Upregulation of p27 and its inhibition of CDK2/cyclin E activity following DNA damage by a novel platinum agent are dependent on the expression of p21

Laminaria japonica cyclic peptides exert anti-colorectal carcinoma effects through apoptosis induction in vitro and in vivo

Laminaria japonica is consumed as a health food and used as a traditional medicine because of its biochemical and pharmacological abilities. However, the anti-tumor effect of L. japonica peptides has not been well explored. In the current study, three novel L. japonica cyclic peptides (LCPs) were isolated using an anti-cancer activity tracking method. LCP-3 [cyclo-(Trp-Leu-His-Val)] significantly induced apoptosis in Caco-2 cells in vitro. LCP-3 increased the Bax/Bcl-2 ratio, activated caspases, and regulated the p53/murine double minute 2 network. LCP-3 blocked Caco-2 cells in G0/G1 phase, which was accompanied by the inhibition of cyclin expression. Furthermore, LCP-3 inhibited colon cancer growth and induced cancer cell apoptosis in tumor-bearing mice. Notably, LCP-3 might be a potential agent for the prevention of colon cancer.

Synthesis of Novel 2-Thiouracil-5-Sulfonamide Derivatives as Potent Inducers of Cell Cycle Arrest and CDK2A Inhibition Supported by Molecular Docking

In an effort to discover potent anticancer agents, 2-thiouracil-5-sulfonamides derivatives were designed and synthesized. The cytotoxic activity of all synthesized compounds was investigated against four human cancer cell lines viz A-2780 (ovarian), HT-29 (colon), MCF-7 (breast), and HepG2 (liver). Compounds 6b,d-g, and 7b showed promising anticancer activity and significant inhibition of CDK2A. Moreover, they were all safe when tested on WI38 normal cells with high selectivity index for cancer cells. Flow cytometric analysis for the most active compound 6e displayed induction of cell growth arrest at G1/S phase (A-2780 cells), S phase (HT-29 and MCF-7 cells), and G2/M phase (HepG2 cells) and stimulated the apoptotic death of all cancer cells. Moreover, 6e was able to cause cycle arrest indirectly through enhanced expression of cell cycle inhibitors p21 and p27. Finally, molecular docking of compound 6e endorsed its proper binding to CDK2A, which clarifies its potent anticancer activity.

BET bromodomain-containing epigenetic reader proteins regulate vascular smooth muscle cell proliferation and neointima formation

AIMS

Recent studies revealed that the bromodomain and extra-terminal (BET) epigenetic reader proteins resemble key regulators in the underlying pathophysiology of cancer, diabetes, or cardiovascular disease. However, whether they also regulate vascular remodelling processes by direct effects on vascular cells is unknown. In this study, we investigated the effects of the BET proteins on human smooth muscle cell (SMC) function in vitro and neointima formation in response to vascular injury in vivo.

METHODS AND RESULTS

Selective inhibition of BETs by the small molecule (+)-JQ1 dose-dependently reduced proliferation and migration of SMCs without apoptotic or toxic effects. Flow cytometric analysis revealed a cell cycle arrest in the G0/G1 phase in the presence of (+)-JQ1. Microarray- and pathway analyses revealed a substantial transcriptional regulation of gene sets controlled by the Forkhead box O (FOXO1)1-transcription factor. Silencing of the most significantly regulated FOXO1-dependent gene, CDKN1A, abolished the antiproliferative effects. Immunohistochemical colocalization, co-immunoprecipitation, and promoter-binding ELISA assay data confirmed that the BET protein BRD4 directly binds to FOXO1 and regulates FOXO1 transactivational capacity. In vivo, local application of (+)-JQ1 significantly attenuated SMC proliferation and neointimal lesion formation following wire-induced injury of the femoral artery in C57BL/6 mice.

CONCLUSION

Inhibition of the BET-containing protein BRD4 after vascular injury by (+)-JQ1 restores FOXO1 transactivational activity, subsequent CDKN1A expression, cell cycle arrest and thus prevents SMC proliferation in vitro and neointima formation in vivo. Inhibition of BET epigenetic reader proteins might thus represent a promising therapeutic strategy to prevent adverse vascular remodelling.

Novel ginsenoside derivative 20(S)-Rh2E2 suppresses tumor growth and metastasis in vivo and in vitro via intervention of cancer cell energy metabolism

Increased energy metabolism is responsible for supporting the abnormally upregulated proliferation and biosynthesis of cancer cells. The key cellular energy sensor AMP-activated protein kinase (AMPK) and the glycolytic enzyme alpha-enolase (α-enolase) have been identified as the targets for active components of ginseng. Accordingly, ginseng or ginsenosides have been demonstrated with their potential values for the treatment and/or prevention of cancer via the regulation of energy balance. Notably, our previous study demonstrated that the R-form derivative of 20(R)-Rh2, 20(R)-Rh2E2 exhibits specific and potent anti-tumor effect via suppression of cancer energy metabolism. However, the uncertain pharmacological effect of S-form derivative, 20(S)-Rh2E2, the by-product during the synthesis of 20(R)-Rh2E2 from parental compound 20(R/S)-Rh2 (with both R- and S-form), retarded the industrialized production, research and development of this novel effective candidate drug. In this study, 20(S)-Rh2E2 was structurally modified from pure 20(S)-Rh2, and this novel compound was directly compared with 20(R)-Rh2E2 for their in vitro and in vivo antitumor efficacy. Results showed that 20(S)-Rh2E2 effectively inhibited tumor growth and metastasis in a lung xenograft mouse model. Most importantly, animal administrated with 20(S)-Rh2E2 up to 320 mg/kg/day survived with no significant body weight lost or observable toxicity upon 7-day treatment. In addition, we revealed that 20(S)-Rh2E2 specifically suppressed cancer cell energy metabolism via the downregulation of metabolic enzyme α-enolase, leading to the reduction of lactate, acetyl-coenzyme (acetyl CoA) and adenosine triphosphate (ATP) production in Lewis lung cancer cells (LLC-1), but not normal cells. These findings are consistent to the results obtained from previous studies using a similar isomer 20(R)-Rh2E2. Collectively, current results suggested that 20(R/S)-Rh2E2 isomers could be the new and safe anti-metabolic agents by acting as the tumor metabolic suppressors, which could be generated from 20(R/S)-Rh2 in industrialized scale with low cost.

Downregulation of GLYR1 contributes to microsatellite instability colorectal cancer by targeting p21 via the p38MAPK and PI3K/AKT pathways

BACKGROUND

GLYR1 has a high mutation frequency in microsatellite instability colorectal cancer (MSI CRC) and is presumed to be a novel tumor suppressor. However, the role of GLYR1 in tumors has never been studied. In particular, the downregulation of GLYR1 in MSI CRC is worthy of further investigation.

METHODS

Western blot and immunohistochemistry analyses were used to detect GLYR1 protein expression in CRC tissues and cell lines, and the clinical significance of GLYR1 was also analyzed. The relationship between GLYR1 and MLH1 was validated by immunofluorescence, immunoprecipitation and bioinformatics analyses. Western blotting, qRT-PCR, CCK-8 assays, colony formation assays, flow cytometry and Hoechst 33258 staining assays were used to assess the effect of GLYR1 on the cell cycle progression, proliferation, differentiation and apoptosis of CRC cells in vitro. The related mechanisms were initially investigated by Western blotting.

RESULTS

GLYR1 was significantly downregulated in MSI CRC and its expression was negatively correlated with tumor size and positively correlated with tumor differentiation in CRC patients. In addition, GLYR1 interacted with MLH1 to regulate its nuclear import and expression. Moreover, downregulation of GLYR1 accelerated G1/S phase transition, promoted proliferation and inhibited differentiation of SW480 and SW620 cells in vitro. Furthermore, downregulation of GLYR1 decreased the sensitivity to 5-fluorouracil (5-FU) by inhibiting the mitochondrial apoptosis pathway in CRC cells. Inhibition of the p38 mitogen-activated protein kinase (p38MAPK) and activation of the phosphatidyl 3-kinase/protein kinase B (PI3K/Akt) signaling pathways were involved in the mechanism by which GLYR1 downregulated p21.

CONCLUSIONS

Ours is the first study to elucidate the role of GLYR1 in tumors and provide evidence for GLYR1 as a biological marker that reflects the degree of malignancy and sensitivity to 5-FU in MSI CRC.

Coupling function of cyclin-dependent kinase 2 and Septin2 in the promotion of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common and aggressive malignant tumor with a poorly defined molecular mechanism. Cyclin‐dependent kinase 2 (CDK2) and Septin2 (SEPT2) are 2 known oncogenic molecules but the mechanism of functional interactions remains unclear. Here, we interestingly found that CDK2 and SEPT2 show very similar dynamic expression during the cell cycle. Both CDK2 and SEPT2 show the highest protein levels in the G2/M phase, resulting in CDK2 interacting with SEPT2 and stabilizing SEPT2 in HCC. In a panel of 8 pairs of fresh HCC tissues and corresponding adjacent tissues, both western blot and immunohistochemistry (IHC) assays demonstrate that CDK2 expression is highly correlated with SEPT2. HCC with high expression of both CDK2 and SEPT2 are more likely to relapse. This observation is further demonstrated by a large panel of 100 HCC patients. In this large panel, high expression of both CDK2 and SEPT2 significantly correlates with tumor differentiation and microvascular invasion, which is an independent prognostic factor in HCC patients. In summary, our results reveal a cooperative function between CDK2 and SEPT2. HCC with high expression of CDK2 and SEPT2 might be more aggressive and respond poorly to current therapy.

Evaluation of the cytotoxicity of the Bithionol-paclitaxel combination in a panel of human ovarian cancer cell lines

Previously, Bithionol (BT) was shown to enhance the chemosensitivity of ovarian cancer cell lines to cisplatin treatment. In the present study, we focused on the anti-tumor potential of the BT-paclitaxel combination when added to a panel of ovarian cancer cell lines. This in vitro study aimed to 1) determine the optimum schedule for combination of BT and paclitaxel and 2) assess the nature and mechanism(s) underlying BT-paclitaxel interactions. The cytotoxic effects of both drugs either alone or in combination were assessed by presto-blue cell viability assay using six human ovarian cancer cell lines. Inhibitory concentrations to achieve 50% cell death (IC₅₀) were determined for BT and paclitaxel in each cell line. Changes in levels of cleaved PARP, XIAP, bcl-2, bcl-xL, p21 and p27 were determined via immunoblot. Luminescent and colorimetric assays were used to determine caspases 3/7 and autotaxin (ATX) activity. Cellular reactive oxygen species (ROS) were measured by flow cytometry. Our results show that the efficacy of the BT-paclitaxel combination depends upon the concentrations and sequence of addition of paclitaxel and BT. Pretreatment with BT followed by paclitaxel resulted in antagonistic interactions whereas synergistic interactions were observed when both drugs were added simultaneously or when cells were pretreated with paclitaxel followed by BT. Synergistic interactions between BT and paclitaxel were attributed to increased ROS generation and enhanced apoptosis. Decreased expression of pro-survival factors (XIAP, bcl-2, bcl-xL) and increased expression of pro-apoptotic factors (caspases 3/7, PARP cleavage) was observed. Additionally, increased expression of key cell cycle regulators p21 and p27 was observed. These results show that BT and paclitaxel interacted synergistically at most drug ratios which, however, was highly dependent on the sequence of the addition of drugs. Our results suggest that BT-paclitaxel combination therapy may be effective in sensitizing ovarian cancer cells to paclitaxel treatment, thus mitigating some of the toxic effects associated with high doses of paclitaxel.

Drug-dependent functionalization of wild-type and mutant p53 in cisplatin-resistant human ovarian tumor cells

Cisplatin (cis-Pt) resistance in tumor cells from p53 dysfunction is a significant clinical problem. Although mutation can inhibit p53 function, >60% of p53 mutants retain normal function according to literature reports. Therefore, we examined the status of p53 in cisplatin-resistant ovarian tumor models and its functional response to cis-Pt and the mechanistically-distinct non-cross-resistant oxaliplatin (oxali-Pt). Relative to sensitive A2780 cells harboring wild-type p53, the 2780CP/Cl-16, OVCAR-10, Hey and OVCA-433 cell lines were 10- to 30-fold resistant to cis-Pt, but was substantially circumvented by oxali-Pt. Mutant p53 in 2780CP/Cl-16 (p53V172F) and OVCAR-10 (p53V172F and p53G266R) cells, predicted as non-functional in p53 database, displayed attenuated response to cis-Pt, as did the polymorphic p53P72R (functionally equivalent to wild-type p53) in HEY and OVCA-433 cell lines. However, p53 was robustly activated by oxali-Pt in all cell lines, with resultant drug potency confirmed as p53-dependent by p53 knockout using CRISPR/Cas9 system. This p53 activation by oxali-Pt was associated with phosphorylation at Ser20 by MEK1/2 based on inhibitor and kinase studies. Cis-Pt, however, failed to phosphorylate Ser20 due to downregulated Chk2, and its clinical impact validated by reduced overall survival of ovarian cancer patients according to TCGA database. In conclusion, cis-Pt resistance occurs in both wild-type and mutant p53 ovarian cancer cells, but is associated with loss of Ser20 phosphorylation. However, these mutant p53, like polymorphic p53, are functional and activated by oxali-Pt-induced Ser20 phosphorylation. Thus, the potential exists for repurposing oxali-Pt or similar drugs against refractory cancers harboring wild-type or specific mutant p53.

Evaluation of the cytotoxicity of the Bithionol - cisplatin combination in a panel of human ovarian cancer cell lines

Background

Combination drug therapy appears a promising approach to overcome drug resistance and reduce drug-related toxicities in ovarian cancer treatments. In this in vitro study, we evaluated the antitumor efficacy of cisplatin in combination with Bithionol (BT) against a panel of ovarian cancer cell lines with special focus on cisplatin-sensitive and cisplatin-resistant cell lines. The primary objectives of this study are to determine the nature of the interactions between BT and cisplatin and to understand the mechanism(s) of action of BT-cisplatin combination.

Methods

The cytotoxic effects of drugs either alone or in combination were evaluated using presto-blue assay. Cellular reactive oxygen species were measured by flow cytometry. Immunoblot analysis was carried out to investigate changes in levels of cleaved PARP, XIAP, bcl-2, bcl-xL, p21 and p27. Luminescent and colorimetric assays were used to test caspases 3/7 and ATX activity.

Results

The efficacy of the BT-cisplatin combination depends upon the cell type and concentrations of cisplatin and BT. In cisplatin-sensitive cell lines, BT and cisplatin were mostly antagonistic except when used at low concentrations, where synergy was observed. In contrast, in cisplatin-resistant cells, BT-cisplatin combination treatment displayed synergistic effects at most of the drug ratios/concentrations. Our results further revealed that the synergistic interaction was linked to increased reactive oxygen species generation and apoptosis. Enhanced apoptosis was correlated with loss of pro-survival factors (XIAP, bcl-2, bcl-xL), expression of pro-apoptotic markers (caspases 3/7, PARP cleavage) and enhanced cell cycle regulators p21 and p27.

Conclusion

In cisplatin-resistant cell lines, BT potentiated cisplatin-induced cytotoxicity at most drug ratios via enhanced ROS generation and modulation of key regulators of apoptosis. Low doses of BT and cisplatin enhanced efficiency of cisplatin treatment in all the ovarian cancer cell lines tested. Our results suggest that novel combinations such as BT and cisplatin might be an attractive therapeutic approach to enhance ovarian cancer chemosensitivity. Combining low doses of cisplatin with subtherapeutic doses of BT can ultimately lead to the development of an innovative combination therapy to reduce/prevent the side effects normally occurring when high doses of cisplatin are administered.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-3034-2) contains supplementary material, which is available to authorized users.

Mitomycin C and decarbamoyl mitomycin C induce p53-independent p21WAF1/CIP1 activation

Mitomycin C (MC), a commonly used anticancer drug, induces DNA damage via DNA alkylation. Decarbamoyl mitomycin C (DMC), another mitomycin lacking the carbamate at C10, generates similar lesions as MC. Interstrand cross-links (ICLs) are believed to be the lesions primarily responsible for the cytotoxicity of MC and DMC. The major ICL generated by MC (α-ICL) has a trans stereochemistry at the guanine-drug linkage whereas the major ICL from DMC (β-ICL) has the opposite, cis, stereochemistry. In addition, DMC can provoke strong p53-independent cell death. Our hypothesis is that the stereochemistry of the major unique β-ICL generated by DMC is responsible for this p53-independent cell death signaling. p53 gene is inactively mutated in more than half of human cancers. p21^WAF1/CIP1 known as a major effector of p53 is involved in p53-dependent and -independent control of cell proliferation and death. This study revealed the role of p21^WAF1/CIP1 on MC and DMC triggered cell damage. MCF-7 (p53-proficient) and K562 (p53-deficient) cells were used. Cell cycle distributions were shifted to the G1/S phase in MCF-7 treated with MC and DMC, but were shifted to the S phase in K562. p21^WAF1/CIP1 activation was observed in both cells treated with MC and DMC, and DMC triggered more significant activation. Knocking down p53 in MCF-7 did not attenuate MC and DMC induced p21^WAF1/CIP1 activation. The α-ICL itself was enough to cause p21^WAF1/CIP1 activation.

Insulin-like growth factor binding protein-3 is a new predictor of radiosensitivity on esophageal squamous cell carcinoma

Insulin-like growth factor binding protein-3 (IGFBP-3) plays an essential role in radiosensitivity of esophageal squamous cell carcinoma (ESCC). However, the underlying mechanism is not completely understood. Here, we observed that IGFBP-3 had favorable impact on the tumorigenicity of ESCC cells in nude mice by using an in vivo imaging system (IVIS) to monitor tumor growth treated with ionizing radiation (IR). Downregulation of IGFBP-3 expression enhanced tumor growth, inhibited anti-proliferative and apoptotic activity and result in IR resistance in vivo. Cell cycle antibody array suggested that silencing IGFBP-3 promoted transition from G0/G1 to S phase, perhaps though influencing Smad3 dephosphorylation and retinoblastoma protein (Rb) phosphorylation. Downregulation of P21 and P27, and upregulation of p-P27 (phospho-Thr187), cyclin-dependent kinase 2 (CDK2), and cyclin E1 might contribute to the G0/G1 to S phase transition promoted by IGFBP-3. Our results suggest that Smad3-P27/P21-cyclin E1/CDK2-phosphorylated retinoblastoma protein pathways might be involved in this IGFBP-3 mediated radiosensitivity transition in ESCC.

Reactive oxygen species and p21Waf1/Cip1 are both essential for p53-mediated senescence of head and neck cancer cells

Treatment of head and neck squamous cell carcinoma, HNSCC, often requires multimodal therapy, including radiation therapy. The efficacy of radiotherapy in controlling locoregional recurrence, the most frequent cause of death from HNSCC, is critically important for patient survival. One potential biomarker to determine radioresistance is TP53 whose alterations are predictive of poor radiation response. DNA-damaging reactive oxygen species (ROS) are a by-product of ionizing radiation that lead to the activation of p53, transcription of p21(cip1/waf1) and, in the case of wild-type TP53 HNSCC cells, cause senescence. The expression of p21 and production of ROS have been associated with the induction of cellular senescence, but the intricate relationship between p21 and ROS and how they work together to induce senescence remains elusive. For the first time, we show that persistent exposure to low levels of the ROS, hydrogen peroxide, leads to the long-term expression of p21 in HNSCC cells with a partially functional TP53, resulting in senescence. We conclude that the level of ROS is crucial in initiating p53's transcription of p21 leading to senescence. It is p21's ability to sustain elevated levels of ROS, in turn, that allows for a long-term oxidative stress, and ensures an active p53-p21-ROS signaling loop. Our data offer a rationale to consider the use of either ROS inducing agents or therapies that increase p21 expression in combination with radiation as approaches in cancer therapy and emphasizes the importance of considering TP53 status when selecting a patient's treatment options.

Mechanism of DNA damage responses induced by exposure to an oligonucleotide homologous to the telomere overhang in melanoma

T-oligo, an 11-base oligonucleotide homologous to the 3'-telomeric overhang, is a novel, potent therapeutic modality in melanoma and multiple other tumor types. T-oligo is proposed to function in a manner similar to experimental disruption of the telomere overhang and induces DNA damage responses including apoptosis, differentiation and senescence. However, important components involved in T-oligo induced responses are not defined, particularly the role of p53, TRF1 and TRF2 in mediating the T-oligo induced responses. In MU, PM-WK, and MM-MC melanoma cells, exposure to T-oligo upregulates p53 expression and phosphorylation, resulting in cellular differentiation and activation of a caspase-mediated apoptotic cascade. However, siRNA-mediated knockdown of p53 completely blocks T-oligo induced differentiation and significantly decreases apoptosis, suggesting that p53 is an important mediator of T-oligo induced responses. In addition, we characterized the roles of telomere binding proteins, TRF1, TRF2, and tankyrase-1, in T-oligo induced damage responses. We demonstrate that tankyrase-1 activity is required for initiation of T-oligo induced damage responses including p53 phosphorylation and reduction of cellular proliferation. These results highlight TRF1, TRF2, tankyrase-1 and p53 as important elements in T-oligo mediated responses and suggest new avenues for research into T-oligo's mechanism of action.

MIF4G domain containing protein regulates cell cycle and hepatic carcinogenesis by antagonizing CDK2-dependent p27 stability

The CDK inhibitor p27(kip1) plays crucial roles in cell cycle regulation and cancer progression. Through yeast two-hybrid screening, we identified MIF4G domain containing protein (MIF4GD) as a novel binding partner for p27. The association of MIF4GD and p27 was verified using immunoprecipitation and glutathione S-transferase (GST) pull-down assays. Interaction with MIF4GD led to the stabilization of p27 both in the nucleus and in the cytoplasm in hepatocellular carcinoma (HCC) cells as a result of suppressed phosphorylation of p27 by CDK2 at threonine187. Serum stimulation decreased the levels of MIF4GD and p27 simultaneously. In addition, MIF4GD overexpression resulted in increased p27 levels and reduced cell proliferation, while knockdown of MIF4GD promoted cell cycle progression with decreased p27 levels in cells. Furthermore, overexpression of MIF4GD reduced colony formation and inhibited xenograft tumor growth in nude mice. Finally, we found that both MIF4GD and p27 were expressed at low levels in HCC tissues compared to non-cancerous tissues, and that low expression levels of MIF4GD and p27 were associated with significantly worse prognosis in HCC patients. Our results suggest that MIF4GD is a potential regulator of p27-dependent cell proliferation in HCC. These findings provide a rational framework for the development of potential HCC therapy by targeting the MIF4GD-p27 interaction.

Napsin A as a marker of clear cell ovarian carcinoma

BACKGROUND

Clear cell carcinomas are aggressive tumors with a distinct biologic behaviour. In a genome-wide screening for genes involved in chemo-resistance, NAPA was over-expressed in cisplatin-resistant cells. The NAPA (protein) Napsin A was described to promote resistance to cisplatin by degradation of the tumor suppressor p53.

METHODS

Totally 131 patients were included in this study all in FIGO-stages I-II; 16 were clear cell tumors which were compared with 40 Type I tumors and 75 type II tumors according to the markers Napsin A, p21, p53 and p27 and some clinical features. For detection of the markers tissue microarrays and immunohistochemistry were used.

RESULTS

Positivity for Napsin A was detected in 12 (80%) out of the 15 clear cell tumors available for analysis compared with 3 (4%) out of the Type I and II tumors in one group (p<0.001). Differences in p21 status, p53 status, and p21+p53- status were striking when clear cell tumors were compared with Type I, Type II, and Type I and II tumors in one group, respectively. The p21+p53-status was associated to positive staining of Napsin A (p=0.0015) and clear cell morphology (p=0.0003). In two separate multivariate logistic regression analyses with Napsin A as endpoint both clear cell carcinoma with OR=153 (95% C.I. 21-1107); (p<001) and p21+p53- status with OR=5.36 (95% C.I. 1.6-17.5); (p=0.005) were independent predictive factors. ROC curves showed that AUC for Napsin A alone was 0.882, for p21+p53- it was 0.720 and for p21+p53-Napsin A+AUC was 0.795. Patients with clear cell tumors had lower (p=0.013) BMI than Type I patients and were younger (p=0.046) at diagnosis than Type II patients. Clear cell tumors had a higher frequency (p=0.039) of capsule rupture at surgery than Type I and II tumors.

CONCLUSIONS

Positivity of Napsin A in an epithelial ovarian tumor might strengthen the morphological diagnosis of clear cell ovarian carcinoma in the process of differential diagnosis between clear cell ovarian tumors and other histological subtypes.

Recruitment of trimeric proliferating cell nuclear antigen by G1-phase cyclin-dependent kinases following DNA damage with platinum-based antitumour agents

BACKGROUND

In cycling tumour cells, the binary cyclin-dependent kinase Cdk4/cyclin D or Cdk2/cyclin E complex is inhibited by p21 following DNA damage to induce G1 cell-cycle arrest. However, it is not known whether other proteins are also recruited within Cdk complexes, or their role, and this was investigated.

METHODS

Ovarian A2780 tumour cells were exposed to the platinum-based antitumour agent 1R,2R-diaminocyclohexane(trans-diacetato)(dichloro)platinum(IV) (DAP), which preferentially induces G1 arrest in a p21-dependent manner. The Cdk complexes were analysed by gel filtration chromatography, immunoblot and mass spectrometry.

RESULTS

The active forms of Cdk4 and Cdk2 complexes in control tumour cells have a molecular size of ~140 kDa, which increased to ~290 kDa when inhibited following G1 checkpoint activation by DAP. Proteomic analysis identified Cdk, cyclin, p21 and proliferating cell nuclear antigen (PCNA) in the inhibited complex, and biochemical studies provided unequivocal evidence that the increase in ~150 kDa of the inhibited complex is consistent with p21-dependent recruitment of PCNA as a trimer, likely bound to three molecules of p21. Although p21 alone was sufficient to inhibit the Cdk complex, PCNA was critical for stabilising p21.

CONCLUSION

G1 Cdk complexes inhibited by p21 also recruit PCNA, which inhibits degradation and, thereby, prolongs activity of p21 within the complex.

Non-small cell lung cancer is susceptible to induction of DNA damage responses and inhibition of angiogenesis by telomere overhang oligonucleotides

Exposure of the telomere overhang acts as a DNA damage signal, and exogenous administration of an 11-base oligonucleotide homologous to the 3'-telomere overhang sequence (T-oligo) mimics the effects of overhang exposure by inducing senescence and cell death in non-small cell lung cancer (NSCLC) cells, but not in normal bronchial epithelial cells. T-oligo-induced decrease in cellular proliferation in NSCLC is likely directed through both p53 and its homolog, p73, with subsequent induction of senescence and expression of senescence-associated proteins, p21, p33(ING), and p27(Kip1) both in vivo and in vitro. Additionally, T-oligo decreases tumor size and inhibits angiogenesis through decreased VEGF signaling and increased TSP-1 expression.

2-Amino-1,3,4-thiadiazole derivative (FABT) inhibits the extracellular signal-regulated kinase pathway and induces cell cycle arrest in human non-small lung carcinoma cells

The anticancer potential of 2-amino-1,3,4-thiadiazole compounds has been documented by in vitro and in vivo studies. In our previous research, we described the synthesis as well as the antiproliferative and neuroprotective activities of 2-(4-fluorophenyloamino)-5-(2,4-dihydroxyphenyl)-1,3,4-thiadiazole (FABT). The aim of the present study was to investigate the molecular mechanisms involved in FABT-induced growth inhibition in A549 lung carcinoma cells. Western blotting analysis revealed that FABT inhibited the activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, and Real-time PCR analysis showed no changes in the expression of P44ERK1 and CREB1 genes. Furthermore, FABT induced cell cycle arrest in the GO/G1 phase and enhanced p27/Kip1 expression. Our results suggest that FABT acts by inhibiting ERK1/2 pathway and cell cycle progression through G1 into S phase in A549 cells. Further studies are needed to completely explain the molecular mechanisms of anticancer action of this 2-aminothiadiazole derivative.

Arecoline downregulates levels of p21 and p27 through the reactive oxygen species/mTOR complex 1 pathway and may contribute to oral squamous cell carcinoma

Arecoline, the major alkaloid of areca nut, has been shown to cause strong genotoxicity and is considered a potential carcinogen. However, the detailed mechanism for arecoline-induced carcinogenesis remains obscure. In this study, we noticed that the levels of p21 and p27 increased in two oral squamous cell carcinoma cell lines with high confluence. Furthermore, when treated with arecoline, elevated levels of p21 and p27 could be downregulated through the reactive oxygen species/mTOR complex 1 (ROS/mTORC1) pathway. Although arecoline decreased the activity of mTORC1, the amounts of autophagosome-like vacuoles or type II LC3 remained unchanged, suggesting that the downregulation of p21 and p27 was independent of autophagy-mediated protein destruction. Arecoline also caused DNA damage through ROS, indicating that the reduced levels of p21 and p27 might facilitate G (1) /S transition of the cell cycle and subsequently lead to error-prone DNA replication. In conclusion, these data have provided a possible mechanism for arecoline-induced carcinogenesis in subcytolytic doses in vivo.

Genetic variants of p27 and p21 as predictors for risk of second primary malignancy in patients with index squamous cell carcinoma of head and neck

Background

Cell cycle deregulation is common in human cancer, and alterations of p27 and p21, two critical cell cycle regulators, have been implicated in the development of many human malignancies. Therefore, we hypothesize that p27 T109G polymorphism individually or in combination with p21 (C98A and C70T) polymorphisms modifies risk of second primary malignancy (SPM) in patients with index squamous cell carcinoma of head and neck (SCCHN).

Methods

A cohort of 1,292 patients with index SCCHN was recruited between May 1995 and January 2007 at the M.D. Anderson Cancer Center and followed for SPM occurrence. Patients were genotyped for the three polymorphisms. A log-rank test and Cox proportional hazards models were used to compare SPM-free survival and SPM risk.

Results

We found that patients with p27 109 TG/GG, p21 98 CA/AA and p21 70 CT/TT variant genotypes had a worse SPM-free survival and an increased SPM risk than those with the corresponding p27109 TT, p21 98 CC, and p21 70 CC common genotypes, respectively. After combining the three polymorphisms, there was a trend for significantly increased SPM risk with increasing number of the variant genotypes (P_trend = 0.0002). Moreover, patients with the variant genotypes had an approximately 2.4-fold significantly increased risk for SPM compared with those with no variant genotypes (HR, 2.4, 95% CI, 1.6-3.6).

Conclusions

These results suggest that p27 T109G polymorphism individually or in combination with p21 (C98A and C70T) polymorphisms increases risk of SPM in patients with index SCCHN.

T0901317 inhibits cisplatin-induced apoptosis in ovarian cancer cells [corrected]

OBJECTIVE

To determine the function of T0901317 in combination treatment with cisplatin in ovarian cancer cells.

METHODS

We screened the effects of 3 nuclear hormone receptor ligands on cell viability in a panel of ovarian cancer cell lines. T0901317 regulation of apoptosis and cell cycle regulators was determined when applied as a single agent or in combination with cisplatin.

RESULTS

Surprisingly, the liver X receptor agonist T0901317 had no significant effects on a panel of 7 ovarian cancer cell lines as a single agent. T0901317 does, however, significantly decrease cisplatin efficacy in at least 3 ovarian cancer cell lines. T0901317 reduces cisplatin-induced apoptosis and reverses cisplatin-induced expression of cell cycle regulators. T0901317 seems to work in a liver X receptor-, pregnane X receptor-, and farnesoid X receptor-independent manner, as agonists of these nuclear hormone receptors did not show similar effects. Interestingly, in the A2780-cp drug-resistant cell line, the effect of T0901317 is lost, suggesting that the pathways stimulated by T0901317 to reduce cisplatin efficacy could be inherently active features of the selected resistance.

CONCLUSIONS

Together, these data suggest that T0901317 inhibits cisplatin in some ovarian cancer cells. These data provide an avenue to investigate when T0901317 may be acting to promote tumor survival and drug resistance through control of apoptosis and when it may be acting as an antitumor agent as has been previously reported.

ADAM17 regulates prostate cancer cell proliferation through mediating cell cycle progression by EGFR/PI3K/AKT pathway

A disintegrin and metalloprotease 17 (ADAM17) is a transmembrane protein that can cleave membrane anchored proteins to release soluble factors and regulate important biological phenomena in cancers. In the present study, we evaluated the effects of ADAM17 on the proliferation and on the cell cycle distribution of human prostate cancer cells. Experiments were also performed to gain insights into the possible mechanism of action of ADAM17. We used over-expression and RNAi strategy to investigate the function of ADAM17 in human prostate cancer cells. Changes in rate of proliferation and cell cycle profile were measured by growth curve, Cell Counting Kit-8 (CCK-8) assay, bromodeoxyuridine (BrdU) incorporation assay and cell cycle analysis. In addition, changes in expression of associated genes and proteins were studied by semiquantitative RT-PCR, western blotting and ELISA analysis. Ectopic over-expression of ADAM17 resulted in increased cell proliferation. We also showed that ADAM17 promoted G1 to S phase transition concomitantly with upregulation of cyclin E, CDK2 and downregulation of p21 and p27 proteins. ADAM17 over-expression cells showed that more TGF-α released to the supernatant and activated the EGFR/PI3K/AKT pathway. Conversely, silencing ADAM17 led to the opposite effect. Both siRNAs knockdown of ADAM17 and blocking the EGFR/PI3K/AKT pathway using specific inhibitor caused downregulation of cyclin E, CDK2, and upregulation of p21 and p27 in prostate cancer cells. Collectively, this study demonstrates that over-expression of ADAM17 might target cyclin E, CDK2, p21, and p27 to promote prostate cancer cell proliferation through activation of the EGFR/PI3K/AKT pathway.

The impact of S- and G2-checkpoint response on the fidelity of G1-arrest by cisplatin and its comparison to a non-cross-resistant platinum(IV) analog

OBJECTIVE

Cisplatin is a DNA-damaging antitumor agent that is highly effective in treating ovarian cancer. It activates the p53/p21 pathway for its cytotoxic mode of action, but it does not induce p21-dependent cell cycle arrest in G1. Therefore, we investigated this paradox, and used the model analog DAP as a positive control for p21-dependent G1-arrest.

METHODS

Studies were conducted in p53-proficient ovarian A2780 tumor cells to examine Cdk activity, cell cycle distribution and DNA damage signaling after cisplatin or DAP in combination with the mitotic inhibitor nocodazole.

RESULTS

Cisplatin consistently induced transient S-phase arrest by inhibiting Cdk2/cyclin A complex in S-phase at 12 h and then a durable G2/M-arrest by inhibiting Cdc2/cyclin B complex at 12-18 h. These inhibitions were associated with Chk1 and Chk2 activation and resultant increase in inhibitory tyrosine phosphorylation of Cdk2 and Cdc2. Cisplatin also potently inhibited G1-phase Cdk4/cyclin D1 and Cdk2/cyclin E activities at ~18 h. In agreement, exposure of cisplatin-treated A2780, HCT-116(p53-/-) and HCT-116(p21-/-) tumor cells to nocodazole revealed limited G1-arrest that was dependent on p53 and p21. In contrast, the durable G1-arrest by DAP, which failed to activate Chk1 and Chk2, was unaffected by nocodazole.

CONCLUSIONS

Cisplatin induced G1-arrest, but at an attenuated level. This was primarily due to orchestration of Cdk inhibition in S-phase first, then in G2, and finally in G1 that effectively blocked cells in G2 and prevented cells from progressing and arresting in G1. These studies demonstrate that cisplatin unequivocally activates G1-checkpoint response, but the fidelity of G1-arrest is compromised by Chk1/2 activation and checkpoint response in S- and G2/M-phase.

von Hippel-Lindau protein promotes Skp2 destabilization on DNA damage

Germline mutations in the von Hippel-Lindau (VHL) tumor suppressor gene cause VHL disease, a rare and autosomal-dominant genetic syndrome. Because VHL protein (pVHL) is the master regulator of hypoxia-inducible factor alpha (HIFα), the most prominent feature of VHL disease is the deregulation of HIFα proteins. However, the precise mechanism by which the loss of pVHL function contributes to tumorigenesis is not fully understood. Here, we show that pVHL destabilizes the F-box protein Skp2, a chief component of Skp, Cullin, F-box-containing complex that promotes DNA synthesis in the S phase. The β-domain of pVHL interacts with Skp2, stimulating proteasome-dependent Skp2 degradation, but the destabilization of Skp2 does not depend on the E3 ubiquitin ligase activity of pVHL. Notably, the generation of DNA damage induces Skp2 degradation, which is attenuated by the suppression of endogenous pVHL expression. One possible mechanism of pVHL-dependent Skp2 degradation entails the antagonizing of Akt-mediated Skp2 phosphorylation, which maintains Skp2 stability. Reintroduction of VHL into VHL-null renal cell carcinoma (RCC) cells decreased Skp2 levels and restored DNA damage-dependent Skp2 degradation. These results identify the tumor suppressor function of pVHL in delaying the S-phase progression to inhibit cell proliferation on DNA damage. Clinically, this report explains as to why Skp2 accumulates abnormally in RCC tissues.

Genetic variants of p21 and p27 and pancreatic cancer risk in non-Hispanic Whites: a case-control study

OBJECTIVES

p21 (WAF1/Cip1/CDKN1A) and p27 (Kip1/CDKN1B) are members of the Cip/Kip family of cyclin-dependent kinase inhibitors, which can induce cell cycle arrest and serve as tumor suppressors. We hypothesized that genetic variants in p21 and p27 may modify individual susceptibility to pancreatic cancer.

METHODS

To test this hypothesis, we evaluated the associations of the Ser31Arg polymorphism in p21 and the Gly109Val polymorphism in p27, and their combinations, with pancreatic cancer risk in a case-control study of 509 pathologically confirmed pancreatic adenocarcinoma patients and 462 age- and sex-matched cancer-free controls in non-Hispanic whites.

RESULTS

We found that the heterozygous and homozygous variant genotypes combined in a dominant model of the p21 polymorphism were associated with increased risk of pancreatic cancer compared with the homozygous wild type (adjusted odds ratio [ORadjusted], 1.70; 95% confidence interval [CI], 1.13-2.55). This increased risk was more pronounced in carriers with the p27 homozygous wild type (ORadjusted, 2.20; 95% CI, 1.32-3.68) and in nonsmokers (ORadjusted, 2.16; 95% CI, 1.14-4.10), although the p27 polymorphism alone was not associated with pancreatic cancer risk.

CONCLUSIONS

These results indicate that the p21 polymorphism may contribute to susceptibility to pancreatic cancer, particularly among p27 homozygous wild-type carriers and nonsmokers.

Restriction of cisplatin induction of acute apoptosis to a subpopulation of cells in a three-dimensional carcinoma culture model

Cisplatin is a clinically important chemotherapeutical agent used to treat epithelial malignancies. High concentrations (20-100 microM) of cisplatin have been used in numerous studies to induce apoptosis of carcinoma cells grown in monolayer culture over 24-48 hr. These conditions may not be relevant to 3-D tumor tissue in vivo and the importance of apoptosis for tumor response is controversial. We here studied the effects of cisplatin on a 3-D colon carcinoma in vitro model (multicellular spheroids). Cisplatin at a dose of 40 microM induced active caspase-3 preferentially in the peripheral 30 microm cell layer of spheroids, mainly during late stages (72-96 hr). The p53 response to cisplatin was also largely confined to peripheral cell layers. Despite the use of a high cisplatin concentration, a significant fraction of the cells in the spheroids survived treatment. A high proportion of surviving cells stained positive for beta-galactosidase, a marker of premature senescence. Cells growth-arrested by cisplatin treatment showed a higher spontaneous cell death rate than untreated proliferating cells. We propose that acute apoptosis is of minor significance for the overall response of carcinoma cells to cisplatin treatment.

Protein kinase inhibitors emodin and dichloro-ribofuranosylbenzimidazole modulate the cellular accumulation and cytotoxicity of cisplatin in a schedule-dependent manner

PURPOSE

Protein kinase inhibitors (PKI) have become prominent agents in cancer therapeutics. However, the specificity for target kinase inhibition can be poor and unwanted effects can emerge in combination regimens. The PKI emodin, for instance, can produce mixed results when combined with cisplatin, and we have sought a biochemical pharmacologic explanation for the negative cytotoxic effects.

METHODS

Human ovarian A2780 tumor cells were exposed to the PKI emodin or dichloro-ribofuranosylbenzimidazole (DRB) with cisplatin using several schedules, and cytotoxicity determined by a growth inhibition assay. Intracellular platinum levels and DNA adducts were estimated by flameless atomic absorption spectrophotometry.

RESULTS

When A2780 cells were exposed first to emodin or DRB and then to cisplatin alone, the cytotoxic effects of cisplatin were significantly enhanced, whereas simultaneous exposure did not enhance the cytotoxicity, but instead inhibited it in the case of DRB. The increase in activity of cisplatin in the sequenced schedule was not due to increases in intracellular levels of cisplatin or DNA adducts, whereas the cytotoxic inhibition was related to a significant fall in both intracellular platinum levels and DNA adducts, which were ascribed to inhibition in cisplatin uptake. Knockdown of hCtr1 (the human copper transporter 1) by siRNA abrogated this inhibition in cisplatin uptake.

CONCLUSION

The results demonstrate that co-exposure of tumor cells to emodin or DRB with cisplatin inhibits platinum drug uptake by impacting the hCtr1 transporter and, thereby, reduce the cytotoxicity of cisplatin. Based on our findings, scheduling of the PKI and the cytotoxic agent should be a major consideration in the clinical design of combination regimens.

Low-Dose BBR3610 Toxicity in Colon Cancer Cells Is p53-Independent and Enhanced by Inhibition of Epidermal Growth Factor Receptor (ERBB1)-Phosphatidyl Inositol 3 Kinase Signaling

We have examined the mechanisms by which the multinuclear platinum chemotherapeutic BBR3610 kills human colon cancer cells. BBR3610 more efficiently killed HCT116, DLD1, SW480, and HT29 cells than BBR3464, cisplatin, or oxaliplatin. The amount of platinum uptake per cell and its incorporation into DNA were identical for BBR3464 and BBR3610. BBR3610 lethality (IC(75)) was unaltered comparing HCT116 wild-type and p53-/- cells, was reduced in p21-/- cells, and was enhanced in K-RAS D13 null cells. Small molecule or molecular inhibition of epidermal growth factor receptor (ERBB1) or phosphatidyl inositol 3 kinase (PI3K) enhanced BBR3610 toxicity in HCT116, DLD1, and SW480 cells. Small molecule or molecular inhibition of caspase 8 function abolished the toxicity of BBR3610 and of BBR3610 + ERBB1 inhibitor treatments, whereas inhibition of caspase 9 suppressed the ability of ERBB1 inhibitors to enhance BBR3610 lethality. Treatment with BBR3610 reduced AKT activity; the expression of dominant-negative AKT enhanced and expression of constitutively active AKT suppressed, respectively, the toxicity of BBR3610 and of BBR3610 + ERBB1 inhibitor treatments. Treatment with BBR3610 reduced expression of c-FLIP-s and MCL-1, levels that were maintained in cells expressing constitutively active AKT. Overexpression of c-FLIP-s or loss of BID function suppressed BBR3610 toxicity, whereas overexpression of XIAP or Bcl-xL suppressed the potentiation of cell killing by ERBB1 inhibitors. Collectively, our data argue that BBR3610 promotes cell killing via a caspase 8-dependent mechanism, which can be enhanced by ERBB1/PI3K inhibitors that promote additional BBR3610-dependent cell killing via activation of BAX and caspase 9.