Gamma-Glutamylcyclotransferase: A Novel Target Molecule for Cancer Diagnosis and Treatment

Unbalanced redox status network as an early pathological event in congenital cataracts

The lens proteome undergoes dramatic composition changes during development and maturation. A defective developmental process leads to congenital cataracts that account for about 30% of cases of childhood blindness. Gene mutations are associated with approximately 50% of early-onset forms of lens opacity, with the remainder being of unknown etiology. To gain a better understanding of cataractogenesis, we utilized a transgenic mouse model expressing a mutant ubiquitin protein in the lens (K6W-Ub) that recapitulates most of the early pathological changes seen in human congenital cataracts. We performed mass spectrometry-based tandem-mass-tag quantitative proteomics in E15, P1, and P30 control or K6W-Ub lenses. Our analysis identified targets that are required for early normal differentiation steps and altered in cataractous lenses, particularly metabolic pathways involving glutathione and amino acids. Computational molecular phenotyping revealed that glutathione and taurine were spatially altered in the K6W-Ub cataractous lens. High-performance liquid chromatography revealed that both taurine and the ratio of reduced glutathione to oxidized glutathione, two indicators of redox status, were differentially compromised in lens biology. In sum, our research documents that dynamic proteome changes in a mouse model of congenital cataracts impact redox biology in lens. Our findings shed light on the molecular mechanisms associated with congenital cataracts and point out that unbalanced redox status due to reduced levels of taurine and glutathione, metabolites already linked to age-related cataract, could be a major underlying mechanism behind lens opacities that appear early in life.

Development of a thyroid cancer prognostic model based on the mitophagy-associated differentially expressed genes

BACKGROUND

The prevalence of thyroid cancer (ThyC), a frequent malignant tumor of the endocrine system, has been rapidly increasing over time. The mitophagy pathway is reported to play a critical role in ThyC onset and progression in many studies. This research aims to create a mitophagy-related survival prediction model for ThyC patients.

METHODS

Genes connected to mitophagy were found in the GeneCards database. The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases provided information on the expression patterns of ThyC-related genes. To identify differentially expressed genes (DEGs), R software was employed. The prognostic significance of each DEG was assessed using the prognostic K-M curve. The prognostic model was built using LASSO, ROC, univariate, and multivariate Cox regression analyses. Finally, a nomogram model was developed to predict the survival outcome of ThyC patients in the clinical setting.

RESULTS

Through differential analysis, functional enrichment analysis, and protein-protein interaction (PPI) network analysis, we screened 10 key genes related to mitophagy in ThyC. The risk model was eventually developed using LASSO and Cox regression analyses based on the six DEGs related to mitophagy. An altered expression level of a mitophagy-related prognostic gene, GGCT, was found to be the most significant one, according to the KM survival curve analysis. An immunohistochemical (IHC) investigation revealed that ThyC tissues expressed higher levels of GGCT than normal thyroid tissues. The ROC curve verified the satisfactory performance of the model in survival prediction. Multivariate Cox regression analysis showed that the pathological grade, residual tumor volume, and initial tumor lesion type were significantly linked to the prognosis. Finally, we created a nomogram to predict the overall survival rate of ThyC patients at 3-, 5-, and 7- year time points.

CONCLUSION

The nomogram risk prediction model was developed to precisely predict the survival rate of ThyC patients. The model was validated based on the most significant DEG GGCT gene expression in ThyC. This model may serve as a guide for the creation of precise treatment plans for ThyC patients.

Biocomputational characterisation of MBO_200107 protein of Mycobacterium tuberculosis variant caprae: a molecular docking and simulation study

The principal objective of this study was to delineate the potentiality of the MBO_200107 protein from the Mycobacterium tuberculosis variant caprae in cancer research. It is a cytoplasmic protein, comprised of a 354-long amino acid chain, alkaline, had a molecular weight of 39089.37 Da, an isoelectric point of 9.62 and a grand average of hydropathicity of -0.345. One of the functional domains was predicted as Gammaglutamylcyclotransferase (GGCT). Among tertiary structures, the Modeller and Phyre2 model satisfied all the quality parameters, though they are truncated; contrarily, the I-TASSER model is full length and contains the sequence for the GGCT domain, though it did not meet all the quality parameters. It also has significant sequence similarities (47.5% by EMBOSS Water and 72.4% by EMBOSS Matcher) with a human GGCT, and the conserved sequences are confined to the GGCT domain of the MBO_200107. According to molecular docking analyses, the protein has a binding affinity of -4.8 kcal/mol by Autodock Vina and -56.465 kcal/mol by HPEPDOCK to the human glutathione (GSH), an essential metabolite for GGCT metabolism. The Molecular dynamic simulation of the docked complex showed the binding efficiency of the GSH to MBO_200107 with a minimal structural alteration. The in silico findings mentioned above revealed that the protein could be used as a supplementary tool in cancer research, such as designing vaccines or drugs where the role of GGCT has been implicated. Further, we recommend fully characterising the protein and conducting essential in vitro and in vivo experiments to determine its detailed usefulness.Communicated by Ramaswamy H. Sarma.

Identification of c-Met as a novel target of γ-glutamylcyclotransferase

γ-Glutamylcyclotransferase (GGCT) is highly expressed in multiple types of cancer tissues and its knockdown suppresses the growth of cancer cells in vitro and in vivo. Although GGCT is a promising target for cancer therapy, the mechanisms underlying the antitumor effects remain unclear. The knockdown of GGCT inhibited the MEK-ERK pathway, and activated the tumor suppressor retinoblastoma gene (RB) at the protein level in cancer cell lines. c-Met was down-regulated by the knockdown of GGCT in cancer cells and its overexpression attenuated the dephosphorylation of RB and cell cycle arrest induced by the knockdown of GGCT in lung cancer A549 cells. STAT3 is a transcription factor that induces c-Met expression. STAT3 phosphorylation and its nuclear expression level were decreased in GGCT-depleted A549 and prostate cancer PC3 cells. The simultaneous knockdown of AMPK and GGCT restored the down-regulated expression of c-Met, and attenuated the dephosphorylation of STAT3 and MEK-ERK-RB induced by the knockdown of GGCT in PC3 cells. An intraperitoneal injection of a GGCT inhibitor decreased c-Met protein expression in a mouse xenograft model of PC3 cells. These results suggest that the knockdown of GGCT activates the RB protein by inhibiting the STAT3-c-Met-MEK-ERK pathway via AMPK activation.

Anti-proliferative effect and underlying mechanism of ethoxy-substituted phylloquinone (vitamin K1 derivative) from Spinacia oleracea leaf and enhancement of its extractability using radiation technology

In our previous studies, a novel antimutagenic compound, 2-ethoxy-3-(3,7,11,15-tetramethylhexadec-2-ethyl) naphthaquinone-1,4-dione (ethoxy-substituted phylloquinone; ESP) from spinach was characterized and mechanism contributing to its antimutagenicity was deduced. In the current study, anti-proliferative activity of ESP was assessed in lung cancer (A549) cells using MTT [3-(4,5-dimethylthiazole-2yl)-2,5-diphenyl tetrazolium bromide], clonogenic assays and cell cycle analysis. ESP treatment showed selective cytotoxicity against lung cancer cells and no cytotoxicity in normal lung (WI38) cells. Cell cycle analysis revealed that ESP treatment arrests A549 cell population in G2-M phase. In-silico analysis indicated positive drug-likeness features of ESP. Molecular docking showed H-bonding and hydrophobic interactions between ESP and B-DNA dodecamer residues at minor groove. SWATH-MS (Sequential Window Acquisition of All Theoretical Mass Spectra) based proteomic analysis indicated down-regulation of proteins involved in EGFR signaling, NEDDylation and other metabolic pathways and up-regulation of tumor suppressor (STAT1 and NDRG1) proteins. Treatment of spinach powder with gamma radiation (5-20 kGy) from cobalt (Co-60) enhanced the extractability of ESP up to 4.4-fold at the highest dose of 20 kGy. Scanning electron microscopy of spinach powder displayed decrease in smoothness and compactness with increase in radiation dose attributing to its enhanced extractability. Increase in the extractability of ESP with increasing radiation doses as measured by fluorescence intensity and dry weight basis was strongly correlated. Nonetheless, radiation treatment did not affect the functionality of ESP in terms of anti-proliferative and antimutagenic activities. Current findings thus highlight broad spectrum bioactivity of ESP from spinach, its underlying mechanism and applicability of radiation technology in enhancing extractability.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03264-6.

Polystyrene nanoplastics induce profound metabolic shift in human cells as revealed by integrated proteomic and metabolomic analysis

Nanoplastics (NPLs) are widespread in our environment. However, their impacts on human health and precise toxicity mechanisms remain poorly understood. Here we studied the internalization, release, and cytotoxicity of polystyrene nanoplastics (PSNPs) using the renal tubular epithelial cell line HKC and human derived liver cell line HL-7702. We also employed an integrated proteomic and metabolomic approach to investigate the potential biological effects of PSNPs on HKC cells. The abundances of 4770 proteins and 100 metabolites were quantified, with 785 proteins and 17 metabolites detected with altered levels in response to PSNPs. Most of the differential proteins and metabolites were enriched in a variety of metabolic pathways, for example, glycolysis, citrate cycle, oxidative phosphorylation, and amino acid metabolism, suggesting the potential effects of NPLs on global cellular metabolism shift in human cells. The altered energy metabolism induced by PSNPs was further confirmed by a Seahorse analysis. Moreover, lysosomal distribution study and western blotting showed that mTORC1 signaling, a central regulator of cellular metabolism, was inhibited upon nanoplastic exposure, likely serving as the link between lysosome dysfunction and metabolic defects. Taken together, our findings systematically mapped the key molecular changes induced by PSNPs in human cells and provide comprehensive biological insights for the risk estimation of NPLs contamination.

miR-877 inhibits the proliferation, migration, and invasion of osteosarcoma cells by targeting gamma-glutamylcyclotransferase

Gamma-glutamylcyclotransferase (GGCT) can promote the progression of osteosarcoma (OS). MicroRNAs also play significant roles in regulating the progression of OS. This study was designed to investigate whether miR-877 exerts its function in OS by targeting GGCT. The proliferation of OS cells (Saos-2 and U2OS) was detected by MTT and colony formation assays. The migration and invasion of OS cells were detected by transwell assays. The expressions of miRNAs and GGCT were detected by quantitative real-time PCR and Western blot. The luciferase reporter assay was performed to assess whether miR-877 could target GGCT. miR-877 was down-regulated both in OS tissues and OS cell lines (Saos-2 and U2OS). The overexpression of miR-877 inhibited the proliferation, migration, and invasion of OS cell lines, while the knockdown of miR-877 could negate effects. The expression of GGCT was increased in Saos-2 and U2OS cells. miR-877 could target GGCT, and the mRNA level of GGCT in Saos-2 and U2OS cells was decreased by the overexpression of miR-877. miR-877 overexpression inhibited the migration and invasion and suppressed the proliferation of Saos-2 and U2OS cells, and the overexpression of GGCT reversed this effects. The knockdown of miR-877 promoted the migration and invasion and facilitated the proliferation of Saos-2 and U2OS cells, and the silence of GGCT abolished this effects. Our findings suggested that miR-877 could inhibit the proliferation, migration, and invasion of OS cells by targeting GGCT.

γ-Glutamylcyclotransferase, a novel regulator of HIF-1α expression, triggers aerobic glycolysis

Metabolic reprogramming leading to aerobic glycolysis, termed the "Warburg effect," is a critical property of cancer cells. However, the precise mechanisms underlying this phenomenon are not fully understood. A growing body of evidence indicates that γ-glutamylcyclotransferase (GGCT), an enzyme involved in glutathione homeostasis that is highly expressed in many types of cancer, represents a promising therapeutic target. In this study, we identified GGCT as a novel regulator of hypoxia-inducible factor-1α (HIF-1α), a transcription factor that plays a role in hypoxia adaptation promoting aerobic glycolysis. In multiple human cancer cell lines, depletion of GGCT downregulated HIF-1α at the mRNA and protein levels. Conversely, in NIH3T3 mouse fibroblasts, overexpression of GGCT upregulated HIF-1α under normoxia. Moreover, depletion of GGCT downregulated HIF-1α downstream target genes involved in glycolysis, whereas overexpression of GGCT upregulated those genes. Metabolomic analysis revealed that modulation of GGCT expression induced a metabolic switch from the citric acid cycle to glycolysis under normoxia. In addition, we found that GGCT regulates expression of HIF-1α protein via the AMPK-mTORC1-4E-BP1 pathway in PC3 cells. Thus GGCT regulates the expression of HIF-1α in cancer cells, causing a switch to glycolysis.

GGCT promotes colorectal cancer migration and invasion via epithelial-mesenchymal transition

Colorectal cancer (CRC) is one of the most common malignancies, and the fourth most common cause of cancer-associated mortality globally. The epithelial to mesenchymal transition (EMT) serves an important function in metastatic dissemination and determines the aggressiveness of CRC. However, the regulatory mechanism of EMT in CRC has not yet been elucidated. γ-glutamylcyclotransferase (GGCT) is an important enzyme in glutathione metabolism and highly expressed in numerous forms of cancer, making it a promising therapeutic target. In the present study, GGCT was demonstrated to be highly expressed in CRC tissues, and patients with CRC with a higher expression of GGCT exhibited a worse prognosis compared with patients exhibiting a lower expression of GGCT. This result suggests that GGCT may serve as a novel prognostic marker for CRC. Furthermore, GGCT was indicated to promote CRC cell migration and invasion through regulating EMT-associated genes, including N-cadherin, Vimentin, snail family transcriptional repressor 2 and snail family transcriptional repressor 1. In conclusion, the present study provides novel insights into the mechanism governing CRC migration and invasion, and identified GGCT as a promising therapeutic target that may be used in the treatment of CRC.

Ras Downstream Effector GGCT Alleviates Oncogenic Stress

How cells adapt to oncogenic transformation-associated cellular stress and become fully transformed is still unknown. Here we identified a novel GGCT-regulated glutathione (GSH)-reactive oxygen species (ROS) metabolic pathway in oncogenic stress alleviation. We identified GGCT as a target of oncogenic Ras and that it is required for oncogenic Ras-induced primary mouse cell proliferation and transformation and in vivo lung cancer formation in the LSL-Kras G12D mouse model. However, GGCT deficiency is compatible with normal mouse development, suggesting that GGCT can be a cancer-specific therapeutic target. Genetically amplified GGCT locus further supports the oncogenic driving function of GGCT. In summary, our study not only identifies an oncogenic function of GGCT but also identifies a novel regulator of GSH metabolism, with implications for further understanding of oncogenic stress and cancer treatment.

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GGCT is a target of Ras and is required for Ras-induced cancer formation

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GGCT deletion is compatible with normal mouse development and tissue function

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GGCT genomic locus is amplified in multiple human cancer types

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GGCT could alleviate oncogenic stress by regulating GSH-ROS metabolism

iTRAQ-Based Quantitative Proteomics Approach Identifies Novel Diagnostic Biomarkers That Were Essential for Glutamine Metabolism and Redox Homeostasis for Gastric Cancer

PURPOSE

To screen the novel biomarkers for gastric cancer and to determine the values of glutaminase 1 (GLS1) and gamma-glutamylcyclotransferase (GGCT) for detecting gastric cancer.

EXPERIMENTAL DESIGN

A discovery group of four paired gastric cancer tissue samples are labeled with Isobaric tag for relative and absolute quantitation agents and identified with LC-ESI-MS/MS. A validation group of 168 gastric cancer samples and 30 healthy controls are used to validate the expression of GLS1 and GGCT.

RESULTS

Four hundred and thirty-one proteins are found differentially expressed in gastric cancer tissues. Of these proteins, GLS1 and GGCT are found overexpressed in gastric cancer patients, with sensitivity of 75.6% (95% CI: 69-82.2%) and specificity of 81% (95% CI: 75-87%) for GLS1, and with sensitivity of 63.1% (95% CI: 55.7-71.5%) and specificity of 60.7% (95% CI: 53.3-68.2%) for GGCT. The co-expression of GLS1 and GGCT in gastric cancer tissues has sensitivity of 78.1% (95% CI: 70.1-86.1%) and specificity of 86.5% (95% CI: 79.5-93.4%). Moreover, both GLS1 and GGCT present higher expression of 82.6% (95% CI: 68.5-99.4%) and 73.9% (95% CI: 54.5-93.3%) in lymph node metastasis specimen than those in non-lymph node metastasis specimen. The areas under ROC curves are up to 0.734 for the co-expression of GLS1 and GGCT in gastric cancer. The co-expression of GLS1 and GGCT is strongly associated with histological grade, lymph node metastasis, and TNM stage Ⅲ/Ⅳ.

CONCLUSIONS AND CLINICAL RELEVANCE

The present study provides the quantitative proteomic analysis of gastric cancer tissues to identify prognostic biomarkers of gastric cancer. The co-expression level of GLS1 and GGCT is of great clinical value to serve as diagnostic and therapeutic biomarkers for early gastric cancer.

Mechanisms of Tumor Growth Inhibition by Depletion of γ-Glutamylcyclotransferase (GGCT): A Novel Molecular Target for Anticancer Therapy

γ-Glutamylcyclotransferase (GGCT), which is one of the major enzymes involved in glutathione metabolism, is upregulated in a wide range of cancers—glioma, breast, lung, esophageal, gastric, colorectal, urinary bladder, prostate, cervical, ovarian cancers and osteosarcoma—and promotes cancer progression; its depletion leads to the suppression of proliferation, invasion, and migration of cancer cells. It has been demonstrated that the suppression or inhibition of GGCT has an antitumor effect in cancer-bearing xenograft mice. Based on these observations, GGCT is now recognized as a promising therapeutic target in various cancers. This review summarizes recent advances on the mechanisms of the antitumor activity of GGCT inhibition.

Depletion of gamma-glutamylcyclotransferase in cancer cells induces autophagy followed by cellular senescence

Gamma-glutamylcyclotransferase (GGCT) was originally identified as a protein highly expressed in bladder cancer tissues by proteomic analysis, and its higher expression in a variety of cancers compared to normal tissues have been shown. Depletion of GGCT in various cancer cells results in antiproliferative effects both in vitro and in vivo; thus it is considered a promising therapeutic target. Although it has been shown that knockdown of GGCT induces cellular senescence and non-apoptotic cell death, associated with upregulation of cyclin-dependent kinase inhibitors (CDKIs) including p21^WAF1/CIP1, the cellular events that follow GGCT depletion are not fully understood. Here, we show that GGCT depletion induced autophagy in MCF7 breast and PC3 prostate cancer cells. Conversely, overexpression of GGCT in NIH3T3 fibroblast under conditions of serum deprivation inhibited autophagy and increased proliferation. Simultaneous knockdown of autophagy related-protein 5, a critical effector of autophagy, along with GGCT in MCF7 and PC3 cells led to significant attenuation of the multiple cellular responses, including upregulation of CDKIs, increased numbers of senescence-associated β-galactosidase positive senescent cells, and growth inhibition. Furthermore, we show that autophagy-promoting signaling cascades including activation of the AMPK-ULK1 pathway and/or inactivation of the mTORC2-Akt pathway were triggered in GGCT-depleted cells. These results indicate that autophagy plays an important role in the growth inhibition of cancer cells caused by GGCT depletion.

A Novel Prodrug of a γ-Glutamylcyclotransferase Inhibitor Suppresses Cancer Cell Proliferation in vitro and Inhibits Tumor Growth in a Xenograft Mouse Model of Prostate Cancer

γ-Glutamylcyclotransferase (GGCT) depletion inhibits cancer cell proliferation. However, whether the enzymatic activity of GGCT is critical for the regulation of cancer cell growth remains unclear. In this study, a novel diester-type cell-permeable prodrug, pro-GA, was developed based on the structure of N-glutaryl-l-alanine (GA), by structure optimization using temporary fluorophore-tagged prodrug candidates. The antiproliferative activity of pro-GA was demonstrated using GGCT-overexpressing NIH-3T3 cells and human cancer cells including MCF7, HL-60, and PC3 cells. By contrast, normal cells were not significantly affected by pro-GA treatment. Moreover, pro-GA administration exhibited anticancer effects in a xenograft model using immunocompromised mice inoculated with PC3 cells. These results indicate that the enzymatic activity of GGCT accelerates tumor growth and that GGCT inhibition is a promising therapeutic strategy for the treatment of GGCT-overexpressing tumors.

Prohibitin-2 is a novel regulator of p21WAF1/CIP1 induced by depletion of γ-glutamylcyclotransferase

Previous studies show that gamma-glutamylcyclotransferase (GGCT) is expressed at high levels in various cancer tissues and that its knockdown inhibits MCF7 cancer cell growth via upregulation of p21^WAF1/CIP1 (p21). However, the detailed underlying mechanism is unclear. Here, we used yeast two-hybrid screening and co-immunoprecipitation to identify Prohibitin-2 (PHB2) as a novel protein that interacts with GGCT. We also show that nuclear expression of PHB2 in MCF7 cells falls upon GGCT knockdown, and that overexpression of PHB2 inhibits p21 upregulation. A chromatin immunoprecipitation assay revealed that nuclear PHB2 proteins bind to the p21 promoter, and that this interaction is abrogated by GGCT knockdown. Moreover, knockdown of PHB2 alone led to significant upregulation of p21 and mimicked the cellular events induced by GGCT depletion, including G0/G1 arrest, cellular senescence, and growth inhibition, in a p21 induction-dependent manner. Taken together, the results indicate that PHB2 plays a central role in p21 upregulation following GGCT knockdown and as such may promote deregulated proliferation of cancer cells by suppressing p21.

DHEA supplementation to dexamethasone-treated rabbits alleviates oxidative stress in kidney-cortex and attenuates albuminuria

Our recent study has shown that dehydroepiandrosterone (DHEA) administered to rabbits partially ameliorated several dexamethasone (dexP) effects on hepatic and renal gluconeogenesis, insulin resistance and plasma lipid disorders. In the current investigation, we present the data on DHEA protective action against dexP-induced oxidative stress and albuminuria in rabbits. Four groups of adult male rabbits were used in the in vivo experiment: (1) control, (2) dexP-treated, (3) DHEA-treated and (4) both dexP- and DHEA-treated. Administration of dexP resulted in accelerated generation of renal hydroxyl free radicals (HFR) and malondialdehyde (MDA), accompanied by diminished superoxide dismutase (SOD) and catalase activities and a dramatic rise in urinary albumin/creatinine ratio. Treatment with DHEA markedly reduced dexP-induced oxidative stress in kidney-cortex due to a decline in NADPH oxidase activity and enhancement of catalase activity. Moreover, DHEA effectively attenuated dexP-evoked albuminuria. Surprisingly, dexP-treated rabbits exhibited elevation of GSH/GSSG ratio, accompanied by a decrease in glutathione peroxidase (GPx) and glutathione-S-transferase (GST) activities as well as an increase in glucose-6-phosphate dehydrogenase (G6PDH) activity. Treatment with DHEA resulted in a decline in GSH/GSSG ratio and glutathione reductase (GR) activity, accompanied by an elevation of GPx activity. Interestingly, rabbits treated with both dexP and DHEA remained the control values of GSH/GSSG ratio. As the co-administration of DHEA with dexP resulted in (i) reduction of oxidative stress in kidney-cortex, (ii) attenuation of albuminuria and (iii) normalization of glutathione redox state, DHEA might limit several undesirable renal side effects during chronic GC treatment of patients suffering from allergies, asthma, rheumatoid arthritis and lupus. Moreover, its supplementation might be particularly beneficial for the therapy of patients with glucocorticoid-induced diabetes.

Depletion of γ-glutamylcyclotransferase inhibits breast cancer cell growth via cellular senescence induction mediated by CDK inhibitor upregulation

BACKGROUND

Chromosome 7 open reading frame 24 (C7orf24) was originally identified as a highly expressed protein in various types of cancer, and later shown to be a γ-glutamylcyclotransferase (GGCT). GGCT depletion in cancer cells has anti-proliferative effects in vitro and in vivo, and it is therefore considered a promising candidate as a therapeutic target. However, the cellular events induced by GGCT depletion remain unclear.

METHODS

GGCT was depleted by siRNA in MCF7, MDA-MB-231, PC3, A172, Hela, and LNCaP cells. Induction of cellular senescence was evaluated with senescence-associated β-galactosidase (SA-β-Gal) staining. Expression levels of p21^WAF1/CIP1 and p16^INK4A were assessed by qRT-PCR and Western blotting. Effects of simultaneous double knockdown of p21^WAF1/CIP1 and p16^INK4A together with GGCT on cell cycle regulation and cell growth was measured by flow cytometry, and trypan blue dye exclusion test.

RESULTS

We found that GGCT knockdown induces significant cellular senescence in various cancer cells. Cyclin dependent kinase inhibitor p21^WAF1/CIP1 and/or p16^INK4A were upregulated in all cell lines tested. Simultaneous knockdown of p21^WAF1/CIP1 recovered the cell cycle arrest, attenuated cellular senescence induction, and rescued the subsequent growth inhibition in GGCT-silenced MCF7 breast cancer cells. In contrast, in GGCT silenced MDA-MB-231 breast cancer cells, GGCT depletion upregulated p16^INK4A, which played a regulatory role in senescence induction, instead of p21^WAF1/CIP1.

CONCLUSIONS

Our findings demonstrate that induction of cellular senescence mediated by the upregulation of cyclin-dependent kinase inhibitors is a major event underlying the anti-proliferative effect of GGCT depletion in breast cancer cells, highlighting the potential of GGCT blockade as a therapeutic strategy to induce cellular senescence.

Transcriptome profile of the early stages of breast cancer tumoral spheroids

Oxygen or nutrient deprivation of early stage tumoral spheroids can be used to reliably mimic the initial growth of primary and metastatic cancer cells. However, cancer cell growth during the initial stages has not been fully explored using a genome-wide approach. Thus, in the present study, we investigated the transcriptome of breast cancer cells during the initial stages of tumoral growth using RNAseq in a model of Multicellular Tumor Spheroids (MTS). Network analyses showed that a metastatic signature was enriched as several adhesion molecules were deregulated, including EPCAM, E-cadherin, integrins and syndecans, which were further supported by an increase in cell migration. Interestingly, we also found that the cancer cells at this stage of growth exhibited a paradoxical hyperactivation of oxidative mitochondrial metabolism. In addition, we found a large number of regulated (long non coding RNA) lncRNAs, several of which were co-regulated with neighboring genes. The regulatory role of some of these lncRNAs on mRNA expression was demonstrated with gain of function assays. This is the first report of an early-stage MTS transcriptome, which not only reveals a complex expression landscape, but points toward an important contribution of long non-coding RNAs in the final phenotype of three-dimensional cellular models.