p21WAF1 and tumourigenesis: 20 years after. Curr Opin Oncol. 2013;25:52-58. [PMID: 23159848 DOI: 10.1097/cco.0b013e32835b639e]

The p53/p73 - p21CIP1 tumor suppressor axis guards against chromosomal instability by restraining CDK1 in human cancer cells

Whole chromosome instability (W-CIN) is a hallmark of human cancer and contributes to the evolvement of aneuploidy. W-CIN can be induced by abnormally increased microtubule plus end assembly rates during mitosis leading to the generation of lagging chromosomes during anaphase as a major form of mitotic errors in human cancer cells. Here, we show that loss of the tumor suppressor genes TP53 and TP73 can trigger increased mitotic microtubule assembly rates, lagging chromosomes, and W-CIN. CDKN1A, encoding for the CDK inhibitor p21^CIP1, represents a critical target gene of p53/p73. Loss of p21^CIP1 unleashes CDK1 activity which causes W-CIN in otherwise chromosomally stable cancer cells. Consequently, induction of CDK1 is sufficient to induce abnormal microtubule assembly rates and W-CIN. Vice versa, partial inhibition of CDK1 activity in chromosomally unstable cancer cells corrects abnormal microtubule behavior and suppresses W-CIN. Thus, our study shows that the p53/p73 - p21^CIP1 tumor suppressor axis, whose loss is associated with W-CIN in human cancer, safeguards against chromosome missegregation and aneuploidy by preventing abnormally increased CDK1 activity.

Chidamide increases the sensitivity of refractory or relapsed acute myeloid leukemia cells to anthracyclines via regulation of the HDAC3 -AKT-P21-CDK2 signaling pathway

BACKGROUND

Induction therapy for acute myeloid leukemia (AML) is an anthracycline-based chemotherapy regimen. However, many patients experience a relapse or exhibit refractory disease (R/R). There is an urgent need for more effective regimens to reverse anthracycline resistance in these patients.

METHODS

In this paper, Twenty-seven R/R AML patients with anthracycline resistance consecutively received chidamide in combination with anthracycline-based regimen as salvage therapy at the Chinese PLA General Hospital.

RESULTS

Of the 27 patients who had received one course of salvage therapy, 13 achieved a complete response and 1 achieved a partial response. We found that the HDAC3-AKT-P21-CDK2 signaling pathway was significantly upregulated in anthracycline-resistant AML cells compared to non-resistant cells. AML patients with higher levels of HDAC3 had lower event-free survival (EFS) and overall survival (OS) rates. Moreover, anthracycline-resistant AML cells are susceptible to chidamide, a histone deacetylase inhibitor which can inhibit cell proliferation, increase cell apoptosis and induce cell-cycle arrest in a time- and dose-dependent manner. Chidamide increases the sensitivity of anthracycline-resistant cells to anthracycline drugs, and these effects are associated with the inhibition of the HDAC3-AKT-P21-CDK2 signaling pathway.

CONCLUSION

Chidamide can increase anthracycline drug sensitivity by inhibiting HDAC3-AKT-P21-CDK2 signaling pathway, thus demonstrating the potential for application.

A Shared Susceptibility Locus in the p53 Gene for both Gastric and Esophageal Cancers in a Northwestern Chinese Population

Background: Upper gastrointestinal tract cancers are the leading causes of cancer-related deaths in Northwest China and they share many similarities in terms of histological type, risk factors, and genetic variants. We hypothesized that shared common single-nucleotide polymorphisms (SNPs) in the p53 pathway exist between patients with gastric and esophageal cancer (EC) patients. Materials and Methods: A case-control study to examine genetic variants in the p53 pathway was conducted with subjects from a high-incidence area for upper gastrointestinal cancers of China. Multiple logistic regression analyses were used to estimate the association of genotypes with gastric cancer and EC risks. Median survival was estimated by using the Kaplan-Meier method and compared by using the log-rank test. Results: Compared with the rs1042522 Pro allele, the rs1042522 Arg allele was associated with an increased risk of gastric cancer (1.810×) and an increased risk of EC (2.285×). The rs1042522 Arg allele carriers who also smoked or consumed alcohol had a further increased risk for gastric cancer odds ratios (OR_smoking = 2.422, OR_drinking = 5.152) and EC (OR_smoking = 5.310, OR_drinking = 8.359). No association was found between the rs1042522 genotypes and survival (p > 0.05). Conclusion: The p53 rs1042522 arg allele together with tobacco smoking and alcohol drinking, was associated with an increased risk, for gastric cancer and EC, but not the survival among northwestern Chinese patients. These associations warrant confirmatory studies.

BCLAF1 induces cisplatin resistance in lung cancer cells

Treatment for non-small cell lung cancer (NSCLC) remains challenging due to frequent recurrence and the development of resistance to platinum-based chemotherapy. The mechanism underlying NSCLC chemoresistance remains unclear. The present study aimed to investigate the mechanism of cisplatin resistance in NSCLC cells and it found that the expression of Bcl-2-associated transcription factor 1 (BCLAF1) was higher in the A549 cell line with cisplatin resistance (A549/DDP) by western blotting and reverse-transcription quantitative PCR, suggesting that elevated BCLAF1 expression is associated with acquired cisplatin resistance in A549 cells. BCLAF1 was found to promote DNA damage repair in A549/DDP cells by regulating γH2A histone family member X foci formation by immunofluorescence and western blotting. BCLAF1 was also demonstrated to regulate ubiquitin-specific peptidase 22 mRNA expression in A549/DDP cells, in addition to regulating G1 phase arrest by targeting p21 expression. Taken together, these findings suggest that BCLAF1 mediates cisplatin resistance by regulating the repair of DNA damage and p21-mediated G1 phase arrest.

SETD8C302R Mutation Revealed from Myofibroblastoma-Discordant Monozygotic Twins Leads to p53/p21 Deficit and WEE1 Inhibitor Sensitivity

High-throughput gene sequencing has identified various genetic variants as the culprits for some common hereditary cancers. However, the heritability of a substantial proportion of cancers remains unexplained, which may result from rare deleterious mutations hidden in a myriad of nonsense genetic variations. This poses a great challenge to the understanding of the pathology and thus the rational design of effective treatments for affected patients. Here, whole genome sequencing is employed in a representative case in which one monozygotic twin is discordant for lung inflammatory myofibroblastoma to disclose rare tumor-related mutations. A missense single nucleotide variation rs61955126 T>C in the lysine methyltransferase SETD8 (accession: NM_020382, SETD8C302R ) is exposed. It is shown that SETD8 is vital for genomic integrity by promoting faithful DNA replication, and its C302R mutation downregulates the p53/p21 pathway. Importantly, the SETD8C302R mutation significantly increases the sensitivity of cancer cells to WEE1 inhibition. Given that WEE1 inhibitors have shown great promise for clinical approval, these results impart a potential therapeutic approach using WEE1 inhibitor for cancer patients carrying the same mutation, and indicate that genome sequencing and genetic functional studies can be integrated into individualized therapies.

p21 can be a barrier to ferroptosis independent of p53

Traditionally, the p21 protein has been viewed as limiting cancer progression and promoting aging. In contrast, there are reports that p21 can enhance cancer survival and limit tissue damage, depending on the tissue of origin and type of stressor involved. Here, we provide evidence to support these latter two roles of p21 by exploring its ability to regulate ferroptosis. Ferroptosis is a form of cell death that is associated with certain degenerative diseases, some of which are aging-related. Our results reveal a correlation between p21 protein levels in cell lines that are resistant to ferroptosis (p21 high) versus cell lines that are sensitive and easily undergo ferroptosis (p21 low). We also show that p21 levels themselves are differentially regulated in response to ferroptosis in a p53-independent manner. Further, experimentally altering the abundance of p21 protein inverts the ferroptosis-sensitivity of both resistant and sensitive human cancer cell lines. Our data also indicate that the interaction of p21 with CDKs is crucial for its ability to restrict the progression of ferroptosis. While this study was performed in cancer cell lines, our results support the potential of p21 to aid in maintenance of healthy tissues by blocking the damage incurred due to ferroptosis.

Transcriptional repression of p21 by EIF1AX promotes the proliferation of breast cancer cells

Objective

Dysregulation of the cell cycle is associated with the progression of malignant cancer, but its precise functional contribution is unknown.

Materials and Methods

The expression of EIF1AX in breast cancer tissues was detected by qRT‐PCR and immunohistochemistry staining. Colony formation and tumour xenograft assays were used to examine the tumorigenesis‐associated function of EIF1AX in vitro and in vivo. RNA‐Seq analysis was used to select the downstream target genes of EIF1AX. Flow cytometry, ChIP and luciferase assays were used to investigate the molecular mechanisms by which EIF1AX regulates p21 in breast cancer cells.

Results

EIF1AX promoted breast cancer cell proliferation by promoting the G1/S cell cycle transition. A mechanistic investigation showed that EIF1AX inhibited the expression of p21, which is an essential cell cycle regulator. We identified that the transcriptional regulation of p21 by EIF1AX was p53‐independent. Clinically, EIF1AX levels were significantly elevated in breast cancer tissues, and the high level of EIF1AX was associated with lower survival rates in breast cancer patients.

Conclusions

Our results imply that EIF1AX may play a key role in the incidence and promotion of breast cancer and may, thus, serve as a valuable target for breast cancer therapy.

A New Inhibitor of Tubulin Polymerization Kills Multiple Cancer Cell Types and Reveals p21-Mediated Mechanism Determining Cell Death after Mitotic Catastrophe

Induction of mitotic catastrophe through the disruption of microtubules is an established target in cancer therapy. However, the molecular mechanisms determining the mitotic catastrophe and the following apoptotic or non-apoptotic cell death remain poorly understood. Moreover, many existing drugs targeting tubulin, such as vincristine, have reduced efficacy, resulting from poor solubility in physiological conditions. Here, we introduce a novel small molecule 2-aminoimidazoline derivative—OAT-449, a synthetic water-soluble tubulin inhibitor. OAT-449 in a concentration range from 6 to 30 nM causes cell death of eight different cancer cell lines in vitro, and significantly inhibits tumor development in such xenograft models as HT-29 (colorectal adenocarcinoma) and SK-N-MC (neuroepithelioma) in vivo. Mechanistic studies showed that OAT-449, like vincristine, inhibited tubulin polymerization and induced profound multi-nucleation and mitotic catastrophe in cancer cells. HeLa and HT-29 cells within 24 h of treatment arrested in G2/M cell cycle phase, presenting mitotic catastrophe features, and 24 h later died by non-apoptotic cell death. In HT-29 cells, both agents altered phosphorylation status of Cdk1 and of spindle assembly checkpoint proteins NuMa and Aurora B, while G2/M arrest and apoptosis blocking was consistent with p53-independent accumulation in the nucleus and largely in the cytoplasm of p21/waf1/cip1, a key determinant of cell fate programs. This is the first common mechanism for the two microtubule-dissociating agents, vincristine and OAT-449, determining the cell death pathway following mitotic catastrophe demonstrated in HT-29 cells.

NCOA5 deficiency promotes a unique liver protumorigenic microenvironment through p21WAF1/CIP1 overexpression, which is reversed by metformin

Prevention and treatment options for hepatocellular carcinoma (HCC) are presently limited, underscoring the necessity for further elucidating molecular mechanisms underlying HCC development and identifying new prevention and therapeutic targets. Here, we demonstrate a unique protumorigenic niche in the livers of Ncoa5+/- mouse model of HCC, which is characterized by altered expression of a subset of genes including p21WAF1/CIP1 and proinflammatory cytokine genes, increased putative hepatic progenitors, and expansions of activated and tissue-resident memory (TRM) CD8+ T lymphocytes, myeloid-derived suppressor cells (MDSCs), and alternatively activated M2 macrophages. Importantly, prophylactic metformin treatment reversed these characteristics including aberrant p21WAF1/CIP1 expression and subsequently reduced HCC incidence in Ncoa5+/- male mice. Heterozygous deletion of the p21WAF1/CIP1 gene alleviated the key features associated with the protumorigenic niche in the livers of Ncoa5+/- male mice. Moreover, transcriptomic analysis reveals that preneoplastic livers of Ncoa5+/- mice are similar to the livers of nonalcoholic steatohepatitis patients as well as the adjacent noncancerous liver tissues of a subset of HCC patients with a relatively poor prognosis. Together, our results suggest that p21WAF1/CIP1 overexpression is essential in the development of protumorigenic microenvironment induced by NCOA5 deficiency and metformin prevents HCC development via alleviating p21WAF1/CIP1 overexpression and protumorigenic microenvironment.

HDAC11 deficiency disrupts oncogene-induced hematopoiesis in myeloproliferative neoplasms

Protein acetylation is an important contributor to cancer initiation. Histone deacetylase 6 (HDAC6) controls JAK2 translation and protein stability and has been implicated in JAK2-driven diseases best exemplified by myeloproliferative neoplasms (MPNs). By using novel classes of highly selective HDAC inhibitors and genetically deficient mouse models, we discovered that HDAC11 rather than HDAC6 is necessary for the proliferation and survival of oncogenic JAK2-driven MPN cells and patient samples. Notably, HDAC11 is variably expressed in primitive stem cells and is expressed largely upon lineage commitment. Although Hdac11is dispensable for normal homeostatic hematopoietic stem and progenitor cell differentiation based on chimeric bone marrow reconstitution, Hdac11 deficiency significantly reduced the abnormal megakaryocyte population, improved splenic architecture, reduced fibrosis, and increased survival in the MPLW515L-MPN mouse model during primary and secondary transplantation. Therefore, inhibitors of HDAC11 are an attractive therapy for treating patients with MPN. Although JAK2 inhibitor therapy provides substantial clinical benefit in MPN patients, the identification of alternative therapeutic targets is needed to reverse MPN pathogenesis and control malignant hematopoiesis. This study establishes HDAC11 as a unique type of target molecule that has therapeutic potential in MPN.

MDM2 and MDMX promote ferroptosis by PPARα-mediated lipid remodeling

Here, Venkatesh et al. investigated the p53-independent roles of MDMX and the MDM2–MDMX complex. They found that MDM2 and MDMX facilitate ferroptosis in cells with or without p53, and that PPARα activity is essential for MDM2 and MDMX to promote ferroptosis, suggesting that the MDM2–MDMX complex regulates lipids through altering PPARα activity.

MDM2 and MDMX, negative regulators of the tumor suppressor p53, can work separately and as a heteromeric complex to restrain p53's functions. MDM2 also has pro-oncogenic roles in cells, tissues, and animals that are independent of p53. There is less information available about p53-independent roles of MDMX or the MDM2–MDMX complex. We found that MDM2 and MDMX facilitate ferroptosis in cells with or without p53. Using small molecules, RNA interference reagents, and mutant forms of MDMX, we found that MDM2 and MDMX, likely working in part as a complex, normally facilitate ferroptotic death. We observed that MDM2 and MDMX alter the lipid profile of cells to favor ferroptosis. Inhibition of MDM2 or MDMX leads to increased levels of FSP1 protein and a consequent increase in the levels of coenzyme Q₁₀, an endogenous lipophilic antioxidant. This suggests that MDM2 and MDMX normally prevent cells from mounting an adequate defense against lipid peroxidation and thereby promote ferroptosis. Moreover, we found that PPARα activity is essential for MDM2 and MDMX to promote ferroptosis, suggesting that the MDM2–MDMX complex regulates lipids through altering PPARα activity. These findings reveal the complexity of cellular responses to MDM2 and MDMX and suggest that MDM2–MDMX inhibition might be useful for preventing degenerative diseases involving ferroptosis. Furthermore, they suggest that MDM2/MDMX amplification may predict sensitivity of some cancers to ferroptosis inducers.

Selenium-binding protein 1 transcriptionally activates p21 expression via p53-independent mechanism and its frequent reduction associates with poor prognosis in bladder cancer

Background

Recent studies have shown that selenium-binding protein 1 (SELENBP1) is significantly down-regulated in a variety of solid tumors. Nevertheless, the clinical relevance of SELENBP1 in human bladder cancer has not been described in any detail, and the molecular mechanism underlying its inhibitory role in cancer cell growth is largely unknown.

Methods

SELENBP1 expression levels in tumor tissues and adjacent normal tissues were evaluated using immunoblotting assay. The association of SELENBP1 expression, clinicopathological features, and clinical outcome was determined using publicly available dataset from The Cancer Genome Atlas bladder cancer (TCGA-BLCA) cohort. DNA methylation in SELENBP1 gene was assessed using online MEXPRESS tool. We generated stable SELENBP1-overexpression and their corresponding control cell lines to determine its potential effect on cell cycle and transcriptional activity of p21 by using flow cytometry and luciferase reporter assay, respectively. The dominant-negative mutant constructs, TAM67 and STAT1 Y701F, were employed to define the roles of c-Jun and STAT1 in the regulation of p21 protein.

Results

Here, we report that the reduction of SELENBP1 is a frequent event and significantly correlates with tumor progression as well as unfavorable prognosis in human bladder cancer. By utilizing TCGA-BLCA cohort, DNA hypermethylation, especially in gene body, is shown to be likely to account for the reduction of SELENBP1 expression. However, an apparent paradox is observed in its 3′-UTR region, in which DNA methylation is positively related to SELENBP1 expression. More importantly, we verify the growth inhibitory role for SELENBP1 in human bladder cancer, and further report a novel function for SELENBP1 in transcriptionally modulating p21 expression through a p53-independent mechanism. Instead, ectopic expression of SELENBP1 pronouncedly attenuates the phosphorylation of c-Jun and STAT1, both of which are indispensable for SELENBP1-mediated transcriptional induction of p21, thereby resulting in the G₀/G₁ phase cell cycle arrest in bladder cancer cell.

Conclusions

Taken together, our findings provide clinical and molecular insights into improved understanding of the tumor suppressive role for SELENBP1 in human bladder cancer, suggesting that SELENBP1 could potentially be utilized as a prognostic biomarker as well as a therapeutic target in future cancer therapy.

The Cell-Cycle Regulatory Protein p21CIP1/WAF1 Is Required for Cytolethal Distending Toxin (Cdt)-Induced Apoptosis

The Aggregatibacter actinomycetemcomitans cytolethal distending toxin (Cdt) induces lymphocytes to undergo cell-cycle arrest and apoptosis; toxicity is dependent upon the active Cdt subunit, CdtB. We now demonstrate that p21^CIP1/WAF1 is critical to Cdt-induced apoptosis. Cdt induces increases in the levels of p21^CIP1/WAF1 in lymphoid cell lines, Jurkat and MyLa, and in primary human lymphocytes. These increases were dependent upon CdtB’s ability to function as a phosphatidylinositol (PI) 3,4,5-triphosphate (PIP3) phosphatase. It is noteworthy that Cdt-induced increases in the levels of p21^CIP1/WAF1 were accompanied by a significant decline in the levels of phosphorylated p21^CIP1/WAF1. The significance of Cdt-induced p21^CIP1/WAF1 increase was assessed by preventing these changes with a two-pronged approach; pre-incubation with the novel p21^CIP1/WAF1 inhibitor, UC2288, and development of a p21^CIP1/WAF1-deficient cell line (Jurkat^p21−) using clustered regularly interspaced short palindromic repeats (CRISPR)/cas9 gene editing. UC2288 blocked toxin-induced increases in p21^CIP1/WAF1, and Jurkat^WT cells treated with this inhibitor exhibited reduced susceptibility to Cdt-induced apoptosis. Likewise, Jurkat^p21− cells failed to undergo toxin-induced apoptosis. The linkage between Cdt, p21^CIP1/WAF1, and apoptosis was further established by demonstrating that Cdt-induced increases in levels of the pro-apoptotic proteins Bid, Bax, and Bak were dependent upon p21^CIP1/WAF1 as these changes were not observed in Jurkat^p21− cells. Finally, we determined that the p21^CIP1/WAF1 increases were dependent upon toxin-induced increases in the level and activity of the chaperone heat shock protein (HSP) 90. We propose that p21^CIP1/WAF1 plays a key pro-apoptotic role in mediating Cdt-induced toxicity.

Fanconi Anemia Pathway: Mechanisms of Breast Cancer Predisposition Development and Potential Therapeutic Targets

The maintenance of genomic stability is crucial for species survival, and its failure is closely associated with tumorigenesis. The Fanconi anemia (FA) pathway, involving 22 identified genes, plays a central role in repairing DNA interstrand cross-links. Importantly, a germline defect in any of these genes can cause Fanconi's anemia, a heterogeneous genetic disorder, characterized by congenital growth abnormalities, bone marrow failure, and predisposition to cancer. On the other hand, the breast cancer susceptibility genes, BRCA1 and BRCA2, also known as FANCS and FANCD1, respectively, are involved in the FA pathway; hence, researchers have studied the association between the FA pathway and cancer predisposition. Here, we mainly focused on and systematically reviewed the clinical and mechanistic implications of the predisposition of individuals with abnormalities in the FA pathway to cancer, especially breast cancer.

UBE2T promotes proliferation via G2/M checkpoint in hepatocellular carcinoma

Background

Growing evidence suggests that the ubiquitin-proteasome system is involved in the pathogenesis and recurrence of hepatocellular carcinoma (HCC); yet, little is known about the role of ubiquitin-conjugating enzyme E2T (UBE2T) in HCC.

Materials and methods

UBE2T levels were detected in HCC tissues and hepatoma cell lines using quantitative reserve transcriptase-polymerase chain reaction and Western blot analysis. Next, the changes of phenotypes after UBE2T knockdown or overexpression were evaluated using in vitro methods. Finally, the mechanism of UBE2T in HCC was tested using ex vivo and in vivo methods.

Results

In the present study, we reported that UBE2T mRNA and protein levels were significantly upregulated in HCC tissues compared to adjacent non-tumor tissues. Additionally, suppression of UBE2T expression inhibited proliferation, colony formation, tumorigenesis, migration, and invasion of hepatoma cells, whereas UBE2T overexpression led to the opposite outcomes. Moreover, suppression of UBE2T expression resulted in an increase in G2/M phase and a decrease in the percentage of cells in G1 phase, which indicated a cell cycle arrest at the G2/M phase. In contrast, the percentage of cells in G2/M phase decreased following UBE2T overexpression. Further study indicated that UBE2T regulated the G2/M transition by modulating cyclin B1 and cyclin-dependent kinase 1.

Conclusion

Taken together, the findings of the present study uncover biological functions of UBE2T in hepatoma cells, and delineate preliminary molecular mechanisms of UBE2T in modulating HCC development and progression.

Environmentally Relevant Concentrations of Bisphenol A Interact with Doxorubicin Transcriptional Effects in Human Cell Lines

The worldwide production of synthetic chemicals, including endocrine disruptor chemicals (EDCs), such as Bisphenol A (BPA) has increased significantly in the last two decades. Human exposure to BPA, particularly through ingestion, is continuous and ubiquitous. Although, considered a weak environmental estrogen, BPA can induce divergent biological responses through several signaling pathways, including carcinogenesis in hormone-responsive organs. However, and despite the continuous increase of tumor cell-resistance to therapeutic drugs, such as doxorubicin (DOX), information regarding BPA drug interactions is still scarce, although its potential role in chemo-resistance has been suggested. This study aims to assess the potential interactions between environmentally relevant levels of BPA and DOX at a therapeutic dosage on Hep-2 and MRC-5 cell lines transciptome. Transcriptional effects in key-player genes for cancer biology, namely c-fos, p21, and bcl-xl, were evaluated through qRT-PCR. The cellular response was analyzed after exposure to BPA, DOX, or co-exposure to both chemicals. Transcriptional analysis showed that BPA exposure induces upregulation of bcl-xl and endorses an antagonistic non-monotonic response on DOX transcriptional effects. Moreover, the BPA interaction with DOX on c-fos and p21 expression emphasize its cellular specificity and divergent effects. Overall, Hep-2 was more susceptible to BPA effects in a dose-dependent manner while MRC-5 transcriptional levels endorsed a non-monotonic response. Our data indicate that BPA environmental exposure may influence chemotherapy outcomes, which emphasize the urgency for a better understanding of BPA interactions with chemotherapeutic agents, in the context of risk assessment.

The Multifaceted p21 (Cip1/Waf1/CDKN1A) in Cell Differentiation, Migration and Cancer Therapy

Loss of cell cycle control is characteristic of tumorigenesis. The protein p21 is the founding member of cyclin-dependent kinase inhibitors and an important versatile cell cycle protein. p21 is transcriptionally controlled by p53 and p53-independent pathways. Its expression is increased in response to various intra- and extracellular stimuli to arrest the cell cycle ensuring genomic stability. Apart from its roles in cell cycle regulation including mitosis, p21 is involved in differentiation, cell migration, cytoskeletal dynamics, apoptosis, transcription, DNA repair, reprogramming of induced pluripotent stem cells, autophagy and the onset of senescence. p21 acts either as a tumor suppressor or as an oncogene depending largely on the cellular context, its subcellular localization and posttranslational modifications. In the present review, we briefly mention the general functions of p21 and summarize its roles in differentiation, migration and invasion in detail. Finally, regarding its dual role as tumor suppressor and oncogene, we highlight the potential, difficulties and risks of using p21 as a biomarker as well as a therapeutic target.

Altered miR-186 and miR-135a contribute to granulosa cell dysfunction by targeting ESR2: A possible role in polycystic ovary syndrome

MicroRNAs (miRNAs) are a group of negative regulators of gene expression that function at the posttranscriptional level. Dysregulation of miRNAs is involved in many pathophysiological processes, including polycystic ovary syndrome (PCOS). In this study, we first detected the expression levels of 6 candidate miRNA in granulosa cells (GCs) from 63 women with PCOS and 20 healthy controls. We found that miR-186 and miR-135a were overexpressed in GCs from PCOS patients. Subsequently, the direct targets of miR-186 and miR-135a were predicted using bioinformatics analysis and verified by luciferase assays and immunoblotting. The present study determined that miR-186 and miR-135a repressed ESR2 expression in GCs, which further inhibited CDKN1A expression, promoted GC proliferation and repressed GC apoptosis. Meanwhile, the levels of miR-186 and miR-135a in GCs were found to positively correlate with serum estradiol levels in patients with PCOS. Furthermore, estradiol treatment directly increased miR-186 and miR-135a levels in KGN and primary GCs, which provides new insight into understanding the pathophysiology of PCOS.

HMGB1 modulates the balance between senescence and apoptosis in response to genotoxic stress

High mobility group box-1 (HMGB1) is involved in various diseases and is associated with the resistance of many types of human cancers to chemotherapy; however, its role in cancer metastasis remains unexplored. This study examined the HMGB1 status of both highly and poorly metastatic cancer cells in response to genotoxic stress. The weakly and highly metastatic mouse melanoma cell lines (B16 vs. B16-F10), human melanoma cell lines (SK-MEL-28 vs. SK-MEL-24), colon cancer cell lines (DLD-1 vs. LS174T), and wild-type (WT) vs. HMGB1 knockout (KO) mouse embryonic fibroblasts (MEFs) were treated with doxorubicin (Dox) and camptothecin (CPT), and then cellular morphology, senescence-associated β-galactosidase staining, lactate dehydrogenase release, and caspase-3 activation were used to assess cell fate. To investigate the role of HMGB1 in p21 expression, HMGB1 and p21 expressions were examined by Western blotting, and the HMGB1-mediated p21 promoter luciferase assay was performed after small interfering RNA or overexpression of HMGB1 prior to Dox treatment. Although highly metastatic mouse melanoma B16-F10 cells preferred senescence, with persistent HMGB1 expression, poorly metastatic B16 cells entered apoptosis, with decreasing HMGB1 levels via cleavage under Dox treatment. Similarly, more metastatic human melanoma SK-MEL-24 and human colon cancer LS174T cells underwent senescence, whereas fewer metastatic melanoma SK-MEL-28 and DLD-1 cells exhibited apoptosis under Dox stimulation. In senescent B16-F10, SK-MEL-24, and LS174T cells treated with Dox, p21 levels were increased by persistent HMGB1 expression. Furthermore, HMGB1 depletion caused a senescence-apoptosis shift with p21 down-regulation in B16-F10 cells, and HMGB1 overexpression switched from apoptosis to senescence concomitantly with increased p21 expression in B16 cells after Dox treatment. The same effects were observed in both cell pairs of mouse melanoma and human colon cancer cells treated with CPT, another genotoxic stressor. Indeed, although WT MEF entered senescence accompanied by p21 increase, HMGB1 KO underwent apoptosis with p21 decrease by Dox treatment. In our cell model system, we demonstrated that highly metastatic cancer cells preferentially enter senescence, whereas apoptosis predominates in weakly metastatic cancer cells under genotoxic stress, which depends on the presence or absence of HMGB1, suggesting that the HMGB1-p21 axis is required for genotoxic stress-induced senescence. These findings suggest that HMGB1 modulation of cancers with different metastatic status could be a strategy for selectively enforcing tumor suppression.-Lee, J.-J., Park, I. H., Rhee, W. J., Kim, H. S., Shin, J.-S. HMGB1 modulates the balance between senescence and apoptosis in response to genotoxic stress.

Regulatory mechanisms of fluvastatin and lovastatin for the p21 induction in human cervical cancer HeLa cells

p21, an inhibitor of cyclin-dependent kinase, functions as an oncogene or tumor suppressor depending on the context of a variety of extracellular and intracellular signals. The expression of p21 could be regulated at the transcriptional and/or post-translational levels. The p21 gene is well-known to be regulated in both p53-dependent and -independent manners. However, the detailed regulatory mechanisms of p21 messenger RNA and protein expression via statins remain unknown, and the possible application of statins as anticancer reagents remains to be controversial. Our data showed that the statins-fluvastatin and lovastatin-induced p21 expression as general histone deacetylase inhibitors in a p53-independent manner, which is mediated through various pathways, such as apoptosis, autophagy, cell cycle progression, and DNA damage, to be involved in the function of p21 in HeLa cells. The curative effect repositioning of digoxin, a cardiovascular medication, was combined with fluvastatin and lovastatin, and the results further implied that p21 induction is involved in a p53-dependent and p53-independent manner. Digoxin modified the effects of statins on ATF3, p21, p53, and cyclin D1 expression, while fluvastatin boosted its DNA damage effect and lovastatin impeded its DNA damage effect. Fluvastatin and lovastatin combined with digoxin further support the localization specificity of their interactivity with our subcellular localization data. This study will not only clarify the regulatory mechanisms of p21 induction by statins but will also shed light on the repurposing of widely cardiovascular medications for the treatment of cervical cancer.

Pancreatic cancer-initiating cell exosome message transfer into noncancer-initiating cells: the importance of CD44v6 in reprogramming

BACKGROUND

Cancer-initiating cell (CIC) exosomes (CIC-TEX) are suggested reprogramming Non-CIC. Mode of message transfer and engagement of CIC-markers being disputed, we elaborated the impact of CD44v6 and Tspan8 on the response of Non-CIC.

METHODS

Non-metastasizing CD44v6- and Tspan8-knockdown (kd) pancreatic cancer cells served as Non-CIC. CIC-TEX coculture-induced changes were evaluated by deep-sequencing and functional assays. Tumor progression was surveyed during in vivo CIC-TEX treatment.

RESULTS

Deep-sequencing of CIC-TEX-cocultured CD44v6kd-Non-CIC revealed pronounced mRNA changes in signaling, transport, transcription and translation; altered miRNA affected metabolism, signaling and transcription. CIC-TEX coculture-induced changes in Tspan8kd-Non-CIC mostly relied on CIC-TEX-Tspan8 being required for targeting. CIC-TEX transfer supported apoptosis resistance and significantly promoted epithelial mesenchymal transition, migration, invasion and (lymph)angiogenesis of the kd Non-CIC in vitro and in vivo, deep-sequencing allowing individual mRNA and miRNA assignment to altered functions. Importantly, CIC-TEX act as a hub, initiated by CD44v6-dependent RTK, GPCR and integrin activation and involving CD44v6-assisted transcription and RNA processing. Accordingly, a kinase inhibitor hampered CIC-TEX-fostered tumor progression, which was backed by an anti-Tspan8 blockade of CIC-TEX binding.

CONCLUSIONS

This in depth report on the in vitro and in vivo impact of CIC-TEX on CD44v6kd and Tspan8kd Non-CIC unravels hub CIC-TEX activity, highlighting a prominent contribution of the CIC-markers CD44v6 to signaling cascade activation, transcription, translation and miRNA processing in Non-CIC and of Tspan8 to CIC-TEX targeting. Blocking CIC-TEX binding/uptake and uptake-initiated target cell activation significantly mitigated the deleterious CIC-TEX impact on CD44v6kd and Tspan8kd Non-CIC.

EZH2 promotes gastric cancer cells proliferation by repressing p21 expression

EZH2 is a core component of the polycomb repressive complex 2 (PRC2), which catalyzes trimethylation of histone H3 lysine 27 (H3K27me3) and promotes carcinogenesis by epigenetically silencing many tumor suppressor genes. Increased EZH2 expression is a marker of advanced and metastatic in many cancers, including lung, prostate and breast cancer, and it has been considered as a potential novel therapeutic target. However, the clinical significance and molecular mechanisms of EZH2 controlling gastric cancer cell proliferation and invasion are not well documented. In this study, immunohistochemical analysis was conducted to investigate the EZH2 expression in gastric cancer. We found that EZH2 levels were increased in gastric cancer tissues compared with adjacent normal tissues. Moreover, patients with high levels of EZH2 expression had a relatively poor prognosis. Furthermore, knockdown of EZH2 expression by siRNA could impair cell proliferation and invasion both in vitro and vivo. Finally, we found that EZH2 influences gastric cancer cells proliferation partly through regulating p21 expression. Our findings present that EZH2 over-expression can be identified as a poor prognostic biomarker in gastric cancer.

Sorting nexin 10 acts as a tumor suppressor in tumorigenesis and progression of colorectal cancer through regulating chaperone mediated autophagy degradation of p21Cip1/WAF1

Chaperone-mediated autophagy (CMA) characterized by the selective degradation of target proteins has been linked with tumorigenesis in recent years. Here, we explored the function of sorting nexin 10 (SNX10), a protein involved in maintaining endosome/lysosome homeostasis, in mediating CMA activity and its impact on the progression of mouse inflammation-driven colorectal cancer. Our results revealed that SNX10 deficiency increased the activation of CMA by preventing the degradation of lysosomal LAMP-2A. In SNX10 KO cells, we disclosed that p21^Cip1/WAF1, a master effector in various tumor suppressor pathways, is a substrate of CMA, and decrease of p21^Cip1/WAF1 caused by SNX10-mediated CMA activation contributes to HCT116 cell proliferation and survival. Moreover, we found that SNX10 KO promoted tumorigenesis in the mouse colorectum which could be restored by SNX10 over-expression. Furthermore, SNX10 was remarkably down-regulated in human CRC tissues which showed the increased activity of CMA and decreased expression of p21^Cip1/WAF1. These findings suggest that SNX10 acts as a tumor suppressor in the mouse colorectum and drives inflammation-associated colorectal cancer by a chaperone-mediated autophagy mechanism.

Antitumor effect of curcumin liposome after transcatheter arterial embolization in VX2 rabbits

Background: Hypoxia may affect the therapeutic efficacy of transcatheter arterial embolization (TAE), which is widely used in nonsurgical hepatocellular carcinoma (HCC). Liposomal curcumin can exert anticancer effect. Our purpose is to explore the antitumor effect of liposomal curcumin on the HCC after TAE.

Methods: The HepG2 cells were cultured under hypoxic condition (1% O₂) and then treated with curcumin liposome. Cell viability, apoptosis and cell cycle were respectively measured by CCK-8 and a flow cytometry. The VX2 rabbits were randomly distributed into three groups: control group with saline embolization, TAE group with lipiodol embolization and curcumin liposome group with curcumin liposome and lipiodol embolization. MRI and CT perfusion scanning were performed after embolization. The hepatocyte apoptosis was measured by the terminal deoxyribonucleotidyl transferse-mediated dUTP nick-end labelling (TUNEL). The vascular endothelial growth factor (VEGF) and microvessel density (MVD) were measured by immunohistochemical. RT-PCR and Western blot were performed to examine mRNA and protein levels.

Results: By regulating the apoptosis-related molecules, curcumin liposome obviously inhibited the cell viability and promoted the apoptosis in G1 phase. Curcumin liposome reduced the tumor size and alleviated neoplasia in VX2 rabbits. Curcumin liposome decreased the expressions of MVD and VEGF and increased the apoptosis of liver tissues. The levels of hypoxia-inducible factor-1α (HIF-1α) and survivin were suppressed by curcumin liposome both in hypoxic cells and liver tissues in the VX2 rabbits.

Conclusion: Curcumin liposome exerted antitumor effect by regulating the proliferation- and apoptosis-related molecules. Curcumin liposome suppressed the HIF-1α and survivin levels and inhibited the angiogenesis in VX2 rabbits after TAE.

Induction of Apoptosis and Cell-Cycle Arrest in Human Colon-Cancer Cells by Whole-Grain Alkylresorcinols via Activation of the p53 Pathway

Colon cancer, one of the leading causes of cancer-associated deaths, is the target of choice for nutrition-based-prevention approaches because of the direct and early contact between the active compounds and the cancerous tissues. We previously reported alkylresorcinols (ARs) as the major active components in wheat bran against human colon cancer. Here, we further investigate the anticancer mechanisms of action of ARs. Our mechanistic studies indicated that AR C15 and AR C17 exert their anticancer activities in colon-cancer cells by inducing apoptosis through PUMA upregulation and mitochondrial-pathway activation, inducing cell-cycle arrest through p21 upregulation, and inhibiting proteasome activity and Mdm2 expression. This cascade of distinct mechanisms was linked to the consequent activation and accumulation of p53. The results of treatment with p53 inhibitor further confirmed that the p53 pathway might play a very important role in AR-induced apoptosis in colon-cancer cells. Altogether these results show that AR C15 and AR C17 can specifically activate the mitochondrial pathway of apoptosis and cause cell-cycle arrest and that inhibition of p53 greatly reduces the activation of this pathway.

A BTB-ZF protein, ZNF131, is required for early B cell development

Members of the BTB-ZF transcription factor family play important roles in lymphocyte development. During T cell development, ZNF131, a BTB-ZF protein, is critical for the double-negative (DN) to double-positive (DP) transition and is also involved in cell proliferation. Here, we report that knockout of Znf131 at the pre-pro-B cell stage in mb1-Cre knock-in mouse resulted in defect of pro-B to pre-B cell transition. ZNF131 was shown to be required for efficient pro-B cell proliferation as well as for immunoglobulin heavy chain gene rearrangement that occurs in the proliferating pro-B cells. We speculate that inefficient gene rearrangement may be due to loss of cell proliferation, since cell cycle progression and immunoglobulin gene rearrangement, which would occur in a mutually exclusive manner, may be interconnected or coupled to avoid occurrence of genomic instability. ZNF131 suppresses expression of Cdk inhibitor, p21^cip1, and that of pro-apoptotic factors, Bax and Puma, targets of p53, to facilitate cell cycle progression and suppress unnecessary apoptosis, respectively, of pro-B cells. There results demonstrate the essential roles of ZNF131 in coordinating the B cell differentiation and proliferation.

Uncovering the pharmacological response of novel sesquiterpene derivatives that differentially alter gene expression and modulate the cell cycle in cancer cells

The present study aimed to assess the pharmacological anticancer profile of three natural and five synthetic sesquiterpenes developed by total chemical synthesis. To this end, their properties at the cellular and molecular level were evaluated in a panel of normal and cancer cell lines. The results obtained by performing cytotoxicity assays and gene expression analysis by reverse transcription-quantitative polymerase chain reaction showed that: i) Among the sesquiterpene derivatives analyzed, VDS58 exhibited a notable anticancer profile within attached (U-87 MG and MCF-7) and suspension (K562 and MEL-745) cancer cell cultures; however, U-87 MG cells were able to recover their proliferation capacity rapidly after 48 h of exposure; ii) gene expression profiling of U-87 MG cells, in contrast to K562 cells, showed a transient induction of cyclin-dependent kinase inhibitor 1A (CDKN1) expression; iii) the expression levels of transforming growth factor β1 (TGFB1) increased after 12 h of exposure of U-87 MG cells to VDS58 and were maintained at this level throughout the treatment period; iv) in K562 cells exposed to VDS58, TGFB1 expression levels were upregulated for 48 h and decrease afterwards; and v) the re-addition of VDS58 in U-87 MG cultures pretreated with VDS58 resulted in a notable increase in the expression of caspases (CASP3 and CASP9), BCL2‑associated agonist of cell death (BAD), cyclin D1, CDK6, CDKN1, MYC proto-oncogene bHLH transcription factor (MYC), TGFB1 and tumor suppressor protein p53. This upregulation persisted only for 24 h for the majority of genes, as afterwards, only the expression of TGFB1 and MYC was maintained at high levels. Through bioinformatic pathway analysis of RNA-Seq data of parental U-87 MG and K562 cells, substantial variation was reported in the expression profiles of the genes involved in the regulation of the cell cycle. This was associated with the differential pharmacological profiles observed in the same cells exposed to VDS58. Overall, the data presented in this study provide novel insights into the molecular mechanisms of action of sesquiterpene derivatives by dysregulating the expression levels of genes associated with the cell cycle of cancer cells.

PLAGL1 gene function during hepatoma cells proliferation

Hepatocellular carcinoma develops as a multistep process, in which cell cycle deregulation is a central feature, resulting in unscheduled proliferation. The PLAGL1 gene encodes a homonym zinc finger protein that is involved in cell-proliferation control. We determined the genomic profile and the transcription and expression level of PLAGL1, simultaneously with that of its molecular partners p53, PPARγ and p21, in cell-lines derived from patients with liver cancer, during in vitro cell growth. Our investigations revealed that genomic and epigenetic changes of PLAGL1 are also present in hepatoma cell-lines. Transcription of PLAGL1 in tumor cells is significantly lower than in normal fibroblasts, but no significant differences in terms of protein expression were detected between these two cell-types, indicating that there is not a direct relationship between the gene transcriptional activity and protein expression. RT-PCR analyses on normal fibroblasts, used as control, also showed that PLAGL1 and p53 genes transcription occurs as an apparent orchestrated process during normal cells proliferation, which gets disturbed in cancer cells. Furthermore, abnormal trafficking of the PLAGL1 protein may occur in hepatocarcinogenesis.

MECHANISMS OF ENDOCRINOLOGY: Cell cycle regulation in adrenocortical carcinoma

Adrenocortical carcinomas (ACCs) are rather rare endocrine tumors that often have a poor prognosis. The reduced survival rate associated with these tumors is due to their aggressive biological behavior, combined with the scarcity of effective treatment options that are currently available. The recent identification of the genomic alterations present in ACC have provided further molecular mechanisms to develop consistent strategies for the diagnosis, prevention of progression and treatment of advanced ACCs. Taken together, molecular and genomic advances could be leading the way to develop personalized medicine in ACCs similarly to similar developments in lung or breast cancers. In this review, we focused our attention to systematically compile and summarize the alterations in the cell cycle regulation that were described so far in ACC as they are known to play a crucial role in cell differentiation and growth. We have divided the analysis according to the major transition phases of the cell cycle, G1 to S and G2 to M. We have analyzed the most extensively studied checkpoints: the p53/Rb1 pathway, CDC2/cyclin B and topoisomerases (TOPs). We reached the conclusion that the most important alterations having a potential application in clinical practice are the ones related to p53/Rb1 and TOP 2. We also present a brief description of on-going clinical trials based on molecular alterations in ACC. The drugs have targeted the insulin-like growth factor receptor 1, TOP 2, polo-like kinase1, cyclin-dependent kinase inhibitors, p53 reactivation and CDC25.

[Expressions of ΔNp63α, DPC4/Smad4 and P21 in cervical squamous cell carcinoma an their clinical significance]

OBJECTIVE

To investigate the expressions of ΔNp63α, DPC4/Smad4 and P21 in cervical squamous cell carcinomas and explore their implications in tumorigenesis, progression and prognosis of the malignancy.

METHODS

The expressions of ΔNp63α, DPC4/Smad4 and P21 were examined with immunohistochemistry in 100 specimens of cervical squamous cell carcinoma, 40 specimens of cervical intraepithelial neoplasia (CIN) and 40 specimens of normal cervical tissues to explore their associations with the occurrence, progression and prognosis of cervical squamous cell carcinoma.

RESULTS

The expressions of ΔNp63α and DPC4/Smad4 decreased and P21 expression increased significantly in the order of normal cervical tissue, CIN and cervical squamous cell carcinoma (P < 0.01), and their expressions were associated with the differentiation, clinical stages and lymph node metastasis of cervical squamous cell carcinoma (P < 0.01). The expression of ΔNp63α was positively correlated with the expression of DPC4/Smad4 (r=0.581, P < 0.05), and they were both negatively correlated with P21 expression (r=-0.449 and -0.254, respectively; P < 0.05). Kaplan-Meier survival analysis showed that patients with cervical squamous cell carcinoma positive for ΔNp63α and DPC4/Smad4 had a significantly higher 5-year survival rate than those negative for ΔNp63α and DPC4/Smad4 (P < 0.001); the patients positive for P21 had a significantly lower 5-year survival rate than the P21-negative patients (P < 0.005).

CONCLUSIONS

The expressions of ΔNp63α, DPC4/Smad4 and P21are related with the differentiation, invasion, lymph node metastasis, pTNM stage and prognosis of in cervical squamous cell carcinomas, suggesting their value as potential markers for prognostic evaluation of patients with cervical squamous cell carcinoma.

Correlation between S100A11 and the TGF-β1/SMAD4 pathway and its effects on the proliferation and apoptosis of pancreatic cancer cell line PANC-1

S100A11 as a S100 protein family member has been documented to play dual-direction regulation over cancer cell proliferation. We explored the role of S100A11 in the proliferation and apoptosis of pancreatic cancer cell line PANC-1 and the potential mechanisms involving the TGF-β₁/SMAD4/p21 pathway. S100A11 and TGF-β₁ protein expressions in 30 paraffin-embedded specimens were evaluated by immunohistochemistry. S100A11 and TGF-β₁ expression in PANC-1 cell line was suppressed using small interfering RNA (siRNA), respectively. Subsequently, pancreatic cancer cell apoptosis was measured by Cell Counting Kit-8 and flow cytometry, and S100A11 and TGF-β1/SMAD4/p21 pathway proteins and genes were detected with Western blotting and quantitative polymerase chain reaction (qPCR). S100A11 cytoplasmic/nuclear protein translocation was examined using NE-PER® cytoplasm/nuclear protein extraction in cells interfered with TGF-β1 siRNA. Our results showed that S100A11 expression was positively correlated with TGF-β₁ expression in pancreatic cancerous tissue. Silencing TGF-β₁ down-regulated intracellular P21^WAF1 expression by 90%, blocked S100A11 from cytoplasm entering nucleus, and enhanced cell proliferation. Silencing S100A11 down-regulated intracellular P21 expression and promoted cell apoptosis without significantly changing TGF-β₁ and SMAD4 expression. Our findings revealed that S100A11 and TGF-β₁/SMAD4 signaling pathway were related but mutually independent in regulating PANC-1 cells proliferation and apoptosis. Other independent mechanisms might be involved in S100A11's regulation of pancreatic cell growth. S100A11 could be a potential gene therapy target for pancreatic cancer.

TSPY1 suppresses USP7-mediated p53 function and promotes spermatogonial proliferation

Testis-specific protein Y-linked 1 (TSPY1) is expressed predominantly in adult human spermatogonia and functions in the process of spermatogenesis; however, our understanding of the underlying mechanism is limited. Here we observed that TSPY1, as an interacting partner of TSPY-like 5 (TSPYL5), enhanced the competitive binding of TSPYL5 to ubiquitin-specific peptidase 7 (USP7) in conjunction with p53. This activity, together with its promotion of TSPYL5 expression by acting as a transcription factor, resulted in increased p53 ubiquitylation. Moreover, TSPY1 could decrease the p53 level by inducing the degradation of ubiquitinated USP7. We demonstrated that the promotion of p53 degradation by TSPY1 influenced the activity of p53 target molecules (CDK1, p21, and BAX) to expedite the G2/M phase transition and decrease cell apoptosis, accelerating cell proliferation. Taken together, the observations reveal the significance of TSPY1 as a suppressor of USP7-mediated p53 function in inhibiting p53-dependent cell proliferation arrest. By simulating TSPY1 function in Tspy1-deficient spermatogonia derived from mouse testes, we found that TSPY1 could promote spermatogonial proliferation by decreasing the Usp7-modulated p53 level. The findings suggest an additional mechanism underlying the regulation of spermatogonial p53 function, indicating the significance of TSPY1 in germline homeostasis maintenance and the potential of TSPY1 in regulating human spermatogonial proliferation via the USP7-mediated p53 signaling pathway.

Deubiquitylation and stabilization of p21 by USP11 is critical for cell-cycle progression and DNA damage responses

Previous studies have demonstrated that p21 occupies a central position in cell-cycle regulation and DNA damage responses. As an unstable protein, the regulation of p21 stability has been extensively investigated over the past 20 years. Although p21 degradation by the ubiquitin-proteasome pathway has been well characterized, it is unclear whether ubiquitylated p21 can be recycled. Here, we identify USP11 as a deubiquitylase that directly removes p21 polyubiquitylation and stabilizes p21 protein, revealing that cellular p21 protein is finely regulated by a dynamic balance of USP11-mediated stabilization and proteasome-mediated degradation. Meanwhile, we also provide evidence that the USP11-p21 axis plays a crucial role in G1/S transition under physiological conditions and in regulating the balance between cytostasis and apoptosis.

p21^WAF1/CIP1 is a broad-acting cyclin-dependent kinase inhibitor. Its stability is essential for proper cell-cycle progression and cell fate decision. Ubiquitylation by the multiple E3 ubiquitin ligase complexes is the major regulatory mechanism of p21, which induces p21 degradation. However, it is unclear whether ubiquitylated p21 can be recycled. In this study, we report USP11 as a deubiquitylase of p21. In the nucleus, USP11 binds to p21, catalyzes the removal of polyubiquitin chains conjugated onto p21, and stabilizes p21 protein. As a result, USP11 reverses p21 polyubiquitylation and degradation mediated by SCF^SKP2, CRL4^CDT2, and APC/C^CDC20 in a cell-cycle–independent manner. Loss of USP11 causes the destabilization of p21 and induces the G1/S transition in unperturbed cells. Furthermore, p21 accumulation mediated by DNA damage is completely abolished in cells depleted of USP11, which results in abrogation of the G2 checkpoint and induction of apoptosis. Functionally, USP11-mediated stabilization of p21 inhibits cell proliferation and tumorigenesis in vivo. These findings reveal an important mechanism by which p21 can be stabilized by direct deubiquitylation, and they pinpoint a crucial role of the USP11-p21 axis in regulating cell-cycle progression and DNA damage responses.

Senescence promotes in vivo reprogramming through p16INK4a and IL-6

Cellular senescence is a damage response aimed to orchestrate tissue repair. We have recently reported that cellular senescence, through the paracrine release of interleukin-6 (IL6) and other soluble factors, strongly favors cellular reprogramming by Oct4, Sox2, Klf4, and c-Myc (OSKM) in nonsenescent cells. Indeed, activation of OSKM in mouse tissues triggers senescence in some cells and reprogramming in other cells, both processes occurring concomitantly and in close proximity. In this system, Ink4a/Arf-null tissues cannot undergo senescence, fail to produce IL6, and cannot reprogram efficiently; whereas p53-null tissues undergo extensive damage and senescence, produce high levels of IL6, and reprogram efficiently. Here, we have further explored the genetic determinants of in vivo reprogramming. We report that Ink4a, but not Arf, is necessary for OSKM-induced senescence and, thereby, for the paracrine stimulation of reprogramming. However, in the absence of p53, IL6 production and reprogramming become independent of Ink4a, as revealed by the analysis of Ink4a/Arf/p53 deficient mice. In the case of the cell cycle inhibitor p21, its protein levels are highly elevated upon OSKM activation in a p53-independent manner, and we show that p21-null tissues present increased levels of senescence, IL6, and reprogramming. We also report that Il6-mutant tissues are impaired in undergoing reprogramming, thus reinforcing the critical role of IL6 in reprogramming. Finally, young female mice present lower efficiency of in vivo reprogramming compared to male mice, and this gender difference disappears with aging, both observations being consistent with the known anti-inflammatory effect of estrogens. The current findings regarding the interplay between senescence and reprogramming may conceivably apply to other contexts of tissue damage.

Bone marrow derived mesenchymal stem cells transplantation rescues premature ovarian insufficiency induced by chemotherapy

Premature ovarian insufficiency (POI) is an important cause of infertility and also cause menopausal symptoms, which greatly reduced the quality of life for women. Hormone replacement therapy (HRT), as an important strategy, improved the quality of life for patients, however, the role of HRT in promoting fertility remains controversial. Therefore, seeking an optimal regime for POI becomes more urgent. In this study, we established POI model induced by CTX and BUS and utilized bone marrow derived mesenchymal stem cells (BM-MSCs) transplantation to treat the POI. We found that the decrease of estrogen and the increase of FSH induced by administration of CTX and BUS were rescued by BM-MSC transplantation. H&E staining and TUNEL assay showed that there were more healthy ovarian follicles and less apoptosis of ovarian cells after treatment with BM-MSCs. Further studies showed that there was an obvious decrease of Bax, p53, and p21 after transplantation, however, CyclinD2 was increased. In conclusion, our results demonstrated that BM-MSCs could restore injured ovarian function. Inhibiting apoptosis and promoting residual ovarian cell proliferation may contribute to the process.

Long noncoding RNA LINC01510 promotes the growth of colorectal cancer cells by modulating MET expression

Background

Abnormal expression of long non-coding RNA (lncRNAs) often facilitates unrestricted growth of cancer cells. Long intergenic non-protein coding RNA 1510, an enhancer lncRNA (LINC01510), a lncRNA enhancer is upregulated in colorectal cancer (CRC), and its expression might relate to MET as revealed by lncRNA microarray data. However, the potential biological role of LINC01510 and its regulatory mechanism in CRC remain unclear. Therefore, we investigated the involvement of LINC01510 in the proliferation of CRC cells.

Methods

Microarray analysis, In situ hybridization, colony formation assay, MTT assay, Western blotting, quantitative RT-PCR and flow cytometry were applied. The two-tailed Student’s t test and analysis of variance or general linear model of single factor variable was used for statistical analyse.

Results

In the present study, we found that LINC01510 was significantly upregulated in CRC tissues and cell lines. The LINC01510 expression level were associated with the clinicopathological grade and stage. Meanwhile, gain- and loss-of-function assays demonstrated that LINC01510 overexpression increased CRC cell proliferation, and promoted cell cycle progression from the G1 phase to the S phase. Further study indicated that LINC01510 was positively correlated with the expression of MET, and its effects were most likely at the transcriptional level.

Conclusions

Taken together, our findings suggested that upregulation of LINC01510 contributes to the proliferation of CRC cells, at least in part, through the regulation of MET protein. LINC01510 could be a candidate prognostic biomarker and a target for new therapies in CRC patients.

Fanconi anaemia and cancer: an intricate relationship

Fanconi anaemia (FA) is a genetic disorder that is characterized by bone marrow failure (BMF), developmental abnormalities and predisposition to cancer. Together with other proteins involved in DNA repair processes and cell division, the FA proteins maintain genome homeostasis, and germline mutation of any one of the genes that encode FA proteins causes FA. Monoallelic inactivation of some FA genes, such as FA complementation group D1 (FANCD1; also known as the breast and ovarian cancer susceptibility gene BRCA2), leads to adult-onset cancer predisposition but does not cause FA, and somatic mutations in FA genes occur in cancers in the general population. Carcinogenesis resulting from a dysregulated FA pathway is multifaceted, as FA proteins monitor multiple complementary genome-surveillance checkpoints throughout interphase, where monoubiquitylation of the FANCD2-FANCI heterodimer by the FA core complex promotes recruitment of DNA repair effectors to chromatin lesions to resolve DNA damage and mitosis. In this Review, we discuss how the FA pathway safeguards genome integrity throughout the cell cycle and show how studies of FA have revealed opportunities to develop rational therapeutics for this genetic disease and for malignancies that acquire somatic mutations within the FA pathway.

A microRNA/Runx1/Runx2 network regulates prostate tumor progression from onset to adenocarcinoma in TRAMP mice

While decades of research have identified molecular pathways inducing and promoting stages of prostate cancer malignancy, studies addressing dynamic changes of cancer-related regulatory factors in a prostate tumor progression model are limited. Using the TRAMP mouse model of human prostate cancer, we address mechanisms of deregulation for the cancer-associated transcription factors, Runx1 and Runx2 by identifying microRNAs with reciprocal expression changes at six time points during 33 weeks of tumorigenesis. We molecularly define transition stages from PIN lesions to hyperplasia/neoplasia and progression to adenocarcinoma by temporal changes in expression of human prostate cancer markers, including the androgen receptor and tumor suppressors, Nkx3.1 and PTEN. Concomitant activation of PTEN, AR, and Runx factors occurs at early stages. At late stages, PTEN and AR are downregulated, while Runx1 and Runx2 remain elevated. Loss of Runx-targeting microRNAs, miR-23b-5p, miR-139-5p, miR-205-5p, miR-221-3p, miR-375-3p, miR-382-5p, and miR-384-5p, contribute to aberrant Runx expression in prostate tumors. Our studies reveal a Runx/miRNA interaction axis centered on PTEN-PI3K-AKT signaling. This regulatory network translates to mechanistic understanding of prostate tumorigenesis that can be developed for diagnosis and directed therapy.

Loss of p21 promoted tumorigenesis in the background of telomere dysfunctions induced by TRF2 and Wrn deficiency

Werner syndrome (WS) is a rare autosomal recessive progeria disease with genetic instability/cancer predisposition, thus a good model in understanding aging related carcinogenesis. Telomere dysfunction induced cellular senescence is essential in the manifestation of the WS phenotype. Our previous data has shown that p21 (encoded by Cdkn1a gene) could induce cellular senescence and suppress cellular growth of ALT (alternative lengthening of telomere) tumors derived from WS, suggested that p21 might play a key role in maintaining senescence of WS cells.

To confirm the role of p21 in suppressing telomere dysfunction induced tumorigenesis, we overexpressed dominant negative protein TRF2^ΔBΔM in p21^-/- mouse embryonic fibroblasts (MEFs). To further stress the cell, we crossed Wrn^-/-mice with p21^-/- mice to obtained p21^-/-Wrn^-/- MEFs, and overexpressed TRF2^ΔBΔM in these MEFs to induce telomere dysfunction similar to that in WS cells. Our data showed that, in the context of p21^-/-TRF2^ΔBΔM, loss of p21 function rescued cellular senescence, and induced p53 mutation, but did not induce tumorigenesis. However, in the set of p21^-/-Wrn^-/-TRF2^ΔBΔM, loss of p21 function induced p53 mutation and tumorigenesis.

To further verify the role of p21 in suppressing telomere dysfunction related tumorigenesis, we knocked down p21 in non-tumorigenic immortalized cells derived from WS MEFs (mTerc^-/-Wrn^-/-), and found that loss of p21 could induce ALT tumorigenesis, which displayed typical smear pattern of telomere length and arc-shaped telomeric DNA. In another hand, recovering telomerase activity in these MEFs could also induce tumorigenesis without affecting p21 expression level. Together our data suggested that p21 controlled cell cycle regulation played an essential role in suppressing telomere dysfunction-related tumorigenesis. These data also suggested that the genetic context is essential in determining the role of p21 in cancer prevention. Therefore, targeting p21 in the treatment of human degenerative diseases would require a personalized genetic background screen.

Acute HSF1 depletion induces cellular senescence through the MDM2-p53-p21 pathway in human diploid fibroblasts

Heat shock transcription factor 1 (HSF1) regulates the expression of a wide array of genes, control of the expression of heat shock proteins (HSPs) and cell growth. Although acute depletion of HSF1 induces cellular senescence, the underlying mechanisms are poorly understood. Here, we report that HSF1 depletion-induced senescence (HDIS) of human diploid fibroblasts (HDFs) was independent of HSP-mediated proteostasis but dependent on activation of the p53-p21 pathway, partly because of the increased expression of dehydrogenase/reductase 2 (DHRS2), a putative MDM2 inhibitor. We observed that HDIS occurred without decreased levels of major HSPs or increased proteotoxic stress in HDFs. Additionally, an inhibitor of HSP70 family proteins increased proteotoxicity and suppressed cell growth, but failed to induce senescence. Importantly, we found that activation of the p53-p21 pathway due to reduced MDM2-dependent p53 degradation was required for HDIS. Furthermore, we provide evidence that increased DHRS2 expression contributes to p53 stabilization and HDIS. Collectively, our observations uncovered a molecular pathway in which HSF1 depletion-induced DHRS2 expression leads to activation of the MDM2-p53-p21 pathway required for HDIS.

TBX2 expression is associated with platinum-sensitivity of ovarian serous carcinoma

The standard treatment for ovarian serous carcinoma comprises maximum debulking surgery and platinum-based chemotherapy. Despite the high response rate to chemotherapy, the majority of patients will be resistant to first-line agents and the prognosis for these patients is particularly poor. At present there are no reliable methods to determine or predict platinum resistance. T-box 2 (TBX2) is widely expressed in cancer cells and is involved in embryonic development and cell cycle regulation. TBX2 enables cells to bypass senescence through its ability to repress the cell cycle regulators p21 and p14^ARF; silencing TBX2 induces senescence. Ectopic expression of TBX2 is associated with conferred resistance to the DNA-damaging chemotherapeutic drugs cisplatin and doxorubicin. In the present study the association between TBX2 expression and platinum sensitivity was investigated. A total of 54 patients with ovarian serous carcinoma (FIGO stages III and IV) were treated at Osaka City University Hospital (Osaka, Japan) from January 2005 to December 2012. Patients were divided into platinum-sensitive (n=27) and resistant (n=27) groups, according to the platinum-free interval calculated from the last platinum administration to the time of recurrence. TBX2 expression in human ovarian serous carcinoma cells was inhibited by a TBX2-specific siRNA and changes in cisplatin and carboplatin sensitivity were determined. The TBX2-weighted score was significantly lower in the platinum-sensitive group than the platinum-resistant group (P=0.005) and the low TBX2 expression group was significantly more sensitive to platinum-based chemotherapy (P=0.004). Sensitivity to cisplatin and carboplatin significantly increased when TBX2 expression was inhibited in human ovarian serous carcinoma cells in vitro (P<0.05). TBX2 expression may serve as a predictive marker of the efficacy of platinum-based chemotherapy for patients with ovarian serous carcinoma.

Knockdown of microRNA-29a regulates the expression of apoptosis-related genes in MCF-7 breast carcinoma cells

MicroRNA (miR), as non-coding small RNA, are key regulators of cancer-related biological cell processes and contribute to tumor growth through regulation of groups of pro- and anti-apoptotic genes. The present study aimed to investigate the effects of miR-29a on the expression of genes involved in apoptosis, including p21, B-cell lymphoma 2 (BCL-2), p53 and survivin. The MCF-7 breast cancer cell line was transfected with anti-miR-29a and treated with Taxol in subdivided treatment groups including: Scramble; anti-miR-29a; anti-miR-29a + Taxol; Taxol; and control. Expression levels of p21, BCL-2, p53 and survivin were evaluated using reverse transcription-quantitative polymerase chain reaction. miR-29a knockdown resulted in p21 and p53 upregulation and a decrease in survivin expression. These results indicated that miR-29a inhibition regulates apoptosis. The present data suggested that miR-29a inhibition may be a promising strategy for the induction of apoptosis of tumor cells.

Curcumin ameliorates the in vitro efficacy of carfilzomib in human multiple myeloma U266 cells targeting p53 and NF-κB pathways

Multiple myeloma (MM) is a malignant B-cell neoplasm with accumulation of malignant plasma cells in bone marrow. Pharmacological therapy improves response frequency even if with various associated toxicities. Herein, we investigated if combination of curcumin with carfilzomib (CFZ) can induce a better cytotoxic effect on in vitro cultured U266 cells. Cell viability data showed that curcumin significantly ameliorates CFZ cytotoxic effect. Furthermore, curcumin alone did not affect proteasome at the tested dose, confirming the involvement of different mechanisms in the observed effects. U266 cells exposure to curcumin or CFZ increased reactive species (RS) levels, although their production did not appear further potentiated following drugs combination. Interestingly, NF-κB nuclear accumulation was reduced by treatment with CFZ or curcumin, and was more deeply decreased in cells treated with CFZ-curcumin combinations, very likely due to the different mechanisms through which they target NF-κB. Our results confirmed the induction of p53/p21 axis and G0/G1 cell cycle arrest in anticancer activities of both drugs, an effect more pronounced for the CFZ-curcumin tested combinations. Furthermore, curcumin addition enhanced CFZ proapoptotic effect. These findings evidence that curcumin can ameliorate CFZ efficacy, and lead us to hypothesize that this effect might be useful to optimize CFZ therapy in MM patients.

miR-30e controls DNA damage-induced stress responses by modulating expression of the CDK inhibitor p21WAF1/CIP1 and caspase-3

MicroRNAs (miRNAs), a class of small non-coding RNAs that usually cause gene silencing by translational repression or degradation of mRNAs, are implicated in DNA damage-induced stress responses. To identify senescence-associated miRNAs, we performed microarray analyses using wild-type and p53-deficient HCT116 colon carcinoma cells that following gamma-irradiation (γIR) are driven into senescence and apoptosis, respectively. Several miRNAs including miR-30e were found upregulated in a p53-dependent manner specifically in senescent cells, but not in apoptotic cells. Overexpression of miR-30e in HCT116 cells not only inhibited γIR-, etoposide- or miR-34a-induced caspase-3-like DEVDase activities and cell death, but greatly accelerated and augmented their senescent phenotype. Consistently, procaspase-3 protein, but not mRNA decreased in the presence of miR-30e, whereas expression of the cyclin-dependent kinase inhibitor p21 increased both at the mRNA and protein level. Performing luciferase reporter gene assays, we identified the 3′-UTR of the caspase-3 mRNA as a direct miR-30e target. In contrast, although miR-30e was unable to bind to the p21 mRNA, it increased expression of a luciferase construct containing the p21 promoter, suggesting that the miR-30e-mediated upregulation of p21 occurs indirectly at the transcriptional level. Interestingly, despite suppressing procaspase-3 expression, miR-30e was unable to protect RKO colon carcinoma cells from DNA damage-induced death or to induce senescence, as miR-30e completely fails to upregulate p21 in these cells. These data suggest that miR-30e functions in a cell type-dependent manner as an important molecular switch for DNA damage-induced stress responses and may thus represent a target of therapeutic value.