PTEN

C. Peter Verrijzer, Jan A. van der Knaap et al., from Department of Biochemistry and Center for Biomedical Genetics at Erasmus University Medical Center, in collaboration with other institutes, have shown the importance of the formation of GMPS-USP7 deubiquitylating complex in the nucleus under stress conditions and focused on the regulation of p53 tumor suppressor pathway, which is strongly related to cell proliferation and therefore to carcinogenesis. As for the GMPS (Guanine Monophosphate Synthase), which converts XMP (xanthosine 5’-monophoshate) to GMP, they have also pointed out its function as a target gene regulator through USP7-mediated deubiquitylation of H2B histone. Based on de novo synthesis of GMP pathway, there is an enzyme upstream of GMPS, which is of great interest; IMPDH (Inosine-5′-Monophosphate Dehydrogenase) which is responsible for the oxidation of IMP to XMP and also involved in transcription regulation through sequence-specific DNA binding. While identifying GMPS-associated factors in human cells, they have noticed IMPDH2 (one of the two isoforms of IMPDH in humans) and the DUB (deubiquitylating enzyme) USP11. In order to study further the GMPS-USP7 complex’s function under cell stress conditions and the cells’ reaction, we also focused on GMPR (GMP Reductase) and USP11 which proteins were expressed for later antibody production. SNF4, the Drosophilla homologue of mammalian AMPK γ-subunit was also produced to be used for antibody production, as it contains a CBS domain, just like IMPDH. To investigate additional pathways that are regulated by GMPS/USP7, apart from the stabilization of p53 and deubiquitylation of H2B, we treated U2OS and HEK293 cells with different drugs. After immunofluorescence experiments, we concluded that GMPS also regulates PTEN and PML, which both are tumor suppressors.

Abstract: The levels of protein tyrosine phosphorylation within a cell is regulated by protein tyrosine kinases and protein tyrosine phosphatases. These protein tyrosine phosphatases (PTP) can act both as positive and negative regulators during cell cycle progression and signal transduction. Phosphatase activity is shown by Phosphatase and Tensin homolog (PTEN) protein encoded by PTEN gene localized on human chromosome 10. Earlier findings established the role of PTEN as a tumor suppressor in Cowden’s disease, where PTEN mutations resulted in disease outcomes. Subsequent studies found the role of PTEN mutations in various human cancers, making it one of the vastly studied tumor suppressor genes. The current review has been planned to get a deeper insight into the potential role of PTEN in a variety of physiological processes involved in normal development like cell growth, migration, and differentiation along with the factors, regulation, and underlying mechanism.

Protein ubiquitination is a dynamic and reversible process of adding single ubiquitin molecules or various ubiquitin chains to target proteins. Here, using multidimensional omic data of 9,125 tumor samples across 33 cancer types from The Cancer Genome Atlas, we perform comprehensive molecular characterization of 929 ubiquitin-related genes and 95 deubiquitinase genes. Among them, we systematically identify top somatic driver candidates, including mutated FBXW7 with cancer-type-specific patterns and amplified MDM2 showing a mutually exclusive pattern with BRAF mutations. Ubiquitin pathway genes tend to be upregulated in cancer mediated by diverse mechanisms. By integrating pan-cancer multiomic data, we identify a group of tumor samples that exhibit worse prognosis. These samples are consistently associated with the upregulation of cell-cycle and DNA repair pathways, characterized by mutated TP53, MYC/TERT amplification, and APC/PTEN deletion. Our analysis highlights the importance of...

Background: Squamous cell carcinoma (SCC) of the uterine cervix is a leading cause of morbidity and mortality among women. The alterations of Phosphatase and tensin homolog (PTEN), B-cell lymphoma 2 (Bcl2) and p53 expression seem to be significant in the development of various types of cancers. The altered expressions of PTEN, Bcl2 and p53 and their involvement in cancer of the uterine cervix are not well recognized. Aim: This study aimed at examining the expression patterns of PTEN, Bcl2 and p53 proteins and comparing them with the grade and stage of cervical cancer. Materials and Methods: Tissue blocks of SCC and ten cases of inflammatory lesions of the uterine cervix were examined immunohistochemically for the expression of PTEN, Bcl2 and p53 proteins. Results: Loss of PTEN expression was identified in 45.33% of cervical SCC and no expression was found in inflammatory lesions (p ≤ 0.05). PTEN expression was significantly associated with the clinical stage of SCC (61.36% and 45.16...

PTEN (phosphatase and tensin homologue deleted on chromosome TEN) is the major negative regulator of phosphatidylinositol 3-kinase signaling and has cell-specific functions including tumor suppression. Nuclear localization of PTEN is vital for tumor suppression; however, outside of cancer, the molecular and physiological events driving PTEN nuclear entry are unknown. In this paper, we demonstrate that cytoplasmic Pten was translocated into the nuclei of neurons after cerebral ischemia in mice. Critically, this transport event was dependent on a surge in the Nedd4 family-interacting protein 1 (Ndfip1), as neurons in Ndfip1-deficient mice failed to import Pten. Ndfip1 binds to Pten, resulting in enhanced ubiquitination by Nedd4 E3 ubiquitin ligases. In vitro, Ndfip1 overexpression increased the rate of Pten nuclear import detected by photobleaching experiments, whereas Ndfip1(-/-) fibroblasts showed negligible transport rates. In vivo, Ndfip1 mutant mice suffered larger infarct sizes associated with suppressed phosphorylated Akt activation. Our findings provide the first physiological example of when and why transient shuttling of nuclear Pten occurs and how this process is critical for neuron survival.

Background The 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. Methods 186 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. Results Mutations 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). Conclusion These 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.

Tyrosine kinase inhibitors (TKIs), imatinib, nilotinib and dasatinib, are the current treatment of chronic myeloid leukemia (CML). BCR-ABL1 point mutations are the principal cause of resistance to treatment; however other mechanisms could be involved in failure to TKI therapy. LYN is a src kinase protein that regulates survival and responsiveness of tumor cells by a BCR-ABL1 independent mechanism. PTEN tumor suppressor gene is downregulated by BCR-ABL1 in CML stem cells and its deletion is associated with acceleration of disease. In this study we evaluated the expression of LYN, PTEN and the ratio of both genes in 40 healthy donors (HD) and in 139 CML patients; 88 of them resistant to TKI in different phases of disease and 51 in chronic phase classified as optimal responders (OR) to TKI [40 treated with imatinib or nilotinib (OR-IN) and 11 treated with dasatinib (OR-D) therapy]. When we analyzed the gene expression values of LYN, an increase was observed only in advanced stages of the disease, however, when we analyzed the ratio between LYN and PTEN genes, the group of resistant patients in chronic phase in imatinib or nilotinib treatment (CP-IN) also showed a significant increase. Resistant patients treated with dasatinib, a src kinase inhibitor, presented a similar ratio to the observed in HD. In addition, the LYN/PTEN ratio and the LYN expression showed a direct significant correlation with BCR-ABL1 transcript levels in unmutated resistant patients treated with non-src kinase inhibitors. We were able to identify 8/35 (23%) of cases in CP-IN and 4/12 (33%) in accelerated phase and blast phase (AP/BC-IN), in which resistance could be associated with an increase in the ratio of the LYN/PTEN. Our data suggest that the LYN/PTEN expression ratio may be a sensitive monitor of disease progression in unmutated CML patients under imatinib or nilotinib treatment. This ratio could detect cases when resistance is related to altered LYN expression, suggesting that the treatment change to a src kinase inhibitor would be most suitable to overcome resistance.

Background: The most recurrent and considered second most frequent cause of cancer-related deaths worldwide in women is the breast cancer. The key to diagnosis is early prediction and a curable stage but still treatment remains a great clinical challenge.

Origin of the Problem: A number of studies have been carried out for the treatment of breast cancer which includes the targeted therapies and increased survival rates in women. Essential PI3K/mTOR signaling pathway activation has been observed in most breast cancers. The cell growth and tumor development in such cases involve phosphoinositide 3 kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) complex intracellular pathway.

Hypothesis: Through preclinical and clinical trials, it has been observed that there are a number of other inhibitors of PI3K/Akt/mTOR pathway, which either alone or in combination with cytotoxic agents can be used for endocrine therapies.

Conclusion: Structure and regulation/deregulation of mTOR provides a greater insight into the action mechanism. Also, through this review, one could easily scan first and second generation inhibitors for PI3K/Akt/mTOR pathway besides targeted therapies for breast cancer and the precise role of mTOR.