DNA repair endonuclease ERCC1�CXPF as a novel therapeutic target to overcome chemoresistance in cancer therapy

The ERCC1–XPF complex is a structure-specific endonuclease essential for the repair of DNA damage by the nucleotide excision repair pathway. It is also involved in other key cellular processes, including DNA interstrand crosslink (ICL) repair and DNA double-strand break (DSB) repair. New evidence has recently emerged, increasing our understanding of its requirement in these additional roles. In this review, we focus on the protein–protein and protein–DNA interactions made by the ERCC1 and XPF proteins and discuss how these coordinate ERCC1–XPF in its various roles. In a number of different cancers, high expression of ERCC1 has been linked to a poor response to platinum-based chemotherapy. We discuss prospects for the development of DNA repair inhibitors that target the activity, stability or protein interactions of the ERCC1–XPF complex as a novel therapeutic strategy to overcome chemoresistance.     

USP45 deubiquitylase controls ERCC1–XPF endonuclease-mediated DNA damage responses

Reversible protein ubiquitylation plays important roles in various processes including DNA repair. Here, we identify the deubiquitylase USP45 as a critical DNA repair regulator. USP45 associates with ERCC1, a subunit of the DNA repair endonuclease XPF–ERCC1, via a short acidic motif outside of the USP45 catalytic domain. Wild-type USP45, but not a USP45 mutant defective in ERCC1 binding, efficiently deubiquitylates ERCC1 in vitro, and the levels of ubiquitylated ERCC1 are markedly enhanced in USP45 knockout cells. Cells lacking USP45 are hypersensitive specifically to UV irradiation and DNA interstrand cross-links, similar to cells lacking ERCC1. Furthermore, the repair of UV-induced DNA damage is markedly reduced in USP45-deficient cells. ERCC1 translocation to DNA damage-induced subnuclear foci is markedly impaired in USP45 knockout cells, possibly accounting for defective DNA repair. Finally, USP45 localises to sites of DNA damage in a manner dependent on its deubiquitylase activity, but independent of its ability to bind ERCC1–XPF. Together, these results establish USP45 as a new regulator of XPF–ERCC1 crucial for efficient DNA repair.     

Role of the autotaxin–lysophosphatidate axis in the development of resistance to cancer therapy

Autotaxin (ATX) is a secreted enzyme that hydrolyzes lysophosphatidylcholine to produce lysophosphatidate (LPA), which signals through six G-protein coupled receptors (GPCRs). Signaling through LPA is terminated by its degradation by a family of three lipid phosphate phosphatases (LPPs). LPP1 also attenuates signaling downstream of the activation of LPA receptors and some other GPCRs. The ATX-LPA axis mediates a plethora of activities such as cell proliferation, survival, migration, angiogenesis and inflammation, which perform an important role in facilitating wound healing. This wound healing response is hijacked by cancers where there is decreased expression of LPP1 and LPP3 and increased expression of ATX. This maladaptive regulation of LPA signaling also causes chronic inflammation, which has been recognized as one of the hallmarks in cancer. The increased LPA signaling promotes cell survival and migration and attenuates apoptosis, which stimulates tumor growth and metastasis. The wound healing functions of increased LPA signaling also protect cancer cells from effects of chemotherapy and radiotherapy. In this review, we will summarize knowledge of the ATX-LPA axis and its role in the development of resistance to chemotherapy and radiotherapy. We will also offer insights for developing strategies of targeting ATX-LPA axis as a novel part of cancer treatment. This article is part of a Special Issue entitled Lysophospholipids and their receptors: New data and new insights into their function edited by Susan Smyth, Viswanathan Natarajan and Colleen McMullen.     

Inhibition of farnesyltransferase: a rational approach to treat cancer?

This article presents in brief the development of farnesyltransferase inhibitors (FTIs) and their preclinical and clinical status. In this review the mechanism of action of FTIs is discussed and their selectivity issue towards tumor cells is also addressed. The significant efficacy of FTIs as single or combined agents in preclinical studies stands in contrast with only moderate effects in Clinical Phase II-III studies. This suggests that there is a need to further explore and understand the complex mechanism of action of FTIs and their interaction with cytotoxic agents.     

miR-181a–Twist1 pathway in the chemoresistance of tongue squamous cell carcinoma

Although many researches have been undertaken to disclose the mechanisms of chemoresistance, the mechanisms remain unclear. The aim of this study is to elucidate the role of miR-181a–Twist1 pathway in the chemoresistance of tongue squamous cell carcinoma (TSCC). We found that cisplatin-induced chemoresistance in TSCC cell lines underwent EMT (epithelial–mesenchymal transition) and was accompanied by enhancing metastatic potential (migration and invasion in vitro), miR-181a downregulation and Twist1 upregulation. Functional analyses indicated that miR-181a reversed chemoresistance, inhibited EMT and metastatic potential in TSCC cells. Twist1 was confirmed as a direct miR-181a target gene by luciferase reporter gene assays. Twist1 knockdown by siRNA led to a reversal of the chemoresistance, inhibited EMT and metastatic potential in TSCC cells. Our study demonstrates that miR-181a–Twist1 pathway may play an important role in the development of cisplatin-chemoresistance, with EMT and an increase the metastatic potential of TSCC cells.     

Inhibition of matrix metalloproteinase-1 activity by the soybean Bowman–Birk inhibitor

Inductively coupled plasma analysis of soybean Bowman-Birk inhibitor (BBI) indicated that BBI was a metalloprotein which contained magnesium, calcium, and zinc at 0.40, 0.43 and 0.008 atom/mol BBI, respectively. Heparin-enhanced gelatin zymography, quenched fluorescence substrate hydrolysis analysis, and the Biotrak assay of the interaction of BBI with the matrix metalloproteinase-1 (MMP-1) demonstrated that demineralized BBI at 30 nM inhibited MMP-1 activity whereas mineralized BBI was inhibitory at 115 nM.     

ERCC1 haplotypes modify bladder cancer risk: A case–control study

Bladder cancer risk is highly influenced by environmental and/or predisposing genetic factors. In the last decades growing evidence of the major role played by DNA repair systems in the developing of bladder cancer has been provided. To better investigate the involvement of DNA repair genes previously reported to be significantly associated with bladder cancer risk, we examined in a case–control study (456 cases and 376 hospital controls) 36 single nucleotide polymorphisms (SNPs) in 10 DNA repair genes, through a better gene coverage and a deep investigation of the haplotype role. A single SNP analysis showed a significantly increased risk given by XRCC1-rs915927 G allele (OR = 1.55, CI 95% 1.02–2.37 for dominant model) and a protective effect of the rare alleles of 3 ERCC1 SNPs: rs967591 (OR = 0.66, CI 95% 0.46–0.95), rs735482 (OR = 0.62, CI 95% 0.42–0.90) and rs2336219 (OR = 0.63, CI 95% 0.43–0.93). Haplotype analysis revealed that cases had a statistically significant excess of XRCC3-TAGT and ERCC1-GAT haplotypes, whereas ERCC1-AAC, MGMT-TA, XRCC1-TGCC and ERCC2-TGAA haplotypes were significantly underrepresented. Together with other published data on large case–control studies, our findings provide epidemiological evidence supporting a link between DNA repair gene variants and bladder cancer development, and suggest that the effects of high-order interactions should be taken into account as modulating factors affecting bladder cancer risk. A detailed characterization of DNA repair genetic variation is warranted and might ultimately help to identify multiple susceptibility variants that could be responsible for joint effects on the risk.     

Contribution of the rest–activity circadian rhythm to quality of life in cancer patients

Quality of life (QoL) is estimated from patients scores to items related to everyday life, including rest and activity. The rest–activity rhythm reflects endogenous circadian clock function. The relation between the individual rhythm in activity and QoL was investigated in 200 patients with metastatic colorectal cancer. Patients wore a wrist actigraph (Ambulatory Monitoring Inc., New York, NY) for 3–5 d before chronotherapy, and completed a QoL questionnaire developed by the European Organization for Research and Treatment of Cancer (QLQ-C30) plus the Hospital Anxiety and Depression Scale. The rest–activity circadian rhythm was characterized by the mean activity level (m), autocorrelation coefficient at 24h (r24), and the dichotomy index (I<O), a ratio between the amount of activity while in and out of bed. The distribution of the rest–activity cycle parameters and that of QoL scores was independent of sex, age, primary tumor, number of metastatic sites, and prior treatment. Both the 24h rhythm indicators were positively correlated with global QoL score as well as physical, emotional, and social functioning. Negative correlations were found between m, r24, or I<O and fatigue, appetite loss, and nausea. The rest–activity circadian rhythm appeared to be an objective indicator of physical welfare and QoL. This analysis suggests that circadian function may be one of the biological determinants of QoL in cancer patients.     

Does the specific recognition of DNA by the restriction endonuclease EcoRI involve a linear diffusion step? Investigation of the processivity of the EcoRI endonuclease.

The time course of the EcoRI endonuclease catalysed cleavage of three substrates, two plasmid DNAs and one oligonucleotide, each with two EcoRI sites, was measured. The two plasmid DNAs with the EcoRI sites 318 and 96 base pairs apart are cut in a distributive fashion, while the oligonucleotide with the EcoRI sites 8 base pairs apart is cut in a partially processive manner. It is concluded that a linear diffusion of the EcoRI endonuclease on its substrate across long stretches of DNA is not likely to be operative during the recognition process. Microscopic dissociation-reassociation processes, however, increase the probability of the enzyme to attack further sites located in the immediate vicinity of a given site.     

Mapping the protein–protein and genetic interactions of cancer to guide precision medicine

Massive efforts to sequence cancer genomes have compiled an impressive catalogue of cancer mutations, revealing the recurrent exploitation of a handful of ‘hallmark cancer pathways’. However, unraveling how sets of mutated proteins in these and other pathways hijack pro-proliferative signaling networks and dictate therapeutic responsiveness remains challenging. Here, we show that cancer driver protein–protein interactions are enriched for additional cancer drivers, highlighting the power of physical interaction maps to explain known, as well as uncover new, disease-promoting pathway interrelationships. We hypothesize that by systematically mapping the protein–protein and genetic interactions in cancer—thereby creating Cancer Cell Maps—we will create resources against which to contextualize a patient’s mutations into perturbed pathways/complexes and thereby specify a matching targeted therapeutic cocktail.     

Role of the autotaxin–lysophosphatidate axis in cancer resistance to chemotherapy and radiotherapy

High expression of autotaxin in cancers is often associated with increased tumor progression, angiogenesis and metastasis. This is explained mainly since autotaxin produces the lipid growth factor, lysophosphatidate (LPA), which stimulates cell division, survival and migration. It has recently become evident that these signaling effects of LPA also produce resistance to chemotherapy and radiation-induced cell death. This results especially from the stimulation of LPA₂ receptors, which depletes the cell of Siva-1, a pro-apoptotic signaling protein and stimulates prosurvival kinase pathways through a mechanism mediated via TRIP-6. LPA signaling also increases the formation of sphingosine 1-phosphate, a pro-survival lipid. At the same time, LPA decreases the accumulation of ceramides, which are used in radiation therapy and by many chemotherapeutic agents to stimulate apoptosis. The signaling actions of extracellular LPA are terminated by its dephosphorylation by a family of lipid phosphate phosphatases (LPP) that act as ecto-enzymes. In addition, lipid phosphate phoshatase-1 attenuates signaling downstream of the activation of both LPA receptors and receptor tyrosine kinases. This makes many cancer cells hypersensitive to the action of various growth factors since they often express low LPP1/3 activity. Increasing our understanding of the complicated signaling pathways that are used by LPA to stimulate cell survival should identify new therapeutic targets that can be exploited to increase the efficacy of chemo- and radio-therapy. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.     

Effect of P-glycoprotein Inhibition on the Penetration of Ceftriaxone Across the Blood–Brain Barrier

Neurochemical Research - Recent studies indicate that inhibition of the efflux transporter P-glycoprotein (P-gp) at the blood–brain barrier (BBB) may represent a putative strategy to increase...     

Phosphinic Dehydrodipeptides: Diversification of the P1′ Residue with the Morita–Baylis–Hillman Acetates and Inhibition of Alanyl Aminopeptidases

International Journal of Peptide Research and Therapeutics - Activated allyl acetates (the Morita–Baylis–Hillman acetates) were confirmed as convenient electrophilic precursors of the...     

β1-Integrin binding to collagen type 1 transmits breast cancer cells into chemoresistance by activating ABC efflux transporters

Molecular interactions of tumor cells with the microenvironment are regarded as onset of chemotherapy resistance, referred to as cell adhesion mediated drug resistance (CAM-DR). Here we elucidate a mechanism of CAM-DR in breast cancer cells in vitro. We show that human MCF-7 and MDA-MB-231 breast cancer cells decrease their sensitivity towards cisplatin, doxorubicin, and mitoxantrone cytotoxicity upon binding to collagen type 1 (COL1) or fibronectin (FN). The intracellular concentrations of doxorubicin and mitoxantrone were decreased upon cell cultivation on COL1, while cellular cisplatin levels remained unaffected. Since doxorubicin and mitoxantrone are transporter substrates, this refers to ATP binding cassette (ABC) efflux transporter activities. The activation of the transporters BCRP, P-gp and MRP1 was shown by fluorescence assays to distinguish the individual input of these transporters to resistance in presence of COL1 and related to their expression levels by western blot. An ABC transporter inhibitor was able to re-sensitize COL1-treated cells for doxorubicin and mitoxantrone toxicity. Antibody-blocking of β₁-integrin (ITGB1) induced sensitization towards the indicated cytostatic drugs by attenuating the increased ABC efflux activity. This refers to a key role of ITGB1 for matrix binding and subsequent transporter activation. A downregulation of α₂β₁ integrin following COL1 binding appears as clear indication for the relationship between ITGB1 and ABC transporters in regulating resistance formation, while knockdown of ITGB1 leads to a significant upregulation of all three transporters. Our data provide evidence for a role of CAM-DR in breast cancer via an ITGB1 – transporter axis and offer promising therapeutic targets for cancer sensitization.