Browsing by Subject "PTEN-null"

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Open Access
Identification and targeting of deregulated metabolic pathways in metastatic prostate cancer cells
(2023-01) Kaysudu, Irmak
Prostate cancer is the most diagnosed cancer type and the second leading cause of death in men globally. The pathogenesis of prostate cancer mainly relies on the androgen signaling axis. Therefore, androgen deprivation therapy is the primary treatment for prostate cancer. Nevertheless, the disease progression proceeds, followed by castration resistance and androgen independence. Aberrant androgen signaling activity intertwined with the hyperactivated PI3K-Akt signaling pathway has important oncogenic consequences for castration resistance mechanisms. PTEN, a negative regulator of the PI3K/Akt pathway, is one of the most altered tumor suppressor genes in prostate cancer. PTEN loss occurs in the initial stages of prostate cancer and the frequency of its alteration increases in metastatic and castration-resistant prostate cancer. PTEN has both lipid and protein phosphatase activity, with the former antagonizing the PI3K-Akt pathway by converting membrane-associated PIP3 to PIP2. PTEN loss may cause metabolic rewiring in metastatic prostate cancer cells and the associated metabolic vulnerabilities may be tackled for the disease therapy. To understand the impact of PTEN loss in metastatic prostate cancer cells, we created a dox-inducible system in PTEN-null metastatic and castration-naïve LNCaP cells to re-express WT-PTEN and various PTEN functional mutants, and we employed targeted metastatic prostate cancer. Our multidirectional omics studies suggest that the acquisition of resistance to castration depends on the deregulation of the sphingolipid metabolism in metastatic prostate cancer cells. Furthermore, we showed that PTEN re-expression in metastatic and castration-naïve LNCaP cells attenuated sphingosine kinase levels, which might switch the sphingolipid metabolism towards increased sphingomyelin biosynthesis and ceramide phosphorylation. Moreover, we showed decreased PI3K/Akt pathway activity when we inhibited sphingosine kinase with opaganib in LNCaP cells. Our results also showed a significant upregulation in sphingolipid metabolism in castration-resistant C4-2 cells compared to castration-naïve LNCaP. We treated these cells with several sphingolipid metabolism inhibitors and discovered that castration-resistant prostate cancer cells were more sensitive to opaganib or ARN14988, but not to fingolimod, than castration-naïve prostate cancer cells. These findings suggest that sphingolipid metabolism might be a promising target for the treatment of metastatic and castration-resistant prostate cancer. Understanding changes in sphingolipid metabolism may be critical for developing rational combinatorial targeting strategies for prostate cancer in the long run.
Open Access
Molecular mechanisms of PI3K isoform dependence in carcinogenesis
(2020-12) Atıcı, Sena
PI3K pathway is important for cellular proliferation, survival and metabolism. PTENloss and activating mutations of PIK3CA are most frequently seen PI3K related alterations in various cancer types. Activating mutations in PIK3CA could render tumors p110α dependent. Also, upon PTEN-loss, p110β isoform of ClassIA PI3Ks becomes prominent. Nevertheless, the mode of action of p110 prevalence is still not clear. Here, we aimed to understand the mechanism of the isoform dependence switch in PTEN-null cancer types. Firstly, we found that PTEN status had an impact on isoform prevalence in both MEFs and PC3s. p110α dependence decreased in PTENdepleted MEFs and reciprocally there was a decrease in dependence to p110β in PTEN-reexpressed PC3 cells. On the other hand, upon modulation of PTEN expression, there was no complete switch-over in dependence from one ClassIA PI3K isoform to the other. Interestingly, when p110β overexpression was performed in PTEN depleted MEFs, cells became less dependent on p110α and more dependent on p110β for cellular viability. However, p110β overexpression in combination with PTEN status change did not again induce a complete isoform switch within ClassIA PI3Ks. To reveal additional modules involved in PI3K isoform prevalence, GSE21543 dataset was analyzed and mRNA levels of AK4, SQLE, CREB3L4 genes were found to be significantly upregulated in constitutively activated p110β in murine models of prostate cancer. Among these genes, SQLE,a rate limiting enzyme in cholesterol synthesis, is highly amplified in various tumor samples according to patient datasets. Breast and prostate cancers have relatively higher amplification rates of SQLE compared to other cancer types. The simultaneous incidence of PTEN mutation and SQLE amplification rate is also frequently observed in breast and prostate cancers. mRNA levels of cholesterol synthesis genes were upregulated in GSE21543 dataset when the PI3K pathway was constitutively activated by p110β myristoylation. Also, the expression levels of the cholesterol synthesis genes were decreased upon PI3K repression with PTEN re-expression in our qPCR results. Constitutively activated p110β MEFs and PTEN-null prostate, breast cancer cell lines were found to be sensitive to inhibitors of rate-limiting enzymes of cholesterol synthesis pathway. Besides in-line with mRNA levels, SQLE protein levels were decreased in PTEN reexpressed prostate cancer cell lines. On the other hand, SQLE protein levels were stabilized upon PTEN expression with protease inhibitor treatment which indicates that PTEN and PI3K activity may affect SQLE transcriptionally as well as posttranslationally. We also demonstrated that tamoxifen therapy responders have lower survival rate and higher SQLE expression according to patient data. In line with this data, in cellular models of tamoxifen resistant breast cancer, we have seen elevated levels of SQLE. All in all, our data emphasizes the critical importance of cholesterol synthesis pathway as a metabolic effector of the PI3K pathway and we can speculate that p110β dependence in PTEN-null cancer types might arise as a result of its excessive activation.
Open Access
Targeted metabolomics revealed a key metabolic reprogramming in cholesterol biosynthesis pathway upon PTEN re-expression in PTEN-null, metastatic and castration-resistant prostate cancer
(2022-06) Güngül, Taha Buğra
Prostate cancer is the second most diagnosed type of cancer in males worldwide. Androgen signaling is a main driver of prostate cancers progression and androgen-deprivation therapies (ADT) are remained to be main treatment for preventing progression of the disease. Although ADT is effective at the first line and prolongs overall survival of the patients, eventually disease is recurred, develop resistance to castration and grow in an androgen-independent state, which completely eliminate ADT option. Metastatic and castration-resistant prostate cancers (mCPRC) are the most fatal type of the disease without any effective treatments currently, which is why, molecular drivers that contribute to emergence of castration-resistant phenotype need to be elucidated in order to develop efficient therapeutics against them. Metabolic reprogramming is one of the crucial hallmarks of cancer and loss-of tumor suppressor PTEN is an early and a frequent genetic alteration in prostate cancers, which leads to a hyperactivation of PI3K/Akt/mTOR axis and affects cellular metabolism widely. In this study, we aimed to unveil changes in the metabolome of C4-2 cells which are the type of mCRPC with a PTEN-null genetic background and target metabolic vulnerabilities of these cells. In order to address the question, we employed high-throughput metabolomics assay and revealed changes on metabolome of the cells upon re-expression of PTEN. We found that PTEN re-expression impaired the sphingolipid and cholesterol biosynthesis pathways of C4-2 cells. Upon PTEN re-expression, metabolism of C4-2 cells had tendency to increase the level of anti-survival metabolite; ceramide, and decrease pro-survival metabolite; sphingosine-1-phosphate. In addition to that, PTEN re-expression significantly impaired and downregulated the cholesterol metabolism of these cells. To target these metabolic vulnerabilities, we combined inhibitors of sphingolipid and cholesterol metabolisms with FDA-approved androgen antagonist, MDV3100, to determine possible synergistic effects from the combination of drugs. MDV3100 single treatment had only cytostatic effect on viability of C4-2 cells and combination of simvastatin, cholesterol metabolism inhibitor, with MDV3100 significantly decreased the cellular viability and resulted in significant synergistic effects in inhibiting the growth of C4-2 cells. Thus targeting cholesterol pathway in combination with androgen-deprivation therapies would be a promising approach to develop new combinatorial therapies and combat mCRPC.