Apoptosis, a Metabolic "Head-to-Head" between Tumor and T Cells: Implications for Immunotherapy.

Induction of apoptosis represents a promising therapeutic approach to drive tumor cells to death. However, this poses challenges due to the intricate nature of cancer biology and the mechanisms employed by cancer cells to survive and escape immune surveillance. Furthermore, molecules released from apoptotic cells and phagocytes in the tumor microenvironment (TME) can facilitate cancer progression and immune evasion. Apoptosis is also a pivotal mechanism in modulating the strength and duration of anti-tumor T-cell responses. Combined strategies including molecular targeting of apoptosis, promoting immunogenic cell death, modulating immunosuppressive cells, and affecting energy pathways can potentially overcome resistance and enhance therapeutic outcomes. Thus, an effective approach for targeting apoptosis within the TME should delicately balance the selective induction of apoptosis in tumor cells, while safeguarding survival, metabolic changes, and functionality of T cells targeting crucial molecular pathways involved in T-cell apoptosis regulation. Enhancing the persistence and effectiveness of T cells may bolster a more resilient and enduring anti-tumor immune response, ultimately advancing therapeutic outcomes in cancer treatment. This review delves into the pivotal topics of this multifaceted issue and suggests drugs and druggable targets for possible combined therapies.

State-of-the-art in transposable element modulation affected by drugs in malignant prostatic cancer cells.

Over recent years, the investigation of transposable elements (TEs) has granted researchers a deeper comprehension of their characteristics and functions, particularly regarding their significance in the mechanisms contributing to cancer development. This manuscript focuses on prostate carcinoma cell lines and offers a comprehensive review intended to scrutinize the associations and interactions between TEs and genes, as well as their response to treatment using various chemical drugs, emphasizing their involvement in cancer progression. We assembled a compendium of articles retrieved from the PubMed database to construct networks demonstrating correlations with genes and pharmaceuticals. In doing so, we linked the transposition of certain TE types to the expression of specific transcripts directly implicated in carcinogenesis. Additionally, we underline that treatment employing different drugs revealed unique patterns of TE reactivation. Our hypothesis gathers the current understanding and guides research toward evidence-based investigations, emphasizing the association between antiviral drugs, chemotherapy, and the reduced expression of TEs in patients affected by prostate cancer.

Metabolic characterisation of transglutaminase 2 inhibitor effects in breast cancer cell lines.

Transglutaminase 2 (TG2), which mediates post-translational modifications of multiple intracellular enzymes, is involved in the pathogenesis and progression of cancer. We used 1 H-NMR metabolomics to study the effects of AA9, a novel TG2 inhibitor, on two breast cancer cell lines with distinct phenotypes, MCF-7 and MDA-MB-231. AA9 can promote apoptosis in both cell lines, but it is particularly effective in MD-MB-231, inhibiting transamidation reactions and decreasing cell migration and invasiveness. This metabolomics study provides evidence of a major effect of AA9 on MDA-MB-231 cells, impacting glutamate and aspartate metabolism, rather than on MCF-7 cells, characterised by choline and O-phosphocholine decrease. Interestingly, AA9 treatment induces myo-inositol alteration in both cell lines, indicating action on phosphatidylinositol metabolism, likely modulated by the G protein activity of TG2 on phospholipase C. Considering the metabolic deregulations that characterise various breast cancer subtypes, the existence of a metabolic pathway affected by AA9 further points to TG2 as a promising hot spot. The metabolomics approach provides a powerful tool to monitor the effectiveness of inhibitors and better understand the role of TG2 in cancer.

Somatic and Germline Variants Affect Prognosis and Susceptibility in Prostate Cancer.

BACKGROUND/AIM: Prostate cancer (PCa) is one of the most common tumors in men accounting for the 7.3% of all cancer-associated diseases in 2020. In advanced stage, this pathology is a lethal disease and is the fifth cause of cancer death in men worldwide. The diagnosis of PCa is performed by prostate-specific antigen (PSA) detection combined with direct rectal examination (DRE). However, high PSA levels can be detected in non-malignant conditions leading to overtreatment of non-oncological patients. Moreover, PSA levels are not associated with disease progression; therefore, the research of novel biomarkers could improve diagnosis and prognosis of this tumor. In this regard, genetic polymorphisms may affect PCa outcome as well as to be associated with cancer familiarity. In fact, germline variations detected in different genes including BRCA1, BRCA2, ATM and HOXB13 seem to be associated with PCa susceptibility and progression. MATERIALS AND METHODS: Somatic and germline polymorphisms were detected by next generation sequencing (NGS) in 48 PCa subjects and paired controls. Gene variants were matched with patient outcome and cancer familiarity to identify mutations linked to prognosis and tumor predisposition. RESULTS: NGS sequencing has allowed to identify different genetic polymorphisms that could be linked to cancer outcome and predisposition. In particular, somatic and germline mutations found in ATM, FOXA1 and SPOP genes correlate with poor prognosis and/or high Gleason score. Moreover, germline variants lying mainly in ATM, but also in ZFHX3, SPOP, CHD1, CDK12 and APC seem to be associated with hereditary-predisposing cancer syndrome. CONCLUSION: Variants correlating with poor prognosis and cancer susceptibility could be usable as possible tumor biomarkers in prostate cancer.

The Role of Genetic Polymorphisms in the Diagnosis and Management of Prostate Cancer: An Update.

Prostate cancer (PCa) is the most common non-cutaneous tumor among men worldwide and, if diagnosed late, it exhibits a high mortality representing the sixth most lethal tumor in men. The main method to detect PCa is the prostate-specific antigen (PSA) level followed by direct rectal examination (DRE). Unfortunately, the PSA test has limited accuracy, as it does not provide information on disease outcome leading to the overtreatment of benign tumors. Thus, PSA analysis does not allow for stratifying PCa patients in high or low risk groups for disease recurrence or distant metastasis. Currently, the detection of several genetic markers might improve the risk stratification, addressing patients with PCa to the best therapeutic option. Here we describe the current clinical practice for PCa patients, the possible genetic polymorphisms associated with diagnosis, prognosis and therapy response as well as variants linked to familial PCa. The use of genetic markers could be routinely introduced in clinical practice leading to improvements in the management of PCa.

The inhibition of MDM2 slows cell proliferation and activates apoptosis in ADPKD cell lines.

INTRODUCTION: Autosomal dominant polycystic kidney disease (ADPKD) is characterised by progressive cysts formation and renal enlargement that in most of cases leads to end stage of renal disease (ESRD). This pathology is caused by mutations of either PKD1 or PKD2 genes that encode for polycystin-1 (PC1) and polycystin-2 (PC2), respectively. These proteins function as receptor-channel complex able to regulate calcium homeostasis. PKD1/2 loss of function impairs different signalling pathways including cAMP and mTOR that are considered therapeutic targets for this disease. In fact, Tolvaptan, a vasopressin-2 antagonist that reduces cAMP levels, is the only drug approved for ADPKD treatment. Nevertheless, some ADPKD patients developed side effects in response to Tolvaptan including liver damage. Conversely, mTOR inhibitors that induced disease regression in ADPKD animal models failed the clinical trials. RESULTS: Here, we show that the inhibition of mTOR causes the activation of autophagy in ADPKD cells that could reduce therapy effectiveness by drug degradation through the autophagic vesicles. Consistently, the combined treatment with rapamycin and chloroquine, an autophagy inhibitor, potentiates the decrease of cell proliferation induced by rapamycin. To overcome the dangerous activation of autophagy by mTOR inhibition, we targeted MDM2 (a downstream effector of mTOR signalling) that is involved in TP53 degradation by using RG7112, a small-molecule MDM2 inhibitor used for the treatment of haematologic malignancies. The inhibition of MDM2 by RG7112 prevents TP53 degradation and increases p21 expression leading to the decrease of cell proliferation and the activation of apoptosis. CONCLUSION: The targeting of MDM2 by RG7112 might represent a new therapeutic option for the treatment of ADPKD.

New Therapeutic Interventions for Kidney Carcinoma: Looking to the Future.

Patients suffering from metastatic renal cell carcinoma (mRCC) show an overall survival rate of lower than 10% after 5 years from diagnosis. Currently, the first-line treatment for mRCC patients is based on antiangiogenic drugs that are able to inhibit tyrosine kinase receptors (TKI) in combination with immuno-oncology (IO) therapy or IO-IO treatments. Second-line therapy involves the use of other TKIs, immunotherapeutic drugs, and mTOR inhibitors. Nevertheless, many patients treated with mTOR and TK inhibitors acquire drug resistance, making the therapy ineffective. Therefore, the research of new therapeutic targets is crucial for improving the overall survival and quality of life of mRCC patients. The investigation of the molecular basis of RCC, especially in clear cell renal cell carcinoma (ccRCC), has led to the identification of different signaling pathways that are involved in renal carcinogenesis. Most of ccRCCs are associated with mutation in VHL gene, which mediates the degradation of hypoxia-inducible factors (HIFs), that, in turn, regulate the pathways related to tumorigenesis, including angiogenesis and invasion. Renal tumorigenesis is also associated with the activation of tyrosine kinases that modulate the PI3K-Akt-mTOR pathway, promoting cell proliferation and survival. In ccRCC, the abnormal activity of mTOR activates the MDM2 protein, which leads to the degradation of tumor suppressor p53 via proteasome machinery. In addition, p53 may be degraded by autophagy in a mechanism involving the enzyme transglutaminase 2 (TG2). Suppression of wild-type p53 promotes cell growth, invasion, and drug resistance. Finally, the activation of ferroptosis appears to inhibit cancer progression in RCC. In conclusion, these pathways might represent new therapeutic targets for mRCC.

Detection of disease-causing mutations in prostate cancer by NGS sequencing.

Gene mutations may affect the fate of many tumors including prostate cancer (PCa); therefore, the research of specific mutations associated with tumor outcomes might help the urologist to identify the best therapy for PCa patients such as surgical resection, adjuvant therapy or active surveillance. Genomic DNA (gDNA) was extracted from 48 paraffin-embedded PCa samples and normal paired tissues. Next, gDNA was amplified and analyzed by next-generation sequencing (NGS) using a specific gene panel for PCa. Raw data were refined to exclude false-positive mutations; thus, variants with coverage and frequency lower than 100× and 5%, respectively were removed. Mutation significance was processed by Genomic Evolutionary Rate Profiling, ClinVar, and Varsome tools. Most of 3000 mutations (80%) were single nucleotide variants and the remaining 20% indels. After raw data elaboration, 312 variants were selected. Most mutated genes were KMT2D (26.45%), FOXA1 (16.13%), ATM (15.81%), ZFHX3 (9.35%), TP53 (8.06%), and APC (5.48%). Hot spot mutations in FOXA1, ATM, ZFHX3, SPOP, and MED12 were also found. Truncating mutations of ATM, lesions lying in hot spot regions of SPOP and FOXA1 as well as mutations of TP53 correlated with poor prognosis. Importantly, we have also found some germline mutations associated with hereditary cancer-predisposing syndrome. gDNA sequencing of 48 cancer tissues by NGS allowed to detect new tumor variants as well as confirmed lesions in genes linked to prostate cancer. Overall, somatic and germline mutations linked to good/poor prognosis could represent new prognostic tools to improve the management of PCa patients.

Dysregulation of Transglutaminase type 2 through GATA3 defines aggressiveness and Doxorubicin sensitivity in breast cancer.

The role of transglutaminase type 2 in cell physiology is related to protein transamidation and signal transduction (affecting extracellular, intracellular and nuclear processes) aided by the expression of truncated isoforms and of two lncRNAs with regulatory functions. In breast cancer TG2 is associated with disease progression supporting motility, epithelial-mesenchymal transition, invasion and drug resistance. The aim of his work is to clarify these issues by emphasizing the interconnections among TGM2 variants and transcription factors associated with an aggressive phenotype, in which the truncated TGH isoform correlates with malignancy. TGM2 transcripts are upregulated by several drugs in MCF-7, but only Doxorubicin is effective in MDA-MB-231 cells. These differences reflect the expression of GATA3, as demonstrated by silencing, suggesting a link between this transcription factor and gene dysregulation. Of note, NC9, an irreversible inhibitor of enzymatic TG2 activities, emerges to control NF-ĸB and apoptosis in breast cancer cell lines, showing potential for combination therapies with Doxorubicin.

The Motility and Mesenchymal Features of Breast Cancer Cells Correlate with the Levels and Intracellular Localization of Transglutaminase Type 2.

We have investigated motility in breast cancer cell lines in association with the expression of Transglutaminase type 2 (TG2) as well as upon the administration of Doxorubicin (Dox), an active cytotoxic agent that is employed in chemotherapy. The exposure of MCF-7 cells to the drug increased TG2 levels, triggering epithelial-mesenchymal transition (EMT), thereby supporting cell motility. The effects of Dox on the movement of MCF-7 cells were counteracted by treatment with NC9, a TG2 inhibitor, which induced morphological changes and also reduced the migration of MDA-MB-231 cells exhibiting high levels of TG2. The physical association of TG2 with the cytoskeletal component vimentin appeared pivotal both in drug-treated MCF-7 and in MDA-MB-231 cells and seemed to be independent of the catalytic activity of TG2. NC9 altered the subcellular distribution of TG2 and, consequently, the co-localization of TG2 with vimentin. Furthermore, NC9 induced a nuclear accumulation of TG2 as a prelude to TG2-dependent gene expression modifications. Since enzyme activity can affect both motility and nuclear functions, targeting of this protein could represent a method to improve therapeutic interventions in breast tumors, particularly those to control progression and to limit drug resistance.

Inhibition of the lncRNA Coded within Transglutaminase 2 Gene Impacts Several Relevant Networks in MCF-7 Breast Cancer Cells.

Long non-coding RNAs are nucleotide molecules that regulate transcription in numerous cellular processes and are related to the occurrence of many diseases, including cancer. In this regard, we recently discovered a polyadenylated long non-coding RNA (named TG2-lncRNA) encoded within the first intron of the Transglutaminase type 2 gene (TGM2), which is related to tumour proliferation in human cancer cell lines. To better characterize this new biological player, we investigated the effects of its suppression in MCF-7 breast cancer cells, using siRNA treatment and RNA-sequencing. In this way, we found modifications in several networks associated to biological functions relevant for tumorigenesis (apoptosis, chronic inflammation, angiogenesis, immunomodulation, cell mobility, and epithelial-mesenchymal transition) that were originally attributed only to Transglutaminase type 2 protein but that could be regulated also by TG2-lncRNA. Moreover, our experiments strongly suggest the ability of TG2-lncRNA to directly interact with important transcription factors, such as RXRα and TP53, paving the way for several regulatory loops that can potentially influence the phenotypic behaviour of MCF-7 cells. These considerations imply the need to further investigate the relative relevance of the TG2 protein itself and/or other gene products as key regulators in the organization of breast cancer program.

Mitochondrial Ca2+ Signaling in Health, Disease and Therapy.

The divalent cation calcium (Ca2+) is considered one of the main second messengers inside cells and acts as the most prominent signal in a plethora of biological processes. Its homeostasis is guaranteed by an intricate and complex system of channels, pumps, and exchangers. In this context, by regulating cellular Ca2+ levels, mitochondria control both the uptake and release of Ca2+. Therefore, at the mitochondrial level, Ca2+ plays a dual role, participating in both vital physiological processes (ATP production and regulation of mitochondrial metabolism) and pathophysiological processes (cell death, cancer progression and metastasis). Hence, it is not surprising that alterations in mitochondrial Ca2+ (mCa2+) pathways or mutations in Ca2+ transporters affect the activities and functions of the entire cell. Indeed, it is widely recognized that dysregulation of mCa2+ signaling leads to various pathological scenarios, including cancer, neurological defects and cardiovascular diseases (CVDs). This review summarizes the current knowledge on the regulation of mCa2+ homeostasis, the related mechanisms and the significance of this regulation in physiology and human diseases. We also highlight strategies aimed at remedying mCa2+ dysregulation as promising therapeutical approaches.

Mitochondria: Insights into Crucial Features to Overcome Cancer Chemoresistance.

Mitochondria are key regulators of cell survival and are involved in a plethora of mechanisms, such as metabolism, Ca2+ signaling, reactive oxygen species (ROS) production, mitophagy and mitochondrial transfer, fusion, and fission (known as mitochondrial dynamics). The tuning of these processes in pathophysiological conditions is fundamental to the balance between cell death and survival. Indeed, ROS overproduction and mitochondrial Ca2+ overload are linked to the induction of apoptosis, while the impairment of mitochondrial dynamics and metabolism can have a double-faceted role in the decision between cell survival and death. Tumorigenesis involves an intricate series of cellular impairments not yet completely clarified, and a further level of complexity is added by the onset of apoptosis resistance mechanisms in cancer cells. In the majority of cases, cancer relapse or lack of responsiveness is related to the emergence of chemoresistance, which may be due to the cooperation of several cellular protection mechanisms, often mitochondria-related. With this review, we aim to critically report the current evidence on the relationship between mitochondria and cancer chemoresistance with a particular focus on the involvement of mitochondrial dynamics, mitochondrial Ca2+ signaling, oxidative stress, and metabolism to possibly identify new approaches or targets for overcoming cancer resistance.

Various Aspects of Calcium Signaling in the Regulation of Apoptosis, Autophagy, Cell Proliferation, and Cancer.

Calcium (Ca2+) is a major second messenger in cells and is essential for the fate and survival of all higher organisms. Different Ca2+ channels, pumps, or exchangers regulate variations in the duration and levels of intracellular Ca2+, which may be transient or sustained. These changes are then decoded by an elaborate toolkit of Ca2+-sensors, which translate Ca2+ signal to intracellular operational cell machinery, thereby regulating numerous Ca2+-dependent physiological processes. Alterations to Ca2+ homoeostasis and signaling are often deleterious and are associated with certain pathological states, including cancer. Altered Ca2+ transmission has been implicated in a variety of processes fundamental for the uncontrolled proliferation and invasiveness of tumor cells and other processes important for cancer progression, such as the development of resistance to cancer therapies. Here, we review what is known about Ca2+ signaling and how this fundamental second messenger regulates life and death decisions in the context of cancer, with particular attention directed to cell proliferation, apoptosis, and autophagy. We also explore the intersections of Ca2+ and the therapeutic targeting of cancer cells, summarizing the therapeutic opportunities for Ca2+ signal modulators to improve the effectiveness of current anticancer therapies.

The induction of AMPK-dependent autophagy leads to P53 degradation and affects cell growth and migration in kidney cancer cells.

The most common subtype of renal cell carcinoma (RCC) is the clear cell RCC (ccRCC) that accounts for 70-80% of cases. The fate of ccRCC is linked to alterations of genes that regulate TP53. The dysfunction of p53 affects several processes including autophagy, which is increased in different advanced carcinomas and could be associated with cancer progression. We report that different kidney cancer cell lines show higher levels of autophagy than control cells. The increased autophagy is associated with the upregulation of miR501-5p, which stimulates mTOR-independent autophagy by the activation of AMP kinase. AMPK activation occurs through the decrease of ATP generation caused by the downregulation of the mitochondrial calcium uniporter (MCU) that leads to the reduction of mitochondrial calcium uptake. Autophagy induction promotes the degradation of p53 through the autophagolysosomal machinery. Consistently, the inhibition of autophagy reduces both cell proliferation and migration enhancing the expression of p53, p21 and E-Cadherin as well as decreasing Vimentin synthesis. Taken together, these findings indicate that autophagy is involved in the progression of kidney cancer. Therefore, the pharmacological targeting of this process could be considered an interesting option for the treatment of advanced renal carcinoma.

The mystery of mitochondria-ER contact sites in physiology and pathology: A cancer perspective.

Mitochondria-associated membranes (MAM), physical platforms that enable communication between mitochondria and the endoplasmic reticulum (ER), are enriched with many proteins and enzymes involved in several crucial cellular processes, such as calcium (Ca2+) homeostasis, lipid synthesis and trafficking, autophagy and reactive oxygen species (ROS) production. Accumulating studies indicate that tumor suppressors and oncogenes are present at these intimate contacts between mitochondria and the ER, where they influence Ca2+ flux between mitochondria and the ER or affect lipid homeostasis at MAM, consequently impacting cell metabolism and cell fate. Understanding these fundamental roles of mitochondria-ER contact sites as important domains for tumor suppressors and oncogenes can support the search for new and more precise anticancer therapies. In the present review, we summarize the current understanding of basic MAM biology, composition and function and discuss the possible role of MAM-resident oncogenes and tumor suppressors.

TRPP2 dysfunction decreases ATP-evoked calcium, induces cell aggregation and stimulates proliferation in T lymphocytes.

BACKGROUND: Autosomal dominant polycystic kidney disease (ADPKD) is mainly characterised by the development and enlargement of renal cysts that lead to end-stage renal disease (ESRD) in adult patients. Other clinical manifestations of this pathology include hypertension, haematuria, abdominal pain, cardiovascular system alterations and intracranial aneurysms. ADPKD is linked to mutations in either PKD1 or PKD2 that codifies polycystin-1 (PC1) and polycystin-2 (PC2 or TRPP2), respectively. PC1 and TRPP2 are membrane proteins that function as receptor-channel elements able to regulate calcium homeostasis. The function of polycystins has been mainly studied in kidney cells; but the role of these proteins in T lymphocytes is not well defined. METHODS: T lymphocytes were produced from ADPKD1 and ADPKD2 patients as well as from non-ADPKD subjects undergoing renal replacement therapy (RRT) and healthy controls. Protein expression and phosphorylation levels were analysed by western blotting, cell proliferation was calculated by direct counting using trypan blue assay and intracellular calcium concentration was measured by Fura-2 method. RESULTS: PKD2 mutations lead to the significant reduction of TRPP2 expression in T lymphocytes derived from ADPKD patients. Furthermore, a smaller TRPP2 truncated protein in T lymphocytes of patients carrying the mutation R872X in PKD2 was also observed, suggesting that TRPP2 mutated proteins may be stably expressed. The silencing or mutation of PKD2 causes a strong reduction of ATP-evoked calcium in Jurkat cells and ADPKD2 T lymphocytes, respectively. Moreover, T lymphocytes derived from both ADPKD1 and ADPKD2 patients show increased cell proliferation, basal chemotaxis and cell aggregation compared with T lymphocytes from non-ADPKD subjects. Similarly to observations made in kidney cells, mutations in PKD1 and PKD2 dysregulate ERK, mTOR, NFkB and MIF pathways in T lymphocytes. CONCLUSIONS: Because the alteration of ERK, mTOR, NFkB and MIF signalling found in T lymphocytes of ADPKD patients may contribute to the development of interstitial inflammation promoting cyst growth and kidney failure (ESRD), the targeting of inflammasome proteins could be an intriguing option to delay the progression of ADPKD.

Involvement of non-coding RNAs and transcription factors in the induction of Transglutaminase isoforms by ATRA.

The multifunctional protein Transglutaminase type 2, is associated with cancer epithelial mesenchymal transition, invasiveness, stemness and drugs resistance. Several variant isoforms and non-coding RNAs are present in cancer and this report explored the expression of these transcripts of the TGM2 gene in cancer cell lines after induction with all-trans retinoic acid. The expression of truncated variants along with two long non-coding RNAs, was demonstrated. One of these is coded from the first intron and the Last Exon Variant is constituted by a sequence corresponding to the last three exons and the 3'UTR. Analysis of ChIP-seq data, from ENCODE project, highlighted factors interacting with intronic sequences, which could interfere with the progression of RNApol II at checkpoints, during the elongation process. Some relevant transcription factors, bound in an ATRA-dependent way, were found by RNA immunoprecipitation, notably GATA3 mainly enriched to Last Exon Variant non-coding RNA. The involvement of NMD in the regulation of the ratio among these transcripts was observed, as the prevalent recovering of Last Exon Variant to phUPF1-complexes, with decrease of the binding towards other selective targets. This study contributes to identify molecular mechanisms regulating the ratio among the variants and improves the knowledge about regulatory roles of the non-coding RNAs of the TGM2 gene.

MicroRNA501-5p induces p53 proteasome degradation through the activation of the mTOR/MDM2 pathway in ADPKD cells.

Cell proliferation and apoptosis are typical hallmarks of autosomal dominant polycystic kidney disease (ADPKD) and cause the development of kidney cysts that lead to end-stage renal disease (ESRD). Many factors, impaired by polycystin complex loss of function, may promote these biological processes, including cAMP, mTOR, and EGFR signaling pathways. In addition, microRNAs (miRs) may also regulate the ADPKD related signaling network and their dysregulation contributes to disease progression. However, the role of miRs in ADPKD pathogenesis has not been fully understood, but also the function of p53 is quite obscure, especially its regulatory contribution on cell proliferation and apoptosis. Here, we describe for the first time that miR501-5p, upregulated in ADPKD cells and tissues, induces the activation of mTOR kinase by PTEN and TSC1 gene repression. The increased activity of mTOR kinase enhances the expression of E3 ubiquitin ligase MDM2 that in turn promotes p53 ubiquitination, leading to its degradation by proteasome machinery in a network involving p70S6K. Moreover, the overexpression of miR501-5p stimulates cell proliferation in kidney cells by the inhibition of p53 function in a mechanism driven by mTOR signaling. In fact, the downregulation of this miR as well as the pharmacological treatment with proteasome and mTOR inhibitors in ADPKD cells reduces cell growth by the activation of apoptosis. Consequently, the stimulation of cell death in ADPKD cells may occur through the inhibition of mTOR/MDM2 signaling and the restoring of p53 function. The data presented here confirm that the impaired mTOR signaling plays an important role in ADPKD.

Double inhibition of cAMP and mTOR signalling may potentiate the reduction of cell growth in ADPKD cells.

BACKGROUND: ADPKD is a renal pathology caused by mutations of PKD1 and PKD2 genes, which encode for polycystin-1 (PC1) and polycystin-2 (PC2), respectively. PC1 plays an important role regulating several signal transducers, including cAMP and mTOR, which are involved in abnormal cell proliferation of ADPKD cells leading to the development and expansion of kidney cysts that are a typical hallmark of this disease. Therefore, the inhibition of both pathways could potentiate the reduction of cell proliferation enhancing benefits for ADPKD patients. METHODS: The inhibition of cAMP- and mTOR-related signalling was performed by Cl-IB-MECA, an agonist of A3 receptors, and rapamycin, respectively. Protein kinase activity was evaluated by immunoblot and cell growth was analyzed by direct cell counting. RESULTS: The activation of A3AR by the specific agonist Cl-IB-MECA causes a marked reduction of CREB, mTOR, and ERK phosphorylation in kidney tissues of Pkd1 flox/-: Ksp-Cre polycystic mice and reduces cell growth in ADPKD cell lines, but not affects the kidney weight. The combined sequential treatment with rapamycin and Cl-IB-MECA in ADPKD cells potentiates the reduction of cell proliferation compared with the individual compound by the inhibition of CREB, mTOR, and ERK kinase activity. Conversely, the simultaneous application of these drugs counteracts their effect on cell growth, because the inhibition of ERK kinase activity is lost. CONCLUSION: The double treatment with rapamycin and Cl-IB-MECA may have synergistic effects on the inhibition of cell proliferation in ADPKD cells suggesting that combined therapies could improve renal function in ADPKD patients.