Increased sensitivity of p53-deficient cells to anticancer agents due to loss of Pms2

Tetrahydrobiopterin from cyanide-degrading bacterium Bacillus pumilus strain SVD06 induces apoptosis in human lung adenocarcinoma cell (A549)

Tetrahydrobiopterin (BH4) is an essential biological cofactor and a derivative of pterin which is considered potent anticancer agents. In continuation of our previous study on the identification of BH4 from cyanide-degrading Bacillus pumilus, the present study focuses on evaluating the anticancer properties of BH4 on A549, a human lung adenocarcinoma. Anticancer activity analysis shows that BH4 inhibited A549 cell growth after 24 h of incubation with 0.02 mg/mL. In acridine orange/ethidium bromide staining, BH4-treated A549 cells showed apoptotic morphology. BH4 treatment caused cell cycle arrest at G0/G1 phase compared to control cells. BH4 augmented p53 expression in alveolar cancer cells by downregulating MDM2 levels. There was downregulation of casp-3 and upregulation of iNOS gene in BH4-treated A549 cells. Further, docking studies indicated that BH4 had significant interactions with the above proteins affirming the apoptosis mechanism. Thus, BH4 could be considered a potential anticancer drug.

The genome of the naturally evolved obesity-prone Ossabaw miniature pig

The feral pigs of Ossabaw Island (USA) have an outstanding propensity to obesity and develop complete metabolic syndrome (MetS) upon prolonged high energy dieting. We now report the first high quality genome of the Ossabaw pig with Contig N50 of ∼6.03 Mb, significantly higher than most other published pig genomes. Genomic comparison to Duroc reveals that variations including SNPs, INDELs and one ∼2 Mb inversion identified in Ossabaw pig may be related to its "thrifty" phenotype. Finally, an important positively selected gene (PSG) was found to be LEPR (leptin receptor) containing two positively selected sites which may lead to pseudogenization of this gene with possible significant effects on obesity and inflammation development. This work provides the first complete mapping of a genome representing a naturally 'feast and famine' evolved phenotype of MetS, serving as a blueprint to guide the search for new targets and new biomarkers for obesity comorbidities.

MTHFR Knockdown Assists Cell Defense against Folate Depletion Induced Chromosome Segregation and Uracil Misincorporation in DNA

Folate depletion causes chromosomal instability by increasing DNA strand breakage, uracil misincorporation, and defective repair. Folate mediated one-carbon metabolism has been suggested to play a key role in the carcinogenesis and progression of hepatocellular carcinoma (HCC) through influencing DNA integrity. Methylenetetrahydrofolate reductase (MTHFR) is the enzyme catalyzing the irreversible conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate that can control folate cofactor distributions and modulate the partitioning of intracellular one-carbon moieties. The association between MTHFR polymorphisms and HCC risk is inconsistent and remains controversial in populational studies. We aimed to establish an in vitro cell model of liver origin to elucidate the interactions between MTHFR function, folate status, and chromosome stability. In the present study, we (1) examined MTHFR expression in HCC patients; (2) established cell models of liver origin with stabilized inhibition of MTHFR using small hairpin RNA delivered by a lentiviral vector, and (3) investigated the impacts of reduced MTHFR and folate status on cell cycle, methyl group homeostasis, nucleotide biosynthesis, and DNA stability, all of which are pathways involved in DNA integrity and repair and are critical in human tumorigenesis. By analyzing the TCGA/GTEx datasets available within GEPIA2, we discovered that HCC cancer patients with higher MTHFR had a worse survival rate. The shRNA of MTHFR (shMTHFR) resulted in decreased MTHFR gene expression, MTHFR protein, and enzymatic activity in human hepatoma cell HepG2. shMTHFR tended to decrease intracellular S-adenosylmethionine (SAM) contents but folate depletion similarly decreased SAM in wildtype (WT), negative control (Neg), and shMTHFR cells, indicating that in cells of liver origin, shMTHFR does not exacerbate the methyl group supply in folate depletion. shMTHFR caused cell accumulations in the G2/M, and cell population in the G2/M was inversely correlated with MTHFR gene level (r = −0.81, p < 0.0001), MTHFR protein expression (r = −0.8; p = 0.01), and MTHFR enzyme activity (r = −0.842; p = 0.005). Folate depletion resulted in G2/M cell cycle arrest in WT and Neg but not in shMTHFR cells, indicating that shMTHFR does not exacerbate folate depletion-induced G2/M cell cycle arrest. In addition, shMTHFR promoted the expression and translocation of nuclei thymidine synthetic enzyme complex SHMT1/DHFR/TYMS and assisted folate-dependent de novo nucleotide biosynthesis under folate restriction. Finally, shMTHFR promoted nuclear MLH1/p53 expression under folate deficiency and further reduced micronuclei formation and DNA uracil misincorporation under folate deficiency. In conclusion, shMTHFR in HepG2 induces cell cycle arrest in G2/M that may promote nucleotide supply and assist cell defense against folate depletion-induced chromosome segregation and uracil misincorporation in the DNA. This study provided insight into the significant impact of MTHFR function on chromosome stability of hepatic tissues. Data from the present study may shed light on the potential regulatory mechanism by which MTHFR modulates the risk for hepatic malignancies.

The Immunome of Colon Cancer: Functional In Silico Analysis of Antigenic Proteins Deduced from IgG Microarray Profiling

Characterization of the colon cancer immunome and its autoantibody signature from differentially-reactive antigens (DIRAGs) could provide insights into aberrant cellular mechanisms or enriched networks associated with diseases. The purpose of this study was to characterize the antibody profile of plasma samples from 32 colorectal cancer (CRC) patients and 32 controls using proteins isolated from 15,417 human cDNA expression clones on microarrays. 671 unique DIRAGs were identified and 632 were more highly reactive in CRC samples. Bioinformatics analyses reveal that compared to control samples, the immunoproteomic IgG profiling of CRC samples is mainly associated with cell death, survival, and proliferation pathways, especially proteins involved in EIF2 and mTOR signaling. Ribosomal proteins (e.g., RPL7, RPL22, and RPL27A) and CRC-related genes such as APC, AXIN1, E2F4, MSH2, PMS2, and TP53 were highly enriched. In addition, differential pathways were observed between the CRC and control samples. Furthermore, 103 DIRAGs were reported in the SEREX antigen database, demonstrating our ability to identify known and new reactive antigens. We also found an overlap of 7 antigens with 48 “CRC genes.” These data indicate that immunomics profiling on protein microarrays is able to reveal the complexity of immune responses in cancerous diseases and faithfully reflects the underlying pathology.

Potential Strategies to Target Protein-Protein Interactions in the DNA Damage Response and Repair Pathways

This review article discusses some insights about generating novel mechanistic inhibitors of the DNA damage response and repair (DDR) pathways by focusing on protein-protein interactions (PPIs) of the key DDR components. General requirements for PPI strategies, such as selecting the target PPI site on the basis of its functionality, are discussed first. Next, on the basis of functional rationale and biochemical feasibility to identify a PPI inhibitor, 26 PPIs in DDR pathways (BER, MMR, NER, NHEJ, HR, TLS, and ICL repair) are specifically discussed for inhibitor discovery to benefit cancer therapies using a DNA-damaging agent.

Expression of CXCL6 and BBS5 that may be glaucoma relevant genes is regulated by PITX2

The transcription factor PITX2 is implicated in glaucoma pathology. In an earlier study we had used microarray analysis to identify genes in the trabecular meshwork (TM) that are affected by knock down of PITX2. Here, those studies were pursued to identify genes that are direct targets of PITX2 and that may be relevant to glaucoma. Initially, bioinformatics tools were used to select among the genes that had been affected by PITX2 knock down those that have PITX2 binding sites and that may be involved in glaucoma related functions. Subsequently, the effect of PITX2 was tested using the dual luciferase assay in four cell cultures including two primary TM cultures co-transfected with vectors containing promoter fragments of six candidate genes upstream of a luciferase gene and a vector that expressed PITX2. Finally, the effect of PITX2 on endogenous expression of two genes was assessed by over expression and knock down of PITX2 in TM cells. Thirty four genes were found to contain PITX2 binding sites in their putative promoter regions, and 16 were found to be associated with TM-specific and/or glaucoma associated functions. Results of dual luciferase assays confirmed that two of six genes tested were directly targeted by PITX2. The two genes were CXCL6 (chemokine (C-X-C motif) ligand 6) and BBS5 (Bardet-Biedl syndrome 5). Over expression and knock down of PITX2 showed that this transcription factor affects endogenous expression of these two genes in TM cells. CXCL6 encodes a pro-inflammatory cytokine, and many studies have suggested that cytokines and other immune system functions are involved in glaucoma pathogenesis. BBS5 is a member of the BBS family of genes that affect ciliary functions, and ciliary bodies in the anterior chamber of the eye produce the aqueous fluid that affects intraocular pressure. Immune related functions and intraocular pressure are both important components of glaucoma pathology. The role of PITX2 in glaucoma may be mediated partly by regulating the expression of CXCL6 and BBS5 and thus affecting immune functions and intraocular pressure.

Stabilization of mismatch repair gene PMS2 by glycogen synthase kinase 3beta is implicated in the treatment of cervical carcinoma

Background

PMS2 expression loss was reported in a variety of human. However, its importance has not been fully understood in cervical carcinoma. The aim of this study was to determine the expression of PMS2 in cervical carcinoma and evaluate the significance of mismatch repair gene PMS2 regulated by glycogen synthase kinase 3β (GSK-3β) in chemosensitivity.

Methods

We examined PMS2 and phosphorylated GSK-3β(s9) expression in cervical carcinoma tissues using immunohistochemical staining. Furthermore, we detected PMS2 expression in HeLa cells and evaluate the interaction with GSK-3β after transfection with GSK-3β by small interference RNA (siRNA), co-immunoprecipitation and immunoblotting. We also evaluated the effect of PMS2 transfection on HeLa cells' chemosensitivity to cisplatin treatment.

Results

We found significant downregulation of PMS2 in cervical carcinoma, which was negatively associated with phosphorylated GSK-3β (s9). Furthermore, we demonstrated GSK-3β transfection was able to interact with PMS2 and enhance PMS2 production in HeLa cells, and increased PMS2 production was responsible for enhanced chemosensitivity.

Conclusions

Our results provide the evidence that stabilization of PMS2 production by GSK-3β was important to improve chemosensitization, indicating the significance of GSK-3β-related PMS2 downregulation in the development of cervical carcinoma and in developing a potential strategy for chemotherapy.

Dependence of the cytotoxicity of DNA-damaging agents on the mismatch repair status of human cells

Mismatch repair (MMR) deficiency was reported to increase resistance of mammalian cells to killing by several genotoxic substances. However, although MMR-deficient cells are approximately 100-fold more resistant to killing by S(N)1 type methylating agents than MMR-proficient controls, the sensitivity differences reported for the other agents were typically <2-fold. To test whether these differences were linked to factors other than MMR status, we studied the cytotoxicities of mitomycin C, chloroethylcyclohexyl nitrosourea, melphalan, psoralen-UVA, etoposide, camptothecin, ionizing radiation, and cis-dichlorodiaminoplatinum (cisplatin) in a strictly isogenic system. We now report that MMR deficiency reproducibly desensitized cells solely to cisplatin.

DNA microarray analysis of the correlation between gene expression patterns and acquired resistance to 5-FU/cisplatin in gastric cancer

The mechanisms of intrinsic and/or acquired anti-cancer drug resistance have been described in in vitro resistance models, but the clinical relevance has remained undefined. We undertook a prospective study to identify correlations between gene expression and clinical resistance to 5-FU/cisplatin. We compared expression profiles from gastric cancer endoscopic biopsy specimens obtained at a chemosensitive state (partial remission after 5-FU/cisplatin) with those obtained at a refractory state (disease progression), using Affymetrix oligonucleotide microarray technology (U133A). Using 119 discriminating probes and a cross-validation approach, we were able to correctly identify the chemo-responsiveness of 7 pairs of training samples and 1 independent test pair. These exploratory data demonstrate that the gene expression profiles differ between chemosensitive and refractory state gastric cancer biopsy samples.

Mismatch repair and response to DNA-damaging antitumour therapies

Most antitumour therapies damage tumour cell DNA either directly or indirectly. DNA damage responses, and particularly DNA repair, influence the outcome of therapy. Because DNA repair normally excises lethal DNA lesions, it is intuitive that efficient repair will contribute to intrinsic drug resistance. Indeed, in certain circumstances reduced levels of DNA nucleotide excision repair are associated with a good therapeutic outlook (Curr Biol 9 (1999) 273). A paradoxical relationship between DNA mismatch repair (MMR) and drug sensitivity has been revealed by model studies in cell lines. This suggests that connections between MMR and tumour therapy might be more complex. Here, we briefly review how MMR deficiency can affect drug resistance and the extent to which loss of MMR is a prognostic factor in certain cancer therapies. We also consider how the inverse relationship between MMR activity and drug resistance might influence the development of treatment-related malignancies which are increasingly linked to MMR defects.

Brostallicin (PNU-166196)--a new DNA minor groove binder that retains sensitivity in DNA mismatch repair-deficient tumour cells

Defects in DNA mismatch repair (MMR) are associated with a predisposition to tumorigenesis and with drug resistance owing to high mutation rates and failure to engage DNA-damage-induced apoptosis. DNA minor groove binders (MGBs) are a class of anticancer agents highly effective in a variety of human cancers. Owing to their mode of action, DNA MGB-induced DNA damage may be a substrate for DNA MMR. This study was aimed at investigating the effect of loss of MMR on the sensitivity to brostallicin (PNU-166196), a novel synthetic α-bromoacrylic, second-generation DNA MGB currently in Phase II clinical trials and structurally related to distamycin A. Brostallicin activity was compared to a benzoyl mustard derivative of distamycin A (tallimustine). We report that the sensitivities of MLH1-deficient and -proficient HCT116 human colon carcinoma cells were comparable after treatment with brostallicin, while tallimustine resulted in a three times lower cytotoxicity in MLH1-deficient than in -proficient cells. MSH2-deficient HEC59 parental endometrial adenocarcinoma cells were as sensitive as the proficient HEC59+ch2 cells after brostallicin treatment, but were 1.8-fold resistant after tallimustine treatment as compared to the MSH2-proficient HEC59+ch2 counterpart. In addition, p53-deficient mouse fibroblasts lacking PMS2 were as sensitive to brostallicin as PMS2-proficient cells, but were 1.6-fold resistant to tallimustine. Loss of neither ATM nor DNA-PK affected sensitivity to brostallicin in p53-deficient mouse embryonic fibroblasts, indicating that brostallicin-induced cytotoxicity in a p53-deficient genetic background does not seem to require these kinases. These data show that, unlike other DNA MGBs, MMR-deficient cells retain their sensitivity to this new α-bromoacrylic derivative, indicating that brostallicin-induced cytotoxicity does not depend on functional DNA MMR. Since DNA MMR deficiency is common in numerous types of tumours, brostallicin potentially offers the advantage of being effective against MMR-defective tumours that are refractory to several anticancer agents.

Tumor p53 status and response to topoisomerase II inhibitors

It is thought that when tumor cells are treated with anticancer drugs, they die through the apoptotic pathway and that cell resistance to cancer chemotherapy is mainly a resistance to apoptosis commitment. p53 is not functional in nearly half of the tumors examined and because of its involvement (directly or through its target genes) in the apoptotic pathway, drug resistance to chemotherapy has been largely attributed to the status of this "tumor suppressor protein". Topoisomerase II (topo II) inhibitors are widely used not only as single agents, but also in the majority of combination treatment protocols for hematologic malignancies and solid tumors. The relationship between p53 and topo II raises many questions about basic regulatory, biochemical, structural and functional characteristics that could be different in cells in different tissues, and most importantly, between different tumor cell types and their normal tissue counterpart. Understanding these relationships may lead to strategies for chemotherapy optimization and further precision targeting of tumor cells in order to avoid drug resistance and thereby chemotherapy failure.