Downregulation of pyrroline-5-carboxylate reductase-2 induces the autophagy of melanoma cells via AMPK/mTOR pathway

Exploration of influenza A virus PA protein-associated cellular proteins discloses its impact on mitochondrial function

Influenza A virus can infect respiratory tracts and may cause severe illness in humans. Proteins encoded by influenza A virus can interact with cellular factors and dysregulate host biological processes to support viral replication and cause pathogenicity. The influenza viral PA protein is not only a subunit of influenza viral polymerase but also a virulence factor involved in pathogenicity during infection. To explore the role of the influenza virus PA protein in regulating host biological processes, we performed immunoprecipitation and LC‒MS/MS to globally identify cellular factors that interact with the PA proteins of the influenza A H1N1, 2009 pandemic H1N1, and H3N2 viruses. The results demonstrated that proteins located in the mitochondrion, proteasome, and nucleus are associated with the PA protein. We further discovered that the PA protein is partly located in mitochondria by immunofluorescence and mitochondrial fractionation and that overexpression of the PA protein reduces mitochondrial respiration. In addition, our results revealed the interaction between PA and the mitochondrial matrix protein PYCR2 and the antiviral role of PYCR2 during influenza A virus replication. Moreover, we found that the PA protein could also trigger autophagy and disrupt mitochondrial homeostasis. Overall, our research revealed the impacts of the influenza A virus PA protein on mitochondrial function and autophagy.

PYCR2, induced by c-Myc, promotes the invasiveness and metastasis of breast cancer by activating AKT signalling pathway

BACKGROUND

Pyrroline-5-carboxylate reductase 2 (PYCR2) expression is aberrantly upregulated in colon cancer. However, the functions and underlying mechanisms of PYCR2 in breast cancer remain elusive. The primary objective of the present study was to elucidate the function of PYCR2 in breast cancer and investigate whether PYCR2 may be transcriptionally regulated by c-Myc to activate the AKT signaling pathway.

METHODS

Immunohistochemical analysis was performed to examine the expression of PYCR2 in breast cancer and adjacent non-cancerous tissues. Western blot and RT-qPCR were utilized to detect PYCR2 expression in breast cancer cells. Cellular functionalities were evaluated through Transwell assays in vitro and lung metastasis formation assays in vivo. Moreover, the impact of PYCR2 on the activation of AKT signaling was determined through western blot and immunohistochemistry analysis. The transcriptional regulation of PYCR2 expression by c-Myc was evaluated via both western blot analysis and luciferase gene reporter assay.

RESULTS

PYCR2 overexpression was noted in breast cancer. Silencing PYCR2 expression attenuated the invasive and metastatic abilities of breast cancer cells. Furthermore, the activation of the AKT signaling pathway is indispensable for the promotion of invasion and metastasis mediated by PYCR2. Lastly, the binding of c-Myc to the promoter sequence of PYCR2 resulted in the upregulation of PYCR2 transcription.

CONCLUSION

Taken together, these results indicate that PYCR2 is transcriptionally regulated by c-Myc and promotes invasion and metastasis in breast cancer through the activation of the AKT pathway.

Targeting PYCR2 inhibits intraperitoneal metastatic tumors of mouse colorectal cancer in a proline-independent approach

Whether proline deficiency is a metabolic vulnerability in colorectal tumors is unknown. The aim of this study was to investigate the effects of proline metabolism-related genes and exogenous proline on the progression of colorectal cancer (CRC). We aimed to further clarify the role of pyrroline-5-carboxylate reductase (PYCR) 2, a key enzyme of proline synthesis, in the regulation of colorectal intraperitoneal metastatic tumors. This study was carried out based on The Cancer Genome Atlas (TCGA) data, database analysis, single-cell functional analysis, tissue microarray, cell experiments, and animal models. We found that, PYCR2 mRNA and protein levels were upregulated in CRC. The mRNA level of PYCR2 was closely related to the prognosis and tumor metastasis of CRC patients. The upregulated PYCR2 expression was at least partly due to low promoter methylation levels. The nomogram constructed based on PYCR2 expression and clinical characteristics of CRC showed good accuracy in predicting lymph node metastasis. Pycr2 knockdown inhibited epithelial-mesenchymal transition (EMT) of mouse CRC cells. Proline supplementation did not rescue the inhibition of mouse CRC cell proliferation and migration by Pycr2 knockdown. Proline supplementation also did not rescue the suppression of subcutaneous tumors and intraperitoneal metastatic tumors in mice by Pycr2 knockdown. PYCR2 co-expressed genes in TCGA-CRC were enriched in epigenetic modification-related biological processes and molecular functions. Four small molecules with the lowest binding energy to the PYCR2 protein were identified. Collectively, Pycr2 knockdown inhibited mouse CRC progression in a proline-independent approach. PYCR2 may be a promising tumor metastasis predictor and therapeutic target in CRC.

Serine hydroxymethyltransferase 1 promotes low-grade glioma progression by activating mTORC1 signaling

OBJECTIVES

This research aimed to explore the role and potential mechanism of serine hydroxymethyltransferase 1 (SHMT1) involvement in low-grade glioma (LGG).

METHODS

GEPIA were employed to analyze the expression and the correlation of LGG patient survival with the levels of SHMT1 in LGG based on the The Cancer Genome Atlas (TCGA) database. qRT-PCR and western blot were used to detect the expression of SHMT1 in LGG cells. Clone formation, EdU staining, MTT, Transwell and wound healing assays were conducted to analyze the proliferation, cell activity, migration and invasion of LGG cells. KEEG analysis was performed for enrichment pathways of SHMT1 in LGG.

RESULTS

SHMT1 was up-regulated in LGG tissues and cells, and SHMT1 level was negatively correlated with survival of patients with LGG. SHMT1 overexpression evidently promoted cell proliferation, migration and invasion, whereas SHMT1 silence obtained the opposite results. Next, KEEG analysis revealed that SHMT1 activated the mTORC1 pathway in LGG. SHMT1 overexpression significantly promoted the phosphorylation of downstream proteins (P70SK6 and S6) in LGG cells. Further, inhibition of the mTORC1 signaling pathway partially abolished the promotion of LGG progression by SHMT1 overexpression.

CONCLUSION

SHMT1 promoted proliferation, invasion and migration of LGG cells via activating mTORC1 signaling pathway. This provided a novel perspective for the treatment of LGG.

Structure, biochemistry, and gene expression patterns of the proline biosynthetic enzyme pyrroline-5-carboxylate reductase (PYCR), an emerging cancer therapy target

Proline metabolism features prominently in the unique metabolism of cancer cells. Proline biosynthetic genes are consistently upregulated in multiple cancers, while the proline catabolic enzyme proline dehydrogenase has dual, context-dependent pro-cancer and pro-apoptotic functions. Furthermore, the cycling of proline and Δ1-pyrroline-5-carboxylate through the proline cycle impacts cellular growth and death pathways by maintaining redox homeostasis between the cytosol and mitochondria. Here we focus on the last enzyme of proline biosynthesis, Δ1-pyrroline-5-carboxylate reductase, known as PYCR in humans. PYCR catalyzes the NAD(P)H-dependent reduction of Δ1-pyrroline-5-carboxylate to proline and forms the reductive half of the proline metabolic cycle. We review the research on the three-dimensional structure, biochemistry, inhibition, and cancer biology of PYCR. To provide a global view of PYCR gene upregulation in cancer, we mined RNA transcript databases to analyze differential gene expression in 28 cancer types. This analysis revealed strong, widespread upregulation of PYCR genes, especially PYCR1. Altogether, the research over the past 20 years makes a compelling case for PYCR as a cancer therapy target. We conclude with a discussion of some of the major challenges for the field, including developing isoform-specific inhibitors, elucidating the function of the long C-terminus of PYCR1/2, and characterizing the interactome of PYCR.

P5C as an Interface of Proline Interconvertible Amino Acids and Its Role in Regulation of Cell Survival and Apoptosis

Studies of cancer metabolism have focused on the production of energy and the interconversion of carbons between cell cycles. More recently, amino acid metabolism, especially non-essential amino acids (NEAAs), has been investigated, underlining their regulatory role. One of the important mediators in energy production and interconversion of carbons in the cell is Δ¹-pyrroline-5-carboxylate (P5C)—the physiological intracellular intermediate of the interconversion of proline, ornithine, and glutamate. As a central component of these conversions, it links the tricarboxylic acid cycle (TCA), urea cycle (UC), and proline cycle (PC). P5C has a cyclic structure containing a tertiary nitrogen atom (N) and is in tautomeric equilibrium with the open-chain form of L-glutamate-γ-semialdehyde (GSAL). P5C is produced by P5C synthase (P5CS) from glutamate, and ornithine via ornithine δ-amino acid transferase (δOAT). It can also be converted to glutamate by P5C dehydrogenase (P5CDH). P5C is both a direct precursor of proline and a product of its degradation. The conversion of P5C to proline is catalyzed by P5C reductase (PYCR), while proline to P5C by proline dehydrogenase/oxidase (PRODH/POX). P5C-proline-P5C interconversion forms a functional redox couple. Their transformations are accompanied by the transfer of a reducing-oxidizing potential, that affect the NADP+/NADPH ratio and a wide variety of processes, e.g., the synthesis of phosphoribosyl pyrophosphate (PRPP), and purine ribonucleotides, which are crucial for DNA synthesis. This review focuses on the metabolism of P5C in the cell as an interconversion mediator of proline, glutamate, and ornithine and its role in the regulation of survival and death with particular emphasis on the metabolic context.

Pyrroline-5-Carboxylate Reductase-2 Promotes Colorectal Cancer Progression via Activating PI3K/AKT/mTOR Pathway

Aim

The aim of this study was to investigate the effect and underlying pathway of pyrroline-5-carboxylate reductase-2 (PYCR2) on colorectal cancer (CRC).

Methods

The Cancer Genome Atlas (TCGA) database was used to analyze PYCR2 expression levels and clinical information. Cell proliferation was evaluated using colony forming and EdU assay. Cell apoptosis rate was determined using flow cytometry. Cell migration and invasion were measured by performing a Transwell assay, and PYCR2, MMP-2, MMP-9, Bax, cleaved caspase-3, Bcl-2, cleaved PARP, p-PI3K, PI3K, p-AKT, AKT, p-mTOR, and mTOR protein levels were detected by Western blot.

Results

A review of the TCGA database revealed that PYCR2 was highly expressed in CRC patients and that high PYCR2 expression was associated with advanced stage, adenocarcinoma, nodal metastasis, and poor survival rate. Moreover, PYCR2 knockdown reduced cell viability, proliferation, migration, and invasion and increased apoptosis. Additionally, PYCR2 knockdown increased Bax, cleaved caspase-3, and cleaved PARP levels and decreased Bcl-2, MMP-2, MMP-9, p-PI3K, p-AKT, and p-mTOR levels in CRC cells. Effects of silencing PYCR2 on proliferation, migration, invasion, apoptosis, and the PI3K/AKT/mTOR pathway in CRC cells were all reversed using a PI3K activator (740Y-P).

Conclusion

PYCR2 was highly expressed in CRC, and its knockdown suppressed CRC tumorigenesis via inhibiting the activation of PI3K/AKT/mTOR pathway. This finding provides a new theoretical foundation for the treatment of CRC.

Proline metabolism in cancer

Cancer cells often change their metabolism to support uncontrolled proliferation. Proline is the only proteogenic secondary amino acid that is abundant in the body. Recent studies have shown that proline metabolism plays an important role in metabolic reprogramming and affects the occurrence and development of cancer. Proline metabolism is related to ATP production, protein and nucleotide synthesis, and redox homeostasis in tumor cells. Proline can be synthesized by aldehyde dehydrogenase family 18 member A1 (ALDH18A1) and delta1-pyrroline-5-carboxylate reductase (PYCR), up-regulating ALDH18A1 and PYCR can promote the proliferation and invasion of cancer cells. As the main storage of proline, collagen can influence cancer cells proliferation, invasion, and metastasis. Its synthesis depends on the hydroxylation of proline catalyzed by prolyl 4-hydroxylases (P4Hs), which will affect the plasticity and metastasis of cancer cells. The degradation of proline occurs in the mitochondria and involves an oxidation step catalyzed by proline dehydrogenase/proline oxidase (PRODH/POX). Proline catabolism has a dual role in cancer, linking apoptosis with the survival and metastasis of cancer cells. In addition, it has been demonstrated that the regulation of proline metabolic enzymes at the genetic and post-translational levels is related to cancer. This article reviews the role of proline metabolic enzymes in cancer proliferation, apoptosis, metastasis, and development. Research on proline metabolism may provide a new strategy for cancer treatment.

African Swine Fever Virus Protein E199L Promotes Cell Autophagy through the Interaction of PYCR2

African swine fever virus (ASFV), as a member of the large DNA viruses, may regulate autophagy and apoptosis by inhibiting programmed cell death. However, the function of ASFV proteins has not been fully elucidated, especially the role of autophagy in ASFV infection. One of three Pyrroline-5-carboxylate reductases (PYCR), is primarily involved in conversion of glutamate to proline. Previous studies have shown that depletion of PYCR2 was related to the induction of autophagy. In the present study, we found for the first time that ASFV E199L protein induced a complete autophagy process in Vero and HEK-293T cells. Through co-immunoprecipitation coupled with mass spectrometry (CoIP-MS) analysis, we firstly identified that E199L interact with PYCR2 in vitro. Importantly, our work provides evidence that E199L down-regulated the expression of PYCR2, resulting in autophagy activation. Overall, our results demonstrate that ASFV E199L protein induces complete autophagy through interaction with PYCR2 and down-regulate the expression level of PYCR2, which provide a valuable reference for the role of autophagy during ASFV infection and contribute to the functional clues of PYCR2.

Disease variants of human Δ1-pyrroline-5-carboxylate reductase 2 (PYCR2)

Pyrroline-5-carboxylate reductase (PYCR in humans) catalyzes the final step of l-proline biosynthesis by catalyzing the reduction of L-Δ¹-pyrroline-5-carboxylate (L-P5C) to l-proline using NAD(P)H as the hydride donor. In humans, three isoforms PYCR1, PYCR2, and PYCR3 are known. Recent genome-wide association and clinical studies have revealed that homozygous mutations in human PYCR2 lead to postnatal microcephaly and hypomyelination, including hypomyelinating leukodystrophy type 10. To uncover biochemical and structural insights into human PYCR2, we characterized the steady-state kinetics of the wild-type enzyme along with two protein variants, Arg119Cys and Arg251Cys, that were previously identified in patients with microcephaly and hypomyelination. Kinetic measurements with PYCR2 suggest a sequential binding mechanism with L-P5C binding before NAD(P)H and NAD(P)⁺ releasing before L-Pro. Both disease-related variants are catalytically impaired. Depending on whether NADPH or NADH was used, the catalytic efficiency of the R119C protein variant was 40 or 366 times lower than that of the wild-type enzyme, while the catalytic efficiency of the R251C protein variant was 7 or 26 times lower than that of the wild-type enzyme. In addition, thermostability and circular dichroism measurements suggest that the R251C protein variant has a pronounced folding defect. These results are consistent with the involvement of Arg119Cys and Arg251Cys in disease pathology.

The Janus-like role of proline metabolism in cancer

The metabolism of the non-essential amino acid L-proline is emerging as a key pathway in the metabolic rewiring that sustains cancer cells proliferation, survival and metastatic spread. Pyrroline-5-carboxylate reductase (PYCR) and proline dehydrogenase (PRODH) enzymes, which catalyze the last step in proline biosynthesis and the first step of its catabolism, respectively, have been extensively associated with the progression of several malignancies, and have been exposed as potential targets for anticancer drug development. As investigations into the links between proline metabolism and cancer accumulate, the complexity, and sometimes contradictory nature of this interaction emerge. It is clear that the role of proline metabolism enzymes in cancer depends on tumor type, with different cancers and cancer-related phenotypes displaying different dependencies on these enzymes. Unexpectedly, the outcome of rewiring proline metabolism also differs between conditions of nutrient and oxygen limitation. Here, we provide a comprehensive review of proline metabolism in cancer; we collate the experimental evidence that links proline metabolism with the different aspects of cancer progression and critically discuss the potential mechanisms involved.

Identification of potential cervical cancer serum biomarkers in Thai patients

Cervical cancer is one of the most common causes of cancer-associated mortality in females worldwide. Serum biomarkers are important tools for diagnosis, disease staging, monitoring treatment and detecting recurrence in different types of cancer. However, only a small number of established biomarkers have been used for clinical diagnosis of cervical cancer. Therefore, the identification of minimally invasive, sensitive and highly specific biomarkers for detection of cervical cancer may improve outcomes. In the present pilot study, changes in disease-relevant proteins in 31 patients with cervical cancer were compared with 16 healthy controls. The Human 14 Multiple Affinity Removal system was used to deplete the 14 most abundant serum proteins to decrease sample complexity and to enrich proteins that exhibited decreased levels of abundance in the serum samples. Immunoaffinity-depleted serum samples were analyzed by in-gel digestion, followed by liquid chromatography mass spectrometry analysis and data processing. Automated quantitative western blot assays and receiver operating characteristic (ROC) curves were used to evaluate the differential protein expression levels between the two groups. Capillary electrophoresis-based western blot analysis was performed to quantitatively determine serum levels of the candidate biomarkers. Significantly increased levels of α-1-antitrypsin (A1AT) and pyrroline-5-carboxylate reductase 2 (PYCR2) were detected, whereas the levels of transthyretin (TTR), apolipoprotein A-I (ApoA-I), vitamin D binding protein (VDBP) and multimerin-1 (MMRN1) were significantly decreased in patients with cervical cancer compared with the healthy controls. ROC curve analysis indicated that the sensitivity and specificity was improved through the combination of the 6 candidate biomarkers. In summary, the results demonstrated that 6 candidate biomarkers (A1AT, PYCR2, TTR, ApoA-I, VDBP and MMRN1) exhibited significantly different expression between serum samples from healthy controls and patients with cervical cancer. These proteins may represent potential biomarkers for distinguishing patients with cervical cancer from healthy controls and for differentiation of patient subgroups.

PYCR1 is Associated with Papillary Renal Cell Carcinoma Progression

Objective

We aimed to determine the function of pyrroline-5-carboxylate reductase 1 (PYCR1) on progression of papillary renal cell carcinoma (PRCC) and related mechanism.

Methods

The TCGA database provided us expression profiles of PYCR1 and overall survival rates. Small interfering RNA (siRNA) was used to knockdown PYCR1; quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting were conducted to identify the expression levels of mRNA and protein. The cell counting kit-8 (CCK-8) and colony formation assays were used to explore cell viability in Ketr-3 cells. The migration and invasion of Ketr-3 cells were investigated by transwell assays.

Results

We found that PYCR1 was over-expressed in PRCC tissues and cells, causing poor outcomes. Moreover, reduction of PYCR1 played a negative role on cell proliferation, migration and invasion in tumor cells. The important Akt/mTOR pathway proteins, phosphorylated Akt (p-Akt) and phosphorylated mTOR (p-mTOR), also showed lower levels compared with control groups.

Conclusion

These findings showed that disordered expression of PYCR1 could modulate PRCC progression through the Akt/mTOR pathway, implying a theoretical basis for PYCR1 as a potential therapeutic target in future clinical PRCC treatment.

Pyrroline-5-Carboxylate Reductase 1 Accelerates the Migration and Invasion of Nonsmall Cell Lung Cancer In Vitro

Background: Pyrroline-5-carboxylate reductase 1 (PYCR1) is involved in tumor progression, for instance, breast cancer and prostate cancer. However, its role in tumor metastasis, especially in nonsmall cell lung cancer (NSCLC), is still elusive. Materials and Methods: The messenger RNA (mRNA) expression of PYCR1 between NSCLC and normal lung specimens was compared using Oncomine database. The endogenous PYCR1 expressions in NSCLC cell lines 95C and H1299 were knocked down by lentiviral-mediated delivery of short hairpin RNA (shRNA). Then the effects of PYCR1 on the migration and invasion of NSCLC cells were studied by wound healing assay and transwell assay. Results: PYCR1 mRNA expression was significantly higher in NSCLC specimens than that in normal lung tissues. Depletion of PYCR1 in NSCLC cell significantly repressed the cell migration and invasion. Moreover, depletion of PYCR1 influenced the expression of epithelial-mesenchymal transition molecules E-cadherin, Vimentin, N-cadherin, and Snail1. Conclusions: Our data suggested that PYCR1 plays a positive role in NSCLC metastasis in vitro and might be a promising target for treating NSCLC.

More Than Skin Deep: Autophagy Is Vital for Skin Barrier Function

The skin is a highly organized first line of defense that stretches up to 1.8 m² and is home to more than a million commensal bacteria. The microenvironment of skin is driven by factors such as pH, temperature, moisture, sebum level, oxidative stress, diet, resident immune cells, and infectious exposure. The skin has a high turnover of cells as it continually bares itself to environmental stresses. Notwithstanding these limitations, it has devised strategies to adapt as a nutrient-scarce site. To perform its protective function efficiently, it relies on mechanisms to continuously remove dead cells without alarming the immune system, actively purging the dying/senescent cells by immunotolerant efferocytosis. Both canonical (starvation-induced, reactive oxygen species, stress, and environmental insults) and non-canonical (selective) autophagy in the skin have evolved to perform astute due-diligence and housekeeping in a quiescent fashion for survival, cellular functioning, homeostasis, and immune tolerance. The autophagic “homeostatic rheostat” works tirelessly to uphold the delicate balance in immunoregulation and tolerance. If this equilibrium is upset, the immune system can wreak havoc and initiate pathogenesis. Out of all the organs, the skin remains under-studied in the context of autophagy. Here, we touch upon some of the salient features of autophagy active in the skin.

Resolving the cofactor-binding site in the proline biosynthetic enzyme human pyrroline-5-carboxylate reductase 1

Pyrroline-5-carboxylate reductase (PYCR) is the final enzyme in proline biosynthesis, catalyzing the NAD(P)H-dependent reduction of Δ1-pyrroline-5-carboxylate (P5C) to proline. Mutations in the PYCR1 gene alter mitochondrial function and cause the connective tissue disorder cutis laxa. Furthermore, PYCR1 is overexpressed in multiple cancers, and the PYCR1 knock-out suppresses tumorigenic growth, suggesting that PYCR1 is a potential cancer target. However, inhibitor development has been stymied by limited mechanistic details for the enzyme, particularly in light of a previous crystallographic study that placed the cofactor-binding site in the C-terminal domain rather than the anticipated Rossmann fold of the N-terminal domain. To fill this gap, we report crystallographic, sedimentation-velocity, and kinetics data for human PYCR1. Structures of binary complexes of PYCR1 with NADPH or proline determined at 1.9 Å resolution provide insight into cofactor and substrate recognition. We see NADPH bound to the Rossmann fold, over 25 Å from the previously proposed site. The 1.85 Å resolution structure of a ternary complex containing NADPH and a P5C/proline analog provides a model of the Michaelis complex formed during hydride transfer. Sedimentation velocity shows that PYCR1 forms a concentration-dependent decamer in solution, consistent with the pentamer-of-dimers assembly seen crystallographically. Kinetic and mutational analysis confirmed several features seen in the crystal structure, including the importance of a hydrogen bond between Thr-238 and the substrate as well as limited cofactor discrimination.