Accumulation of hRad9 protein in the nuclei of nonsmall cell lung carcinoma cells

Exonucleases: Degrading DNA to Deal with Genome Damage, Cell Death, Inflammation and Cancer

Although DNA degradation might seem an unwanted event, it is essential in many cellular processes that are key to maintaining genomic stability and cell and organism homeostasis. The capacity to cut out nucleotides one at a time from the end of a DNA chain is present in enzymes called exonucleases. Exonuclease activity might come from enzymes with multiple other functions or specialized enzymes only dedicated to this function. Exonucleases are involved in central pathways of cell biology such as DNA replication, repair, and death, as well as tuning the immune response. Of note, malfunctioning of these enzymes is associated with immune disorders and cancer. In this review, we will dissect the impact of DNA degradation on the DNA damage response and its links with inflammation and cancer.

MiR-340-3p-HUS1 axis suppresses proliferation and migration in lung adenocarcinoma cells

AIMS

The functions and molecular mechanisms of miR-340-3p in lung adenocarcinoma (LUAD) progression remain unclear. On the other hand, the role of HUS1 in LUAD progression should be further explored.

MAIN METHODS

Data from cancer database were subjected to bioinformatics analysis. Quantitative real-time PCR and western blot were performed to detect gene expression. Colony formation and MTT assay were performed to examine cell growth in vitro. Wound healing assays and transwell assays were performed to examine cell migration.

KEY FINDINGS

Here, our results showed that miR-340-3p was lower expressed in LUAD tissues and LUAD-derived cell lines. And miR-340-3p suppressed the proliferation and migration ability of LUAD cells. Further, miR-340-3p inhibits HUS1 expression, which was higher expressed in LUAD tissues and promoted the proliferation and migration ability of LUAD cells. Moreover, higher HUS1 expression was associated with poor survival rate and shorter survival time in patients with LUAD, and HUS1 expression was negative correlated with that of miR-340-3p in clinical samples. In addition, overexpression of HUS1 counteracted the downregulation of cell growth by miR-340-3p.

SIGNIFICANCE

The study mainly indicated that miR-340-3p may play a tumor suppressor role in the progression of LUAD, with the function of restraining HUS1 expression, highlighting a potential therapeutic target for LUAD.

HUS1 checkpoint clamp component (HUS1) is a potential tumor suppressor in primary hepatocellular carcinoma

The HUS1 checkpoint clamp component (HUS1), which is a member of an evolutionarily conserved, genotoxin-activated checkpoint complex (Rad9-Rad1-Hus1 [9-1-1] complex), is involved in cell cycle arrest and DNA repair in response to DNA damage. We conducted this study to investigate the biological significances of HUS1 expression in hepatocellular carcinoma (HCC) development. The mRNA and protein expression levels of HUS1 were determined using Real-time PCR and Western blot, respectively. One hundered and twenty four paraffin sections from HCC tissues were analyzed by immunohistochemistry to assess the association between HUS1 expression and clinicopathological characteristics of patients. The Kaplan-Meier method was performed to calculate the OS and RFS curves. Cell proliferation and colony formation assays, cell migration and invasion assays and cell cycle assays were used to determine the suppressor role of HUS1 in vitro. A mouse model was used to determine the effect of HUS1 on tumorigenesis. The expression of HUS1 was significantly decreased in HCC cell lines and tissues, and low HUS1 expression was associated with poor prognosis of HCC patients. Upregulation of HUS1 expression inhibited the cell proliferation, colony formation, migration, and invasion, as well as arrested cell cycle at G0/G1 in HCC cells in vitro. Moreover, sufficient HUS1 expression inhibited the tumor growth in nude mice. Our study revealed for the first time that HUS1 is a potential tumor suppressor that might produce an antitumor effect in human HCC. Furthermore, HUS1 may serve as a prognostic indicator and could be used for therapeutic application in HCC patients.

HUS1 regulates in vivo responses to genotoxic chemotherapies

Cells are under constant attack from genotoxins and rely on a multifaceted DNA damage response (DDR) network to maintain genomic integrity. Central to the DDR are the ATM and ATR kinases, which respond primarily to double-strand DNA breaks (DSBs) and replication stress, respectively. Optimal ATR signaling requires the RAD9A-RAD1-HUS1 (9-1-1) complex, a toroidal clamp that is loaded at damage sites and scaffolds signaling and repair factors. Whereas complete ATR pathway inactivation causes embryonic lethality, partial Hus1 impairment has been accomplished in adult mice using hypomorphic (Hus1(neo)) and null (Hus1(Δ1)) Hus1 alleles, and here we use this system to define the tissue- and cell type-specific actions of the HUS1-mediated DDR in vivo. Hus1(neo/Δ1) mice showed hypersensitivity to agents that cause replication stress, including the crosslinking agent mitomycin C (MMC) and the replication inhibitor hydroxyurea, but not the DSB inducer ionizing radiation. Analysis of tissue morphology, genomic instability, cell proliferation and apoptosis revealed that MMC treatment caused severe damage in highly replicating tissues of mice with partial Hus1 inactivation. The role of the 9-1-1 complex in responding to MMC was partially ATR-independent, as a HUS1 mutant that was proficient for ATR-induced checkpoint kinase 1 phosphorylation nevertheless conferred MMC hypersensitivity. To assess the interplay between the ATM and ATR pathways in responding to replication stress in vivo, we used Hus1/Atm double mutant mice. Whereas Hus1(neo/neo) and Atm(-/-) single mutant mice survived low-dose MMC similar to wild-type controls, Hus1(neo/neo)Atm(-/-) double mutants showed striking MMC hypersensitivity, consistent with a model in which MMC exposure in the context of Hus1 dysfunction results in DSBs to which the ATM pathway normally responds. This improved understanding of the inter-dependency between two major DDR mechanisms during the response to a conventional chemotherapeutic illustrates how inhibition of checkpoint factors such as HUS1 may be effective for the treatment of ATM-deficient and other cancers.

Over expression of hRad9 protein correlates with reduced chemosensitivity in breast cancer with administration of neoadjuvant chemotherapy

Human Rad 9 (hRad9), part of the Rad9-Hus1-Rad1 complex plays an important role in DNA damage repair as an up-stream regulator of checkpoint signaling, however little is known about its role in response to chemotherapy of breast cancer and whether hRad9 inhibition can potentiate the cytotoxic effects of chemotherapy on breast cancer cells remains to be elucidated. Fifty cases of breast cancer receiving neoadjuvant therapy were collected. All these cases were revised and classified into chemotherapy sensitive (CS) or chemotherapy resistant (CR) group according to the Miller and Payne (MP) grading system. Immunohistochemically, hRad9 positive tumours showed nuclear and/or cytoplasmic staining. hRad9 over-expression was associated with an impaired neoadjuvant chemotherapy response. A significant correlation was found between expression of hRad9 and Cyclin D1. In vitro, hRad9 was knocked down using siRNA in breast cancer cell line MCF-7 and MDA-MB-231. Deregulated expression of Rad9 accompanied by down expression of chk1 enhanced the sensitivity of human breast cancer cells to doxorubicin. Our work suggests that hRad9 might be a potential predictor for the response to chemotherapy in patients with breast cancer and its clinical value as a target for improving chemosensitivity needs further exploration.

hRAD9 functions as a tumor suppressor by inducing p21-dependent senescence and suppressing epithelial-mesenchymal transition through inhibition of Slug transcription

Senescence and epithelial-mesenchymal transition (EMT) have opposing roles in tumor progression, in that, one is a barrier against tumorigenesis, whereas the other is required for invasive malignancies. Here, we report that the DNA damage response (DDR) protein hRAD9 contributes to induction of senescence and inhibition of EMT. Our data show that hRAD9 is frequently downregulated in breast and lung cancers. Loss of hRAD9 expression is associated with tumor stage in breast and lung cancers, as well as with acquisition of an invasive phenotype. Ectopic hRAD9 expression in highly invasive cancer cell lines, H1299 and MDA-MB 231, with low endogenous hRAD9 induced senescence by upregulation of nuclear p21, independent of the p53 status. Ectopic expression of hRAD9 also significantly attenuated cellular migration and invasion in vitro and tumor growth in a xenograft mouse model in vivo. In contrast, silencing hRAD9 in lower invasive cancer cell lines, A549 and MCF7, with high endogenous hRAD9 dramatically increased their migration and invasion abilities, and simultaneously activated EMT. Knockdown of hRAD9 increased, whereas ectopic expression of hRAD9 decreased, the expression of Slug. Moreover, hRAD9 directly bound to the promoter region of slug gene and repressed its transcriptional activity. Taken together, these results suggest that hRAD9 is a potential tumor suppressor in breast and lung cancers and that it is likely to function by upregulating p21 and inhibiting Slug to regulate tumorigenesis.

Ligand-Based Pharmacophore Modeling and Virtual Screening of RAD9 Inhibitors

Human RAD9 is a key cell-cycle checkpoint protein that participates in DNA repair, activation of multiple cell cycle phase checkpoints, and apoptosis. Aberrant RAD9 expression has been linked to breast, lung, thyroid, skin, and prostate tumorigenesis. Overexpression of RAD9 interacts with BCL-2 proteins and blocks the binding sites of BCL-2 family proteins to interact with chemotherapeutic drugs and leads to drug resistance. Focusing on this interaction, the present study was designed to identify the interaction sites of RAD9 to bind BCL-2 protein and also to inhibit RAD9-BCL-2 interactions by designing novel small molecule inhibitors using pharmacophore modeling and to restore BCL-2 for interacting with anticancer drugs. The bioactive molecules of natural origin act as excellent leads for new drug development. Thus, in the present study, we used the compounds of natural origin like camptothecin, ascididemin, and Dolastatin and also compared them with synthetic molecule NSC15520. The results revealed that camptothecin can act as an effective inhibitor among all the ligands taken and can be used as an RAD9 inhibitor. The amino acids ARG45 and ALA134 of RAD9 protein are interacting commonly with the drugs and BCL-2 protein.

Contributions of Rad9 to tumorigenesis

Rad9 plays a crucial role in maintaining genomic stability by regulating cell cycle checkpoints, DNA repair, telomere stability, and apoptosis. Rad9 controls these processes mainly as part of the heterotrimeric 9-1-1 (Rad9-Hus1-Rad1) complex. However, in recent years it has been demonstrated that Rad9 can also act independently of the 9-1-1 complex as a transcriptional factor, participate in immunoglobulin class switch recombination, and show 3'-5' exonuclease activity. Aberrant Rad9 expression has been associated with prostate, breast, lung, skin, thyroid, and gastric cancers. High expression of Rad9 is causally related to, at least, human prostate cancer growth. On the other hand, deletion of Mrad9, the mouse homolog, is responsible for increased skin cancer incidence. These results reveal that Rad9 can act as an oncogene or tumor suppressor. Which of the many functions of Rad9 are causally related to initiation and progression of tumorigenesis and the mechanistic details by which Rad9 induces or suppresses tumorigenesis are presently not known, but are crucial for the development of targeted therapeutic interventions.

Reduced mRNA and protein expression of the genomic caretaker RAD9A in primary fibroblasts of individuals with childhood and independent second cancer

Background

The etiology of secondary cancer in childhood cancer survivors is largely unclear. Exposure of normal somatic cells to radiation and/or chemotherapy can damage DNA and if not all DNA lesions are properly fixed, the mis-repair may lead to pathological consequences. It is plausible to assume that genetic differences, i.e. in the pathways responsible for cell cycle control and DNA repair, play a critical role in the development of secondary cancer.

Methodology/Findings

To identify factors that may influence the susceptibility for second cancer formation, we recruited 20 individuals who survived a childhood malignancy and then developed a second cancer as well as 20 carefully matched control individuals with childhood malignancy but without a second cancer. By antibody microarrays, we screened primary fibroblasts of matched patients for differences in the amount of representative DNA repair-associated proteins. We found constitutively decreased levels of RAD9A and several other DNA repair proteins in two-cancer patients, compared to one-cancer patients. The RAD9A protein level increased in response to DNA damage, however to a lesser extent in the two-cancer patients. Quantification of mRNA expression by real-time RT PCR revealed lower RAD9A mRNA levels in both untreated and 1 Gy γ-irradiated cells of two-cancer patients.

Conclusions/Significance

Collectively, our results support the idea that modulation of RAD9A and other cell cycle arrest and DNA repair proteins contribute to the risk of developing a second malignancy in childhood cancer patients.

Multiple functions of rad9 for preserving genomic integrity

DNA-damage checkpoints sense and respond to genomic damage. Human Rad9 (hRad9), an evolutionarily conserved gene with multiple functions for preserving genomic integrity, plays multiple roles in fundamental biological processes, including the regulation of the DNA damage response, cell cycle checkpoint control, DNA repair, apoptosis, transcriptional regulation, exonuclease activity, ribonucleotide synthesis and embryogenesis. This review examines work that provides significant insight into the molecular mechanisms of several individual cellular processes which might be beneficial for developing novel therapeutic approaches to cancerous diseases with genomic instability.

The role of RAD9 in tumorigenesis

RAD9 regulates multiple cellular processes that influence genomic integrity, and for at least some of its functions the protein acts as part of a heterotrimeric complex bound to HUS1 and RAD1 proteins. RAD9 participates in DNA repair, including base excision repair, homologous recombination repair and mismatch repair, multiple cell cycle phase checkpoints and apoptosis. In addition, functions including the transactivation of downstream target genes, immunoglobulin class switch recombination, as well as 3'-5' exonuclease activity have been reported. Aberrant RAD9 expression has been linked to breast, lung, thyroid, skin and prostate tumorigenesis, and a cause-effect relationship has been demonstrated for the latter two. Interestingly, human RAD9 overproduction correlates with prostate cancer whereas deletion of Mrad9, the corresponding mouse gene, in keratinocytes leads to skin cancer. These results reveal that RAD9 protein can function as an oncogene or tumor suppressor, and aberrantly high or low levels can have deleterious health consequences. It is not clear which of the many functions of RAD9 is critical for carcinogenesis, but several alternatives are considered herein and implications for the development of novel cancer therapies based on these findings are examined.

Application of hRad9 in lung cancer treatment as a molecular marker and a molecular target

DNA damage sensor proteins work as upstream components of the DNA damage checkpoint signaling pathways that are essential for cell cycle control and the induction of apoptosis. hRad9 is a member of a family of proteins that act as DNA damage sensors and plays an important role as an upstream regulator of checkpoint signaling. We clarified the significant accumulation of hRad9 in the nuclei of tumor cells in surgically-resected non-small-cell lung cancer (NSCLC) specimens and found the capacity to produce a functional hRad9 protein was intact in lung cancer cells. This finding suggested that hRad9 was a vital component in the pathways that lead to the survival and progression of NSCLC and suggested that hRad9 was a good candidate for a molecular target to control lung cancer cell growth. RNA interference targeting hRad9 was performed to examine this hypothesis. The impairment of the DNA damage checkpoint signaling pathway induced cancer cell death. hRad9 might be a novel molecular target for lung cancer treatment.

Mouse Rad1 deletion enhances susceptibility for skin tumor development

Background

Cells are constantly exposed to stresses from cellular metabolites as well as environmental genotoxins. DNA damage caused by these genotoxins can be efficiently fixed by DNA repair in cooperation with cell cycle checkpoints. Unrepaired DNA lesions can lead to cell death, gene mutation and cancer. The Rad1 protein, evolutionarily conserved from yeast to humans, exists in cells as monomer as well as a component in the 9-1-1 protein complex. Rad1 plays crucial roles in DNA repair and cell cycle checkpoint control, but its contribution to carcinogenesis is unknown.

Results

To address this question, we constructed mice with a deletion of Mrad1. Matings between heterozygous Mrad1 mutant mice produced Mrad1^+/+ and Mrad1^+/- but no Mrad1^-/- progeny, suggesting the Mrad1 null is embryonic lethal. Mrad1^+/- mice demonstrated no overt abnormalities up to one and half years of age. DMBA-TPA combinational treatment was used to induce tumors on mouse skin. Tumors were larger, more numerous, and appeared earlier on the skin of Mrad1^+/- mice compared to Mrad1^+/+ animals. Keratinocytes isolated from Mrad1^+/- mice had significantly more spontaneous DNA double strand breaks, proliferated slower and had slightly enhanced spontaneous apoptosis than Mrad1^+/+ control cells.

Conclusion

These data suggest that Mrad1 is important for preventing tumor development, probably through maintaining genomic integrity. The effects of heterozygous deletion of Mrad1 on proliferation and apoptosis of keratinocytes is different from those resulted from Mrad9 heterozygous deletion (from our previous study), suggesting that Mrad1 also functions independent of Mrad9 besides its role in the Mrad9-Mrad1-Mhus1 complex in mouse cells.

Nonsynonymous single nucleotide polymorphisms in DNA damage repair pathways and lung cancer risk

BACKGROUND

Several reports have revealed the association between single nucleotide polymorphisms (SNPs) and the development of cancer. Although many SNPs have been investigated, they were tested individually. In this study, nonsynonymous SNPs present in DNA damage response genes were comprehensively analyzed for lung cancer susceptibility.

METHODS

The authors selected 37 nonsynonymous SNPs in 23 genes involved in DNA damage repair pathways. Fifty lung adenocarcinoma patients resected at their institution between 2002 and 2005 and 50 individuals without any known history of cancer were recruited for a case-control study.

RESULTS

Three variants (XRCC1 194Trp homozygotes, POLdelta1 119His homozygotes, and RAD9 239Arg heterozygotes) tended to coassociate with lung cancer risk. The authors analyzed and calculated whether the association between combinations of these 3 SNPs significantly affected the risk of lung cancer. Compared with carriers of either XRCC1 194Trp homozygote or RAD9 239Arg heterozygote variants, noncarriers were at a significantly decreased risk for lung cancer (odds ratio [OR], 0.282; confidence interval [CI], 0.089-0.893). The same results were found for the combination of POLdelta1 119His homozygotes and RAD9 239Arg heterozygotes (OR, 0.277; CI, 0.077-0.993). Moreover, compared with carriers that had at least 1 of the 3 variants, noncarriers showed a more significant decrease in risk (OR, 0.263; CI, 0.090-0.767).

CONCLUSIONS

Analysis of the presence of XRCC1 194Trp homozygote, POLdelta1 119His homozygote, and RAD9 239Arg heterozygote variants revealed that their coassociation leads to a significant risk for the development of lung adenocarcinoma. Inclusive analyses of different SNPs were important in this cancer risk study.

Dual inactivation of Hus1 and p53 in the mouse mammary gland results in accumulation of damaged cells and impaired tissue regeneration

In response to DNA damage, checkpoint proteins halt cell cycle progression and promote repair or apoptosis, thereby preventing mutation accumulation and suppressing tumor development. The DNA damage checkpoint protein Hus1 associates with Rad9 and Rad1 to form the 9-1-1 complex, which localizes to DNA lesions and promotes DNA damage signaling and repair. Because complete inactivation of mouse Hus1 results in embryonic lethality, we developed a system for regulated Hus1 inactivation in the mammary gland to examine roles for Hus1 in tissue homeostasis and tumor suppression. Hus1 inactivation in the mammary epithelium resulted in genome damage that induced apoptosis and led to depletion of Hus1-null cells from the mammary gland. Conditional Hus1 knockout females retained grossly normal mammary gland morphology, suggesting compensation by cells that failed to undergo Cre-mediated Hus1 deletion. p53-deficiency delayed the clearance of Hus1-null cells from conditional Hus1 knockout mice and caused the accumulation of damaged, dying cells in the mammary gland. Notably, compensatory responses were impaired following combined Hus1 and p53 loss, resulting in aberrant mammary gland morphology and lactation defects. Overall, these results establish a requirement for Hus1 in the survival and proliferation of mammary epithelium and identify a role for p53 in mammary gland tissue regeneration and homeostasis.

Targeted deletion of Rad9 in mouse skin keratinocytes enhances genotoxin-induced tumor development

The Rad9 gene is evolutionarily conserved from yeast to humans and plays crucial roles in genomic maintenance, DNA repair, and cell cycle checkpoint controls. However, the function of this gene with respect to tumorigenesis is not well-understood. A Rad9-null mutation in mice causes embryonic lethality. In this study, we created mice in which mouse Rad9, Mrad9, was deleted only in keratinocytes to permit examination of the potential function of the gene in tumor development. Mice with Mrad9(+/-) or Mrad9(-/-) keratinocytes showed no overt, spontaneous morphologic defects and seemed similar to wild-type controls. Painting the carcinogen 7,12-dimethylbenzanthracene (DMBA) onto the skin of the animals caused earlier onset and more frequent formation of tumors and senile skin plaques in Mrad9(-/-) mice, compared with Mrad9(+/-) and Mrad9(+/+) littermates. DNA damage response genes p21, p53, and Mrad9B were expressed at higher levels in Mrad9(-/-) relative to Mrad9(+/+) skin. Keratinocytes isolated from Mrad9(-/-) skin had more spontaneous and DMBA-induced DNA double strand breaks than Mrad9(+/+) keratinocytes, and the levels were reduced by incubation with the antioxidant epigallocatechin gallate. These data suggest that Mrad9 plays an important role in maintaining genomic stability and preventing tumor development in keratinocytes.

Localization of hRad9 in breast cancer

Background

hRad9 is a cell cycle checkpoint gene that is up-regulated in breast cancer. We have previously shown that the mRNA up-regulation correlated with tumor size and local recurrence. Immunohistochemical studies were made to better define the role of hRad9 in breast carcinogenesis.

Methods

Localisation of hRad9 protein were performed on paired tumor and normal breast tissues. Immunoblotting with and without dephosphorylation was used to define the protein isolated from breast cancer cells.

Results

Increased hRad9 protein was observed in breast cancer cells nucleus compared to non-tumor epithelium. This nuclear protein existed in hyperphosphorylated forms which may be those of the hRad9-hRad1-hHus1 complex.

Conclusion

Finding of hyperphosphorylated forms of hRad9 in the nucleus of cancer cells is in keeping with its function in ameliorating DNA instability, whereby it inadvertently assists tumor growth.

Rad9 has a functional role in human prostate carcinogenesis

Prostate cancer is currently the most common type of neoplasm found in American men, other than skin cancer, and is the second leading cause of cancer death in males. Because cell cycle checkpoint proteins stabilize the genome, the relationship of one such protein, Rad9, to prostate cancer was investigated. We found that four prostate cancer cell lines (CWR22, DU145, LNCaP, and PC-3), relative to PrEC normal prostate cells, have aberrantly high levels of Rad9 protein. The 3'-end region of intron 2 of Rad9 in DU145 cells is hypermethylated at CpG islands, and treatment with 5'-aza-2'-deoxycytidine restores near-normal levels of methylation and reduces Rad9 protein abundance. Southern blot analyses indicate that PC-3 cells contain an amplified Rad9 copy number. Therefore, we provide evidence that Rad9 levels are high in prostate cancer cells due at least in part to aberrant methylation or gene amplification. The effectiveness of small interfering RNA to lower Rad9 protein levels in CWR22, DU145, and PC-3 cells correlated with reduction of tumorigenicity in nude mice, indicating that Rad9 actively contributes to the disease. Rad9 protein levels were high in 153 of 339 human prostate tumor biopsy samples examined and detectable in only 2 of 52 noncancerous prostate tissues. There was a strong correlation between Rad9 protein abundance and cancer stage. Rad9 protein level can thus provide a biomarker for advanced prostate cancer and is causally related to the disease, suggesting the potential for developing novel diagnostic, prognostic, and therapeutic tools based on detection or manipulation of Rad9 protein abundance.

Rad9 modulates the P21WAF1 pathway by direct association with p53

Background

Previous studies suggest that human RAD9 (hRad9), encoding a DNA damage checkpoint molecule, which is frequently amplified in epithelial tumor cells of breast, lung, head and neck cancer, participates in regulation of the tumor suppressor p53-dependent transactivation of pro-survival P21^WAF1. This study examined the exact mechanism of the hRad9 function, especially through the phosphorylation of the C-terminus, in the transcription regulation of P21^WAF1.

Results

The transfection of phosphorylation-defective hRAD9 mutants of C-terminus resulted in reduction of the p53-dependent P21^WAF1 transactivation; the knockdown of total hRad9 elicited an increased P21^WAF1 mRNA expression. Immunoprecipitation and a ChIP assay showed that hRad9 and p53 formed a complex and both were associated with two p53-consensus DNA-binding sequences in the 5' region of P21^WAF1 gene. The association was reduced in the experiment of phosphorylation-defective hRAD9 mutants.

Conclusion

The present study indicates the direct involvement of hRad9 in the p53-dependent P21^WAF1 transcriptional mechanism, presumably via the phosphorylation sites, and alterations of the hRad9 pathway might therefore contribute to the perturbation of checkpoint activation in cancer cells.

Diagnostic and prognostic value of cell-cycle regulatory genes in malignant thyroid neoplasms

BACKGROUND

Approximately 30% of patients with thyroid nodules have indeterminate or suspicious fine-needle aspiration (FNA) biopsy results. Because their risk of cancer is approximately 20%, these patients undergo thyroidectomy. We hypothesized that genes that regulate cell-cycle progression would be differentially expressed in malignant versus benign thyroid nodules and could serve as diagnostic markers and markers of disease aggressiveness.

METHODS

We used a cDNA array with 96 cell-cycle regulatory genes to identify differentially expressed genes in pooled benign versus malignant thyroid neoplasms. Genes up- or down-regulated by more than 2-fold in malignant thyroid neoplasms were further evaluated by real-time quantitative polymerase chain reaction (PCR) in 95 patients with hyperplastic nodules (n = 19), follicular adenoma (n = 19), follicular thyroid cancer (n = 19), the follicular variant of papillary thyroid cancer (n = 19), and papillary thyroid cancer (n = 19).

RESULTS

cDNA array analysis showed that cyclin B1, MCM5, MCM7, RAD9, ubiquitin C, CDK6, SKP2, and APAF1 were up-regulated in malignant thyroid neoplasms. Real-time quantitative PCR showed that MCM5, MCM7, and RAD9 mRNA expression were significantly higher in malignant than in benign thyroid neoplasms (< or = 0.0012). The combined use of MCM5, MCM7, and RAD9 mRNA expression had a sensitivity of 98.2% and a specificity of 65.7%. The level of MCM7 mRNA expression was higher in T4 than in T1, T2, and T3 differentiated thyroid cancers (P < 0.0127).

CONCLUSIONS

MCM5, MCM7, and RAD9 are overexpressed in malignant thyroid neoplasms of follicular cell origin. These genes may be useful markers of malignant thyroid neoplasms as an adjunct to FNA biopsy. MCM7 mRNA expression is higher in locally invasive differentiated thyroid cancer.

Rad9, an evolutionarily conserved gene with multiple functions for preserving genomic integrity

The Rad9 gene is evolutionarily conserved. Analysis of the gene from yeast, mouse and human reveal roles in multiple, fundamental biological processes primarily but not exclusively important for regulating genomic integrity. The encoded mammalian proteins participate in promoting resistance to DNA damage, cell cycle checkpoint control, DNA repair, and apoptosis. Other functions include a role in embryogenesis, the transactivation of multiple target genes, co-repression of androgen-induced transcription activity of the androgen receptor, a 3'-5' exonuclease activity, and the regulation of ribonucleotide synthesis. Analyses of the functions of Rad9, and in particular its role in regulating and coordinating numerous fundamental biological activities, should not only provide information about the molecular mechanisms of several individual cellular processes, but might also lend insight into the more global control and coordination of what at least superficially present as independent pathways.

Mammalian Rad9 plays a role in telomere stability, S- and G2-phase-specific cell survival, and homologous recombinational repair

The protein products of several rad checkpoint genes of Schizosaccharomyces pombe (rad1+, rad3+, rad9+, rad17+, rad26+, and hus1+) play crucial roles in sensing changes in DNA structure, and several function in the maintenance of telomeres. When the mammalian homologue of S. pombe Rad9 was inactivated, increases in chromosome end-to-end associations and frequency of telomere loss were observed. This telomere instability correlated with enhanced S- and G2-phase-specific cell killing, delayed kinetics of gamma-H2AX focus appearance and disappearance, and reduced chromosomal repair after ionizing radiation (IR) exposure, suggesting that Rad9 plays a role in cell cycle phase-specific DNA damage repair. Furthermore, mammalian Rad9 interacted with Rad51, and inactivation of mammalian Rad9 also resulted in decreased homologous recombinational (HR) repair, which occurs predominantly in the S and G2 phases of the cell cycle. Together, these findings provide evidence of roles for mammalian Rad9 in telomere stability and HR repair as a mechanism for promoting cell survival after IR exposure.

His239Arg SNP of HRAD9 is associated with lung adenocarcinoma

BACKGROUND

It was previously reported that a functional human (h) Rad9 protein accumulated in the nuclei of non-small cell lung carcinoma (NSCLC) cells. Those experiments, however, did not examine whether the hRad9 gene was mutated in those cells. The sequence of the HRAD9 gene in NSCLC cells was investigated.

METHODS

The sequence of the HRAD9 was examined in tumor and peripheral normal lung tissues obtained from 50 lung adenocarcinoma patients during surgery. The expression of its mRNA using reverse transcription polymerase chain reaction (RT-PCR) was also examined.

RESULTS

No sequence alterations were detected in the HRAD9 gene, which was found to be normally transcribed in surgically resected lung carcinoma cells. However, in eight (16.0%) cases a single nucleotide polymorphism (SNP) was observed at the second position of codon 239 (His/Arg heterozygous variant) of the gene. This frequency was significantly higher than that found in the normal population.

CONCLUSIONS

Whereas the capacity to produce a functional hRad9 protein was intact in lung adenocarcinoma cells, a nonsynonymous SNP of HRAD9 was detected that might be associated with the development of lung adenocarcinoma.