Functional links between transcription, DNA repair and apoptosis

Impact of combined treatment with nimesulide and cisplatin on oral carcinoma cells

Background

Despite significant advances in diagnosis and therapy, the rate of survival of patients with oral cancers still remains poor as an appropriate treatment has not been found yet, due to side effects of chemo/radiotherapy.

Aim

This study aimed to identify molecular mechanisms of cell death of oral cancer cells caused by treatment with a nonselective Cox-2 inhibitor in combination with a low-dose chemotherapeutic drug.

Methods

Squamous cell carcinoma (SCC) cells SCC9 and SCC25 were subjected to mono- and combination therapy with nimesulide and cisplatin. Fluorescence-activated cell sorting (FACS), immunohistochemistry, high-pressure liquid chromatography (HPLC), microarray gene chips, and isobaric tags for a relative and absolute quantitation (iTRAQ) system were used.

Results

Increased numbers of apoptotic and necrotic SCC9/SCC25 cells were detected after combined exposure. ATP levels and the energy charge of SCC9 cells were significantly decreased after both individual and combined treatment. We detected and quantified a responsible gene, keratin 6a, and 540 relevant proteins. In SCC25 cells, ATP levels significantly decreased only after combination therapy. After combined treatment of SCC9 cells, significant upregulation of Histon-H2A/H2B/H4 was found, with a local discovery false rate of 0.003 for Histon-H2A and 0.0027 for Histon-H2B, respectively.

Conclusion

Compared to the single-drug treatment, combined treatment of the oral cancer cells with nimesulide and cisplatin increases and induces necrosis and apoptosis through different pathways. A significant effect of the cytoplasmic increase was also observed in histones of cell lines SCC9 and SCC25 that were previously treated with combined nimesulide and cisplatin therapy.

Defining the minimal peptide sequence of the ING1b tumour suppressor capable of efficiently inducing apoptosis

The ING1b protein is a type-II tumour suppressor and stoichiometric member of the Sin3 histone deacetylase (HDAC) protein complex in which it acts to target HDAC activity to regulate chromatin structure. Altering ING1 levels by ectopic expression of ING1b in cancer cells promotes apoptosis, whereas altering levels by knockout in normal murine fibroblasts alters sensitivity to doxorubicin-induced apoptosis. We have identified a minimal region of ING1b capable of inducing levels of apoptosis in targeted cells as effectively as full-length ING1b, using transient overexpression of ING1b fragments followed by the Annexin V assay. We observed high levels of apoptosis in 14 of 14 cancer cell lines tested. Infecting triple-negative tumorigenic MDA-MB-468 breast cancer, U2OS or Saos-2 cells at multiplicities of infection (MOIs) ranging from 10 to 20 rapidly triggered apoptosis in ~80% of infected cells within 48 h. This was not due to the effects of virus, as infection at the same MOI with a control adenovirus expressing GFP was not effective in inducing apoptosis. When used at low MOIs, the ING1b fragment showed a cell-killing efficacy that was higher than native, full-length ING1b. Using a doxycycline-regulated inducible p53 expression system demonstrated that apoptosis induced by the ING1b fragment was p53 independent. Given the growing importance of combination therapies, we evaluated whether there was synergism between the ING1b fragment and HDAC inhibitors. Combination treatments with TSA, LBH 589 and SAHA reduced cancer cell survival by 3.9–4.7-fold as compared with single-drug treatment, and resulted in ~90% reduction in cell survival. Normalized isobologram analysis confirmed strong synergism between the ING1b fragment and drugs tested. These findings provide support for using ING1b-derived therapeutics as adjuvant treatments in combination with existing epigenetic therapies.

The ING family tumor suppressors: from structure to function

The Inhibitor of Growth (ING) proteins belong to a well-conserved family which presents in diverse organisms with several structural and functional domains for each protein. The ING family members are found in association with many cellular processes. Thus, the ING family proteins are involved in regulation of gene transcription, DNA repair, tumorigenesis, apoptosis, cellular senescence and cell cycle arrest. The ING proteins have multiple domains that are potentially capable of binding to many partners. It is conceivable, therefore, that such proteins could function similarly within protein complexes. In this case, within this family, each function could be attributed to a specific domain. However, the role of ING domains is not definitively clear. In this review, we summarize recent advances in structure-function relationships in ING proteins. For each domain, we describe the known biological functions and the approaches utilized to identify the functions associated with ING proteins.

ING Genes Work as Tumor Suppressor Genes in the Carcinogenesis of Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer in the world. The evolution and progression of HNSCC are considered to result from multiple stepwise alterations of cellular and molecular pathways in squamous epithelium. Recently, inhibitor of growth gene (ING) family consisting of five genes, ING1 to ING5, was identified as a new tumor suppressor gene family that was implicated in the downregulation of cell cycle and chromatin remodeling. In contrast, it has been shown that ING1 and ING2 play an oncogenic role in some cancers, this situation being similar to TGF-β. In HNSCC, the ING family has been reported to be downregulated, and ING translocation from the nucleus to the cytoplasm may be a critical event for carcinogenesis. In this paper, we describe our recent results and briefly summarize current knowledge regarding the biologic functions of ING in HNSCC.

Cytogenetic perspective of ageing and longevity in men and women

Analysis of relationships between the ageing cell phenotype and the age of cell donors is one of the ways towards understanding the link between cellular and organismal ageing. Cytogenetically, ageing is associated with a number of gross cellular changes, including altered size and morphology, genomic instability, and changes in expression and proliferation. Genomic instability can be easily assessed by analyzing the level of cytogenetic aberrations. In this review, we focus on the differences in the level and profile of cytogenetic aberrations observed in donors of different age and gender. Centenarians are a small fraction of the population at the extreme of human longevity. Their inclusion in such studies may shed light on one of the basic questions: whether genome stability is better maintained in successfully aged individuals compared to the rest of the population. At the same time, comparing the profile of age-related amount of chromosomal aberrations in men and women may help explaining the commonly observed gender differences in longevity.

The ING gene family in the regulation of cell growth and tumorigenesis

The five members of the inhibitor of growth (ING) gene family have garnered significant interest due to their putative roles as tumor suppressors. However, the precise role(s) of these ING proteins in regulating cell growth and tumorigenesis remains uncertain. Biochemical and molecular biological analysis has revealed that all ING members encode a PHD finger motif proposed to bind methylated histones and phosphoinosital, and all ING proteins have been found as components of large chromatin remodeling complexes that also include histone acetyl transferase (HAT) and histone deacetylase (HDAC) enzymes, suggesting a role for ING proteins in regulating gene transcription. Additionally, the results of forced overexpression studies performed in tissue culture have indicated that several of the ING proteins can interact with the p53 tumor suppressor protein and/or the nuclear factor-kappa B (NF-kappaB) protein complex. As these ING-associated proteins play well-established roles in numerous cell processes, including DNA repair, cell growth and survival, inflammation, and tumor suppression, several models have been proposed that ING proteins act as key regulators of cell growth not only through their ability to modify gene transcription but also through their ability to alter p53 and NF-kappaB activity. However, these models have yet to be substantiated by in vivo experimentation. This review summarizes what is currently known about the biological functions of the five ING genes based upon in vitro experiments and recent mouse modeling efforts, and will highlight the potential impact of INGs on the development of cancer.

Cells from long-lived mutant mice exhibit enhanced repair of ultraviolet lesions

Fibroblasts isolated from long-lived hypopituitary dwarf mice are resistant to many cell stresses, including ultraviolet (UV) light and methyl methane sulfonate (MMS), which induce cell death by producing DNA damage. Here we report that cells from Snell dwarf mice recover more rapidly than controls from the inhibition of RNA synthesis induced by UV damage. Recovery of messenger RNA (mRNA) synthesis in particular is more rapid in dwarf cells, suggesting enhanced repair of the actively transcribing genes in dwarf-derived cells. At early time points, there was no difference in the repair of cyclobutane pyrimidine dimers (CPD) or 6-4 photoproducts (6-4PP) in the whole genome, nor was there any significant difference in the repair of UV lesions in specific genes. However, at later time points we found that more lesions had been removed from the genome of dwarf-derived cells. We have also found that cells from dwarf mice express higher levels of the nucleotide excision repair proteins XPC and CSA, suggesting a causal link to enhanced DNA repair. Overall, these data suggest a mechanism for the UV resistance of Snell dwarf-derived fibroblasts that could contribute to the delay of aging and neoplasia in these mice.

Interaction of the tumor metastasis suppressor nonmetastatic protein 23 homologue H1 and estrogen receptor alpha alters estrogen-responsive gene expression

Metastasis of cancer cells from the primary tumor is associated with poor prognosis and decreased overall survival. One protein implicated in inhibiting metastasis is the tumor metastasis suppressor nonmetastatic protein 23 homologue 1 (NM23-H1). NM23-H1 is a multifunctional protein, which, in addition to limiting metastasis, has DNase and histidine protein kinase activities. We have identified new functions for NM23-H1 in influencing estrogen receptor alpha (ER alpha)-mediated gene expression. Using a battery of molecular and biochemical techniques, we show that NM23-H1 interacts with ER alpha and increases the ER alpha-estrogen response element (ERE) interaction. When NM23-H1 expression is increased in U2 osteosarcoma and MDA-MB-231 breast cancer cells, transcription of a transiently transfected, estrogen-responsive reporter plasmid is decreased. More importantly, when endogenous NM23-H1 expression is knocked down in MCF-7 human breast cancer cells using small interfering RNA, estrogen responsiveness of the progesterone receptor (PR), Bcl-2, cathepsin D, and cyclin D1 genes, but not the pS2 gene, is enhanced. Furthermore, NM23-H1 associates with the region of the PR gene containing the +90 activator protein 1 site, but not with the ERE-containing region of the pS2 gene, indicating that NM23-H1 mediates gene-specific effects by association with endogenous chromatin. Our studies suggest that the capacity of NM23-H1 to limit the expression of estrogen-responsive genes such as cathepsin D and Bcl-2, which are involved in cell migration, apoptosis, and angiogenesis, may help to explain the metastasis-suppressive effects of this protein. The complementary abilities of ER alpha and NM23-H1 together to influence gene expression, cell migration, and apoptosis could be key factors in helping to determine tumor cell fate.

The quiet embryo hypothesis: molecular characteristics favoring viability

It has been proposed that the viability of early mammalian embryos is associated with a metabolism that is "quiet" rather than "active" (Leese HJ, 2002:BioEssays 24:845-849). The data on which this hypothesis was based were largely drawn from measurements on the depletion and appearance of amino acids from the culture medium. Data on the de novo synthesis of protein in in vivo- and in vitro-derived bovine embryos, as determined from the flux of radiolabeled methionine, have provided further support of the hypothesis and are interpreted to provide a new set of testable propositions that could illuminate the molecular basis of the quiet metabolism phenotype. The propositions are based on the premise that the extent of DNA damage, and the RNA and protein content of the immature oocyte, are key factors in determining whether the zygote progresses to the blastocyst stage. We propose that stochastic events and environmental stresses determine whether the condition of the genome, transcriptome, and proteome of the zygote will support development. Several molecular components are identified that may determine the viability of a zygote, and we speculate that the cellular response to unfavorable events or excessive DNA damage may be the premature activation of the embryonic genome and of apoptosis.

S-Adenosylmethionine decarboxylase partially regulates cell growth of HL-60 cells by controlling the intracellular ROS level: Early senescence and sensitization to γ-radiation

S-Adenosylmethionine decarboxylase (SAMDC) is a key enzyme for the biosynthesis of spermidine. SAMDC-suppressed HL-60 cells overproduced intracellular reactive oxygen species (ROS), which led to cell growth defect and partial cell death. ROS overproduction was caused by a decrease of the total glutathione (GSH) and the ratio of reduced to oxidized GSH, and by an increase of the intracellular iron uptake. When analyzed by real-time polymerase chain reaction, the transcripts of the genes involved in the GSH synthesis (gamma-glutamyl cysteine synthetase, GSH synthetase), as well as the gene of the GSH-reducing enzyme (NADP+-dependent isocitrate dehydrogenase), were decreased dramatically in these cells. DNA-repairing genes (ATM, PARP, RAD51 and MSH2) also were not activated transcriptionally. In these situations, excessive ROS induced severe DNA damage, which could not be repaired, and ultimately led the cells to a spontaneous cell death or an early senescence state. For such cells, gamma-radiation and cisplatin, which are direct DNA-damaging agents, were very effective for promoting cell death.

Clusterin and DNA repair: a new function in cancer for a key player in apoptosis and cell cycle control

The glycoprotein clusterin (CLU), has two known isoforms generated in human cells. A nuclear form of CLU protein (nCLU) is pro-apoptotic, while a secretory form (sCLU) is pro-survival. Both forms are implicated in various cell functions, including DNA repair, cell cycle regulation, and apoptotic cell death. CLU expression has been associated with tumorigenesis and the progression of various malignancies. In response to DNA damage, cell survival can be enhanced by activation of DNA repair mechanisms, while simultaneously stimulating energy-expensive cell cycle checkpoints that delay the cell cycle progression to allow more time for DNA repair. This review summarizes our current understanding of the role of clusterin in DNA repair, apoptosis, and cell cycle control and the relevance.

The involvement of ataxia-telangiectasia mutated protein activation in nucleotide excision repair-facilitated cell survival with cisplatin treatment

DNA damage can lead to either DNA repair with cell survival or to apoptotic cell death. Although the biochemical processes underlying DNA repair and apoptosis have been extensively studied, the mechanisms by which cells determine whether the damage will be repaired or the apoptotic pathway will be activated is largely unknown. We have studied the role of nucleotide excision repair (NER) in cisplatin DNA damage-induced apoptotic cell death using both normal human fibroblasts and NER-defective xeroderma pigmentosum (XP) XPA and XPG cells. The caspase-3 activation experiment demonstrated a greatly increased casapse-3 activation in the NER-defective cells following cisplatin treatment. The flow cytometry experiment revealed an altered cell cycle arrest pattern of the NER-defective cells following cisplatin treatment. The results obtained from the Western blot experiment showed that NER defects resulted in enhanced CHK1 phosphorylation and p21 induction after cisplatin treatment. The cisplatin treatment-induced ATM phosphorylation, however, was attenuated in NER-defective cells. The results obtained from our immunoprecipitation experiment further demonstrated that the ATM protein interacted with the TFIIH basal transcription factor and the XPG protein of the NER pathway. It also showed that a functional XPC protein was required for the association of the ATM protein to genomic DNA. These results suggest that the NER process may prevent the cisplatin treatment-induced apoptosis by activating the ATM protein, and that the presence of the XPC protein is essential for recruiting the ATM protein to the DNA template.

Effects of anticancer drugs on transcription factor–DNA interactions

DNA-interacting anticancer drugs are able to affect the propensity of DNA to interact with proteins through either reversible binding or covalent bond formation. The effect of the drugs on transcription factor interactions with DNA is reviewed. These effects can be classified as (i) competition between a drug and regulatory protein for target sequences; (ii) weakening of this interaction; (iii) enhancement of this interaction by chemical modification of the DNA and the creation of non-natural binding sites; and (iv) a 'suicide' mechanism, which is observed when a transcription factor induces changes in DNA structure, allowing a drug to bind to a target sequence. Several new strategies -- the antigene approach with oligonucleotides, peptide nucleic acids or locked nucleic acids, and sequence-specific polyamides -- are also reviewed.