Proline oxidase silencing induces proline-dependent pro-survival pathways in MCF-7 cells

A Multiomics, Molecular Atlas of Breast Cancer Survivors

Breast cancer imposes a significant burden globally. While the survival rate is steadily improving, much remains to be elucidated. This observational, single time point, multiomic study utilizing genomics, proteomics, targeted and untargeted metabolomics, and metagenomics in a breast cancer survivor (BCS) and age-matched healthy control cohort (N = 100) provides deep molecular phenotyping of breast cancer survivors. In this study, the BCS cohort had significantly higher polygenic risk scores for breast cancer than the control group. Carnitine and hexanoyl carnitine were significantly different. Several bile acid and fatty acid metabolites were significantly dissimilar, most notably the Omega-3 Index (O3I) (significantly lower in BCS). Proteomic and metagenomic analyses identified group and pathway differences, which warrant further investigation. The database built from this study contributes a wealth of data on breast cancer survivorship where there has been a paucity, affording the ability to identify patterns and novel insights that can drive new hypotheses and inform future research. Expansion of this database in the treatment-naïve, newly diagnosed, controlling for treatment confounders, and through the disease progression, can be leveraged to profile and contextualize breast cancer and breast cancer survivorship, potentially leading to the development of new strategies to combat this disease and improve the quality of life for its victims.

Proline Dehydrogenase (PRODH) Is Expressed in Lung Adenocarcinoma and Modulates Cell Survival and 3D Growth by Inducing Cellular Senescence

The identification of markers for early diagnosis, prognosis, and improvement of therapeutic options represents an unmet clinical need to increase survival in Non-Small Cell Lung Cancer (NSCLC), a neoplasm still characterized by very high incidence and mortality. Here, we investigated whether proline dehydrogenase (PRODH), a mitochondrial flavoenzyme catalyzing the key step in proline degradation, played a role in NSCLC tumorigenesis. PRODH expression was investigated by immunohistochemistry; digital PCR, quantitative PCR, immunoblotting, measurement of reactive oxygen species (ROS), and functional cellular assays were carried out. PRODH expression was found in the majority of lung adenocarcinomas (ADCs). Patients with PRODH-positive tumors had better cancer-free specific and overall survival compared to those with negative tumors. Ectopic modulation of PRODH expression in NCI-H1299 and the other tested lung ADC cell lines decreased cell survival. Moreover, cell proliferation curves showed delayed growth in NCI-H1299, Calu-6 and A549 cell lines when PRODH-expressing clones were compared to control clones. The 3D growth in soft agar was also impaired in the presence of PRODH. PRODH increased reactive oxygen species production and induced cellular senescence in the NCI-H1299 cell line. This study supports a role of PRODH in decreasing survival and growth of lung ADC cells by inducing cellular senescence.

Metformin Induces PRODH/POX-Dependent Apoptosis in Breast Cancer Cells

Although the antineoplastic activity of metformin (MET) is well established, the underlying mechanism of the activity is not understood. Since MET activates AMP kinase (AMPK) and proline dehydrogenase/proline oxidase (PRODH/POX) is stimulated by AMPK ligands (implicated in the regulation of cancer cell survival/apoptosis), the effect of MET on PRODH/POX-dependent apoptosis in wild-type MCF-7 cells (MCF-7^WT) and POX knockdown MCF-7 cells (MCF-7^crPOX cells) was studied. PRODH/POX catalyzes proline degradation generating ROS-induced apoptosis or autophagy. Availability of proline for PRODH/POX functions is regulated by the activity of prolidase (enzyme releasing proline from imidodipeptides), collagen biosynthesis (process consuming proline), and metabolism of proline, ornithine, and glutamic acid. We have found that MET is cytotoxic for MCF-7 cells (IC50∼17 mM), and to the lower extent for MCF-7^crPOX cells (IC50∼28 mM). In MCF-7^WT cells, the effect was accompanied by the inhibition of DNA biosynthesis, collagen biosynthesis, stimulation of ROS formation, AMPKα phosphorylation, and expression of prolidase, p53, caspase 8, caspase 9, and cleaved PARP. In MET-treated MCF-7^crPOX cells, the processes were less affected than in MCF-7^WT cells and the expression of caspase 9 was decreased, while cleaved caspase 8 and cleaved PARP were not detected. The effects were accompanied by an increase in the prolidase activity and proline concentration. The mechanism for MET-induced apoptosis involves the up-regulation of prolidase activity and a decrease in collagen biosynthesis contributing to an increase in the concentration of substrate (proline) for PRODH/POX-dependent ROS formation and activation of caspases −9 and −8. The data suggest that PRODH/POX participates in the MET-induced intrinsic and extrinsic apoptosis in MCF-7 cells.

Proline Metabolism in Malignant Gliomas: A Systematic Literature Review

Simple Summary

Studies of various types of cancers have found proline metabolism to be a key player in tumor development, involved in basic metabolic pathways, regulating cell proliferation, survival, and signaling. Here, we systematically searched the literature to find data on proline metabolism in malignant glial tumors. Despite limited availability, existing studies have found several ways in which proline metabolism may affect the development of gliomas, involving the maintenance of redox balance, providing essential glutamate, and affecting major signaling pathways. Metabolomic profiling has revealed the importance of proline as a link to basic cell metabolic cycles and shown it to be correlated with overall survival. Emerging knowledge on the role of proline in general oncology encourages further studies on malignant gliomas.

Abstract

Background: Proline has attracted growing interest because of its diverse influence on tumor metabolism and the discovery of the regulatory mechanisms that appear to be involved. In contrast to general oncology, data on proline metabolism in central nervous system malignancies are limited. Materials and Methods: We performed a systematic literature review of the MEDLINE and EMBASE databases according to PRISMA guidelines, searching for articles concerning proline metabolism in malignant glial tumors. From 815 search results, we identified 14 studies pertaining to this topic. Results: The role of the proline cycle in maintaining redox balance in IDH-mutated gliomas has been convincingly demonstrated. Proline is involved in restoring levels of glutamate, the main glial excitatory neurotransmitter. Proline oxidase influences two major signaling pathways: p53 and NF- κB. In metabolomics studies, the metabolism of proline and its link to the urea cycle was found to be a prognostic factor for survival and a marker of malignancy. Data on the prolidase concentration in the serum of glioblastoma patients are contradictory. Conclusions: Despite a paucity of studies in the literature, the available data are interesting enough to encourage further research, especially in terms of extrapolating what we have learned of proline functions from other neoplasms to malignant gliomas.

Proline Dehydrogenase/Proline Oxidase (PRODH/POX) Is Involved in the Mechanism of Metformin-Induced Apoptosis in C32 Melanoma Cell Line

The role of proline dehydrogenase/proline oxidase (PRODH/POX) in the mechanism of antineoplastic activity of metformin (MET) was studied in C32 melanoma cells. PRODH/POX is a mitochondrial enzyme-degrading proline that is implicated in the regulation of cancer cell survival/apoptosis. The enzyme is activated by AMP kinase (AMPK). It has been found that MET induced a significant decrease in cell viability and DNA biosynthesis accompanied by an increase in the expressions of AMPK and PRODH/POX in C32 cells. The mechanism for MET-dependent cytotoxicity on C32 cells was found at the level of PRODH/POX-induced ROS generation and activation of Caspase-3 and Caspase-9 expressions in these cells. The effects were not observed in MET-treated PRODH/POX knock-out C32 cells. Of interest is an MET-dependent increase in the concentration of proline, which is a substrate for PRODH/POX. This phenomenon is due to the MET-dependent inhibition of collagen biosynthesis, which is the main proline-utilizing process. It has been found that the underlying mechanism of anticancer activity of MET involves the activation of AMPK, PRODH/POX, increase in the cytoplasmic concentration of proline, inhibition of collagen biosynthesis, and stimulation of PRODH/POX-dependent ROS generation, which initiate the apoptosis of melanoma cells.

Troglitazone-Induced PRODH/POX-Dependent Apoptosis Occurs in the Absence of Estradiol or ERβ in ER-Negative Breast Cancer Cells

Simple Summary

PRODH/POX (proline dehydrogenase/proline oxidase) is a mitochondrial enzyme that catalyzes proline degradation generating reactive oxygen species (ROS). Estrogens limit proline availability for PRODH/POX by stimulating collagen biosynthesis. It has been considered that estrogens determine efficiency of troglitazone (TGZ)-induced PRODH/POX-dependent apoptosis in breast cancer cells. The studies were performed in wild-type and PRODH/POX-silenced estrogen-dependent MCF-7 cells and estrogen-independent MDA-MB-231 cells. DNA and collagen biosynthesis were determined by radiometric method, ROS production was measured by fluorescence assay, protein expression was determined by Western blot and proline concentration by LC/MS analysis. We found that: i/TGZ-induced apoptosis in MDA-MB-231 occurs only in the absence of estradiol or ERβ, ii/the process is mediated by PRODH/POX, iii/and is facilitated by proline availability for PRODH/POX by TGZ-dependent inhibition of collagen biosynthesis (proline utilizing process). The data suggest that combined TGZ and anti-estrogen treatment could be considered in experimental therapy of ER negative breast cancers.

Abstract

The impact of estradiol on troglitazone (TGZ)-induced proline dehydrogenase/proline oxidase (PRODH/POX)-dependent apoptosis was studied in wild-type and PRODH/POX-silenced estrogen receptor (ER) dependent MCF-7 cells and ER-independent MDA-MB-231 cells. DNA and collagen biosynthesis were determined by radiometric method, prolidase activity evaluated by colorimetric method, ROS production was measured by fluorescence assay. Protein expression was determined by Western blot and proline concentration by LC/MS analysis. PRODH/POX degrades proline yielding reactive oxygen species (ROS). Estrogens stimulate collagen biosynthesis utilizing free proline and limiting its availability for PRODH/POX-dependent apoptosis. TGZ cytotoxicity was highly pronounced in wild-type MDA-MB-231 cells cultured in medium without estradiol or in the cells cultured in medium with estradiol but deprived of ERβ (by ICI-dependent degradation), while in PRODH/POX-silenced cells the process was not affected. The TGZ cytotoxicity was accompanied by increase in PRODH/POX expression, ROS production, expression of cleaved caspase-3, caspase-9 and PARP, inhibition of collagen biosynthesis, prolidase activity and decrease in intracellular proline concentration. The phenomena were not observed in PRODH/POX-silenced cells. The data suggest that TGZ-induced apoptosis in MDA-MB-231 cells cultured in medium without estradiol or deprived of ERβ is mediated by PRODH/POX and the process is facilitated by proline availability for PRODH/POX by TGZ-dependent inhibition of collagen biosynthesis. It suggests that combined TGZ and antiestrogen treatment could be considered in experimental therapy of estrogen receptor negative breast cancers.

PRODH/POX-Dependent Celecoxib-Induced Apoptosis in MCF-7 Breast Cancer

Celecoxib (Cx), an inhibitor of cyclooxygenase 2, induces apoptosis of cancer cells. However, the mechanism of the chemopreventive effect remains not fully understood. We aimed to investigate the role of PRODH/POX that is involved in the regulation of apoptosis induced by celecoxib. MCF-7 breast cancer cell line and the corresponding MCF-7 cell line with silenced PRODH/POX (MCF-7^shPRODH/POX) were used. The effects of Cx on cell viability, proliferation, and cell cycle were evaluated. The expressions of protein markers for apoptosis (Bax, caspase 9, and PARP) and autophagy (Atg5, Beclin 1, and LC3A/B) were investigated by Western immunoblotting. To analyze the proline metabolism, collagen biosynthesis, prolidase activity, proline concentration, and the expression of proline-related proteins were evaluated. The generation of ATP, ROS, and the ratio of NAD+/NADH and NADP+/NADPH were determined to test the effect of Cx on energetic metabolism in breast cancer cells. It has been found that Cx attenuated MCF-7 cell proliferation via arresting the cell cycle. Cx induced apoptosis in MCF-7 breast cancer cells, while in MCF-7^shPRODH/POX, autophagy occurred more predominantly. In MCF-7 breast cancer cells, Cx affected proline metabolism through upregulation of proline biosynthesis, PRODH/POX and PYCRs expressions, PEPD activity, and downregulation of collagen biosynthesis. In MCF-7^shPRODH/POX clones, these processes, as well as energetic metabolism, were remarkably suppressed. The data for the first time suggest that celecoxib induces apoptosis through upregulation of PRODH/POX in MCF-7 breast cancer cells.

Proline oxidase silencing inhibits p53-dependent apoptosis in MCF-7 breast cancer cells

Proline oxidase (POX) is mitochondrial proline-degrading enzyme of dual apoptosis/survival function. POX expression and proline availability are considered an underlying mechanism for differential POX functions. The mechanism for POX-dependent regulation of cell death/survival was studied in wild-type (MCF-7^WT) and shRNA POX-silenced breast cancer cells (MCF-7^iPOX). Proline concentration and proteomic analyses were determined by LC/MS/QTOF and LC/MS/ORBITRA, respectively. Inhibition of collagen biosynthesis (proline utilizing process) by 2-methoxyestradiol (2ME) contributed to induction of apoptosis in MCF-7^WT cells, as detected by increase in the expression of active caspase-3, -9 and p53. The process was not shown in MCF-7^iPOX. In MCF-7^iPOX cells prolidase activity and expression as well as proline concentration were drastically increased, compared to MCF-7^WT cells. Down-regulation of p53 in MCF-7^iPOX cells was corroborated by proteomic analysis showing decrease in the expression of p53-related proteins. The mechanism for down-regulation of p53 expression in MCF-7^iPOX cells was found at the level of p53-PEPD complex formation that was counteracted by hydrogen peroxide treatment. In this study, we found that silencing POX modulate pro-survival phenotype of MCF-7 cells and suggest that the mechanism of this process undergoes through down-regulation of p53-dependent signaling.

Understanding the role of key amino acids in regulation of proline dehydrogenase/proline oxidase (prodh/pox)-dependent apoptosis/autophagy as an approach to targeted cancer therapy

In stress conditions, as neoplastic transformation, amino acids serve not only as nutrients to maintain the cell survival but also as mediators of several regulatory pathways which are involved in apoptosis and autophagy. Especially, under glucose deprivation, in order to maintain the cell survival, proline and glutamine together with other glutamine-derived products such as glutamate, alpha-ketoglutarate, and ornithine serve as alternative sources of energy. They are substrates for production of pyrroline-5-carboxylate which is the product of conversion of proline by proline dehydrogenase/ proline oxidase (PRODH/POX) to produce ATP for protective autophagy or reactive oxygen species for apoptosis. Interconversion of proline, ornithine, and glutamate may therefore regulate PRODH/POX-dependent apoptosis/autophagy. The key amino acid is proline, circulating between mitochondria and cytoplasm in the proline cycle. This shuttle is known as proline cycle. It is coupled to pentose phosphate pathway producing nucleotides for DNA biosynthesis. PRODH/POX is also linked to p53 and AMP-activated protein kinase (AMPK)-dependent pathways. Proline availability for PRODH/POX-dependent apoptosis/autophagy is regulated at the level of collagen biosynthesis (proline utilizing process) and prolidase activity (proline supporting process). In this review, we suggest that amino acid metabolism linking TCA and Urea cycles affect PRODH/POX-dependent apoptosis/autophagy and the knowledge might be useful to targeted cancer therapy.

Proline-containing peptides-New insight and implications: A Review

The family of regulatory proline-containing peptides (PCPs), also known as glyprolines, exhibit significant biological activity. The group of glyprolines includes Gly-Pro (GP), Pro-Gly-Pro (PGP), cyclic Gly-Pro (cGP), as well as PGP derivatives, for example, N-acetylated PGP (N-a-PGP) and N-methylated PGP (N-m-PGP). PCPs are engaged in various biological processes including the proinflammatory neutrophil chemoattraction in lung diseases, inflammatory bowel diseases or ischemic stroke. Glyprolines have been also postulated to play an important role as atheroprotective and anticoagulant agents, exhibit neuroprotective effects in Parkinson's disease, as well as regulate insulin-like growth factor (IGF) homeostasis. It was also noticed that PCPs inhibit proliferation and migration of keratinocytes in wound healing, protection of the gastric mucosa and stimulation of its regeneration. The regulatory glyprolines are derived from endogenous and exogenous sources. Most PCPs are derived from collagen or diet protein degradation. Recently, great interest is concentrated on short proline-rich oligopeptides derived from IGF-1 degradation. The mechanism of PCPs biological activity is not fully explained. It involves receptor-mediated mechanisms, for example, N-a-PGP acts as CXCR1/2 receptor ligand, whereas cGP regulates IGF-1 bioavailability by modifying the IGF-1 binding to the IGF-1 binding protein-3. PGP has been observed to interact with collagen-specific receptors. The data suggest a promising role of PGP as a target of various diseases therapy. This review is focused on the effect of PCPs on metabolic processes in different tissues and the molecular mechanism of their action as an approach to pharmacotherapy of PCPs-dependent diseases.

Effect of 2nd and 3rd generation PAMAM dendrimers on proliferation, differentiation, and pro-inflammatory cytokines in human keratinocytes and fibroblasts

Background

Poly(amidoamine) (PAMAM) dendrimers are of considerable interest when used as a carrier for topical drugs for the skin, although little is known about their possible side effects. Therefore, our study was about the impact of 2nd and 3rd generation PAMAM dendrimers on human keratinocytes and fibroblasts cells.

Methods

The effect of the tested compounds on collagen biosynthesis was determined using 5[³H]-proline incorporation bioassay. Morphological changes accompanying cell growth inhibition were observed using a confocal microscope. To evaluate the percentage of apoptotic/necrotic cells and the cell growth dynamic of apoptotic features, we performed Annexin V/PI double staining assay, assessed caspase activity, and performed cell cycle analysis by flow cytometry. The flow cytometry method was also used to determine the effect of dendrimers on pro-inflammatory cytokines (IL-6, IL-8 IL-1β).

Results

The obtained results showed that as the concentration and the generation of dendrimers increased, collagen biosynthesis decreased. We also observed abnormalities in cell differentiation, which may have caused disturbed secretion of pro-inflammatory cytokines. We found that dendrimers cause chronic inflammation which may cause adverse changes in the skin, ultimately– leading to apoptosis in the case of dendrimers in lower concentrations or necrosis at higher concentrations (especially 3rd generation dendrimers). In addition, the inflammatory path induced by the tested compounds was caused by damage in the mitochondria, which we observed as a significant decrease in the mitochondrial membrane potential.

Conclusion

The results of our study showed that PAMAM dendrimers can cause disorders of cell proliferation and differentiation and may be the cause of cell cycle deregulation and chronic adverse inflammation.