Regulation of the unfolded protein response through ATF4 and FAM129A in prostate cancer

TRIM2 promotes metabolic adaptation to glutamine deprivation via enhancement of CPT1A activity

Cancer cells undergo metabolic adaptation to promote their survival and growth under energy stress conditions, yet the underlying mechanisms remain largely unclear. Here, we report that tripartite motif-containing protein 2 (TRIM2) is upregulated in response to glutamine deprivation by the transcription factor cyclic AMP-dependent transcription factor (ATF4). TRIM2 is shown to specifically interact with carnitine O-palmitoyltransferase 1 (CPT1A), a rate-limiting enzyme of fatty acid oxidation. Via this interaction, TRIM2 enhances the enzymatic activity of CPT1A, thereby regulating intracellular lipid levels and protecting cells from glutamine deprivation-induced apoptosis. Furthermore, TRIM2 is able to promote both in vitro cell proliferation and in vivo xenograft tumor growth via CPT1A. Together, these findings establish TRIM2 as an important regulator of the metabolic adaptation of cancer cells to glutamine deprivation and implicate TRIM2 as a potential therapeutic target for cancer.

Activating transcription factor 4: a regulator of stress response in human cancers

Activating transcription factor 4 (ATF4) is an adaptive response regulator of metabolic and oxidative homeostasis. In response to cellular stress, ATF4 is activated and functions as a regulator to promote cell adaptation for survival. As a transcriptional regulator, ATF4 also widely participates in the regulation of amino acid metabolism, autophagy, redox homeostasis and endoplasmic reticulum stress. Moreover, ATF4 is associated with the initiation and progression of glioblastoma, hepatocellular carcinoma, colorectal cancer, gastric cancer, breast cancer, prostate cancer and lung cancer. This review primarily aims to elucidate the functions of ATF4 and its role in multiple cancer contexts. This review proposes potential therapeutic targets for clinical intervention.

CCT020312 exerts anti-prostate cancer effect by inducing G1 cell cycle arrest, apoptosis and autophagy through activation of PERK/eIF2α/ATF4/CHOP signaling

PERK/eIF2α/ATF4/CHOP signaling pathway is one of three major branches of unfolded protein response (UPR) and has been implicated in tumor progression. CCT020312 is a selective PERK activator and may have a potential anti-tumor effect. Here we investigated the anti-prostate cancer effect and its underlying mechanism of CCT020312. Our results showed that CCT020312 inhibited prostate cancer cell viability by inducing cell cycle arrest, apoptosis and autophagy through activation of PERK/eIF2α/ATF4/CHOP signaling. CCT020312 treatment caused cell cycle arrest at G1 phase and increased the levels of cleaved-Caspase3, cleaved-PARP and Bax in prostate cancer C4-2 and LNCaP cells. Moreover, CCT020312 increased LC3II/I, Atg12-Atg5 and Beclin1 levels and induced autophagosome formation. Furthermore, knockdown of CHOP reversed CCT020312-induced cell viability decrease, apoptosis and autophagy. Bafilomycin A1 reversed CCT020312-induced cell viability decrease but had no effect on CCT020312-induced CHOP activation in C4-2 and LNCaP cells. In vivo, CCT020312 suppressed tumor growth in C4-2 cells-derived xenograft mouse model, activated PERK pathway, and induced autophagy and apoptosis. Our study illustrates that CCT020312 exerts an anti-tumor effect in prostate cancer via activating the PERK pathway, thus indicating that CCT020312 may be a potential drug for prostate cancer.

THEM6 is a prognostic biomarker for breast cancer and is associated with immune infiltration

To characterize the implications of lipid metabolism-related gene thioesterase superfamily member 6 (THEM6) in breast cancer. Several databases including The Cancer Genome Atlas (TCGA) were utilized for our meticulous bioinformatics analysis. We further performed qRT-PCR, immunoblotting and IHC assays to validate the expression of THEM6 in various breast cancer cells and tissues. In addition, we have carried out relevant functional experiments to explore the regulatory role of THEM6 in vitro. Lipid metabolism-related genes are independent factors for overall survival. According to several databases, THEM6 was significantly more expressed in cancerous tissues of breast invasive carcinoma (BRCA) compared to its paracancerous tissues. Furthermore, THEM6 overexpression was correlated with poorer overall survival of BRCA patients, serving as a separate prognostic factor for BRCA. Biological functional analyses revealed that THEM6 was associated with tumor progression and pathogenesis. Finally, we discovered that in BRCA, THEM6 expression was linked to multiple immune cell types. qRT-PCR and Western blotting experiments demonstrated a general upregulation of THEM6 expression in breast carcinoma cells. IHC showed that THEM6 was expressed in both breast cancer tissues and para-cancer tissues, but its expression level was significantly higher in carcinoma tissues. In vitro studies indicated that THEM6 increased proliferation, invasion, and inhibited apoptosis of breast carcinoma cells, while also affecting the cell cycle and promoting cancer progression. Furthermore, THEM6 may influence macrophage recruitment and polarization in the tumor microenvironment by regulating CCL2 secretion, which in turn affects macrophage recruitment in the tumor microenvironment. Our findings indicate that the overexpression of THEM6, which is linked to the development of breast cancer, is a predictor of a poor prognosis and has an impact on the degree of immune cell infiltration. Therefore, THEM6 has the potential to be a valuable target for BRCA.

FAM129A promotes self-renewal and maintains invasive status via stabilizing the Notch intracellular domain in glioma stem cells

BACKGROUND

Glioma stem cells (GSCs) are a subpopulation of tumor cells with self-renewal and tumorigenic capabilities in glioblastomas (GBMs). Diffuse infiltration of GSCs facilitates tumor progression and frustrates efforts at effective treatment. Further compounding this situation is the currently limited understanding of what drives GSC invasion. Here we comprehensively evaluated the significance of a novel invasion-related protein, Family with Sequence Similarity 129 Member A (FAM129A), in infiltrative GSCs.

METHODS

Western blotting, immunohistochemistry, and gene expression analysis were used to quantify FAM129A in glioma specimens and cancer datasets. Overexpression and knockdown of FAM129A in GSCs were used to investigate its effects on tumor growth and invasion. RNA-seq, qRT-PCR, western blotting, and co-precipitation assays were used to investigate FAM129A signaling mechanisms.

RESULTS

FAM129A is preferentially expressed in invasive frontiers. Targeting FAM129A impairs GSC invasion and self-renewal. Mechanistically, FAM129A acted as a positive regulator of Notch signaling by binding with the Notch1 intracellular domain (NICD1) and preventing its degradation.

CONCLUSIONS

FAM129A and NICD1 provide a precise indicator for identifying tumor margins and aiding prognosis. Targeting them may provide a significantly therapeutic strategy for GSCs.

The PERK pathway: beneficial or detrimental for neurodegenerative diseases and tumor growth and cancer

Protein kinase R (PKR)-like endoplasmic reticulum (ER) kinase (PERK) is one of the three major sensors in the unfolded protein response (UPR). The UPR is involved in the modulation of protein synthesis as an adaptive response. Prolonged PERK activity correlates with the development of diseases and the attenuation of disease severity. Thus, the current debate focuses on the role of the PERK signaling pathway either in accelerating or preventing diseases such as neurodegenerative diseases, myelin disorders, and tumor growth and cancer. In this review, we examine the current findings on the PERK signaling pathway and whether it is beneficial or detrimental for the above-mentioned disorders.

ONC201 in combination with paxalisib for the treatment of H3K27-altered diffuse midline glioma

Diffuse midline gliomas (DMG), including diffuse intrinsic pontine gliomas (DIPGs), are the most lethal of childhood cancers. Palliative radiotherapy is the only established treatment, with median patient survival of 9-11 months. ONC201 is a DRD2 antagonist and ClpP agonist that has shown preclinical and emerging clinical efficacy in DMG. However, further work is needed to identify the mechanisms of response of DIPGs to ONC201 treatment and to determine whether recurring genomic features influence response. Using a systems-biological approach, we showed that ONC201 elicits potent agonism of the mitochondrial protease ClpP to drive proteolysis of electron transport chain and tricarboxylic acid cycle proteins. DIPGs harboring PIK3CA-mutations showed increased sensitivity to ONC201, while those harboring TP53-mutations were more resistant. Metabolic adaptation and reduced sensitivity to ONC201 was promoted by redox-activated PI3K/Akt signaling, which could be counteracted using the brain penetrant PI3K/Akt inhibitor, paxalisib. Together, these discoveries coupled with the powerful anti-DIPG/DMG pharmacokinetic and pharmacodynamic properties of ONC201 and paxalisib have provided the rationale for the ongoing DIPG/DMG phase II combination clinical trial NCT05009992.

Newly developed MEIS inhibitor selectively blocks MEIS High prostate cancer growth and induces apoptosis

Prostate cancer (PCa) is the second most diagnosed cancer in males. Understanding the molecular mechanism and investigation of novel ways to block PCa growth or metastasis are vital and a medical necessity. In this study, we examined differential expression of MEIS1/2/3 and its associated factors in PCa cell lines. MEIS1/2/3 content, reactive oxygen species, and cell cycle status were analyzed in PCa cells post MEIS inhibitor (MEISi) treatments, which is developed in our laboratory as a first-in-class small molecule inhibitor. A correlation was detected between MEIS content and MEISi IC50 values of PCa cells. MEISi decreased the viability of PC-3, DU145, 22Rv-1 and LNCaP cells, and significantly increased apoptosis in parallel with the increased cellular ROS content. The efficacy of MEISi was shown to positively correlate with the levels of MEIS1/2/3 proteins and the long term exposure to MEISi elevated MEIS1/2/3 protein content in PCa cells. Our findings suggest that MEISi could be used to target PCa with high MEIS expression in order to reduce PCa viability and growth; however, more research is needed before this can be translated into clinical settings.

Molecular interplay between NOX1 and autophagy in cadmium-induced prostate carcinogenesis

Chronic exposure to cadmium (Cd), a class I carcinogen, leads to malignant transformation of normal prostate epithelial cells (RWPE-1). The constant generation of Cd-induced ROS and resulting ER stress induces cellular responses that are needed for cell survival, and autophagy has an important role in this process. However, the mechanisms that regulate Cd-induced ROS and how these differ in terms of acute and chronic cadmium exposure remain unexplained. Here, we show that acute or chronic Cd exposure facilitates NOX1 assembly by activating its cytosolic regulators p47phox and p67phox in RWPE-1 cells. Upregulation of NOX1 complex proteins and generation of ROS activates unfolded protein response (UPR) via phosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor 2 alpha (eIF2α), and selective translation of activating transcription factor 4 (ATF4). Chronic Cd exposure constantly activates NOX1 complex and generates consistent ROS and ER stress that led to defective autophagy, wherein ATG5 expression is downregulated in contrast to acute Cd exposure. As a result, selective/defective autophagy creates depletion of autophagosome-lysosome fusion that gives a survival advantage to transforming cells, which is not available to RWPE-1 cells acutely exposed to Cd. Knockdown of key molecules in a lockstep manner directly affects the most downstream autophagy pathways in transforming cells. Overall, this study demonstrates that assembly of NOX1 complex proteins is indispensable for Cd-induced persistent ROS and controls ER stress-induced defective autophagy in mice and humans.

Endoplasmic reticulum stress and lipids in health and diseases

The endoplasmic reticulum (ER) is a complex and dynamic organelle that regulates many cellular pathways, including protein synthesis, protein quality control, and lipid synthesis. When one or multiple ER roles are dysregulated and saturated, the ER enters a stress state, which, in turn, activates the highly conserved unfolded protein response (UPR). By sensing the accumulation of unfolded proteins or lipid bilayer stress (LBS) at the ER, the UPR triggers pathways to restore ER homeostasis and eventually induces apoptosis if the stress remains unresolved. In recent years, it has emerged that the UPR works intimately with other cellular pathways to maintain lipid homeostasis at the ER, and so does at cellular levels. Lipid distribution, along with lipid anabolism and catabolism, are tightly regulated, in part, by the ER. Dysfunctional and overwhelmed lipid-related pathways, independently or in combination with ER stress, can have reciprocal effects on other cellular functions, contributing to the development of diseases. In this review, we summarize the current understanding of the UPR in response to proteotoxic stress and LBS and the breadth of the functions mitigated by the UPR in different tissues and in the context of diseases.

The endoplasmic reticulum stress response in prostate cancer

In order to proliferate in unfavourable conditions, cancer cells can take advantage of the naturally occurring endoplasmic reticulum-associated unfolded protein response (UPR) via three highly conserved signalling arms: IRE1α, PERK and ATF6. All three arms of the UPR have key roles in every step of tumour progression: from cancer initiation to tumour growth, invasion, metastasis and resistance to therapy. At present, no cure for metastatic prostate cancer exists, as targeting the androgen receptor eventually results in treatment resistance. New research has uncovered an important role for the UPR in prostate cancer tumorigenesis and crosstalk between the UPR and androgen receptor signalling pathways. With an improved understanding of the mechanisms by which cancer cells exploit the endoplasmic reticulum stress response, targetable points of vulnerability can be uncovered.

GCN2 eIF2 kinase promotes prostate cancer by maintaining amino acid homeostasis

A stress adaptation pathway termed the integrated stress response has been suggested to be active in many cancers including prostate cancer (PCa). Here, we demonstrate that the eIF2 kinase GCN2 is required for sustained growth in androgen-sensitive and castration-resistant models of PCa both in vitro and in vivo, and is active in PCa patient samples. Using RNA-seq transcriptome analysis and a CRISPR-based phenotypic screen, GCN2 was shown to regulate expression of over 60 solute-carrier (SLC) genes, including those involved in amino acid transport and loss of GCN2 function reduces amino acid import and levels. Addition of essential amino acids or expression of 4F2 (SLC3A2) partially restored growth following loss of GCN2, suggesting that GCN2 targeting of SLC transporters is required for amino acid homeostasis needed to sustain tumor growth. A small molecule inhibitor of GCN2 showed robust in vivo efficacy in androgen-sensitive and castration-resistant mouse models of PCa, supporting its therapeutic potential for the treatment of PCa.

CK2 and the Hallmarks of Cancer

Cancer is a leading cause of death worldwide. Casein kinase 2 (CK2) is commonly dysregulated in cancer, impacting diverse molecular pathways. CK2 is a highly conserved serine/threonine kinase, constitutively active and ubiquitously expressed in eukaryotes. With over 500 known substrates and being estimated to be responsible for up to 10% of the human phosphoproteome, it is of significant importance. A broad spectrum of diverse types of cancer cells has been already shown to rely on disturbed CK2 levels for their survival. The hallmarks of cancer provide a rationale for understanding cancer's common traits. They constitute the maintenance of proliferative signaling, evasion of growth suppressors, resisting cell death, enabling of replicative immortality, induction of angiogenesis, the activation of invasion and metastasis, as well as avoidance of immune destruction and dysregulation of cellular energetics. In this work, we have compiled evidence from the literature suggesting that CK2 modulates all hallmarks of cancer, thereby promoting oncogenesis and operating as a cancer driver by creating a cellular environment favorable to neoplasia.

Induction of Genes Implicated in Stress Response and Autophagy by a Novel Quinolin-8-yl-nicotinamide QN523 in Pancreatic Cancer

Using a cytotoxicity-based phenotypic screen of a highly diverse library of 20,000 small-molecule compounds, we identified a quinolin-8-yl-nicotinamide, QN519, as a promising lead. QN519 represents a novel scaffold with drug-like properties, showing potent in vitro cytotoxicity in a panel of 12 cancer cell lines. Subsequently, lead optimization campaign generated compounds with IC50 values < 1 μM. An optimized compound, QN523, shows significant in vivo efficacy in a pancreatic cancer xenograft model. QN523 treatment significantly increased the expression of HSPA5, DDIT3, TRIB3, and ATF3 genes, suggesting activation of the stress response pathway. We also observed a significant increase in the expression of WIPI1, HERPUD1, GABARAPL1, and MAP1LC3B, implicating autophagy as a major mechanism of action. Due to the lack of effective treatments for pancreatic cancer, discovery of novel agents such as the QN series of compounds with unique mechanism of action has the potential to fulfill a clear unmet medical need.

NIBAN1, Exploring its Roles in Cell Survival Under Stress Context

Cell survival must quickly activate specific mechanisms that enable to detect changes in the cellular microenvironment. The impact of these cell alteration has direct consequences on cellular homeostasis. Cellular stress, as well as its regulation and implication, has been studied in different pathologies. In this sense, the alteration in NIBAN1 expression seems to act in response to different cellular disturbances. Over the years, the knowledge of NIBAN1 functions has improved, demonstrating its important cell roles, favoring the cell survival under stress context. In response to the disturbances, NIBAN1 seems to be involved in the decision-making process between cell survival and death. The increase in NIBAN1 expression has been related to cellular mechanisms that seek to minimize the damage caused to cellular homeostasis. In this review, the main biological insights attributed to the NIBAN1 gene in different cellular contexts and its role as a mediator of cellular stress are discussed.

The role of cellular proteostasis in anti-tumor immunity

Immune checkpoint blockade therapy is perhaps the most important development in cancer treatment in recent memory. It is based on decades of investigation into the biology of immune cells and the role of the immune system in controlling cancer growth. While the molecular circuitry that governs the immune system in general - and anti-tumor immunity in particular - is intensely studied, far less attention has been paid to the role of cellular stress in this process. Proteostasis, intimately linked to cell stress responses, refers to the dynamic regulation of the cellular proteome and is maintained through a complex network of systems that govern the synthesis, folding, and degradation of proteins in the cell. Disruption of these systems can result in the loss of protein function, altered protein function, the formation of toxic aggregates, or pathologies associated with cell stress. However, the importance of proteostasis extends beyond its role in maintaining proper protein function; proteostasis governs how tolerant cells may be to mutations in protein coding genes and the overall half-life of proteins. Such gene expression changes may be associated with human diseases including neurodegenerative diseases, metabolic disease, and cancer and manifest at the protein level against the backdrop of the proteostasis network in any given cellular environment. In this review, we focus on the role of proteostasis in regulating immune responses against cancer as well the role of proteostasis in determining immunogenicity of cancer cells.

THEM6-mediated reprogramming of lipid metabolism supports treatment resistance in prostate cancer

Despite the clinical benefit of androgen-deprivation therapy (ADT), the majority of patients with advanced prostate cancer (PCa) ultimately develop lethal castration-resistant prostate cancer (CRPC). In this study, we identified thioesterase superfamily member 6 (THEM6) as a marker of ADT resistance in PCa. THEM6 deletion reduces in vivo tumour growth and restores castration sensitivity in orthograft models of CRPC. Mechanistically, we show that the ER membrane-associated protein THEM6 regulates intracellular levels of ether lipids and is essential to trigger the induction of the ER stress response (UPR). Consequently, THEM6 loss in CRPC cells significantly alters ER function, reducing de novo sterol biosynthesis and preventing lipid-mediated activation of ATF4. Finally, we demonstrate that high THEM6 expression is associated with poor survival and correlates with high levels of UPR activation in PCa patients. Altogether, our results highlight THEM6 as a novel driver of therapy resistance in PCa as well as a promising target for the treatment of CRPC.

The Regulatory Role of GBF1 on Osteoclast Activation Through EIF2a Mediated ER Stress and Novel Marker FAM129A Induction

Bone-resorbing activities of osteoclasts (OCs) are highly dependent on actin cytoskeleton remodeling, plasma membrane reorganization, and vesicle trafficking pathways, which are partially regulated by ARF-GTPases. In the present study, the functional roles of Golgi brefeldin A resistance factor 1 (GBF1) are proposed. GBF1 is responsible for the activation of the ARFs family and vesicular transport at the endoplasmic reticulum–Golgi interface in different stages of OCs differentiation. In the early stage, GBF1 deficiency impaired OCs differentiation and was accompanied with OCs swelling and reduced formation of mature OCs, indicating that GBF1 participates in osteoclastogenesis. Using siRNA and the specific inhibitor GCA for GBF1 knockdown upregulated endoplasmic reticulum stress-associated signaling molecules, including BiP, p-PERK, p-EIF2α, and FAM129A, and promoted autophagic Beclin1, Atg7, p62, and LC3 axis, leading to apoptosis of OCs. The present data suggest that, by blocking COPI-mediated vesicular trafficking, GBF1 inhibition caused intense stress to the endoplasmic reticulum and excessive autophagy, eventually resulting in the apoptosis of mature OCs and impaired bone resorption function.

Adipocyte-driven unfolded protein response is a shared transcriptomic signature of metastatic prostate carcinoma cells

A critical unknown in the field of skeletal metastases is how cancer cells find a way to thrive under harsh conditions, as exemplified by metastatic colonization of adipocyte-rich bone marrow by prostate carcinoma cells. To begin understanding molecular processes that enable tumor cells to survive and progress in difficult microenvironments such as bone, we performed unbiased examination of the transcriptome of two different prostate cancer cell lines in the absence or presence of bone marrow adipocytes. Our RNAseq analyses and subsequent quantitative PCR and protein-based assays reveal that upregulation of endoplasmic reticulum (ER) stress and unfolded protein response (UPR) genes is a shared signature between metastatic prostate carcinoma cell lines of different origin. Pathway analyses and pharmacological examinations highlight the ER chaperone BIP as an upstream coordinator of this transcriptomic signature. Additional patient-based data support our overall conclusion that ER stress and UPR induction are shared, important factors in the response and adaptation of metastatic tumor cells to their micro-environment. Our studies pave the way for additional mechanistic investigations and offer new clues towards effective therapeutic interventions in metastatic disease.

SLFN5 Regulates LAT1-Mediated mTOR Activation in Castration-Resistant Prostate Cancer

Androgen deprivation therapy (ADT) is the standard of care for treatment of nonresectable prostate cancer. Despite high treatment efficiency, most patients ultimately develop lethal castration-resistant prostate cancer (CRPC). In this study, we performed a comparative proteomic analysis of three in vivo, androgen receptor (AR)-responsive orthograft models of matched hormone-naïve prostate cancer and CRPC. Differential proteomic analysis revealed that distinct molecular mechanisms, including amino acid (AA) and fatty acid metabolism, are involved in the response to ADT in the different models. Despite this heterogeneity, Schlafen family member 5 (SLFN5) was identified as an AR-regulated protein in CRPC. SLFN5 expression was high in CRPC tumors and correlated with poor patient outcome. In vivo, SLFN5 depletion strongly impaired tumor growth in castrated conditions. Mechanistically, SLFN5 interacted with ATF4 and regulated the expression of LAT1, an essential AA transporter. Consequently, SLFN5 depletion in CRPC cells decreased intracellular levels of essential AA and impaired mTORC1 signaling in a LAT1-dependent manner. These results confirm that these orthograft models recapitulate the high degree of heterogeneity observed in patients with CRPC and further highlight SLFN5 as a clinically relevant target for CRPC. SIGNIFICANCE: This study identifies SLFN5 as a novel regulator of the LAT1 amino acid transporter and an essential contributor to mTORC1 activity in castration-resistant prostate cancer.

Dynamic alteration in miRNA and mRNA expression profiles at different stages of chronic arsenic exposure-induced carcinogenesis in a human cell culture model of skin cancer

Chronic arsenic exposure causes skin cancer, although the underlying molecular mechanisms are not well defined. Altered microRNA and mRNA expression likely play a pivotal role in carcinogenesis. Changes in genome-wide differential expression of miRNA and mRNA at 3 strategic time points upon chronic sodium arsenite (As3+) exposure were investigated in a well-validated HaCaT cell line model of arsenic-induced cutaneous squamous cell carcinoma (cSCC). Quadruplicate independent HaCaT cell cultures were exposed to 0 or 100 nM As3+ for up to 28-weeks (wk). Cell growth was monitored throughout the course of exposure and epithelial-mesenchymal transition (EMT) was examined employing immunoblot. Differentially expressed miRNA and mRNA profiles were generated at 7, 19, and 28-wk by RNA-seq, followed by identification of differentially expressed mRNA targets of differentially expressed miRNAs through expression pairing at each time point. Pathway analyses were performed for total differentially expressed mRNAs and for the miRNA targeted mRNAs at each time point. RNA-seq predictions were validated by immunoblot of selected target proteins. While the As3+-exposed cells grew slower initially, growth was equal to that of unexposed cells by 19-wk (transformation initiation), and exposed cells subsequently grew faster than passage-matched unexposed cells. As3+-exposed cells had undergone EMT at 28-wk. Pathway analyses demonstrate dysregulation of carcinogenesis-related pathways and networks in a complex coordinated manner at each time point. Immunoblot data largely corroborate RNA-seq predictions in the endoplasmic reticulum stress (ER stress) pathway. This study provides a detailed molecular picture of changes occurring during the arsenic-induced transformation of human keratinocytes.

Stress-Mediated Reprogramming of Prostate Cancer One-Carbon Cycle Drives Disease Progression

One-carbon (1C) metabolism has a key role in metabolic programming with both mitochondrial (m1C) and cytoplasmic (c1C) components. Here we show that activating transcription factor 4 (ATF4) exclusively activates gene expression involved in m1C, but not the c1C cycle in prostate cancer cells. This includes activation of methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) expression, the central player in the m1C cycle. Consistent with the key role of m1C cycle in prostate cancer, MTHFD2 knockdown inhibited prostate cancer cell growth, prostatosphere formation, and growth of patient-derived xenograft organoids. In addition, therapeutic silencing of MTHFD2 by systemically administered nanoliposomal siRNA profoundly inhibited tumor growth in preclinical prostate cancer mouse models. Consistently, MTHFD2 expression is significantly increased in human prostate cancer, and a gene expression signature based on the m1C cycle has significant prognostic value. Furthermore, MTHFD2 expression is coordinately regulated by ATF4 and the oncoprotein c-MYC, which has been implicated in prostate cancer. These data suggest that the m1C cycle is essential for prostate cancer progression and may serve as a novel biomarker and therapeutic target. SIGNIFICANCE: These findings demonstrate that the mitochondrial, but not cytoplasmic, one-carbon cycle has a key role in prostate cancer cell growth and survival and may serve as a biomarker and/or therapeutic target.

The Effects of Bergamot Polyphenolic Fraction, Cynara cardunculus, and Olea europea L. Extract on Doxorubicin-Induced Cardiotoxicity

Doxorubicin is an anthracycline that is commonly used as a chemotherapy drug due to its cytotoxic effects. The clinical use of doxorubicin is limited due to its known cardiotoxic effects. Treatment with anthracyclines causes heart failure in 15–17% of patients, resulting in mitochondrial dysfunction, the accumulation of reactive oxygen species, intracellular calcium dysregulation, the deterioration of the cardiomyocyte structure, and apoptotic cell death. Polyphenols have a wide range of beneficial properties, and particular importance is given to Bergamot Polyphenolic Fraction; Oleuropein, one of the main polyphenolic compounds of olive oil; and Cynara cardunculus extract. These natural compounds have particular beneficial characteristics, owing to their high polyphenol contents. Among these, their antioxidant and antoproliferative properties are the most important. The aim of this paper was to investigate the effects of these three plant derivatives using an in vitro model of cardiotoxicity induced by the treatment of rat embryonic cardiomyoblasts (H9c2) with doxorubicin. The biological mechanisms involved and the crosstalk existing between the mitochondria and the endoplasmic reticulum were examined. Bergamot Polyphenolic Fraction, Oleuropein, and Cynara cardunculus extract were able to decrease the damage induced by exposure to doxorubicin. In particular, these natural compounds were found to reduce cell mortality and oxidative damage, increase the lipid content, and decrease the concentration of calcium ions that escaped from the endoplasmic reticulum. In addition, the direct involvement of this cellular organelle was demonstrated by silencing the ATF6 arm of the Unfolded Protein Response, which was activated after treatment with doxorubicin.

Differential microRNA Expression in Newcastle Disease Virus-Infected HeLa Cells and Its Role in Regulating Virus Replication

As an oncolytic virus, Newcastle disease virus (NDV) can specifically kill tumor cells and has been tested as an attractive oncolytic agent for cancer virotherapy. Virus infection can trigger the changes of the cellular microRNA (miRNA) expression profile, which can greatly influence viral replication and pathogenesis. However, the interplay between NDV replication and cellular miRNA expression in tumor cells is still largely unknown. In the present study, we compared the profiles of cellular miRNAs in uninfected and NDV-infected HeLa cells by small RNA deep sequencing. Here we report that NDV infection in HeLa cells significantly changed the levels of 40 miRNAs at 6 h post-infection (hpi) and 62 miRNAs at 12 hpi. Among 23 highly differentially expressed miRNAs, NDV infection greatly promoted the levels of 3 miRNAs and suppressed the levels of 20 miRNAs at both time points. These 23 miRNAs are predicted to target various genes involved in virus replication and antiviral immunity such as ErbB, Jak-STAT, NF-kB and RIG-I-like receptor. Verification of deep sequencing results by quantitative RT-PCR showed that 9 out of 10 randomly selected miRNAs chosen from this 23-miRNA pool were consistent with deep sequencing data, including 6 down-regulated and 3 up-regulated. Further functional research revealed that hsa-miR-4521, a constituent in this 23-miRNA pool, inhibited NDV replication in HeLa cells. Moreover, dual-luciferase and gene expression array uncovered that the member A of family with sequence similarity 129 (FAM129A) was directly targeted by hsa-miR-4521 and positively regulated NDV replication in HeLa cells, indicating that hsa-miR-4521 may regulate NDV replication via interaction with FAM129A. To our knowledge, this is the first report of the dynamic cellular miRNA expression profile in tumor cells after NDV infection and may provide a valuable basis for further investigation on the roles of miRNAs in NDV-mediated oncolysis.

The Hydroxyquinoline Analogue YUM70 Inhibits GRP78 to Induce ER Stress-Mediated Apoptosis in Pancreatic Cancer

GRP78 (glucose-regulated protein, 78 kDa) is a key regulator of endoplasmic reticulum (ER) stress signaling. Cancer cells are highly proliferative and have high demand for protein synthesis and folding, which results in significant stress on the ER. To respond to ER stress and maintain cellular homeostasis, cells activate the unfolded protein response (UPR) that promotes either survival or apoptotic death. Cancer cells utilize the UPR to promote survival and growth. In this study, we describe the discovery of a series of novel hydroxyquinoline GRP78 inhibitors. A representative analogue, YUM70, inhibited pancreatic cancer cell growth in vitro and showed in vivo efficacy in a pancreatic cancer xenograft model with no toxicity to normal tissues. YUM70 directly bound GRP78 and inactivated its function, resulting in ER stress-mediated apoptosis. A YUM70 analogue conjugated with BODIPY showed colocalization of the compound with GRP78 in the ER. Moreover, a YUM70-PROTAC (proteolysis targeting chimera) was synthesized to force degradation of GRP78 in pancreatic cancer cells. YUM70 showed a strong synergistic cytotoxicity with topotecan and vorinostat. Together, our study demonstrates that YUM70 is a novel inducer of ER stress, with preclinical efficacy as a monotherapy or in combination with topoisomerase and HDAC inhibitors in pancreatic cancer. SIGNIFICANCE: This study identifies a novel ER stress inducer that binds GRP78 and inhibits pancreatic cancer cell growth in vitro and in vivo, demonstrating its potential as a therapeutic agent for pancreatic cancer.

STAMP2 Expression Mediated by Cytokines Attenuates Their Growth-Limiting Effects in Prostate Cancer Cells

Simple Summary

Prostate cancer (PCa) is the most common non-skin cancer and one of the leading causes of cancer death in men. Despite significant developments in therapy options with improved survival, no curative treatment is currently available. We have previously identified six transmembrane protein of prostate 2 (STAMP2) as an important factor for PCa growth and survival. We now show that STAMP2 expression is regulated by inflammatory signaling, which has recently been implicated in PCa. Two proinflammatory cytokines, interleukin 6 and interleukin 1 beta, synergize with each other to induce STAMP2 expression. Interestingly, STAMP2 knockdown increased the sensitivity of PCa cells to cytokine treatment. Thus, STAMP2 that acts as a survival factor in PCa, is both independently and synergistically regulated by inflammatory signaling that may affect disease progression.

Abstract

Inflammatory events and dysregulated cytokine expression are implicated in prostate cancer (PCa), but the underlying molecular mechanisms are poorly understood at present. We have previously identified six transmembrane protein of the prostate 2 (STAMP2, also known as STEAP4) as an androgen-regulated gene, as well as a key regulator of PCa growth and survival. STAMP2 is also regulated by, and participates in, inflammatory signaling in other tissues and pathologies. Here, we show that the proinflammatory cytokines interleukin 6 (IL-6) and Interleukin 1 beta (IL-1β) significantly increase and strongly synergize in promoting STAMP2 expression in PCa cells. The two cytokines increase androgen-induced STAMP2 expression, but not expression of other known androgen target genes, suggesting a unique interplay of androgens and cytokines in regulating STAMP2 expression. Interestingly, STAMP2 knockdown significantly increased the ability of IL-6 and IL-1β to inhibit PCa cell growth in vitro. These results suggest that STAMP2 may represent a unique node through which inflammatory events mediate their effects on PCa growth and survival.

Methylated PP2A stabilizes Gcn4 to enable a methionine-induced anabolic program

Methionine, through S-adenosylmethionine, activates a multifaceted growth program in which ribosome biogenesis, carbon metabolism, and amino acid and nucleotide biosynthesis are induced. This growth program requires the activity of the Gcn4 transcription factor (called ATF4 in mammals), which facilitates the supply of metabolic precursors that are essential for anabolism. However, how Gcn4 itself is regulated in the presence of methionine is unknown. Here, we discover that Gcn4 protein levels are increased by methionine, despite conditions of high cell growth and translation (in which the roles of Gcn4 are not well-studied). We demonstrate that this mechanism of Gcn4 induction is independent of transcription, as well as the conventional Gcn2/eIF2α-mediated increased translation of Gcn4. Instead, when methionine is abundant, Gcn4 phosphorylation is decreased, which reduces its ubiquitination and therefore degradation. Gcn4 is dephosphorylated by the protein phosphatase 2A (PP2A); our data show that when methionine is abundant, the conserved methyltransferase Ppm1 methylates and alters the activity of the catalytic subunit of PP2A, shifting the balance of Gcn4 toward a dephosphorylated, stable state. The absence of Ppm1 or the loss of the PP2A methylation destabilizes Gcn4 even when methionine is abundant, leading to collapse of the Gcn4-dependent anabolic program. These findings reveal a novel, methionine-dependent signaling and regulatory axis. Here methionine directs the conserved methyltransferase Ppm1 via its target phosphatase PP2A to selectively stabilize Gcn4. Through this, cells conditionally modify a major phosphatase to stabilize a metabolic master regulator and drive anabolism.

Genome-scale reconstruction of Gcn4/ATF4 networks driving a growth program

Growth and starvation are considered opposite ends of a spectrum. To sustain growth, cells use coordinated gene expression programs and manage biomolecule supply in order to match the demands of metabolism and translation. Global growth programs complement increased ribosomal biogenesis with sufficient carbon metabolism, amino acid and nucleotide biosynthesis. How these resources are collectively managed is a fundamental question. The role of the Gcn4/ATF4 transcription factor has been best studied in contexts where cells encounter amino acid starvation. However, high Gcn4 activity has been observed in contexts of rapid cell proliferation, and the roles of Gcn4 in such growth contexts are unclear. Here, using a methionine-induced growth program in yeast, we show that Gcn4/ATF4 is the fulcrum that maintains metabolic supply in order to sustain translation outputs. By integrating matched transcriptome and ChIP-Seq analysis, we decipher genome-wide direct and indirect roles for Gcn4 in this growth program. Genes that enable metabolic precursor biosynthesis indispensably require Gcn4; contrastingly ribosomal genes are partly repressed by Gcn4. Gcn4 directly binds promoter-regions and transcribes a subset of metabolic genes, particularly driving lysine and arginine biosynthesis. Gcn4 also globally represses lysine and arginine enriched transcripts, which include genes encoding the translation machinery. The Gcn4 dependent lysine and arginine supply thereby maintains the synthesis of the translation machinery. This is required to maintain translation capacity. Gcn4 consequently enables metabolic-precursor supply to bolster protein synthesis, and drive a growth program. Thus, we illustrate how growth and starvation outcomes are both controlled using the same Gcn4 transcriptional outputs that function in distinct contexts.

Alterations in niban gene expression as a response to stress conditions in 3T3-L1 adipocytes

Adipocyte death is important in obesity development. Understanding and prevention of adipocyte deaths may be a molecular approach in the treatment. In the study, we aimed to understand role of Niban gene, which acts as an anti-apoptotic molecule as a response to stress conditions, in adipocytes. 3T3-L1 adipocytes were treated with different doses of linoleic acid, hydrogen peroxide and ethanol; and proliferation of the cells examined with real time monitoring iCELLingence system. Gene expression levels were measured by q-PCR. As a response to 24h 480 µM linoleic acid treatment, Niban gene expression was found to be higher than control group (p = 0.008), whereas 24 h 90 mM ethanol treatment was determined to be lower than control group (p = 0.008). The highest value of Niban gene expression among H₂O₂ treatment groups was detected in 4h 600µM H₂O₂ in comparison to control group (p = 0.008). To understand role of Niban in adipogenesis, Niban gene expressions were compared between pre-adipocytes and advanced fat accumulated adipocytes and determined to be significantly different (p = 0.042). Our results suggest that Niban might be involved in stress response process in adipocytes. However, the exact molecular role of Niban needs to be investigated in further studies.

DENR promotes translation reinitiation via ribosome recycling to drive expression of oncogenes including ATF4

Translation efficiency varies considerably between different mRNAs, thereby impacting protein expression. Translation of the stress response master-regulator ATF4 increases upon stress, but the molecular mechanisms are not well understood. We discover here that translation factors DENR, MCTS1 and eIF2D are required to induce ATF4 translation upon stress by promoting translation reinitiation in the ATF4 5'UTR. We find DENR and MCTS1 are only needed for reinitiation after upstream Open Reading Frames (uORFs) containing certain penultimate codons, perhaps because DENR•MCTS1 are needed to evict only certain tRNAs from post-termination 40S ribosomes. This provides a model for how DENR and MCTS1 promote translation reinitiation. Cancer cells, which are exposed to many stresses, require ATF4 for survival and proliferation. We find a strong correlation between DENR•MCTS1 expression and ATF4 activity across cancers. Furthermore, additional oncogenes including a-Raf, c-Raf and Cdk4 have long uORFs and are translated in a DENR•MCTS1 dependent manner.

A cell permeant phosphopeptide mimetic of Niban inhibits p38 MAPK and restores endothelial function after injury

Vascular injury leads to membrane disruption, ATP release, and endothelial dysfunction. Increases in the phosphorylation of p38 mitogen‐activated protein kinase (p38 MAPK) and decreases in the phosphorylation of Niban, a protein implicated in ER stress and apoptosis, are associated with vascular injury. A cell permeant phosphopeptide mimetic of Niban (NiPp) was generated. The effects of NiPp in restoring endothelial function were determined ex vivo using intact rat aortic tissue (RA) after pharmacological activation of p38 MAPK and also in multiple clinically relevant injury models. Anisomycin (Aniso) increased p38 MAPK phosphorylation and reduced endothelial‐dependent relaxation in RA. Treatment with NiPp prevented Ansio‐induced reduction in endothelial function and increases in p38 MAPK phosphorylation. NiPp treatment also restored endothelial function after stretch injury (subfailure stretch), treatment with acidic Normal Saline (NS), and P2X7R activation with 2′(3′)‐O‐(4‐Benzoylbenzoyl)adenosine 5′‐triphosphate (BzATP). Aged, diseased, human saphenous vein (HSV) remnants obtained from patients undergoing coronary bypass surgical procedures have impaired endothelial function. Treatment of these HSV segments with NiPp improved endothelial‐dependent relaxation. Kinome screening experiments indicated that NiPp inhibits p38 MAPK. These data demonstrate that p38 MAPK and Niban signaling have a role in endothelial function, particularly in response to injury. Niban may represent an endogenous regulator of p38 MAPK activation. The NiPp peptide may serve as an experimental tool to further elucidate p38 MAPK regulation and as a potential therapeutic for endothelial dysfunction.

MYC and the unfolded protein response in cancer: synthetic lethal partners in crime?

The transcription factors of the MYC family play pivotal roles in the initiation and progression of human cancers. High oncogenic level of MYC invades low‐affinity sites and enhancer sequences, which subsequently alters the transcriptome, causes metabolic imbalance, and induces stress response. The endoplasmic reticulum (ER) not only plays a central role in maintaining proteostasis, but also contributes to other key biological processes, including Ca²⁺ metabolism and the synthesis of lipids and glucose. Stress conditions, such as shortage in glucose or oxygen and disruption of Ca²⁺ homeostasis, may perturb proteostasis and induce the unfolded protein response (UPR), which either restores homeostasis or triggers cell death. Crucial roles of ER stress and UPR signaling have been implicated in various cancers, from oncogenesis to treatment response. Here, we summarize the current knowledge on the interaction between MYC and UPR signaling, and its contribution to cancer development. We also discuss the potential of targeting key UPR signaling nodes as novel synthetic lethal strategies in MYC‐driven cancers.

Thapsigargin promotes colorectal cancer cell migration through upregulation of lncRNA MALAT1

Colorectal cancer (CRC) is the third most common tumor in the world; however, the role and mechanism of endoplasmic reticulum (ER) stress in CRC metastasis remains largely unclear. Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is a long non-coding RNA (lncRNA), which has previously been associated with CRC metastasis. It has been suggested that ER stress pathways regulate lncRNA expression; however, the effect of ER stress on MALAT1 expression in cancer is unknown. The present study aimed to investigate the relationship between ER stress pathways, MALAT1 expression and cell migration in CRC cells. ER stress was induced by thapsigargin (TG); low dose TG induced the migration of HT29 and HCT116 cells, but not SW1116 and SW620 cells. This effect was associated with increased expression levels of MALAT1, as the knockdown of MALAT1 prevented TG-induced cell migration. TG-induced MALAT1 expression was associated with inositol-requiring enzyme 1 (IRE1) expression and activation of the protein kinase R (PKR)-like ER kinase (PERK) signaling pathway. X-box-binding protein 1 (XBP1) and activating transcription factor 4 (ATF4) binding sites were predicted to be located in the MALAT1 gene promoter regions and the expression of MALAT1 was positively associated with XBP1 and ATF4 expression levels in CRC tissue samples. Thus, these findings indicated that ER stress may promote the migration of CRC cells and contribute to the progression of CRC through the activation of the IRE1/XBP1 and PERK/eIF2α/ATF4 signaling pathways. In conclusion, to the best of our knowledge, this study is the first report that lncRNA MALAT1 expression is regulated by the IRE1/XBP1 pathway in CRC.

Targeting the Unfolded Protein Response in Hormone-Regulated Cancers

Cancer cells exploit many of the cellular adaptive responses to support their survival needs. One of these is the unfolded protein response (UPR), a highly conserved signaling pathway that is mounted in response to endoplasmic reticulum (ER) stress. Recent work showed that steroid hormones, in particular estrogens and androgens, regulate the canonical UPR pathways in breast cancer (BCa) and prostate cancer (PCa). In addition, UPR has pleiotropic effects in advanced disease and development of therapy resistance. These findings implicate the UPR pathway as a novel target in hormonally regulated cancers in the clinic. Here, we review the potential therapeutic value of recently developed small molecule inhibitors of UPR in hormone regulated cancers.

Dual role of Endoplasmic Reticulum Stress-Mediated Unfolded Protein Response Signaling Pathway in Carcinogenesis

Cancer constitutes a grave problem nowadays in view of the fact that it has become one of the main causes of death worldwide. Poor clinical prognosis is presumably due to cancer cells metabolism as tumor microenvironment is affected by oxidative stress. This event triggers adequate cellular response and thereby creates appropriate conditions for further cancer progression. Endoplasmic reticulum (ER) stress occurs when the balance between an ability of the ER to fold and transfer proteins and the degradation of the misfolded ones become distorted. Since ER is an organelle relatively sensitive to oxidative damage, aforementioned conditions swiftly cause the activation of the unfolded protein response (UPR) signaling pathway. The output of the UPR, depending on numerous factors, may vary and switch between the pro-survival and the pro-apoptotic branch, and hence it displays opposing effects in deciding the fate of the cancer cell. The role of UPR-related proteins in tumorigenesis, such as binding the immunoglobulin protein (BiP) and inositol-requiring enzyme-1α (IRE1α), activating transcription factor 6 (ATF6) or the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), has already been specifically described so far. Nevertheless, due to the paradoxical outcomes of the UPR activation as well as gaps in current knowledge, it still needs to be further investigated. Herein we would like to elicit the actual link between neoplastic diseases and the UPR signaling pathway, considering its major branches and discussing its potential use in the development of a novel, anti-cancer, targeted therapy.