositol 3-kinase alpha (p85alpha-p110alpha) in cell survival and for phosphatidylinositol 3-kinase beta (p85alpha-p110beta) in de novo DNA synthesis of human colon carcinoma cells

We have previously shown an important function of phosphatidylinositol 3-kinase (PI3K)alpha(p85alpha-p110alpha) and PI3Kbeta (p85-alpha-p110beta) for DNA synthesis induced by various mitogens in non transformed fibroblasts and we now report a specific role of these enzymes in human colon cancer cell growth. Using antibodies specific to p110alpha and to p110beta catalytic subunits, increase in PI3Kalpha and PI3Kbeta activities was detected in 15/19 human tumour biopsies relative to adjacent normal mucosa of human colon and bladder. Increase in such activities was also observed in adenocarcinoma cell lines CaCo2, CO115, HCT 116, LS 174T and WiDr relative to non-transformed fibroblasts. Maximal PI3Kalpha activity was observed for LS 174T and PI3Kbeta activity for WiDr cells. This was partly correlated with an increase in p110alpha and p110beta protein levels both in some primary tumours and established cell lines, suggesting that PI3K overexpression is involved in enzymatic deregulation. Functional consequence of such activation was assessed by a microinjection approach. An injection of neutralizing antibody specific to p110beta in WiDr, HCT116 and CO 115 cells inhibited de novo DNA synthesis, whereas antibodies specific to p110gamma had no effect. Neutralizing antibodies specific to p110alpha induced apoptosis, a response that was reverted by treating cells with the caspase inhibitor z-VAD-fmk. However anti-p110beta and anti-p110gamma antibodies did not affect cell survival. We concluded that PI3Kalpha and PI3Kbeta play important roles in human colon cancer cell growth with a specific function for PI3Kbeta in de novo DNA synthesis and an involvement of PI3Kalpha in cell survival.

Structural determinants of phosphoinositide 3-kinase inhibition by wortmannin, LY294002, quercetin, myricetin, and staurosporine

The specific phosphoinositide 3-kinase (PI3K) inhibitors wortmannin and LY294002 have been invaluable tools for elucidating the roles of these enzymes in signal transduction pathways. The X-ray crystallographic structures of PI3Kgamma bound to these lipid kinase inhibitors and to the broad-spectrum protein kinase inhibitors quercetin, myricetin, and staurosporine reveal how these compounds fit into the ATP binding pocket. With a nanomolar IC50, wortmannin most closely fits and fills the active site and induces a conformational change in the catalytic domain. Surprisingly, LY294002 and the lead compound on which it was designed, quercetin, as well as the closely related flavonoid myricetin bind PI3K in remarkably different orientations that are related to each other by 180 degrees rotations. Staurosporine/PI3K interactions are reminiscent of low-affinity protein kinase/staurosporine complexes. These results provide a rich basis for development of isoform-specific PI3K inhibitors with therapeutic potential.