The p21(cip1/waf1) cyclin-dependent kinase inhibitor enhances the cytotoxic effect of cisplatin in human ovarian carcinoma cells

Cell cycle machinery in oncology: A comprehensive review of therapeutic targets

The cell cycle is tightly regulated to ensure controlled cell proliferation. Dysregulation of the cell cycle machinery is a hallmark of cancer that leads to unchecked growth. This review comprehensively analyzes key molecular regulators of the cell cycle and how they contribute to carcinogenesis when mutated or overexpressed. It focuses on cyclins, cyclin-dependent kinases (CDKs), CDK inhibitors, checkpoint kinases, and mitotic regulators as therapeutic targets. Promising strategies include CDK4/6 inhibitors like palbociclib, ribociclib, and abemaciclib for breast cancer treatment. Other possible targets include the anaphase-promoting complex/cyclosome (APC/C), Skp2, p21, and aurora kinase inhibitors. However, challenges with resistance have limited clinical successes so far. Future efforts should focus on combinatorial therapies, next-generation inhibitors, and biomarkers for patient selection. Targeting the cell cycle holds promise but further optimization is necessary to fully exploit it as an anti-cancer strategy across diverse malignancies.

cGAS Regulates the Radioresistance of Human Head and Neck Squamous Cell Carcinoma Cells

Cyclic GMP-AMP synthase (cGAS) plays an important role in biological responses to pathogens. The activation of the cGAS pathway in immune cells is known to induce antitumor effects, but the role of cGAS in cancer cells remains poorly understood. In silico analysis using public databases suggested that high cGAS expression in head and neck squamous cell carcinoma (HNSCC) is indicative of a poor prognosis for HNSCC patients. We therefore investigated the role of cGAS in malignancies and the cellular radiation response of human HNSCC cells (SAS and Ca9-22) in vitro, because radiotherapy is one of the treatments most commonly used for HNSCC. Although cGAS knockdown failed to suppress the proliferation of non-irradiated HNSCC cells, it enhanced the radiosensitivity of HNSCC cells. The administration of the cGAS agonist increased the radioresistance of HNSCC cells. cGAS knockdown increased radiation-induced mitotic catastrophe, apoptosis, or cellular senescence, depending on the cell line, and this cell line-dependent response might be due to different responses of p21 after irradiation. Collectively, our findings indicate that the cGAS pathway regulates the radioresistance of HNSCC cells.

The Active Subunit of the Cytolethal Distending Toxin, CdtB, Derived From Both Haemophilus ducreyi and Campylobacter jejuni Exhibits Potent Phosphatidylinositol-3,4,5-Triphosphate Phosphatase Activity

Human lymphocytes exposed to Aggregatibacter actinomycetemcomitans (Aa) cytolethal distending toxin (Cdt) undergo cell cycle arrest and apoptosis. In previous studies, we demonstrated that the active Cdt subunit, CdtB, is a potent phosphatidylinositol (PI) 3,4,5-triphosphate phosphatase. Moreover, AaCdt-treated cells exhibit evidence of PI-3-kinase (PI-3K) signaling blockade characterized by reduced levels of PIP3, pAkt, and pGSK3β. We have also demonstrated that PI-3K blockade is a requisite of AaCdt-induced toxicity in lymphocytes. In this study, we extended our observations to include assessment of Cdts from Haemophilus ducreyi (HdCdt) and Campylobacter jejuni (CjCdt). We now report that the CdtB subunit from HdCdt and CjCdt, similar to that of AaCdt, exhibit potent PIP3 phosphatase activity and that Jurkat cells treated with these Cdts exhibit PI-3K signaling blockade: reduced levels of pAkt and pGSK3β. Since non-phosphorylated GSK3β is the active form of this kinase, we compared Cdts for dependence on GSK3β activity. Two GSK3β inhibitors were employed, LY2090314 and CHIR99021; both inhibitors blocked the ability of Cdts to induce cell cycle arrest. We have previously demonstrated that AaCdt induces increases in the CDK inhibitor, p21^CIP1/WAF1, and, further, that this was a requisite for toxin-induced cell death via apoptosis. We now demonstrate that HdCdt and CjCdt also share this requirement. It is also noteworthy that p21^CIP1/WAF1 was not involved in the ability of the three Cdts to induce cell cycle arrest. Finally, we demonstrate that, like AaCdt, HdCdt is dependent upon the host cell protein, cellugyrin, for its toxicity (and presumably internalization of CdtB); CjCdt was not dependent upon this protein. The implications of these findings as they relate to Cdt’s molecular mode of action are discussed.

Chloroquine reverses chemoresistance via upregulation of p21WAF1/CIP1 and autophagy inhibition in ovarian cancer

Overcoming drug-resistance is a big challenge to improve the survival of patients with epithelial ovarian cancer (EOC). In this study, we investigated the effect of chloroquine (CQ) and its combination with cisplatin (CDDP) in drug-resistant EOC cells. We used the three EOC cell lines CDDP-resistant A2780-CP20, RMG-1 cells, and CDDP-sensitive A2780 cells. The CQ-CDDP combination significantly decreased cell proliferation and increased apoptosis in all cell lines. The combination induced expression of γH2AX, a DNA damage marker protein, and induced G2/M cell cycle arrest. Although the CQ-CDDP combination decreased protein expression of ATM and ATR, phosphorylation of ATM was increased and expression of p21^WAF1/CIP1 was also increased in CQ-CDDP-treated cells. Knockdown of p21^WAF1/CIP1 by shRNA reduced the expression of γH2AX and phosphorylated ATM and inhibited caspase-3 activity but induced ATM protein expression. Knockdown of p21^WAF1/CIP1 partly inhibited CQ-CDDP-induced G2/M arrest, demonstrating that knockdown of p21^WAF1/CIP1 overcame the cytotoxic effect of the CQ-CDDP combination. Ectopic expression of p21^WAF1/CIP1 in CDDP-treated ATG5-shRNA/A2780-CP20 cells increased expression of γH2AX and caspase-3 activity, demonstrating increased DNA damage and cell death. The inhibition of autophagy by ATG5-shRNA demonstrated similar results upon CDDP treatment, except p21^WAF1/CIP1 expression. In an in vivo efficacy study, the CQ-CDDP combination significantly decreased tumor weight and increased expression of γH2AX and p21^WAF1/CIP1 in A2780-CP20 orthotopic xenografts and a drug-resistant patient-derived xenograft model of EOC compared with controls. These results demonstrated that CQ increases cytotoxicity in combination with CDDP by inducing lethal DNA damage by induction of p21^WAF1/CIP1 expression and autophagy inhibition in CDDP-resistant EOC.

Brucella abortus BspJ Is a Nucleomodulin That Inhibits Macrophage Apoptosis and Promotes Intracellular Survival of Brucella

To date, a variety of Brucella effector proteins have been found to mediate host cell secretion, autophagy, inflammation, and other signal pathways, but nuclear effector proteins have not yet been reported. We identified the first Brucella nucleomodulin, BspJ, and we screened out the BspJ interaction host proteins NME/NM23 nucleoside diphosphate kinase 2 (NME2) and creatine kinase B (CKB) through yeast two-hybrid and co-immunoprecipitation assays. These proteins are related to the host cell energy synthesis, metabolism, and apoptosis pathways. Brucella nucleomodulin BspJ will decrease the expression level of NME2 and CKB. In addition, BspJ gene deletion strains promoted the apoptosis of macrophages and reduced the intracellular survival of Brucella in host cells. In short, we found nucleomodulin BspJ may directly or indirectly regulate host cell apoptosis through the interaction with NME2 and CKB by mediating energy metabolism pathways in response to the intracellular circulation of Brucella infection, but the mechanism needs further study.

Multifaceted p21 in carcinogenesis, stemness of tumor and tumor therapy

Cancer cells possess metabolic properties that are different from those of benign cells. p21, encoded by CDKN1A gene, also named p21^Cip1/WAF1, was first identified as a cyclin-dependent kinase regulator that suppresses cell cycle G1/S phase and retinoblastoma protein phosphorylation. CDKN1A (p21) acts as the downstream target gene of TP53 (p53), and its expression is induced by wild-type p53 and it is not associated with mutant p53. p21 has been characterized as a vital regulator that involves multiple cell functions, including G1/S cell cycle progression, cell growth, DNA damage, and cell stemness. In 1994, p21 was found as a tumor suppressor in brain, lung and colon cancer by targeting p53 and was associated with tumorigenesis and metastasis. Notably, p21 plays a significant role in tumor development through p53-dependent and p53-independent pathways. In addition, expression of p21 is closely related to the resting state or terminal differentiation of cells. p21 is also associated with cancer stem cells and acts as a biomarker for such cells. In cancer therapy, given the importance of p21 in regulating the G1/S and G2 check points, it is not surprising that p21 is implicated in response to many cancer treatments and p21 promotes the effect of oncolytic virotherapy.

CDKN1A upregulation and cisplatin‑pemetrexed resistance in non‑small cell lung cancer cells

Cisplatin-pemetrexed is a frequently adopted first-line treatment for patients with advanced non-small cell lung cancer (NSCLC) ineligible for biological therapy, notwithstanding its limited efficacy. In the present study, the RAL cell line, an epidermal growth factor receptor (EGFR)-wild-type, p53- and KRAS-mutated model of NSCLC, was used to investigate novel biomarkers of resistance to this treatment. Cells were analyzed 96 h (96 h-post wo) and 21 days (21 days-post wo) after the combined treatment washout. Following an initial moderate sensitivity to the treatment, the cell growth proliferative capability had fully recovered. Gene expression analysis of the resistant surviving cells revealed a significant upregulation of CDKN1A expression in the cells at 96-h post-wo and, although to a lesser extent, in the cells at 21 days-post wo, accompanied by an enrichment of acetylated histone H3 in its promoter region. CDKN1A was also upregulated at the protein level, being mainly detected in the cytoplasm of the cells at 96 h-post wo. A marked increase in the number of apoptotic cells, together with a significant G1 phase block, were observed at 96-h post wo in the cells in which CDKN1A was knocked down, suggesting its involvement in the modulation of the response of RAL cells to the drug combination. On the whole, these data suggest that CDKN1A plays a role in the response to the cisplatin-pemetrexed combination in advanced KRAS-mutated NSCLC, thus suggesting that it may be used as a promising predictive marker.

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.

The influence of long non-coding RNAs on the response to chemotherapy in ovarian cancer

With 240,000 new cases and 152,000 deaths per year, ovarian cancer is the leading cause of death from gynecologic malignancies. Late diagnosis because of asymptomatic development in early stages and resistance to existing treatments are the major causes of therapeutic failure in ovarian cancer. The recent discovery of tens of thousands of long non-coding RNAs and their action as oncogenes or tumor suppressors in pathways matching all the hallmarks of cancer in most - if not all - malignancies have attracted attention of the scientific community. A growing number of studies have implicated lncRNAs in diverse aspects of ovarian carcinoma biology. We present lncRNAs which have been involved in response to the different drugs currently used for the treatment of ovarian cancers, from first-line platinum salts and taxanes to the newly available PARP inhibitors. The data already available supports the potential use of several lncRNAs, alone or in combination with other molecules, as potential biomarkers for the prediction of response to treatment. Understanding the determinants of their action might reveal new potential therapeutic targets.

Targeting Antitumoral Proteins to Breast Cancer by Local Administration of Functional Inclusion Bodies

Two structurally and functionally unrelated proteins, namely Omomyc and p31, are engineered as CD44-targeted inclusion bodies produced in recombinant bacteria. In this unusual particulate form, both types of protein materials selectively penetrate and kill CD44+ tumor cells in culture, and upon local administration, promote destruction of tumoral tissue in orthotropic mouse models of human breast cancer. These findings support the concept of bacterial inclusion bodies as versatile protein materials suitable for application in chronic diseases that, like cancer, can benefit from a local slow release of therapeutic proteins.

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.

Cytoplasmic p21 Mediates 5-Fluorouracil Resistance by Inhibiting Pro-Apoptotic Chk2

The oncogenic cytoplasmic p21 contributes to cancer aggressiveness and chemotherapeutic failure. However, the molecular mechanisms remain obscure. Here, we show for the first time that cytoplasmic p21 mediates 5-Fluorouracil (5FU) resistance by shuttling p-Chk2 out of the nucleus to protect the tumor cells from its pro-apoptotic functions. We observed that cytoplasmic p21 levels were up-regulated in 5FU-resistant colorectal cancer cells in vitro and the in vivo Chorioallantoic membrane (CAM) model. Kinase array analysis revealed that p-Chk2 is a key target of cytoplasmic p21. Importantly, cytoplasmic form of p21 mediated by p21^T145D transfection diminished p-Chk2-mediated activation of E2F1 and apoptosis induction. Co-immunoprecipitation, immunofluorescence, and proximity ligation assay showed that p21 forms a complex with p-Chk2 under 5FU exposure. Using in silico computer modeling, we suggest that the p21/p-Chk2 interaction hindered the nuclear localization signal of p-Chk2, and therefore, the complex is exported out of the nucleus. These findings unravel a novel mechanism regarding an oncogenic role of p21 in regulation of resistance to 5FU-based chemotherapy. We suggest a possible value of cytoplasmic p21 as a prognosis marker and a therapeutic target in colorectal cancer patients.

FOXD1 is targeted by miR-30a-5p and miR-200a-5p and suppresses the proliferation of human ovarian carcinoma cells by promoting p21 expression in a p53-independent manner

High-grade serous ovarian carcinoma (HGSOC) accounts for the highest number of deaths among patients with epithelial ovarian cancer. However, the molecular mechanisms underlying HGSOC tumorigenesis are currently unclear. In the present study, a lentiviral expression system was employed to manipulate forkhead box D1 (FOXD1) expression in ovarian cancer cells. Immunohistochemical staining was used to examine the expression of FOXD1 in tissue samples. Clonogenic and MTT assays were employed to evaluate cell proliferation, and flow cytometry was applied for cell cycle analysis. Dual-luciferase reporter and chromatin immunoprecipitation assays were used to determine the role of FOXD1 in regulating p21 expression. The results demonstrated that FOXD1 expression was downregulated in HGSOC, and high expression levels of FOXD1 were found to be a predictor of good prognosis. FOXD1 significantly inhibited the proliferation of human ovarian cancer cells and induced cell cycle arrest at G1 phase in vitro. In addition, exogenous FOXD1 expression inhibited ovarian cancer cell growth in vivo. Furthermore, microRNA (miR)-30a-5p and miR-200a-5p were observed to be upregulated in HGSOC, and function as direct negative regulators of FOXD1 by targeting its 3'-untranslated region. The present study also revealed that FOXD1 promotes p21 expression in a p53-independent manner. In conclusion, the results of the present study indicate a direct association between FOXD1 and p21 that may be mediated by miR-30a-5p and miR-200a-5p. The authors hypothesize that FOXD1 may serve as a biomarker or therapeutic target in HGSOC.

Ripening-induced chemical modifications of papaya pectin inhibit cancer cell proliferation

Papaya (Carica papaya L.) is a fleshy fruit with a rapid pulp softening during ripening. Ripening events are accompanied by gradual depolymerization of pectic polysaccharides, including homogalacturonans, rhamnogalacturonans, arabinogalactans, and their modified forms. During intermediate phases of papaya ripening, partial depolymerization of pectin to small size with decreased branching had enhanced pectin anti-cancer properties. These properties were lost with continued decomposition at later phases of ripening. Pectin extracted from intermediate phases of papaya ripening markedly decreased cell viability, induced necroptosis, and delayed culture wound closing in three types of immortalized cancer cell lines. The possible explanation for these observations is that papaya pectins extracted from the third day after harvesting have disrupted interaction between cancer cells and the extracellular matrix proteins, enhancing cell detachment and promoting apoptosis/necroptosis. The anticancer activity of papaya pectin is dependent on the presence and the branch of arabinogalactan type II (AGII) structure. These are first reports of AGII in papaya pulp and the first reports of an in vitro biological activity of papaya pectins that were modified by natural action of ripening-induced pectinolytic enzymes. Identification of the specific pectin branching structures presents a biological route to enhancing anti-cancer properties in papaya and other climacteric fruits.

The lauric acid-activated signaling prompts apoptosis in cancer cells

The saturated medium-chain fatty-acid lauric acid (LA) has been associated to certain health-promoting benefits of coconut oil intake, including the improvement of the quality of life in breast cancer patients during chemotherapy. As it concerns the potential to hamper tumor growth, LA was shown to elicit inhibitory effects only in colon cancer cells. Here, we provide novel insights regarding the molecular mechanisms through which LA triggers antiproliferative and pro-apoptotic effects in both breast and endometrial cancer cells. In particular, our results demonstrate that LA increases reactive oxygen species levels, stimulates the phosphorylation of EGFR, ERK and c-Jun and induces the expression of c-fos. In addition, our data evidence that LA via the Rho-associated kinase-mediated pathway promotes stress fiber formation, which exerts a main role in the morphological changes associated with apoptotic cell death. Next, we found that the increase of p21^Cip1/WAF1 expression, which occurs upon LA exposure in a p53-independent manner, is involved in the apoptotic effects prompted by LA in both breast and endometrial cancer cells. Collectively, our findings may pave the way to better understand the anticancer action of LA, although additional studies are warranted to further corroborate its usefulness in more comprehensive therapeutic approaches.

Resveratrol induces cell cycle arrest and apoptosis with docetaxel in prostate cancer cells via a p53/ p21WAF1/CIP1 and p27KIP1 pathway

Resveratrol (RES) is the most effective natural products used for the treatment of a variety of cancers. In this study, we tested the effect of RES in enhancing the efficacy of docetaxel (DTX) treatment in prostate cancer (PCa) cells. The C4-2B and DU-145 cell lines were treated with RES, DTX and combination followed by evaluating the apoptosis and cell cycle progression. The combined drug treatment up-regulates the pro-apoptotic genes (BAX, BID, and BAK), cleaved PARP and down regulates the anti-apoptotic genes (MCL-1, BCL-2, BCL-XL) promoting apoptosis. In C4-2B cells the combination up regulated the expression of p53, and cell cycle inhibitors (p21^WAF1/CIP1, p27^KIP), which, in turn, inhibited the expression of CDK4, cyclin D1, cyclin E1 and induced hypo-phosphorylation of Rb thus blocking the transition of cells in the G₀/G₁ to S phase. In contrast, the synergistic effect was not profound in DU145 due to its lesser sensitivity to DTX. The suppression of cyclin B1 and CDK1 expression in both cell lines inhibits the further progression of cells in G₂/M phase. The current study demonstrates that combination treatment blocks the cell cycle arrest by modulation of key regulators and promotes apoptosis via p53 dependent and independent mechanism in PCa.

p53-independent p21 induction by MELK inhibition

MELK play critical roles in human carcinogenesis through activation of cell proliferation, inhibition of apoptosis and maintenance of stemness. Therefore, MELK is a promising therapeutic target for a wide range of cancers. Although p21 is a well-known p53-downstream gene, we found that treatment with a potent MELK inhibitor, OTS167, could induce p21 protein expression in cancer cell lines harboring loss-of-function TP53 mutations. We also confirmed that MELK knockdown by siRNA induced the p21 expression in p53-deficient cancer cell lines and caused the cell cycle arrest at G1 phase. Further analysis indicated that FOXO1 and FOXO3, two known transcriptional regulators of p21, were phosphorylated by MELK and thus be involved in the induction of p21 after MELK inhibition. Collectively, our herein findings suggest that MELK inhibition may be effective for human cancers even if TP53 is mutated.

Synthesis and in vitro anticancer activity of new 2-thioxo-oxazolidin-4-one derivatives

BACKGROUND

Oxazolidinones derivatives exhibit different biological properties, including anticancer activity. This work aimed to investigate the anticancer potential of five novel 2-Thioxo-oxazolidin-4-one derivatives.

METHODS

Cytotoxicity assays were performed in human peripheral blood mononuclear cells (PBMCs) from healthy individuals and seven tumor cell lines. Apoptosis detection and cell cycle were evaluated by flow cytometry and the expression of genes involved in cell death processes by Real-Time PCR.

RESULTS

All oxazolinedione derivatives were not cytotoxic in PBMCs. NB-5 showed the best results in cancer cells, inhibiting the growth of all tumor cell lines tested. NB-4 exhibited the highest cytotoxicity in Jurkat cells (IC₅₀=15.19μM) and NB-3 showed better anticancer effects in HL-60 (17.84μM). Only NB-4 significantly induced apoptosis in acute leukemia cells (p=0.001). All compounds caused a significant increase in expression of pro-apoptotic gene BID (p<0.05) and BECN1 (p<0.05). NB-3 significantly modulated the expression of RIPK3 (p=0.02) and DDIT3 (p=0.014), while NB-2 induced an increase of CDKN1A (p=0.03) and NB-4 induced PPARγ gene (p=0.0006).

CONCLUSION

NB-5 showed antitumor effects in solid and hematopoietic cancer cells, while other derivatives produced higher activity against hematopoietic cells. In acute leukemia cells, oxazolidinone derivatives modulated the expression of genes involved in apoptosis, ER stress, necroptosis and inflammation.

Inhibitory Effects of Oligostilbenoids from the Bark of Shorea roxburghii on Malignant Melanoma Cell Growth: Implications for Novel Topical Anticancer Candidates

Human malignant melanomas remain associated with dismal prognosis due to their resistance to apoptosis and chemotherapy. There is growing interest in plant oligostilbenoids owing to their pleiotropic biological activities, including anti-inflammatory, antioxidant, and anticancer effects. Recent studies have demonstrated that resveratrol, a well-known stilbenoid from red wine, exhibits cell cycle-disrupting and apoptosis-inducing activities on melanoma cells. The objective of our study was to evaluate the anti-melanoma effect of oligostilbenoids isolated from the bark of Shorea roxburghii. Among the isolates, four resveratrol oligomers, i.e., (-)-hopeaphenol, vaticanol B, hemsleyanol D, and (+)-α-viniferin, possessed more potent antiproliferative action than did resveratrol against SK-MEL-28 melanoma cells. Cell cycle analysis revealed that (-)-hopeaphenol, hemsleyanol D, and (+)-α-viniferin arrested cell division cycle at the G1 phase, whereas vaticanol B had little effect on the cell cycle. In addition, cell proliferation assay also revealed that (+)-α-viniferin induced DNA damage followed by induction of apoptosis in SK-MEL-28 cells, which was confirmed by an increased expression of γ-H2AX and cleaved caspase-3, respectively. The compounds vaticanol B, hemsleyanol D, and resveratrol significantly increased the expression of p21, suggesting that they are able to block cell cycle progression. Moreover, these oligostilbenoids downmodulated cylin D1 expression and extracellular signal-regulated kinase (ERK) activation. Furthermore, hemsleyanol D, (+)-α-viniferin, and resveratrol significantly decreased the expression of cyclin B1, which could also suppress cell cycle progression. The present study thus suggests that these plant oligostilbenoids are effective as therapeutic or chemopreventive agents against melanoma.

Benzofuran-2-acetic ester derivatives induce apoptosis in breast cancer cells by upregulating p21Cip/WAF1 gene expression in p53-independent manner

Breast cancer is the most common malignancy and the leading cause of cancer-related death in women worldwide. High toxicity of used chemotherapeutics and resistance of cancer cells to treatments are a driving force for searching the new drug candidates for breast cancer therapy. In this study, we tested the antiproliferative effects of a series of benzofuran-2-acetic methyl ester derivatives, synthesized by a palladium-catalyzed carbonylative heterocyclization approach, on breast cancer cells. We observed that benzofuran compounds bearing a phenyl or tert-butyl substituent α to the methoxycarbonyl group significantly inhibited anchorage-dependent and -independent cell growth, and induced G0/G1 cell cycle arrest in human estrogen receptor alpha positive (MCF-7 and T47D) and in triple negative MDA-MB-231 breast cancer cells, without affecting growth of MCF-10A normal breast epithelial cells. Mechanistically, benzofuran derivatives enhanced the cyclin-dependent kinase inhibitor p21^Cip/WAF1 expression at both mRNA and protein levels and this occurs transcriptionally in an Sp1-dependent manner. Moreover, benzofuran derivatives induced apoptosis, increased poly (ADP-ribose) polymerase cleavage and Bax/Bcl-2 ratio along with a marked DNA fragmentation along with a marked DNA fragmentation and a strong increase in TUNEL-positive breast cancer cells. Overall, we provide evidence that the newly tested benzofuran derivatives showed antiproliferative and pro-apoptotic activities against breast cancer cells regardless estrogen receptor status, suggesting their possible clinical development as anticancer agents.

An Elk transcription factor is required for Runx-dependent survival signaling in the sea urchin embryo

Elk proteins are Ets family transcription factors that regulate cell proliferation, survival, and differentiation in response to ERK (extracellular-signal regulated kinase)-mediated phosphorylation. Here we report the embryonic expression and function of Sp-Elk, the single Elk gene of the sea urchin Strongylocentrotus purpuratus. Sp-Elk is zygotically expressed throughout the embryo beginning at late cleavage stage, with peak expression occurring at blastula stage. Morpholino antisense-mediated knockdown of Sp-Elk causes blastula-stage developmental arrest and embryo disintegration due to apoptosis, a phenotype that is rescued by wild-type Elk mRNA. Development is also rescued by Elk mRNA encoding a serine to aspartic acid substitution (S402D) that mimics ERK-mediated phosphorylation of a conserved site that enhances DNA binding, but not by Elk mRNA encoding an alanine substitution at the same site (S402A). This demonstrates both that the apoptotic phenotype of the morphants is specifically caused by Elk depletion, and that phosphorylation of serine 402 of Sp-Elk is critical for its anti-apoptotic function. Knockdown of Sp-Elk results in under-expression of several regulatory genes involved in cell fate specification, cell cycle control, and survival signaling, including the transcriptional regulator Sp-Runt-1 and its target Sp-PKC1, both of which were shown previously to be required for cell survival during embryogenesis. Both Sp-Runt-1 and Sp-PKC1 have sequences upstream of their transcription start sites that specifically bind Sp-Elk. These results indicate that Sp-Elk is the signal-dependent activator of a feed-forward gene regulatory circuit, consisting also of Sp-Runt-1 and Sp-PKC1, which actively suppresses apoptosis in the early embryo.

p21 induction plays a dual role in anti-cancer activity of ursolic acid

Previous studies have shown that induction of G1 arrest and apoptosis by ursolic acid is associated with up-regulation of cyclin-dependent kinase inhibitor (CDKI) protein p21 in multiple types of cancer cells. However, the functional role of p21 induction in G1 cell cycle arrest and apoptosis, and the mechanisms of p21 induction by ursolic acid have not been critically addressed. In the current study, we demonstrated that p21 played a mediator role in G1 cell cycle arrest by ursolic acid, whereas p21-mediated up-regulation of Mcl-1 compromised apoptotic effect of ursolic acid. These results suggest that p21 induction plays a dual role in the anti-cancer activity of ursolic acid in terms of cell cycle and apoptosis regulation. p21 induction by ursolic acid was attributed to p53 transcriptional activation. Moreover, we found that ursolic acid was able to inhibit murine double minute-2 protein (MDM2) and T-LAK cell-originated protein kinase (TOPK), the two negative regulator of p53, which in turn contributed to ursolic acid-induced p53 activation. Our findings provided novel insights into understanding of the mechanisms involved in cell cycle arrest and apoptosis induction in response to ursolic acid exposure.

Loss of compensatory pro-survival and anti-apoptotic modulator, IKKε, sensitizes ovarian cancer cells to CHEK1 loss through an increased level of p21

Ovarian cancer (OC) is extremely heterogeneous, implying that therapeutic strategies should be specifically designed based on molecular characteristics of an individual's tumor. Previously, we showed that IKKε promotes invasion and metastasis in a subset of OCs. Here, we identified CHEK1 as an IKKε-dependent lethal gene from shRNA kinome library screen. In subsequent pharmacological intervention studies, the co-inhibition of IKKε and CHEK1 was more effective in killing OC cells than single treatment. At the molecular level, co-inhibition dramatically decreased pro-survival proteins, but increased proteins involved in DNA damage and apoptosis. IKKε-knockdown increased p21 levels, while overexpression of wild-type IKKε, but not a kinase dead IKKε mutant decreased p21 levels. We further demonstrated that the depletion of p21 rendered OC cells more resistant to cell death induced by co-inhibition of IKKε and CHEK1. In conclusion, we revealed a novel interplay between IKKε, CHEK1 and p21 signaling in survival of OC. Our study provides a rationale for the clinical development of specific IKKε inhibitor and for usage of IKKε as an exploratory marker for resistance to CHEK1 inhibitors in the clinic. The interplay provides one potential explanation as to why very few clinical responses were achieved in patients treated with single-agent CHEK1 inhibitors.

The leukemia inhibitory factor (LIF) and p21 mediate the TGFβ tumor suppressive effects in human cutaneous melanoma

BACKGROUND

Cutaneous melanoma is the most lethal skin cancer and its incidence in developed countries has dramatically increased over the past decades. Localized tumors are easily treated by surgery, but advanced melanomas lack efficient treatment and are associated with very poor outcomes. Thus, understanding the processes underlying melanoma development and progression is critical. The Transforming Growth Factor beta (TGFβ) acts as a potent tumor suppressor in human melanoma, by inhibiting cell growth and preventing cellular migration and invasion.

METHODS

In this study, we aimed at elucidating the molecular mechanisms underlying TGFβ-mediated tumor suppression. Human cutaneous melanoma cell lines, derived from different patients, were used to assess for cell cycle analysis, apoptosis/caspase activity and cell migration. Techniques involved immunoblotting, immunohistochemistry, real time PCR and luciferase reporter assays.

RESULTS

We found the leukemia inhibitory factor (LIF) to be strongly up-regulated by TGFβ in melanoma cells, defining LIF as a novel TGFβ downstream target gene in cutaneous melanoma. Interestingly, we also showed that TGFβ-mediated LIF expression is required for TGFβ-induced cell cycle arrest and caspase-mediated apoptosis, as well as for TGFβ-mediated inhibition of cell migration. Moreover, we found that TGFβ-mediated LIF expression leads to activation of transcription of the cell cycle inhibitor p21 in a STAT3-dependent manner, and further showed that p21 is required for TGFβ/LIF-mediated cell cycle arrest and TGFβ-induced gene activation of several pro-apoptotic genes.

CONCLUSIONS

Together, our results define the LIF/p21 signaling cascade as a novel tumor suppressive-like pathway in melanoma, acting downstream of TGFβ to regulate cell cycle arrest and cell death, further highlight new potential therapeutic strategies for the treatment of cutaneous melanoma.

Protein kinase C-activating tumor promoters modulate the DNA damage response in UVC-irradiated TK6 cells

12-O-Tetradecanoylphorbol-13-acetate (TPA) is a non-genotoxic tumor promoter that dysregulates the protein kinase C (PKC) pathway and causes variable cellular responses to DNA damage in different experimental models. In the present study, we pretreated human lymphoblastoid TK6 cells (wild-type p53) for 72 h with TPA, and five other PKC-activating tumor promoters, to determine how sustained exposure to these chemicals modulates key DNA damage response (DDR) endpoints induced by UVC-irradiation. Here we show that pre-treatment with PKC-activating tumor promoters augmented the sensitivity of TK6 cells to UVC-irradiation characterized by a synergistic increase in apoptosis compared to that induced by either stress alone. In addition, high residual levels of the DNA damage repair signal γH2AX was observed in tumor promoter treated cells indicating a delayed DDR recovery. NH32 (p53-null, isogenic to TK6) cells were resistant to the synergistic effects on apoptosis implicating p53 as a central mediator of the DDR modulating effects. In addition, analysis of p53 target genes in TPA-pre-treated TK6 cells revealed a significant modulation of UVC-induced gene expression that supported a shift toward a pro-apoptotic phenotype. Therefore, sustained exposure to tumor promoting agents modulates the UVC-induced DDR in TK6 cells, which may represent important synergistic interactions that occur during tumor promotion.

PTEN-deficient tumors depend on AKT2 for maintenance and survival

Loss of PTEN is a common event in many cancers and leads to hyperactivation of the PI3K-AKT signaling pathway. The mechanisms by which AKT isoforms mediate signaling to phenotypes associated with PTEN inactivation in cancer have not been defined. Here, we show that AKT2 is exclusively required for PTEN-deficient prostate tumor spheroid maintenance, whereas AKT1 is dispensable. shRNA silencing of AKT2 but not AKT1 promotes regression of prostate cancer xenografts. Mechanistically, we show that AKT2 silencing upregulates p21 and the proapoptotic protein BAX and downregulates the insulin-like growth factor receptor-1. We also show that p21 is an effector of AKT2 in mediating prostate tumor maintenance. Moreover, AKT2 is also exclusively required for the maintenance and survival of other PTEN-deficient solid tumors, including breast cancer and glioblastoma. These findings identify a specific function for AKT2 in mediating survival of PTEN-deficient tumors and provide a rationale for developing therapeutics targeting AKT2.

SIGNIFICANCE

Depletion of AKT2, but not AKT1, induces potent tumor regression in PTEN-deficient prostate cancer xenografts, concomitant with upregulation of p21, which may serve as a potential biomarker for screening AKT2 activity in clinical samples. The specific role of AKT2 in tumor maintenance provides a rationale for the development of isoform-specific inhibitors for patients with PTEN-deficient cancers.

Cell cycle arrest in Batten disease lymphoblast cells

Batten disease is an inherited neurodegenerative disorder caused by a CLN3 gene mutation. Batten disease is characterized by blindness, seizures, cognitive decline, and early death. Although apoptotic cell death is one of the pathological hallmarks of Batten disease, little is known about the regulatory mechanism of apoptosis in this disease. Since the CLN3 gene is suggested to be involved in the cell cycle in a yeast model, we investigated the cell cycle profile and its regulatory factors in lymphoblast cells from Batten disease patients. We found G1/G0 cell cycle arrest in Batten disease cells, with overexpression of p21, sphingosine, glucosylceramide, and sulfatide as possible cell cycle regulators.

Knockdown of creatine kinase B inhibits ovarian cancer progression by decreasing glycolysis

Creatine kinase plays a key role in the energy homeostasis of vertebrate cells. Creatine kinase B (CKB), a cytosolic isoform of creatine kinase, shows upregulated expression in a variety of cancers. In this research, we confirmed that some ovarian cancer tissues had elevated CKB expression at the protein level. The functions of CKB in ovarian cancer progression were investigated in the ovarian cancer cell line Skov3, which has a high CKB expression. It was found that CKB knockdown inhibited Skov3 cell proliferation and induced apoptosis under hypoxia or hypoglycemia conditions. CKB depletion also sensitized Skov3 to chemotherapeutic agents. Furthermore, the CKB knockdown reduced glucose consumption and lactate production, and increased ROS production and oxygen consumption. This suggested that CKB knockdown decreased cytosolic glycolysis and resulted in a tumor suppressive metabolic state in Skov3 cells. Consequently, we found that the knockdown of CKB induced G2 arrest in cell cycle by elevating p21 expression and affected the PI3K/Akt and AMPK pathways. These findings provide new insights in the role of CKB in cancer cell survival and tumor progression. Our results also suggest that CKB depletion/inhibition in combination with chemotherapeutic agents might have synergistic effects in ovarian cancer therapy.

Targeting cell cycle regulation in cancer therapy

Cell proliferation is an essential mechanism for growth, development and regeneration of eukaryotic organisms; however, it is also the cause of one of the most devastating diseases of our era: cancer. Given the relevance of the processes in which cell proliferation is involved, its regulation is of paramount importance for multicellular organisms. Cell division is orchestrated by a complex network of interactions between proteins, metabolism and microenvironment including several signaling pathways and mechanisms of control aiming to enable cell proliferation only in response to specific stimuli and under adequate conditions. Three main players have been identified in the coordinated variation of the many molecules that play a role in cell cycle: i) The cell cycle protein machinery including cyclin-dependent kinases (CDK)-cyclin complexes and related kinases, ii) The metabolic enzymes and related metabolites and iii) The reactive-oxygen species (ROS) and cellular redox status. The role of these key players and the interaction between oscillatory and non-oscillatory species have proved essential for driving the cell cycle. Moreover, cancer development has been associated to defects in all of them. Here, we provide an overview on the role of CDK-cyclin complexes, metabolic adaptations and oxidative stress in regulating progression through each cell cycle phase and transitions between them. Thus, new approaches for the design of innovative cancer therapies targeting crosstalk between cell cycle simultaneous events are proposed.

Manganese activates caspase-9-dependent apoptosis in human bronchial epithelial cells

Acute inhalation exposure to high levels of manganese (Mn) is associated with pulmonary edema and impaired function. The immune-mediated lung epithelium injury of Mn in vivo and in vitro experiments has been well characterized, whereas its apoptotic effect is not well defined. Our results show that human bronchial epithelial (16HBE) cells undergo caspase-9-mediated cell death in response to Mn. Loss of mitochondrial membrane potential (ΔΨm), the formation of reactive oxygen species and release of cytochrome c were regulated during this process. In addition, decreasing c-Myc level and increasing of phosphorylated p53 (Ser 15) and WAF1/p21 were also taken part in Mn-mediated lung toxicity. Proteasome inhibitor MG132 could increase c-Myc protein in abundance. Taking together, our results demonstrate that caspase-9-dependent intrinsic pathway, the downregulation of c-Myc and the upregulation of p53 and phosphorylated p53 might be responsible for Mn-mediated apoptosis in 16HBE cells. Moreover, c-Myc decrease might be due to increased degradation through the ubiquitin-proteasome pathway.

Tumour suppressor genes in chemotherapeutic drug response

Since cancer is one of the leading causes of death worldwide, there is an urgent need to find better treatments. Currently, the use of chemotherapeutics remains the predominant option for cancer therapy. However, one of the major obstacles for successful cancer therapy using these chemotherapeutics is that patients often do not respond or eventually develop resistance after initial treatment. Therefore identification of genes involved in chemotherapeutic response is critical for predicting tumour response and treating drug-resistant cancer patients. A group of genes commonly lost or inactivated are tumour suppressor genes, which can promote the initiation and progression of cancer through regulation of various biological processes such as cell proliferation, cell death and cell migration/invasion. Recently, mounting evidence suggests that these tumour suppressor genes also play a very important role in the response of cancers to a variety of chemotherapeutic drugs. In the present review, we will provide a comprehensive overview on how major tumour suppressor genes [Rb (retinoblastoma), p53 family, cyclin-dependent kinase inhibitors, BRCA1 (breast-cancer susceptibility gene 1), PTEN (phosphatase and tensin homologue deleted on chromosome 10), Hippo pathway, etc.] are involved in chemotherapeutic drug response and discuss their applications in predicting the clinical outcome of chemotherapy for cancer patients. We also propose that tumour suppressor genes are critical chemotherapeutic targets for the successful treatment of drug-resistant cancer patients in future applications.

Activation of p21-Dependent G1/G2 Arrest in the Absence of DNA Damage as an Antiapoptotic Response to Metabolic Stress

The folate enzyme, FDH (10-formyltetrahydrofolate dehydrogenase, ALDH1L1), a metabolic regulator of proliferation, activates p53-dependent G1 arrest and apoptosis in A549 cells. In the present study, we have demonstrated that FDH-induced apoptosis is abrogated upon siRNA knockdown of the p53 downstream target PUMA. Conversely, siRNA knockdown of p21 eliminated FDH-dependent G1 arrest and resulted in an early apoptosis onset. The acceleration of FDH-dependent apoptosis was even more profound in another cell line, HCT116, in which the p21 gene was silenced through homologous recombination (p21(-/-) cells). In contrast to A549 cells, FDH caused G2 instead of G1 arrest in HCT116 p21(+/+) cells; such an arrest was not seen in p21-deficient (HCT116 p21(-/-)) cells. In agreement with the cell cycle regulatory function of p21, its strong accumulation in nuclei was seen upon FDH expression. Interestingly, our study did not reveal DNA damage upon FDH elevation in either cell line, as judged by comet assay and the evaluation of histone H2AX phosphorylation. In both A549 and HCT116 cell lines, FDH induced a strong decrease in the intracellular ATP pool (2-fold and 30-fold, respectively), an indication of a decrease in de novo purine biosynthesis as we previously reported. The underlying mechanism for the drop in ATP was the strong decrease in intracellular 10-formyltetrahydrofolate, a substrate in two reactions of the de novo purine pathway. Overall, we have demonstrated that p21 can activate G1 or G2 arrest in the absence of DNA damage as a response to metabolite deprivation. In the case of FDH-related metabolic alterations, this response delays apoptosis but is not sufficient to prevent cell death.

Targeted p21WAF1/CIP1 activation by RNAa inhibits hepatocellular carcinoma cells

RNA activation (RNAa) is a mechanism of gene activation triggered by promoter-targeted small double-stranded RNA (dsRNA), also known as small activating RNA (saRNA). p21(WAF1/CIP1) (p21) is a putative tumor suppressor gene due to its role as a key negative regulator of the cell cycle and cell proliferation. It is frequently downregulated in cancer including hepatocellular carcinoma (HCC), but is rarely mutated or deleted, making it an ideal target for RNAa-based overexpression to restore its tumor suppressor function. In the present study, we investigated the antigrowth effects of p21 RNAa in HCC cells. Transfection of a p21 saRNA (dsP21-322) into HepG2 and Hep3B cells significantly induced the expression of p21 at both the mRNA and protein levels, and inhibited cell proliferation and survival. Further analysis of dsP21-322 transfected cells revealed that dsP21-322 arrested the cell cycle at the G(0)/G(1) phase in HepG2 cells but at G(2)/M phase in Hep3B cells which lack functional p53 and Rb genes, and induced both early and late stage apoptosis by activating caspase 3 in both cell lines. These results demonstrated that RNAa of p21 has in vitro antigrowth effects on HCC cells via impeding cell cycle progression and inducing apoptotic cell death. This study suggests that targeted activation of p21 by RNAa may be explored as a novel therapy for the treatment of HCC.

Astragalus saponins modulate cell invasiveness and angiogenesis in human gastric adenocarcinoma cells

AIM OF THE STUDY

We had reported that Astragalus saponins (AST) exert promising anti-tumorigenic effects by suppressing the growth of HT-29 human colon cancer cells and tumor xenograft. In the present study, we further investigated the anti-angiogenic property of AST in human gastric adenocarcinoma cells (AGS) and attempted to elucidate the underlying mechanism.

MATERIALS AND METHODS

Viability of AGS cells was measured by using the MTT reduction method. Western blotting was performed to examine the effect of AST on apoptotic- and cell growth-related protein expression. Effect of AST on cell cycle progression was also evaluated using PI staining. A Matrigel invasion assay was then employed to demonstrate the effect of AST on the invasiveness of gastric cancer cells. The expression of invasion-associated proteins (VEGF and MMPs) was also investigated.

RESULTS

AST could induce apoptosis in AGS cells by activating caspase 3 with subsequent cleavage of poly(ADP-ribose) polymerase. Besides, cell cycle arrest at the G2/M phase had been observed in AST-treated cells, leading to substantial growth inhibition. The anti-proliferative effect of AST was associated with the regulation of cyclin B1, p21 and c-myc. Results indicate that the number of AGS cells invaded through the Matrigel membrane was significantly reduced upon AST treatment, with concomitant down-regulation of the pro-angiogenic protein vascular endothelial growth factor (VEGF) as well as the metastatic proteins metalloproteinase (MMP)-2 and MMP-9.

CONCLUSION

AST derived from the medicinal plant Astragalus membranaceus could modulate the invasiveness and angiogenesis of AGS cells besides its pro-apoptotic and anti-proliferative activities. These findings also suggest that AST has the potential to be further developed into an effective chemotherapeutic agent in treating advanced and metastatic gastric cancers.

Resistance and gain-of-resistance phenotypes in cancers harboring wild-type p53

Chemotherapy is the bedrock for the clinical management of cancer, and the tumor suppressor p53 has a central role in this therapeutic modality. This protein facilitates favorable antitumor drug response through a variety of key cellular functions, including cell cycle arrest, senescence, and apoptosis. These functions essentially cease once p53 becomes mutated, as occurs in ∼50% of cancers, and some p53 mutants even exhibit gain-of-function effects, which lead to greater drug resistance. However, it is becoming increasingly evident that resistance is also seen in cancers harboring wild-type p53. In this review, we discuss how wild-type p53 is inactivated to render cells resistant to antitumor drugs. This may occur through various mechanisms, including an increase in proteasomal degradation, defects in post-translational modification, and downstream defects in p53 target genes. We also consider evidence that the resistance seen in wild-type p53 cancers can be substantially greater than that seen in mutant p53 cancers, and this poses a far greater challenge for efforts to design strategies that increase drug response in resistant cancers already primed with wild-type p53. Because the mechanisms contributing to this wild-type p53 "gain-of-resistance" phenotype are largely unknown, a concerted research effort is needed to identify the underlying basis for the occurrence of this phenotype and, in parallel, to explore the possibility that the phenotype may be a product of wild-type p53 gain-of-function effects. Such studies are essential to lay the foundation for a rational therapeutic approach in the treatment of resistant wild-type p53 cancers.

Alterations in nuclear pore architecture allow cancer cell entry into or exit from drug-resistant dormancy

Phenotypic diversity arises in tumors just as it does in developing organisms, and tumor recurrence frequently manifests from the selective survival of divergent drug-resistant cells. Although the expanding tumor cell population may be successfully targeted, drug-resistant cells may persist and sustain the tumor or enter dormancy before igniting a future relapse. Herein, we show that partial knockdown of nucleoporin p62 (NUP62) by small-interfering RNA confers cisplatin resistance to cultured high-grade ovarian carcinoma cells. Treatment with NUP62 small-interfering RNA and cisplatin leaves resistant cells in a state of dormancy; some dormant cells can be induced to proliferate by transient induction of NUP62 expression from an ectopic expression construct. In addition to suggesting functional links between nuclear pore complex architecture and cancer cell survival, the culture system provides a novel experimental window into the dynamics of tumor cell drug resistance and dormancy.

Overexpression of p18INK⁴C in LLC-PK1 cells increases resistance to cisplatin-induced apoptosis

Studies have demonstrated that cyclin-dependent kinase inhibitors (CDKI) that inhibit cell-cycle progression have a protective effect against acute kidney injury (AKI). Most studies have focused on the CIP/KIP family members of CDKI; only a few have explored the role of INK4 family members in AKI. Because INK4 family members block the G1-S transition, we postulated that they should have protective effects against AKI. The most conserved INK4 member is p18, so we selected it to explore its effects on cisplatin-induced renal cell injury. We overexpressed p18 in renal tubular epithelial cells (LLC-PK1) by transient transfection and investigated its effects on the cell cycle and proliferation. After transfection, cell injury was induced by cisplatin (100 μM) incubation for 24 h in a standard medium. The effect of p18 was assayed by assessing cell necrosis and apoptosis in transfected cells. The endoplasmic reticulum stress (ERS) pathway was evaluated to interpret the possible mechanism of p18 action in cisplatin-induced renal cell injury. Overexpression of p18 arrested cell cycle progression in the G1 phase and inhibited proliferation. Compared with vehicle transfection, p18 overexpression did not affect cisplatin-induced necrosis, but it reduced the percentage of apoptotic cells significantly. The severity of ERS induced by cisplatin was also decreased by p18 overexpression. P18 protects against cisplatin-induced renal cell injury. The mechanism of p18 protection may lie in its effect on the cell death pathway.

The ETS family transcription factor ELK-1 regulates induction of the cell cycle-regulatory gene p21(Waf1/Cip1) and the BAX gene in sodium arsenite-exposed human keratinocyte HaCaT cells

Cyclin-dependent kinase inhibitor (CDKN1A), often referred to as p21(Waf1/Cip1) (p21), is induced by a variety of environmental stresses. Transcription factor ELK-1 is a member of the ETS oncogene superfamily. Here, we show that ELK-1 directly trans-activates the p21 gene, independently of p53 and EGR-1, in sodium arsenite (NaASO(2))-exposed HaCaT cells. Promoter deletion analysis and site-directed mutagenesis identified the presence of an ELK-1-binding core motif between -190 and -170 bp of the p21 promoter that confers inducibility by NaASO(2). Chromatin immunoprecipitation and electrophoretic mobility shift analyses confirmed the specific binding of ELK-1 to its putative binding sequence within the p21 promoter. In addition, NaASO(2)-induced p21 promoter activity was enhanced by exogenous expression of ELK-1 and reduced by expression of siRNA targeted to ELK-1 mRNA. The importance of ELK-1 in response to NaASO(2) was further confirmed by the observation that stable expression of ELK-1 siRNA in HaCaT cells resulted in the attenuation of NaASO(2)-induced p21 expression. Although ELK-1 was activated by ERK, JNK, and p38 MAPK in response to NaASO(2), ELK-1-mediated activation of the p21 promoter was largely dependent on ERK. In addition, EGR-1 induced by ELK-1 seemed to be involved in NaASO(2)-induced expression of BAX. This supports the view that the ERK/ELK-1 cascade is involved in p53-independent induction of p21 and BAX gene expression.

Xanthohumol decreases Notch1 expression and cell growth by cell cycle arrest and induction of apoptosis in epithelial ovarian cancer cell lines

OBJECTIVE

Notch1 signaling is active in ovarian cancer and is a promising pathway for new therapies in ovarian cancer. We have previously detected high Notch1 expression in ovarian tumors. Xanthohumol has been shown to inhibit cancer cell growth and invasion, including Kaposi's sarcoma, which also highly expresses Notch1. We hypothesized that the Notch1 signaling pathway is targeted by xanthohumol leading to decreased ovarian cancer cell growth.

METHODS

SKOV3 and OVCAR3 cells were utilized. MTT growth assays were conducted following treatment with xanthohumol. Quantitative RT-PCR and Western blot analyses were conducted to assess Notch1 down-regulation. Luciferase reporter assays were performed to assess functional down-regulation of Notch1. Cell cycle analysis was performed by flow cytometry.

RESULTS

Significant growth inhibition and down-regulation of Notch1 transcription and protein expression were found following xanthohumol treatment. In addition, xanthohumol increased Hes6 transcription and decreased Hes1 transcription, known downstream targets of Notch 1. These observations were associated with cell cycle inhibition as demonstrated by an increase in p21 expression and S and G2/M cell cycle arrest confirmed by an increase in phosphorylated cdc2. Furthermore, an increase in the apoptotic markers, cleaved caspase-3 and cleaved PARP were observed.

CONCLUSION

Xanthohumol was a potent inhibitor of ovarian cancer cell growth, and our results suggest that xanthohumol may be influencing the Notch1 pathway. These findings suggest that xanthohumol could be useful as a therapeutic agent in ovarian cancer.

A human ribonuclease induces apoptosis associated with p21WAF1/CIP1 induction and JNK inactivation

Background

Ribonucleases are promising agents for use in anticancer therapy. Among the different ribonucleases described to be cytotoxic, a paradigmatic example is onconase which manifests cytotoxic and cytostatic effects, presents synergism with several kinds of anticancer drugs and is currently in phase II/III of its clinical trial as an anticancer drug against different types of cancer. The mechanism of cytotoxicity of PE5, a variant of human pancreatic ribonuclease carrying a nuclear localization signal, has been investigated and compared to that of onconase.

Methods

Cytotoxicity was measured by the MTT method and by the tripan blue exclusion assay. Apoptosis was assessed by flow cytometry, caspase enzymatic detection and confocal microscopy. Cell cycle phase analysis was performed by flow cytometry. The expression of different proteins was analyzed by western blot.

Results

We show that the cytotoxicity of PE5 is produced through apoptosis, that it does not require the proapoptotic activity of p53 and is not prevented by the multiple drug resistance phenotype. We also show that PE5 and onconase induce cell death at the same extent although the latter is also able to arrest the cell growth. We have compared the cytotoxic effects of both ribonucleases in the NCI/ADR-RES cell line by measuring their effects on the cell cycle, on the activation of different caspases and on the expression of different apoptosis- and cell cycle-related proteins. PE5 increases the number of cells in S and G₂/M cell cycle phases, which is accompanied by the increased expression of cyclin E and p21^WAF1/CIP1 together with the underphosphorylation of p46 forms of JNK. Citotoxicity of onconase in this cell line does not alter the cell cycle phase distribution and it is accompanied by a decreased expression of XIAP

Conclusions

We conclude that PE5 kills the cells through apoptosis associated with the p21^WAF1/CIP1 induction and the inactivation of JNK. This mechanism is significantly different from that found for onconase.

Methotrexate induces apoptosis through p53/p21-dependent pathway and increases E-cadherin expression through downregulation of HDAC/EZH2

Methotrexate (MTX) is a dihydrofolate reductase (DHFR) inhibitor widely used as an anticancer drug in different kinds of human cancers. Here we investigated the anti-tumor mechanism of MTX against non-small cell lung cancer (NSCLC) A549 cells. MTX not only inhibited in vitro cell growth via induction of apoptosis, but also inhibited tumor formation in animal xenograft model. RNase protection assay (RPA) and RT-PCR demonstrated its induction of p53 target genes including DR5, p21, Puma and Noxa. Moreover, MTX promoted p53 phosphorylation at Ser15 and acetylaion at Lys373/382, which increase its stability and expression. The apoptosis and inhibition of cell viability induced by MTX were dependent on p53 and, partially, on p21. In addition, MTX also increased E-cadherin expression through inhibition of histone deacetylase (HDAC) activity and downregulation of polycomb group protein enhancer of zeste homologue 2 (EZH2). Therefore, the anticancer mechanism of MTX acts through initiation of p53-dependent apoptosis and restoration of E-cadherin expression by downregulation of HDAC/EZH2.

Up-regulation of p21 and TNF-alpha is mediated in lycorine-induced death of HL-60 cells

Background

Leukemia is one of the most life-threatening cancers today, and acute promyelogenous leukemia (APL) is a common type of leukemia. Many natural compounds have already been found to exhibit significant anti-tumor effects. Lycorine, a natural alkaloid extracted from Amaryllidaceae, exhibited anti-leukemia effects in vitro and in vivo. The survival rate of HL-60 cells exposed to lycorine was decreased, cell growth was slowed down, and cell regeneration potential was inhibited. HL-60 cells exhibited typical apoptotic characteristic. Lycorine can suppress leukemia growth and reduce cell survival and inducing apoptosis of tumor cells. The purpose of this work is to elucidate the mechanism by which lycorine induces APL cells.

Results

When HL-60 cells were treated with different concentration of lycorine, the expression of p21 and TNF-α was up-regulated in a concentration-dependent manner as shown by real-time quantitative reverse transcriptase-polymerase chain reaction and Western blotting. Lycorine also down-regulated p21-related gene expression, including Cdc2, Cyclin B, Cdk2 and Cyclin E, promoted Bid truncation, decreased IκB phosphorylation and blocked NF-κB nuclear import. Cytochrome c was released from mitochondria as observed with confocal laser microscopy.

Conclusions

The TNF-α signal transduction pathway and p21-mediated cell-cycle inhibition were involved in the apoptosis of HL-60 cells induced by lycorine. These results contribute to the development of new lycorine-based anti-leukemia drugs.

Growth hormone-releasing hormone antagonist induces apoptosis of human endometrial cancer cells through PKCδ-mediated activation of p53/p21

The growth hormone-releasing hormone (GHRH) antagonists have been shown to inhibit growth of human cancer cells, but the underlying molecular mechanisms and their actions have not been fully investigated. In this study, we first showed that GHRH-R splice variant 1 (SV1) was expressed in two human endometrial cancer cell lines, Ishikawa and ECC-1. By using MTT assay, immunoblotting for cleaved caspase-3 and TUNEL assays, we found that cell growth inhibition and apoptosis were induced in GHRH antagonist, JMR-132-treated cells by activating PKCδ and could be inhibited by treatment with PKC inhibitor, GF109203X. In addition, activation and protein expression of p53 as well as the expression of its downstream effector, p21, were increased by JMR-132 treatment. Moreover, JMR-132-induced p53 and p21 expression were diminished by treatment with PKC inhibitor. Knockdown of endogenous p53 and p21 by siRNAs abolished the JMR-132-induced cell growth inhibition and apoptosis. This study demonstrates a novel mechanism in which GHRH antagonist-induced cell growth inhibition and apoptosis through PKCδ-mediated activation of p53/p21 in human endometrial cancer cells. These findings may suggest the feasibility of GHRH antagonists as a therapeutic approach for human cancer.

CDK inhibitor p21 is prosurvival in adriamycin-induced podocyte injury, in vitro and in vivo

In response to injury, the highly specialized and terminally differentiated glomerular visceral epithelial cell, or podocyte, may undergo several cell fates, including dedifferentiation and proliferation, persistent cell cycle arrest, hypertrophy, apoptosis, or necrosis. Common to these potential outcomes of injury is their ultimate regulation at the level of the cell cycle. There is now a large body of literature confirming the importance of cell cycle regulatory proteins in the cellular response to injury. Although CDK inhibitor p21 levels increase in podocytes following injury, the role of p21 is unclear in focal segmental glomerulosclerosis (FSGS), in part because its function depends heavily on the cytotoxic stimulus and the cellular context. Adriamycin (ADR) is a podocyte toxin used to induce experimental FSGS. The purpose of this study was to define the role of p21 in ADR-induced podocyte injury. BALB/c mice, a strain carrying the recessive ADR susceptibility gene, were backcrossed against c57B6 p21-/- mice to yield a 12th generation BALB/c p21-/- strain. Experimental FSGS was induced by injection of ADR 12 mg/kg × 2 doses (n = 8/group), with mice killed at 1, 2, 8, and 11 wk. Diseased p21-/- mice demonstrated worse albuminuria, more widespread glomerulosclerosis, and higher blood urea nitrogen compared with diseased p21+/+ mice. In diseased p21-/- mice vs. p21+/+ mice, apoptosis [measured by TdT-mediated dUTP nick end labeling (TUNEL) assay] was increased, and podocyte number (measured by WT-1 immunostaining) was decreased. To validate these findings in vitro, we utilized differentiated mouse podocytes, p21-/- and p21+/+, exposed to 0.125 μg/ml ADR. Apoptosis, measured by Hoechst 33342 staining and TUNEL assay, was greater in cultured p21-/- podocytes compared with p21+/+ podocytes. Reconstitution of p21 via retroviral transfection rescued the p21-/- podocytes from apoptosis. We conclude that p21 is prosurvival in the podocyte's response to ADR-induced injury. Ongoing studies are defining the mechanisms of this protective effect as it relates to DNA damage and apoptosis.