Summary Hyper-activation of the PI 3-Kinase/AKT pathway is a driving force of many cancers. Here we identify the AKT-inactivating phosphatase PHLPP1 as a prostate tumor suppressor. We show that Phlpp1-loss causes neoplasia and, upon partial Pten-loss, carcinoma in mouse prostate. This genetic setting initially triggers a growth suppressive response via p53 and the Phlpp2 ortholog, and reveals spontaneous Trp53 inactivation as a condition for full-blown disease. Surprisingly, the co-deletion of PTEN and PHLPP1 in patient samples is highly restricted to metastatic disease and tightly correlated to deletion of TP53 and PHLPP2. These data establish a conceptual framework for progression of PTEN-mutant prostate cancer to life-threatening disease.

PTEN nuclear entry driven by ubiquitination is mediated by the ligase-interacting protein Ndfip1 and is essential for neuronal survival in mice after cerebral ischemia.

SUMMARY A hallmark of advanced prostate cancer (PC) is the concomitant loss of PTEN and p53 function. To selectively eliminate such cells, we screened cytotoxic compounds on Pten−/−;Trp53−/− fibroblasts and their Pten-WT reference. Highly selective killing of Pten-null cells can be achieved by deguelin, a natural insecticide. Deguelin eliminates Pten-deficient cells through inhibition of mitochondrial complex I (CI). Five hundred-fold higher drug doses are needed to obtain the same killing of Pten-WT cells, even though deguelin blocks their electron transport chain equally well. Selectivity arises because mitochondria of Pten-null cells consume ATP through complex V, instead of producing it. The resulting glucose dependency can be exploited to selectively kill Pten-null cells with clinically relevant CI inhibitors, especially if they are lipophilic. In vivo, deguelin suppressed disease in our genetically engineered mouse model for metastatic PC. Our data thus introduce a vulnerability for highly selective targeting of incurable PC with inhibitors of CI.

Summary PTEN is proposed to function at the plasma membrane, where receptor tyrosine kinases are activated. However, the majority of PTEN is located throughout the cytoplasm. Here, we show that cytoplasmic PTEN is distributed along microtubules, tethered to vesicles via phosphatidylinositol 3-phosphate (PI(3)P), the signature lipid of endosomes. We demonstrate that the non-catalytic C2 domain of PTEN specifically binds PI(3)P through the CBR3 loop. Mutations render this loop incapable of PI(3)P binding and abrogate PTEN-mediated inhibition of PI 3-kinase/AKT signaling. This loss of function is rescued by fusion of the loop mutant PTEN to FYVE, the canonical PI(3)P binding domain, demonstrating the functional importance of targeting PTEN to endosomal membranes. Beyond revealing an upstream activation mechanism of PTEN, our data introduce the concept of PI 3-kinase signal activation on the vast plasma membrane that is contrasted by PTEN-mediated signal termination on the small, discrete surfaces of internalized vesicles.

Phosphatidylinositol phosphate (PIP) second messengers relay extracellular growth cues through the phosphorylation status of the inositol sugar, a signal transduction system that is deregulated in cancer. In stark contrast to PIP inositol head group phosphorylation, changes in phosphatidylinositol (PI) lipid acyl chains in cancer have remained ill-defined. Here, we apply a mass spectrometry-based method capable of unbiased high-throughput identification and quantification of cellular PI acyl chain composition. Using this approach we find that PI lipid chains represent a cell-specific fingerprint and are unperturbed by serum-mediated signaling in contrast to the inositol head group. We find that mutation of Trp53 results in PIs containing reduced-length fatty acid moieties. Our results suggest that the anchoring tails of lipid second messengers form an additional layer of PIP signaling in cancer that operates independently of PTEN/PI3-Kinase activity, but is instead linked somehow to p53.

Background: BRAF and K-ras proto-oncogenes encode components of the ERK signalling pathway and are frequently mutated in colorectal cancer. This study investigates the associations between BRAF and K-ras mutations and clinicopathological, lifestyle and dietary factors in colorectal cancers. Methods: 186 adenocarcinomas and 16 adenomas from the EPIC Norfolk study were tested for BRAF and K-ras mutations. Diet and lifestyle data were collected prospectively using seven day food diaries. Results: BRAF V600E mutation was found in 15.6% of colorectal cancers but at higher frequencies in cancers with proximal location, poor differentiation and microsatellite instability (MSI) (all p < 0.001). K-ras mutation (mostly in codons 12 and 13) was found in 22.0% of colorectal cancers but at higher frequencies in cancers of more advanced Dukes' stage (p = 0.001), microsatellite stable (MSS) status (p = 0.002) and in individuals with lower blood high-density lipoprotein concentrations (p = 0.04). Analysis of dietary factors demonstrated no link between BRAF mutation and any specific dietary constituent, however, K-ras mutation was found at higher frequencies in individuals with higher white meat consumption (p < 0.001). Further analysis of specific mutation type demonstrated that G to A transitions in K-ras were observed at higher frequencies in individuals consuming lower amounts of fruit (p = 0.02). Conclusion: These data support the model of BRAF and K-ras mutations arising in distinct colorectal cancer subsets associated with different clinicopathological and dietary factors, acting as mutually exclusive mechanisms of activation of the same signalling pathway.

BackgroundThe PTEN tumour suppressor gene and PIK3CA proto-oncogene encode proteins which contribute to regulation and propagation of signal transduction through the PI3K/AKT signalling pathway. This study investigates the prevalence of loss of PTEN expression and mutations in both PTEN and PIK3CA in colorectal cancers (CRC) and their associations with tumour clinicopathological features, lifestyle factors and dietary consumptions.Methods186 adenocarcinomas and 16 adenomas from the EPIC Norfolk study were tested for PTEN and PIK3CA mutations by DNA sequencing and PTEN expression changes by immunohistochemistry. Dietary and lifestyle data were collected prospectively using seven day food diaries and lifestyle questionnaires.ResultsMutations in exons 7 and 8 of PTEN were observed in 2.2% of CRC and PTEN loss of expression was identified in 34.9% CRC. Negative PTEN expression was associated with lower blood low-density lipoprotein concentrations (p = 0.05). PIK3CA mutations were observed in 7% of cancers and were more frequent in CRCs in females (p = 0.04). Analysis of dietary intakes demonstrated no link between PTEN expression status and any specific dietary factor. PTEN expression negative, proximal CRC were of more advanced Dukes' stage (p = 0.02) and poor differentiation (p < 0.01). Testing of the prevalence of PIK3CA mutations and loss of PTEN expression demonstrated that these two events were independent (p = 0.55).ConclusionThese data demonstrated the frequent occurrence (34.9%) of PTEN loss of expression in colorectal cancers, for which gene mutations do not appear to be the main cause. Furthermore, dietary factors are not associated with loss of PTEN expression. PTEN expression negative CRC were not homogenous, as proximal cancers were associated with a more advanced Dukes' stage and poor differentiation, whereas distal cancers were associated with earlier Dukes' stage.

The tumour suppressor APC is the most commonly altered gene in colorectal cancer (CRC). Genetic and epigenetic alterations of APC may therefore be associated with dietary and lifestyle risk factors for CRC. Analysis of APC mutations in the extended mutation cluster region (codons 1276-1556) and APC promoter 1A methylation was performed on 185 archival CRC samples collected from participants of the European Prospective Investigation into Cancer (EPIC)-Norfolk study, with the aim of relating these to high-quality seven-day dietary and lifestyle data collected prospectively. Truncating APC mutations (APC(+) ) and promoter 1A methylation (PM(+) ) were identified in 43% and 23% of CRCs analysed, respectively. Distal CRCs were more likely than proximal CRCs to be APC(+) or PM(+) (p = 0.04). APC(+) CRCs were more likely to be moderately/well differentiated and microsatellite stable than APC(-) CRCs (p = 0.05 and 0.03). APC(+) CRC cases consumed more alcohol than their counterparts (p = 0.01) and PM(+) CRC cases consumed lower levels of folate and fibre (p = 0.01 and 0.004). APC(+) or PM(+) CRC cases consumed higher levels of processed meat and iron from red meat and red meat products (p = 0.007 and 0.006). Specifically, CRC cases harbouring GC-to-AT transition mutations consumed higher levels of processed meat (35 versus 24 g/day, p = 0.04) and iron from red meat and red meat products (0.8 versus 0.6 mg/day, p = 0.05). In a logistic regression model adjusted for age, sex and cigarette-smoking status, each 19 g/day (1SD) increment increase in processed meat consumption was associated with cases with GC-to-AT mutations (OR 1.68, 95% CI 1.03-2.75). In conclusion, APC(+) and PM(+) CRCs may be influenced by diet and GC-to-AT mutations in APC are associated with processed meat consumption, suggesting a mechanistic link with dietary alkylating agents, such as N-nitroso compounds.