Antitumor mechanisms when pRb and p53 are genetically inactivated

IDH1 mutation produces R-2-hydroxyglutarate (R-2HG) and induces mir-182-5p expression to regulate cell cycle and tumor formation in glioma

BACKGROUND

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2), are present in most gliomas. IDH1 mutation is an important prognostic marker in glioma. However, its regulatory mechanism in glioma remains incompletely understood.

RESULTS

miR-182-5p expression was increased within IDH1-mutant glioma specimens according to TCGA, CGGA, and online dataset GSE119740, as well as collected clinical samples. (R)-2-hydroxyglutarate ((R)-2HG) treatment up-regulated the expression of miR-182-5p, enhanced glioma cell proliferation, and suppressed apoptosis; miR-182-5p inhibition partially eliminated the oncogenic effects of R-2HG upon glioma cells. By direct binding to Cyclin Dependent Kinase Inhibitor 2 C (CDKN2C) 3'UTR, miR-182-5p inhibited CDKN2C expression. Regarding cellular functions, CDKN2C knockdown promoted R-2HG-treated glioma cell viability, suppressed apoptosis, and relieved cell cycle arrest. Furthermore, CDKN2C knockdown partially attenuated the effects of miR-182-5p inhibition on cell phenotypes. Moreover, CDKN2C knockdown exerted opposite effects on cell cycle check point and apoptosis markers to those of miR-182-5p inhibition; also, CDKN2C knockdown partially attenuated the functions of miR-182-5p inhibition in cell cycle check point and apoptosis markers. The engineered CS-NPs (antagomir-182-5p) effectively encapsulated and delivered antagomir-182-5p, enhancing anti-tumor efficacy in vivo, indicating the therapeutic potential of CS-NPs(antagomir-182-5p) in targeting the miR-182-5p/CDKN2C axis against R-2HG-driven oncogenesis in mice models.

CONCLUSIONS

These insights highlight the potential of CS-NPs(antagomir-182-5p) to target the miR-182-5p/CDKN2C axis, offering a promising therapeutic avenue against R-2HG's oncogenic influence to glioma.

Identification and validation of an E2F-related gene signature for predicting recurrence-free survival in human prostate cancer

BACKGROUND

It is well-established that biochemical recurrence is detrimental to prostate cancer (PCa). In the present study, we explored the mechanisms underlying PCa progression.

METHODS

Five cohorts from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus databases were used to perform gene set variation analysis (GSVA) between nonrecurrent and recurrent PCa patients. We obtained the intersection of pathway enrichment results and extracted the corresponding gene list. LASSO Cox regression analysis was used to identify recurrence-free survival (RFS)-related significant genes and establish an RFS prediction gene signature and nomogram. MTT and colony formation assays were conducted to validate our findings.

RESULTS

The E2F signaling pathway was activated in recurrent PCa patients compared to nonrecurrent patients. We established an E2F-related gene signature for RFS prediction based on the four identified E2F-related genes (CDKN2C, CDKN3, RACGAP1, and RRM2) using LASSO Cox regression in the Memorial Sloan Kettering Cancer Center (MSKCC) cohort. The risk score of each patient in MSKCC was calculated based on the expression levels of CDKN2C, CDKN3, RACGAP1, and RRM2. PCa patients with low-risk scores exhibited higher RFS than those with high-risk scores. Receiver operating characteristic (ROC) curve analysis validated the good performance and prognostic accuracy of the E2F-related gene signature, which was validated in the TCGA-prostate adenocarcinoma (TCGA-PRAD) cohort. Compared to patients with low Gleason scores and early T stages, PCa patients with high Gleason scores and advanced T stages had high-risk scores. Moreover, the E2F-related gene signature-based nomogram yielded good performance in RFS prediction. Functional experiments further confirmed these results.

CONCLUSIONS

The E2F signaling pathway is associated with biochemical recurrence in PCa. Our established E2F-related gene signature and nomogram yielded good accuracy in predicting the biochemical recurrence in PCa.

Targeting the untargetable: RB1-deficient tumours are vulnerable to Skp2 ubiquitin ligase inhibition

Proteins that regulate the cell cycle are accumulated and degraded in a coordinated manner during the transition from one cell cycle phase to the next. The rapid loss of a critical protein, for example, to allow the cell to move from G1/G0 to S phase, is often regulated by its ubiquitination and subsequent proteasomal degradation. Protein ubiquitination is mediated by a series of three ligases, of which the E3 ligases provide the specificity for a particular protein substrate. One such E3 ligase is SCF^Skp1/Cks1, which has a substrate recruiting subunit called S-phase kinase-associated protein 2 (Skp2). Skp2 regulates cell proliferation, apoptosis, and differentiation, can act as an oncogene, and is overexpressed in human cancer. A primary target of Skp2 is the cyclin-dependent kinase inhibitor p27 (CDKN1b) that regulates the cell cycle at several points. The RB1 tumour suppressor gene regulates Skp2 activity by two mechanisms: by controlling its mRNA expression, and by an effect on Skp2's enzymatic activity. For the latter, the RB1 protein (pRb) directly binds to the substrate-binding site on Skp2, preventing protein substrates from being ubiquitinated and degraded. Inactivating mutations in RB1 are common in human cancer, becoming more frequent in aggressive, metastatic, and drug-resistant tumours. Hence, RB1 mutation leads to the loss of pRb, an unrestrained increase in Skp2 activity, the unregulated decrease in p27, and the loss of cell cycle control. Because RB1 mutations lead to the loss of a functional protein, its direct targeting is not possible. This perspective will discuss evidence validating Skp2 as a therapeutic target in RB1-deficient cancer.

Integration of Adverse Outcome Pathways, Causal Networks and ‘Omics to Support Chemical Hazard Assessment

Several approaches have been used in an attempt to simplify and codify the events that lead to adverse effects of chemicals including systems biology, ‘omics, in vitro assays and frameworks such as the Adverse Outcome Pathway (AOP). However, these approaches are generally not integrated despite their complementary nature. Here we propose to integrate toxicogenomics data, systems biology information and AOPs using causal biological networks to define Key Events in AOPs. We demonstrate this by developing a causal subnetwork of 28 nodes that represents the Key Event of regenerative proliferation – a critical event in AOPs for liver cancer. We then assessed the effects of three chemicals known to cause liver injury and cell proliferation (carbon tetrachloride, aflatoxin B₁, thioacetamide) and two with no known cell proliferation effects (diazepam, simvastatin) on the subnetwork using rat liver gene expression data from the toxicogenomic database Open TG-GATEs. Cyclin D1 (Ccnd1), a gene both causally linked to and sufficient to infer regenerative proliferation activity, was overexpressed after exposures to carbon tetrachloride, aflatoxin B₁ and thioacetamide, but not in exposures to diazepam and simvastatin. These results were consistent with known effects on rat livers and liver pathology of exposed rats. Using these approaches, we demonstrate that transcriptomics, AOPs and systems biology can be applied to examine the presence and progression of AOPs in order to better understand the hazards of chemical exposure.

One-shot dual gene editing for drug-resistant pancreatic cancer therapy

It is challenging to diagnose patients with pancreatic ductal adenocarcinoma (PDAC) early on, and their treatment is often complex. Gemcitabine (GEM) is the first-line treatment for PDAC, but its efficacy is limited in most patients due to the GEM resistance from KRAS and P53 gene mutations. We describe the correction of a double gene mutation and therapeutic effect for the GEM resistant PDAC. Bio-available nanoliposomes (NL) possessing Cas9-ribonucleoproteins and adenine-base editors were developed to conduct KRAS and P53 mutation gene editing directly. NLs were conjugated with EGFR antibodies to tumor-specific delivery, and the anti-cancer effect was verified in vitro and in vivo Model. Our GEM-combinatorial therapeutic strategies using double gene editing systems with one-shot may be a potent therapy for PDAC, overcoming chemoresistance.

Anticancer Effect and Phytochemical Profile of the Extract from Achillea ketenoglui against Human Colorectal Cancer Cell Lines

BACKGROUND

In the treatment of colorectal cancer (CRC), the search for new antineoplastic drugs with fewer side effects and more effectiveness continues. A significant part of these pursuits and efforts focus on medicinal herbs and plant components derived from these plants. A. ketenoglui is one of these medicinal plants, and its anticancer potential has never been studied before.

METHODS

The phenolic and flavonoid content, and antioxidant activity of A. ketenoglui extracts were determined. The phytochemical profiling and quantification analysis of major components were performed by HPLC-ESI-Q-TOF-MS. Cytotoxicity, proliferation, apoptosis and cell cycle were evaluated to reveal the anticancer activity of the extract on CRC cells (HCT 116 and HT-29). The determined anticancer activity was confirmed by mRNA (RT-qPCR) and protein (Western blotting) analyzes.

RESULTS

A. ketenoglui methanol extract was found to have high phenolic (281.89±0.23) and flavonoid (33.80±0.15) content and antioxidant activity (IC50 40.03±0.38). According to the XTT assay, the extract has strong cytotoxic activity (IC50 350 µM in HCT 116 and IC50 263 µM in HT-29 cell line). The compounds most commonly found in the plant are, in descending order, chlorogenic acid, apigenin, genistin, baicalin, eupatorin, casticin, and luteolin. In flowcytometric analysis, the extract was found to induce greater apoptosis and cell cycle arrest in both cell lines than in both control and positive control (casticin). According to the results of the mRNA expression analysis, the extract treatment upregulated the expression of the critical genes of the cell cycle and apoptosis, such as p53, p21, caspase-3, and caspase-9. In protein expression analysis, an increase in caspase-3 and p53 expression was observed in both cell lines treated with the extract. In addition, caspase-9 expression was increased in HT-29 cells.

CONCLUSION

The findings show that A. ketenoglui has an anticancer potential by inducing apoptosis and arresting the cancer cell cycle and may be promising for CRC therapy. This potential of the plant is realized through the synergistic effects of its newly identified components.

The Biological and Biomechanical Role of Transglutaminase-2 in the Tumour Microenvironment

Transglutaminase-2 (TG2) is the most highly and ubiquitously expressed member of the transglutaminase enzyme family and is primarily involved in protein cross-linking. TG2 has been implicated in the development and progression of numerous cancers, with a direct role in multiple cellular processes and pathways linked to apoptosis, chemoresistance, epithelial-mesenchymal transition, and stem cell phenotype. The tumour microenvironment (TME) is critical in the formation, progression, and eventual metastasis of cancer, and increasing evidence points to a role for TG2 in matrix remodelling, modulation of biomechanical properties, cell adhesion, motility, and invasion. There is growing interest in targeting the TME therapeutically in response to advances in the understanding of its critical role in disease progression, and a number of approaches targeting biophysical properties and biomechanical signalling are beginning to show clinical promise. In this review we aim to highlight the wide array of processes in which TG2 influences the TME, focussing on its potential role in the dynamic tissue remodelling and biomechanical events increasingly linked to invasive and aggressive behaviour. Drug development efforts have yielded a range of TG2 inhibitors, and ongoing clinical trials may inform strategies for targeting the biomolecular and biomechanical function of TG2 in the TME.

Exosomes of Adipose-derived Stem Cells Conditioned Media Promotes Retinoblastoma and Forkhead-Box M1 Protein Expression

BACKGROUND: In the senescence process, the retinoblastoma (Rb) protein binds to E2F in hypophosphorylated conditions, preventing the cell to enter the S-phase in the cell cycle. Human Forkhead Box M1 (FOXM1) protein, key regulator G1/S and G2/M phases, decreases in the senescence process. Many studies have been carried out to reverse this system, one of which used exosomes of adipose-derived stem c ells conditioned media (ADSC-CM). These exosomes contain a variety of specific proteins which have pro-proliferation properties, however, little is known on the role of these exosomes toward the change of phosphorylated Rb and FOXM1. AIM: This study aims to find out the involvement of exosomes of ADSC-CM on these two proteins on senescence human dermal fibroblasts (HDFs). METHODS: In vitro experiment was undergone randomization sample and non-blinded pre-/post-test control group. The primary culture of senescent HDFs was transfected with exosomes of ADSC-CM; then, its effect on migration and senescence reversal was observed through analyzing Sa-β-gal, Rb, and FOXM1 protein expression. RESULTS: The expression of Sa-β-gal was higher in the control group. Our result demonstrated the exosome of ADSC-CM significantly induced the expression of Rb and FOXM1 protein in senescent HDFs (p < 0.05). CONCLUSION: It proved that exosomes of ADSC-CM could shift the senescent fibroblast into metabolically active cells.

The Function of SUMOylation and Its Role in the Development of Cancer Cells under Stress Conditions: A Systematic Review

Malignant tumors still pose serious threats to human health due to their high morbidity and mortality. Recurrence and metastasis are the most important factors affecting patient prognosis. Chemotherapeutic drugs and radiation used to treat these tumors mainly interfere with tumor metabolism, destroy DNA integrity, and inhibit protein synthesis. The upregulation of small ubiquitin-like modifier (SUMO) is a prevalent posttranslational modification (PTM) in various cancers and plays a critical role in tumor development. The dysregulation of SUMOylation can protect cancer cells from stresses exerted by external or internal stimuli. SUMOylation is a dynamic process finely regulated by SUMOylation enzymes and proteases to maintain a balance between SUMOylation and deSUMOylation. An increasing number of studies have reported that SUMOylation imbalance may contribute to cancer development, including metastasis, angiogenesis, invasion, and proliferation. High level of SUMOylation is required for cancer cells to survive internal or external stresses. Downregulation of SUMOylation may inhibit the development of cancer, making it an important potential clinical therapeutic target. Some studies have already begun to treat tumors by inhibiting the expression of SUMOylation family members, including SUMO E1 or E2. The tumor cells become more aggressive under internal and external stresses. The prevention of tumor development, metastasis, recurrence, and radiochemotherapy resistance by attenuating SUMOylation requires further exploration. This review focused on SUMOylation in tumor cells to discuss its effects on tumor suppressor proteins and oncoproteins as well as classical tumor pathways to identify new insights for cancer clinical therapy.

Role of tissue and circulating microRNAs and DNA as biomarkers in medullary thyroid cancer

Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor comprising hereditary or sporadic form with frequent mutations in the rearranged during transfection (RET) or RAS genes. Diagnosis is based on the presence of thyroid tumor mass with altered levels of calcitonin (Ctn) and carcinoembryonal antigen (CEA) in the serum and/or in the cytological smears from fine needle aspiration biopsies. Treatment consists of total thyroidectomy, followed by tyrosine kinase inhibitors (TKi) in case of disease persistence. During TKi treatment, Ctn and CEA levels can fluctuate regardless of tumor volume, metastasis or response to therapy. Research for more reliable non-invasive biomarkers in MTC is still underway. In this context, circulating nucleic acids, namely circulating microRNAs (miRNAs) and cell free DNA (cfDNA), have been evaluated by different research groups. Aiming to shed light on whether miRNAs and cfDNA are suitable as MTC biomarkers we searched three different databases, PubMed, Scopus, WOS and reviewed the literature. We classified 83 publications fulfilling our search criteria and summarized the results. We report data on miRNAs and cfDNA that can be evaluated for validation in independent studies and clinical application.

Glucose Transporter 1 Promotes the Malignant Phenotype of Non-Small Cell Lung Cancer through Integrin β1/Src/FAK Signaling

Background: Glucose transporter 1 (GLUT1) is the main factor of Warburg effect, which is associated with poor prognosis in many tumors. However, the underlying molecular mechanism of GLUT1 in the progression of non-small cell lung cancer (NSCLC) is unclear.

Methods: We used quantitative real-time PCR to detect GLUT1 mRNA expression in bronchial brushing samples and performed Western Blot and biological behavior testing to check the effect of GLUT1 on NSCLC cell proliferation, migration, invasion and apoptosis.

Results: We found that the C(t) normalized value of GLUT1 in malignant bronchial brushing samples was significantly higher than that in benign samples (P<0.05). GLUT1 significantly increased the expressions of cyclin A, cyclin D1, cyclin E, cyclin dependent kinase 2 (CDK2), CDK4, CDK6 and matrix metalloproteinase 2 (MMP2), but decreased the expressions of p53 and p130 in NSCLC cells. The biological behavior testing indicated that GLUT1 enhanced NSCLC cell proliferation, invasion and migration but inhibited cell apoptosis. In addition, GLUT1 upregulated the expression of integrin β1 and promoted the phosphorylation of focal adhesion kinase (FAK, phosphorylation at Tyr576/577) and Src (Src phosphorylation at Tyr530). siRNA knock down of integrin β1 expression suppressed GLUT1 induced NSCLC cell biological behavior, as well as the phosphorylation of FAK and Src.

Conclusion: Taken together, our data confirms that GLUT1 promotes the malignant phenotype of NSCLC through integrin β1/Src/FAK signaling, which provides a new therapeutic target for the treatment and research of lung cancer.

The silencing of long non-coding RNA ANRIL suppresses invasion, and promotes apoptosis of retinoblastoma cells through the ATM-E2F1 signaling pathway

As one of the most common primary intraocular carcinomas, retinoblastoma generally stems from the inactivation of the retinoblastoma RB1 gene in retinal cells. Antisense non-coding RNA in the INK4 locus (ANRIL), a long non-coding RNA (lncRNA), has been reported to affect tumorigenesis and progression of various cancers, including gastric cancer and non-small cell lung cancer. However, limited investigations emphasized the role of ANRIL in human retinoblastoma. Hence, the current study was intended to investigate the effects of ANRIL on the proliferation, apoptosis, and invasion of retinoblastoma HXO-RB₄₄ and Y79 cells. The lentivirus-based packaging system was designed to aid the up-regulation of ANRIL and ATM expressions or employed for the down-regulation of ANRIL in human retinoblastoma cells. Afterward, ANRIL expression, mRNA and protein expression of ATM and E2F1, and protein expression of INK4b, INK4a, alternate reading frame (ARF), p53 and retinoblastoma protein (pRB) were determined in order to elucidate the regulation effect associated with ANRIL on the ATM-E2F1 signaling pathway. In addition, cell viability, apoptosis, and invasion were detected accordingly. The results indicated that the down-regulation of ANRIL or up-regulation of ATM led to an increase in the expressions of ATM, E2F1, INK4b, INK4a, ARF, p53, and pRB. The silencing of ANRIL or up-regulation of ATM exerted an inhibitory effect on the proliferation and invasion while improving the apoptosis of HXO-RB₄₄ and Y79 cells. In conclusion, the key observations of our study demonstrated that ANRIL depletion could act to suppress retinoblastoma progression by activating the ATM-E2F1 signaling pathway. These results provide a potentially promising basis for the targetted intervention treatment of human retinoblastoma.

FGF9/FGFR2 increase cell proliferation by activating ERK1/2, Rb/E2F1, and cell cycle pathways in mouse Leydig tumor cells

Fibroblast growth factor 9 (FGF9) promotes cancer progression; however, its role in cell proliferation related to tumorigenesis remains elusive. We investigated how FGF9 affected MA‐10 mouse Leydig tumor cell proliferation and found that FGF9 significantly induced cell proliferation by activating ERK1/2 and retinoblastoma (Rb) phosphorylations within 15 minutes. Subsequently, the expressions of E2F1 and the cell cycle regulators: cyclin D1, cyclin E1 and cyclin‐dependent kinase 4 (CDK4) in G₁ phase and cyclin A1, CDK2 and CDK1 in S‐G₂/M phases were increased at 12 hours after FGF9 treatment; and cyclin B1 in G₂/M phases were induced at 24 hours after FGF9 stimulation, whereas the phosphorylations of p53, p21 and p27 were not affected by FGF9. Moreover, FGF9‐induced effects were inhibited by MEK inhibitor PD98059, indicating FGF9 activated the Rb/E2F pathway to accelerate MA‐10 cell proliferation by activating ERK1/2. Immunoprecipitation assay and ChIP‐quantitative PCR results showed that FGF9‐induced Rb phosphorylation led to the dissociation of Rb‐E2F1 complexes and thereby enhanced the transactivations of E2F1 target genes, Cyclin D1, Cyclin E1 and Cyclin A1. Silencing of FGF receptor 2 (FGFR2) using lentiviral shRNA inhibited FGF9‐induced ERK1/2 phosphorylation and cell proliferation, indicating that FGFR2 is the obligate receptor for FGF9 to bind and activate the signaling pathway in MA‐10 cells. Furthermore, in a severe combined immunodeficiency mouse xenograft model, FGF9 significantly promoted MA‐10 tumor growth, a consequence of increased cell proliferation and decreased apoptosis. Conclusively, FGF9 interacts with FGFR2 to activate ERK1/2, Rb/E2F1 and cell cycle pathways to induce MA‐10 cell proliferation in vitro and tumor growth in vivo.

Genomic structure, expression, and functional characterization of checkpoint kinase 1 from Penaeus monodon

Chk1 is a cell-cycle regulator. Chk1 has been identified in organisms ranging from yeast to humans, but few researchers have studied Chk1 in shrimps. We cloned Chk1 from the black tiger shrimp (Penaeus monodon). The full-length cDNA sequence of PmChk1 had 3,334 base pairs (bp), with an open reading frame of 1,455 bp. The complete genomic sequence of PmChk1 (11,081 bp) contained 10 exons separated by nine introns. qRT-PCR showed that PmChk1 was highly expressed in the ovaries and gills of P. monodon. The lowest PmChk1 expression was noted in stage III of ovarian development in P. monodon. PmChk1 expression decreased significantly after injection of 5-hydroxytryptamine and eyestalk ablation in P. monodon ovaries. RNA interference experiments were undertaken to examine the expression of PmChk1, PmCDC2, and PmCyclin B. PmChk1 knockdown in the ovaries and hepatopancreas by dsRNA-Chk1 was successful. The localization and level of PmChk1 expression in the hepatopancreas was studied using in situ hybridization, which showed that data were in accordance with those of qRT-PCR. The Gonadosomatic Index of P. monodon after dsRNA-Chk1 injection was significantly higher than that after injection of dsRNA-GFP or phosphate-buffered saline. These data suggest that PmChk1 may have important roles in the ovarian maturation of P. monodon.

Aryl hydrocarbon receptor regulates histone deacetylase 8 expression to repress tumor suppressive activity in hepatocellular carcinoma

Histone deacetylase 8 (HDAC8), a unique member of class I histone deacetylases, shows remarkable correlation with advanced disease stage and multiple malignant tumors However, little is known about the contribution of HDAC8 to the tumorigenesis of hepatocellular carcinoma (HCC). The present study investigated the expression of HDAC8 regulated by the aryl hydrocarbon receptor (AHR) in HCC cell lines and tissues, and the roles of HDAC8 overexpression in cell proliferation, including potentially underlying mechanisms. We assessed the correlation between the clinic-pathological parameters and the expression of AHR and HDAC8. Further, we analyzed the AHR siRNA transfection and HDAC8 inhibitors to explore the functions of HDAC8 in HCC progression in vitro and in vivo. In a panel of 289 HCC patients, HDAC8 was shown to be highly correlated with AHR expression at both mRNA and protein levels. HCC patients with high AHR expression showed a shorter survival time than that with low AHR expression. We then found that the expression of both AHR and HDAC8 was significantly upregulated in both HCC cell lines and tumor tissues compared to human normal hepatocytes and matched non-tumor tissues. Furthermore, HDAC8 inhibition remarkably inhibited hepatoma cell proliferation and transformation activity via upregulation of RB1 in vitro and in vivo. Our data revealed an important role of the AHR-HDAC8 axis in promoting HCC tumorigenesis, thus identifying HDAC8 as a potential therapeutic target for HCC treatment.

Effects of concomitant inactivation of p53 and pRb on response to doxorubicin treatment in breast cancer cell lines

Loss of TP53 and RB1 function have both been linked to poor response to DNA damaging drugs in breast cancer patients. We inactivated TP53 and/or RB1 by siRNA mediated knockdown in breast cancer cell lines varying with respect to ER/PgR and Her-2 status as well as TP53 and RB1 mutation status (MCF-7, T47D, HTB-122 and CRL2324) and determined effects on cell cycle arrest, apoptosis and senescence with or without concomitant treatment with doxorubicin. In T47D cells, we found the cell cycle phase distribution to be altered when inactivating TP53 (P=0.0003) or TP53 and RB1 concomitantly (P≤0.001). No similar changes were observed in MCF-7, HTB-122 or CRL2324 cells. While no significant change was observed for the CRL2324 cells upon doxorubicin treatment, MCF-7, T47D as well as HTB-122 cells responded to knockdown of TP53 and RB1 in concert, with a decrease in the fraction of cells in G1/G0-phase (P=0.042, 0.021 and 0.027, respectively). Inactivation of TP53 and/or RB1 caused no change in induction of apoptosis. Upon doxorubicin treatment, inactivation of TP53 or RB1 separately caused no induction of apoptosis in MCF-7 and HTB-122 cells; however, concomitant inactivation leads to a slightly reduced activation of apoptosis. Interestingly, upon doxorubicin treatment, concomitant inactivation of TP53 and RB1 caused a decrease in senescence in MCF-7 cells (P=0.027). Comparing the effects of concomitant knockdown on apoptosis and senescence, we observed a strong interaction (P=0.001). We found concomitant inactivation of TP53 and RB1 to affect various routes of response to doxorubicin treatment in breast cancer cells.

Role of CDKN2C Copy Number in Sporadic Medullary Thyroid Carcinoma

BACKGROUND

The cyclin-dependent-kinase inhibitors (CDKN)/retinoblastoma (RB1) pathway has been implicated as having a role in medullary thyroid carcinoma (MTC) tumorigenesis. CDKN2C loss has been associated with RET-mediated MTC in humans but with minimal phenotypic correlation provided. The objective of this study was to evaluate the association between tumor RET mutation status, CDKN2C loss, and aggressiveness of MTC in a cohort of patients with sporadic disease.

METHODS

Tumors from patients with sporadic MTC treated at a single institution were evaluated for somatic RET^M918T mutation and CDKN2C copy number loss. These variables were compared to patient demographics, pathology detail, clinical course, and disease-specific and overall survival.

RESULTS

Sixty-two MTC cases with an initial surgery date ranging from 1983 to 2009 met the inclusion criteria, of whom 36 (58%) were male. The median age at initial surgery was 53 years (range 22-81 years). The median tumor size was 30 mm (range 6-145 mm) with 29 (57%) possessing extrathyroidal extension. Nodal and/or distant metastasis at presentation was found in 47/60 (78%) and 12/61 (20%) patients, respectively. Median follow-up time was 10.5 years (range 1.1-27.8 years) for the censored observations. The presence of CDKN2C loss was associated with worse M stage and overall AJCC stage. Median overall survival of patients with versus without CDKN2C loss was 4.14 [confidence interval (CI) 1.93-NA] versus 18.27 [CI 17.24-NA] years (p < 0.0001). Median overall survival of patients with a combined somatic RET^M918T mutation and CDKN2C loss versus no somatic RET^M918T mutation and CDKN2C loss versus somatic RET^M918T mutation and CDKN2C 2N versus no somatic RET^M918T mutation and CDKN2C 2N was 2.38 [CI 1.67-NA] years versus 10.81 [CI 2.46-NA] versus 17.24 [CI 9.82-NA] versus not reached [CI 13.46-NA] years (p < 0.0001).

CONCLUSIONS

The detection of somatic CDKN2C loss is associated with the presence of distant metastasis at presentation as well decreased overall survival, a relationship enhanced by concomitant RET^M918T mutation. Further defining the genes involved in the progression of metastatic MTC will be an important step toward identifying pathways of disease progression and new therapeutic targets.

Indirect p53-dependent transcriptional repression of Survivin, CDC25C, and PLK1 genes requires the cyclin-dependent kinase inhibitor p21/CDKN1A and CDE/CHR promoter sites binding the DREAM complex

The transcription factor p53 is central to cell cycle control by downregulation of cell cycle-promoting genes upon cell stress such as DNA damage. Survivin (BIRC5), CDC25C, and PLK1 encode important cell cycle regulators that are repressed following p53 activation. Here, we provide evidence that p53-dependent repression of these genes requires activation of p21 (CDKN1A, WAF1, CIP1). Chromatin immunoprecipitation (ChIP) data indicate that promoter binding of B-MYB switches to binding of E2F4 and p130 resulting in a replacement of the MMB (Myb-MuvB) by the DREAM complex. We demonstrate that this replacement depends on p21. Furthermore, transcriptional repression by p53 requires intact DREAM binding sites in the target promoters. The CDE and CHR cell cycle promoter elements are the sites for DREAM binding. These elements as well as the p53 response of Survivin, CDC25C, and PLK1 are evolutionarily conserved. No binding of p53 to these genes is detected by ChIP and mutation of proposed p53 binding sites does not alter the p53 response. Thus, a mechanism for direct p53-dependent transcriptional repression is not supported by the data. In contrast, repression by DREAM is consistent with most previous findings and unifies models based on p21-, E2F4-, p130-, and CDE/CHR-dependent repression by p53. In conclusion, the presented data suggest that the p53-p21-DREAM-CDE/CHR pathway regulates p53-dependent repression of Survivin, CDC25C, and PLK1.

Bringing Down Cancer Aircraft: Searching for Essential Hypomutated Proteins in Skin Melanoma

We propose an approach to detection of essential genes/proteins required for cancer cell survival. A gene is considered essential if a mutation with high impact upon the function of encoded protein causes death of the cancer cell. We draw an analogy between essential cancer proteins and well-known Abraham Wald's work on estimating the plane critical areas using data on survivability of aircraft encountering enemy fire. Wald reasoned that parts with no bullet holes on the airplanes returned to the airbase from a combat flight are the most crucial ones for the airplane functioning: a hit in one of these parts downs an airplane, so it does not return back for the survey. We have envisaged that the airplane surface is a cancer genome and the bullets are somatic mutations with high impact upon protein function. Similarly we propose that genes specifically essential for tumor cell survival should carry less high-impact mutations in cancer cells compared to polymorphisms found in normal cells. We used data on mutations from the Cancer Genome Atlas and polymorphisms found in healthy humans (from 1000 Genomes Project) to predict 91 protein-coding genes essential for melanoma. These genes were selected according to several criteria, including negative selection, expression in melanocytes and decrease in the proportion of high-impact mutations in cancer compared with normal cells. The Gene Ontology analysis revealed enrichment of essential proteins related to membrane and cell periphery. We speculate that this could be a sign of immune system-driven negative selection of cancer neo-antigens. Another finding is the overrepresentation of semaphorin receptors, which can mediate distinctive signaling cascades and are involved in various aspects of tumor development. Cytokine receptors CCR5 and CXCR1 were also identified as cancer essential proteins and this is confirmed by other studies. Overall, our goal was to illustrate the idea of detecting proteins whose sequence integrity and functioning is important for cancer cell survival. Hopefully, this prediction of essential cancer proteins may point to new targets for anti-tumor therapies.

The p53 tetramer shows an induced-fit interaction of the C-terminal domain with the DNA-binding domain

The Trp53 gene is the most frequently mutated gene in all human cancers. Its protein product p53 is a very powerful transcription factor that can activate different biochemical pathways and affect the regulation of metabolism, senescence, DNA damage response, cell cycle and cell death. The understanding of its function at the molecular level could be of pivotal relevance for therapy. Investigation of long-range intra- and interdomain communications in the p53 tetramer–DNA complex was performed by means of an atomistic model that included the tetramerization helices in the C-terminal domain, the DNA-binding domains and a consensus DNA-binding site of 18 base pairs. Nonsymmetric dynamics are illustrated in the four DNA-binding domains, with loop L1 switching from inward to outward conformations with respect to the DNA major groove. Direct intra- and intermonomeric long-range communications between the tetramerization and DNA-binding domains are noted. These long-distance conformational changes link the C terminus with the DNA-binding domain and provide a biophysical rationale for the reported functional regulation of the p53 C-terminal region. A fine characterization of the DNA deformation caused by p53 binding is obtained, with ‘static' deformations always present and measured by the slide parameter in the central thymine–adenine base pairs; we also detect ‘dynamic' deformations switched on and off by particular p53 tetrameric conformations and measured by the roll and twist parameters in the same base pairs. These different conformations can indeed modulate the electrostatic potential isosurfaces of the whole p53–DNA complex. These results provide a molecular/biophysical understanding of the evident role of the C terminus in post-translational modification that regulates the transcriptional function of p53. Furthermore, the unstructured C terminus is able to facilitate contacts between the core DNA-binding domains of the tetramer.

Substituting threonine 187 with alanine in p27Kip1 prevents pituitary tumorigenesis by two-hit loss of Rb1 and enhances humoral immunity in old age

p27Kip1 (p27) is an inhibitor of cyclin-dependent kinases. Inhibiting p27 protein degradation is an actively developing cancer therapy strategy. One focus has been to identify small molecule inhibitors to block recruitment of Thr-187-phosphorylated p27 (p27T187p) to SCF(Skp2/Cks1) ubiquitin ligase. Since phosphorylation of Thr-187 is required for this recruitment, p27T187A knockin (KI) mice were generated to determine the effects of systemically blocking interaction between p27 and Skp2/Cks1 on tumor susceptibility and other proliferation related mouse physiology. Rb1(+/-) mice develop pituitary tumors with full penetrance and the tumors are invariably Rb1(-/-), modeling tumorigenesis by two-hit loss of RB1 in humans. Immunization induced humoral immunity depends on rapid B cell proliferation and clonal selection in germinal centers (GCs) and declines with age in mice and humans. Here, we show that p27T187A KI prevented pituitary tumorigenesis in Rb1(+/-) mice and corrected decline in humoral immunity in older mice following immunization with sheep red blood cells (SRBC). These findings reveal physiological contexts that depend on p27 ubiquitination by SCF(Skp2-Cks1) ubiquitin ligase and therefore help forecast clinical potentials of Skp2/Cks1-p27T187p interaction inhibitors. We further show that GC B cells and T cells use different mechanisms to regulate their p27 protein levels, and propose a T helper cell exhaustion model resembling that of stem cell exhaustion to understand decline in T cell-dependent humoral immunity in older age.

Thyroid C-Cell Biology and Oncogenic Transformation

The thyroid parafollicular cell, or commonly named "C-cell," functions in serum calcium homeostasis. Elevations in serum calcium trigger release of calcitonin from the C-cell, which in turn functions to inhibit absorption of calcium by the intestine, resorption of bone by the osteoclast, and reabsorption of calcium by renal tubular cells. Oncogenic transformation of the thyroid C-cell is thought to progress through a hyperplastic process prior to malignancy with increasing levels of serum calcitonin serving as a biomarker for tumor burden. The discovery that multiple endocrine neoplasia type 2 is caused by activating mutations of the RET gene serves to highlight the RET-RAS-MAPK signaling pathway in both initiation and progression of medullary thyroid carcinoma (MTC). Thyroid C-cells are known to express RET at high levels relative to most cell types; therefore, aberrant activation of this receptor is targeted primarily to the C-cell, providing one possible cause of tissue-specific oncogenesis. The role of RET signaling in normal C-cell function is unknown though calcitonin gene transcription appears to be sensitive to RET activation. Beyond RET, the modeling of oncogenesis in animals and screening of human tumors for candidate gene mutations have uncovered mutation of RAS family members and inactivation of Rb1 regulatory pathway as potential mediators of C-cell transformation. A growing understanding of how RET interacts with these pathways, both in normal C-cell function and during oncogenic transformation, will help in the development of novel molecular-targeted therapies.