Fhit modulation of the Akt-survivin pathway in lung cancer cells: Fhit-tyrosine 114 (Y114) is essential

Integrated DNA methylation analysis of peripheral blood from asbestos exposed populations and patients with malignant mesothelioma reveals novel methylation driver genes of diagnostic and prognostic relevance

Effective biomarkers are paramount importance for the early detection and prognosis prediction of malignant mesothelioma (MM) which mainly caused by asbestos exposure, and DNA methylation has been demonstrated to be a potentially powerful diagnostic tool. To elucidate the relationship between asbestos exposure and alterations in DNA methylation patterns, as well as the potential diagnostic and prognostic value of differentially methylated regions and CpG sites (DMRs/DMCs) in the progression of MM. The current study employed reduced representation bisulfite sequencing (RRBS) to examine the genome-wide DNA methylation profiles in the peripheral blood of individuals exposed to asbestos and those diagnosed with MM, in comparison to the controls, and DMRs/DMCs were subsequently validated by targeted bisulfite sequencing (TBS). Our results suggested that there were 12 DMRs/DMCs exhibiting a consistent change trend of DNA methylation in both RRBS and TBS results. Significant correlations were observed between DNA methylation levels of DMRs/DMCs and the duration of occupational asbestos exposure. The evaluation of the receiver operating characteristic (ROC) curve suggested that the DNA methylation status of FHIT, CCR12P and CDH15 may serve as diagnosis indicator in distinguishing MM patients from healthy controls and those exposed to asbestos. Our findings offer a foundation for the role of DNA methylation in the development of MM induced by asbestos exposure. The potential significance of FHIT, CCR12P and CDH15 DNA methylation alterations in the pathogenesis and advancement of MM disease suggests their potential as diagnostic and prognostic biomarkers.

Arabidopsis Fhit-like tumor suppressor resumes early terminated constitutive triple response1-10 mRNA translation

The Arabidopsis (Arabidopsis thaliana) constitutive triple response1-10 (ctr1-10) mutant produces a reduced level of CTR1 protein and exhibits a weak ctr1 mutant phenotype. Sequence analysis revealed highly active translation of the upstream open reading frame (uORF) at the extended 5'-UTR of the ctr1-10 mRNA, resulting from T-DNA insertion. Enhancer screening for ctr1-10 isolated the fragile histidine triad-1 (fhit-1) mutation. The fhit-1 ctr1-10 mutant phenotypically resembled strong ctr1 mutants and barely produced CTR1, and the fhit-1 mutation reduced the translation efficiency of ctr1-10 but not that of CTR1 mRNA. The human (Homo sapiens) Fhit that involves tumorigenesis and genome instability has the in vitro dinucleotide 5',5'″-P1, P3-triphosphate hydrolase activity, and expression of the human HsFHIT or the hydrolase-defective HsFHITH96N transgene reversed the fhit-1 ctr1-10 mutant phenotype and restored CTR1 levels. Genetic editing that in situ disrupts individual upstream ATG codons proximal to the ctr1-10 mORF elevated CTR1 levels in ctr1-10 plants independent of FHIT. EUKARYOTIC INITIATION FACTOR3G (eIF3G), which is involved in translation and reinitiation, interacted with FHIT, and both were associated with the polysome. We propose that FHIT resumes early terminated ctr1-10 mORF translation in the face of active and complex uORF translation. Our study unveils a niche that may lead to investigations on the molecular mechanism of Fhit-like proteins in translation reinitiation. The biological significance of FHIT-regulated translation is discussed.

Liver Transcriptome Shows Differences between Acute Hypoxia-Tolerant and Intolerant Individuals of Greater Amberjack (Seriola dumerili)

Acute hypoxia is a common abiotic stress in commercial aquaculture and has significant effects on fish physiology and metabolism. Due to its large size and rapid growth, the greater amberjack (Seriola dumerili) is an economically important fish with high farming value. This species is intolerant to hypoxia, which makes it susceptible to mass mortality and hinders the progress of amberjack cultivation. Based on a comparative analysis of the liver transcriptome between acute hypoxia-tolerant (HT) and -intolerant (HS) groups, this study first explored the molecular mechanisms of acute hypoxia in greater amberjack. By simulating the acute hypoxic environment and using RNA sequencing (RNA-Seq), the differences in liver transcriptional changes between the acute hypoxia-tolerant (HT) and hypoxia-intolerant (HS) groups of greater amberjack were probed. Based on differential expression analysis, 829 differentially expressed genes (DEGs) were screened in both groups. Relative to the HS group, 374 DEGs were upregulated and 455 were downregulated in the HT group. Compared with the HS group, genes such as slc2a5 and prkaa2 related to promoting sugar transport and inhibiting lipid syntheses were upregulated, while genes that inhibit gluconeogenesis and promote lipid syntheses, such as pgp and aacs, were downregulated. The expression of odc1 was significantly and relatively downregulated in the HT group, which would lead to the inhibition of intracellular antioxidant activity and decreased scavenging of ROS. The NF-kB pathway was also promoted to some extent in individuals in the HT group relative to the HS group to resist apoptosis. In addition, the relative downregulation of apoptosis and autophagy-related genes, such as endog, hm13, and casp6, was also detected in the HT group. The present findings first reported the regulation mechanism by which liver tissue coped with the acute hypoxia stress in greater amberjack, which will provide important technical support for preventing acute hypoxia-induced death in advance and reducing economic losses.

The Rosetta Stone Hypothesis-Based Interaction of the Tumor Suppressor Proteins Nit1 and Fhit

In previous studies, we have identified the tumor suppressor proteins Fhit (fragile histidine triad) and Nit1 (Nitrilase1) as interaction partners of β-catenin both acting as repressors of the canonical Wnt pathway. Interestingly, in D. melanogaster and C. elegans these proteins are expressed as NitFhit fusion proteins. According to the Rosetta Stone hypothesis, if proteins are expressed as fusion proteins in one organism and as single proteins in others, the latter should interact physically and show common signaling function. Here, we tested this hypothesis and provide the first biochemical evidence for a direct association between Nit1 and Fhit. In addition, size exclusion chromatography of purified recombinant human Nit1 showed a tetrameric structure as also previously observed for the NitFhit Rosetta Stone fusion protein Nft-1 in C. elegans. Finally, in line with the Rosetta Stone hypothesis we identified Hsp60 and Ubc9 as other common interaction partners of Nit1 and Fhit. The interaction of Nit1 and Fhit may affect their enzymatic activities as well as interaction with other binding partners.

Germinal epimutation of Fragile Histidine Triad (FHIT) gene is associated with progression to acute and chronic adult T-cell leukemia diseases

BACKGROUND

Human T cell Leukemia virus type 1 (HTLV-I) is etiologically linked to adult T cell leukemia/lymphoma (ATL) and an inflammatory neurodegenerative disease called HTLV-I-associated myelopathy or tropical spastic paraparesis (HAM/TSP). The exact genetic or epigenetic events and/or environmental factors that influence the development of ATL, or HAM/TSP diseases are largely unknown. The tumor suppressor gene, Fragile Histidine Triad Diadenosine Triphosphatase (FHIT), is frequently lost in cancer through epigenetic modifications and/or deletion. FHIT is a tumor suppressor acting as genome caretaker by regulating cellular DNA repair. Indeed, FHIT loss leads to replicative stress and accumulation of double DNA strand breaks. Therefore, loss of FHIT expression plays a key role in cellular transformation.

METHODS

Here, we studied over 400 samples from HTLV-I-infected individuals with ATL, TSP/HAM, or asymptomatic carriers (AC) for FHIT loss and expression. We examined the epigenetic status of FHIT through methylation specific PCR and bisulfite sequencing; and correlated these results to FHIT expression in patient samples.

RESULTS

We found that epigenetic alteration of FHIT is specifically found in chronic and acute ATL but is absent in asymptomatic HTLV-I carriers and TSP/HAM patients' samples. Furthermore, the extent of FHIT methylation in ATL patients was quantitatively comparable in virus-infected and virus non-infected cells. We also found that longitudinal HTLV-I carriers that progressed to smoldering ATL and descendants of ATL patients harbor FHIT methylation.

CONCLUSIONS

These results suggest that germinal epigenetic mutation of FHIT represents a preexisting mark predisposing to the development of ATL diseases. These findings have important clinical implications as patients with acute ATL are rarely cured. Our study suggests an alternative strategy to the current "wait and see approach" in that early screening of HTLV-I-infected individuals for germinal epimutation of FHIT and early treatment may offer significant clinical benefits.

Distinct Signatures of Genomic Copy Number Variants Define Subgroups of Merkel Cell Carcinoma Tumors

Simple Summary

Cancer results from genetic changes in cells. These changes are often mutations that alter the DNA sequence of critical genes. However, duplications and deletions in cancer-related genes can also contribute to malignant transformation. In this study we use Nanostring technology to assess DNA copy number changes in samples of Merkel cell carcinoma (MCC), a rare and aggressive neuroendocrine skin tumor. We were able to identify recurrent amplifications and deletions in cancer-related genes. We also found that MCC tumors grouped into three distinct copy number variant profiles. The first group consisted of tumors with multiple deletions. The second group contained tumors with low levels of genomic structural alterations. The last group comprised tumors containing multiple amplifications. Our study suggests that most MCC tumors are associated with deletions in cancer-related genes or are lacking in copy number changes, whereas a small percentage of tumors are associated with genomic amplifications.

Abstract

Merkel cell carcinoma (MCC) is a rare, aggressive neuroendocrine skin cancer. Most MCC tumors contain integrated Merkel cell polyomavirus DNA (virus-positive MCC, VP-MCC) and carry a low somatic mutation burden whereas virus-negative MCC (VN-MCC) possess numerous ultraviolet-signature mutations. In contrast to viral oncogenes and sequence mutations, little is known about genomic structural variants in MCC. To identify copy number variants in commonly altered genes, we analyzed genomic DNA from 31 tumor samples using the Nanostring nCounter copy number cancer panel. Unsupervised clustering revealed three tumor groups with distinct genomic structural variant signatures. The first cluster was characterized by multiple recurrent deletions in genes such as RB1 and WT1. The second cluster contained eight VP-MCC and displayed very few structural variations. The final cluster contained one VP-MCC and four VN-MCC with predominantly genomic amplifications in genes like MDM4, SKP2, and KIT and deletions in TP53. Overall, VN-MCC contained more structure variation than VP-MCC but did not cluster separately from VP-MCC. The observation that most MCC tumors demonstrate a deletion-dominated structural group signature, independent of virus status, suggests a shared pathophysiology among most VP-MCC and VN-MCC tumors.

A Fhit-mimetic peptide suppresses annexin A4-mediated chemoresistance to paclitaxel in lung cancer cells

We recently reported that Fhit is in a molecular complex with annexin A4 (ANXA4); following to their binding, Fhit delocalizes ANXA4 from plasma membrane to cytosol in paclitaxel-resistant lung cancer cells, thus restoring their chemosensitivity to the drug. Here, we demonstrate that Fhit physically interacts with A4 through its N-terminus; molecular dynamics simulations were performed on a 3D Fhit model to rationalize its mechanism of action. This approach allowed for the identification of the QHLIKPS heptapeptide (position 7 to 13 of the wild-type Fhit protein) as the smallest Fhit sequence still able to preserve its ability to bind ANXA4. Interestingly, Fhit peptide also recapitulates the property of the native protein in inhibiting Annexin A4 translocation from cytosol to plasma membrane in A549 and Calu-2 lung cancer cells treated with paclitaxel. Finally, the combination of Tat-Fhit peptide and paclitaxel synergistically increases the apoptotic rate of cultured lung cancer cells and blocks in vivo tumor formation.

Our findings address to the identification of chemically simplified Fhit derivatives that mimic Fhit tumor suppressor functions; intriguingly, this approach might lead to the generation of novel anticancer drugs to be used in combination with conventional therapies in Fhit-negative tumors to prevent or delay chemoresistance.

FHIT down-regulation was inversely linked to aggressive behaviors and adverse prognosis of gastric cancer: a meta- and bioinformatics analysis

FHIT (fragile histine triad) acts as diadenosine P1, P3-bis (5'-adenosyl)-triphosphate adenylohydrolase involved in purine metabolism, and induces apoptosis as a tumor suppressor. We performed a systematic meta- and bioinformatics analysis through multiple online databases up to March 14, 2017. The down-regulated FHIT expression was found in gastric cancer, compared with normal mucosa and dysplasia (p < 0.05). FHIT expression was negatively with depth of invasion, lymph node metastasis, distant metastasis, TNM staging and dedifferentiation of gastric cancer (p < 0.05). A positive association between FHIT expression and favorable overall survival was found in patients with gastric cancer (p < 0.05). According to Kaplan-Meier plotter, we found that a higher FHIT expression was negatively correlated with overall and progression-free survival rates of all cancer patients, even stratified by aggressive parameters (p < 0.05). These findings indicated that FHIT expression might be employed as a potential marker to indicate gastric carcinogenesis and subsequent progression, even prognosis.

The one-carbon metabolism pathway highlights therapeutic targets for gastrointestinal cancer (Review)

After the initial use of anti-folates for treatment of malignancies, folate metabolism has emerged as a rational diagnostic and therapeutic target in gastrointestinal cancer. The one-carbon metabolic pathway, which comprises three critical reactions (i.e., folate and methionine cycles), underlies this effect in conjunction with the trans-sulfuration pathway. Understanding of the one-carbon metabolism pathway has served to unravel the link between the causes and effects of cancer phenotypes leading to several seminal discoveries such as that of diadenosine tri-phosphate hydrolase, microRNAs, 5-FU and, more recently, trifluridine. In the folate cycle, glycine and serine fuel the mitochondrial enzymes SHMT2, MTHFD2 and ALDH1L2, which play critical roles in the cancer survival and proliferation presumably through purine production. In the methionine cycle, S-adenocyl methionine serves hydrocarbons and polyamines that are critical for the epigenetic controls. The trans-sulfuration pathway is a critical component in the synthesis of glutathione, which is involved in the production of reactive oxygen species in cancer stem cells. Therefore, characterization of one-carbon metabolism is indispensable to the development of precision medicine in the context of cancer diagnostics and therapeutics. In the present study, we review the historical issues associated with one-carbon metabolism and highlight the recent advances in cancer research.

New interactions between tumor suppressor Fhit protein and a nonhydrolyzable analog of its AP4 A substrate

Fragile histidine triad protein (Fhit) is a protein which primarily hydrolyses dinucleoside polyphosphates. To investigate possible interactions between the protein and a substrate, we used a nonhydrolyzable phosphorothioate analog of Ap₄ A, containing 5-bromo-2'-deoxyuridine instead of one adenosine residue. Photocrosslinking, followed by LC-MS experiments, determined a complex in which the probe was covalently linked to the NDSIYEELQK peptide (residues 110-119). The peptide was located within the 'disordered' region, which is invisible in the known crystal structures of Fhit. This invisible and flexible part seems to play a role in the stabilization of the Fhit-substrate complex, which may be important for its tumor suppressor activity.

Identification of Fhit as a post-transcriptional effector of Thymidine Kinase 1 expression

FHIT is a genome caretaker gene that is silenced in >50% of cancers. Loss of Fhit protein expression promotes accumulation of DNA damage, affects apoptosis and epithelial-mesenchymal transition, though molecular mechanisms underlying these alterations have not been fully elucidated. Initiation of genome instability directly follows Fhit loss and the associated reduced Thymidine Kinase 1 (TK1) protein expression. The effects on TK1 of Fhit knockdown and Fhit induction in the current study confirmed the role of Fhit in regulating TK1 expression. Changes in Fhit expression did not impact TK1 protein turnover or transcription from the TK1 promoter, nor steady-state levels of TK1 mRNA or turnover. Polysome profile analysis showed that up-regulated Fhit expression resulted in decreased TK1 RNA in non-translating messenger ribonucleoproteins and increased ribosome density on TK1 mRNA. Fhit does not bind RNA but its expression increased luciferase expression from a transgene bearing the TK1 5'-UTR. Fhit has been reported to act as a scavenger decapping enzyme, and a similar result with a mutant (H96) that binds but does not cleave nucleoside 5',5'-triphosphates suggests the impact on TK1 translation is due to its ability to modulate the intracellular level of cap-like molecules. Consistent with this, cells expressing Fhit mutants with reduced activity toward cap-like dinucleotides exhibit DNA damage resulting from TK1 deficiency, whereas cells expressing wild-type Fhit or the H96N mutant do not. The results have implications for the mechanism by which Fhit regulates TK1 mRNA, and more broadly, for its modulation of multiple functions as tumor suppressor/genome caretaker.

Role of Akt signaling in resistance to DNA-targeted therapy

The Akt signal transduction pathway controls most hallmarks of cancer. Activation of the Akt cascade promotes a malignant phenotype and is also widely implicated in drug resistance. Therefore, the modulation of Akt activity is regarded as an attractive strategy to enhance the efficacy of cancer therapy and irradiation. This pathway consists of phosphatidylinositol 3 kinase (PI3K), mammalian target of rapamycin, and the transforming serine-threonine kinase Akt protein isoforms, also known as protein kinase B. DNA-targeted agents, such as platinum agents, taxanes, and antimetabolites, as well as radiation have had a significant impact on cancer treatment by affecting DNA replication, which is aberrantly activated in malignancies. However, the caveat is that they may also trigger the activation of repairing mechanisms, such as upstream and downstream cascade of Akt survival pathway. Thus, each target can theoretically be inhibited in view of improving the potency of conventional treatment. Akt inhibitors, e.g., MK-2206 and perifosine, or PI3K modulators, e.g., LY294002 and Wortmannin, have shown some promising results in favor of sensitizing the cancer cells to the therapy in vitro and in vivo, which have provided the rationale for incorporation of these novel agents into multimodality treatment of different malignancies. Nevertheless, despite the acceptable safety profile of some of these agents in the clinical studies, with regard to the efficacy, the results are still too preliminary. Hence, we need to wait for the upcoming data from the ongoing trials before utilizing them into the standard care of cancer patients.

Prognostic and Clinicopathological Significance of Survivin Expression in Renal Cell Carcinoma: A Systematic Review and Meta-Analysis

Previous studies have elevated the prognostic value of survivin in renal cell carcinoma (RCC). To increase statistical power and improve translation, we systematically searched PubMed, Web of Science, and Embase to identify relevant studies until December 2015 and conducted a standard meta-analysis. Based on the inclusion and exclusion criteria, a total of 12 studies, including 2051 patients, were eligible for further analysis. Results showed that high survivin expression in RCC was associated with poor OS (HR = 2.84, 95% CI 1.68-4.79), CSS (HR = 2.36, 95% CI 1.41-3.95), and PFS (HR = 2.20, 95% CI 1.58-3.08). Survivin expression was also correlated with TNM stage (RR = 2.75, 95% CI 2.21-3.44), pathological T stage (RR = 2.19, 95% CI 1.75-2.75), lymph node metastasis (RR = 2.28, 95% CI 1.61-3.25), distant metastasis (RR = 1.56, 95% CI 1.16-2.08), Fuhrman grade (RR = 2.81, 95% CI 2.29-3.45), tumor size (RR = 1.49, 95% CI 1.24-1.78). Our study suggested that survivin was a prognostic marker in RCC. High survivin expression was correlated with poor prognosis and more advanced clinicopathological features, and it could serve as a biomarker for disease management.

Genome-wide association study identifies two new susceptibility loci for colorectal cancer at 5q23.3 and 17q12 in Han Chinese

Genome-wide association studies (GWAS) have reported a number of loci harboring common variants that influence risk of colorectal cancer (CRC) in European descent. But all the SNPs identified explained a small fraction of total heritability. To identify more genetic factors that modify the risk of CRC, especially Chinese Han specific, we conducted a three-stage GWAS including a screening stage (932 CRC cases and 966 controls) and two independent validations (Stage 2: 1,759 CRC cases and 1,875 controls; Stage 3: 943 CRC cases and 1,838 controls). In the combined analyses, we discovered two novel loci associated with CRC: rs12522693 at 5q23.3 (CDC42SE2-CHSY3, OR = 1.31, P = 2.08 × 10-8) and rs17836917 at 17q12 (ASIC2-CCL2, OR = 0.75, P = 4.55 × 10-8). Additionally, we confirmed two previously reported risk loci, rs6983267 at 8q24.21 (OR = 1.17, P = 7.17 × 10-7) and rs10795668 at 10p14 (OR = 0.86, P = 2.96 × 10-6) in our cohorts. These results bring further insights into the CRC susceptibility and advance our understanding on etiology of CRC.

Prognostic significance of survivin in breast cancer: meta-analysis

Survivin, an inhibitor of apoptosis protein, is a potentially prognostic factor and therapeutic target in breast carcinoma, but no consensus exists based on heterogeneous data. The aim of this present study is to clarify the prognostic relevance of survivin in breast cancer patients. Relevant articles were screened in PubMed and EMBASE databases. Patients' clinical characteristics, overall survival (OS), disease/recurrence-free survival (DFS/RFS) and positive expressed survivin rates were extracted for further analysis. Statistics extracted from Kaplan-Meier survival curves were calculated indirectly with methods developed by Parmar, Williamson, and Tierney. Multivariate Cox hazard regression analysis data were used directly in Stata 11.0. Pooled hazard ratio (HR) and 95% confidence interval (CI) were calculated to evaluate the prognostic role of survivin in breast cancer. Online literature search identified 23 articles containing 3,259 breast cancer patients. Our meta-analysis of all included studies about survival outcomes showed positive correlation between poor prognosis and survivin expression. Pooled HRs (95% CIs) for OS and DFS/RFS were 1.37 (1.12-1.68) and 1.34 (1.02-1.76), respectively. Subgroup analyses considering methods used to detect survivin (immunohistochemistry or not) and localization of survivin (whole, nuclear or cytoplasm of the cell) were also conducted, and all the above analyses supported the stability of the prognostic role of survivin. In addition, our study revealed a significant association between survivin expression and lymph node metastasis (OR: 2.74; 95% CI: 1.27-5.93) or stage of breast cancer (OR: 2.01; 95% CI: 1.29-3.13). Positive expression of survivin demonstrated a significantly higher risk of recurrence and decreased OS rates in breast cancer.

FHIT loss confers cisplatin resistance in lung cancer via the AKT/NF-κB/Slug-mediated PUMA reduction

Fragile histidine triad (FHIT) loss by the two-hit mechanism of loss of heterozygosity and promoter hypermethylation commonly occurrs in non-small cell lung cancer (NSCLC) and may confer cisplatin resistance in NSCLC cells. However, the underlying mechanisms of FHIT loss in cisplatin resistance and the response to cisplatin-based chemotherapy in NSCLC patients have not yet been reported. In the present study, inhibition concentration of 50% cell viability induced by cisplatin (IC50) and soft agar growth and invasion capability were increased and decreased in FHIT-knockdown and -overexpressing cells, respectively. Mechanistically, Slug transcription is upregulated by AKT/NF-κB activation due to FHIT loss and, in turn, Slug suppresses PUMA expression; this decrease of PUMA by FHIT loss is responsible for cisplatin resistance. In addition, cisplatin resistance due to FHIT loss can be conquered by AKT inhibitor-perifosine in xenograft tumors. Among NSCLC patients, low FHIT, high p-AKT, high Slug and low PUMA were correlated with shorter overall survival, relapse-free survival and poorer response to cisplatin-based chemotherapy. Therefore, the AKT inhibitor perifosine might potentially overcome the resistance to cisplatin-based chemotherapy in NSCLC patients with low-FHIT tumors, and consequently improve the outcome.

Fragile histidine triad (FHIT) suppresses proliferation and promotes apoptosis in cholangiocarcinoma cells by blocking PI3K-Akt pathway

Fragile histidine triad (FHIT) is a tumor suppressor protein that regulates cancer cell proliferation and apoptosis. However, its exact mechanism of action is poorly understood. Phosphatidylinositol 3-OH kinase (PI3K)-Akt-survivin is an important signaling pathway that was regulated by FHIT in lung cancer cells. To determine whether FHIT can regulate this pathway in cholangiocarcinoma QBC939 cells, we constructed an FHIT expression plasmid and used it to transfect QBC939 cells. Protein and mRNA expression were measured by western blotting and qRT-PCR, respectively. The viability and apoptosis of QBC939 cells were then assessed using MTT assays and flow cytometry. Our results revealed that the expression of survivin and Bcl-2 was downregulated, and caspase 3 was upregulated, in cells overexpressing FHIT. In addition, FHIT suppressed the phosphorylation of Akt. The changes in cell proliferation and apoptosis were obvious in cells overexpressing FHIT which parallels that of treatment with LY294002, a potent inhibitor of phosphoinositide 3-kinases. Treatment with LY294002 further decreased the expression of survivin and Bcl-2 and increased caspase-3 levels. These results suggest that FHIT can block the PI3K-Akt-survivin pathway by suppressing the phosphorylation of Akt and the expression of survivin and Bcl-2 and upregulating caspase 3.

Transcriptional regulation of the survivin gene

Survivin, a small member of the inhibitors of the apoptosis protein family, is highly deregulated in cancer. It is weakly expressed in normal tissues but very strongly expressed in malignant lesions. Survivin is involved in cell-cycle progression, especially in the G2/M transition, and has anti-apoptotic activity, which correlates with its strong expression in cases with a poor cancer treatment response and poor outcomes. Several therapies that target the survivin transcript or protein are currently being tested in clinical trials. However, focusing new therapies on the origins of survivin overexpression and targeting these upstream deregulations could be more effective. For this reason, it seems important to make an inventory of the transcriptional (de)regulation of survivin. This review will gather the important points concerning the regulation of survivin mRNA expression: structure of the survivin promoter, epigenetic modifications and genetic abnormalities, transcription factors, and signalling pathways that affect survivin mRNA expression.

Fhit delocalizes annexin a4 from plasma membrane to cytosol and sensitizes lung cancer cells to paclitaxel

Fhit protein is lost or reduced in a large fraction of human tumors, and its restoration triggers apoptosis and suppresses tumor formation or progression in preclinical models. Here, we describe the identification of candidate Fhit-interacting proteins with cytosolic and plasma membrane localization. Among these, Annexin 4 (ANXA4) was validated by co-immunoprecipitation and confocal microscopy as a partner of this novel Fhit protein complex. Here we report that overexpression of Fhit prevents Annexin A4 translocation from cytosol to plasma membrane in A549 lung cancer cells treated with paclitaxel. Moreover, paclitaxel administration in combination with AdFHIT acts synergistically to increase the apoptotic rate of tumor cells both in vitro and in vivo experiments.

Activation of Gαq subunits up-regulates the expression of the tumor suppressor Fhit

The tumor suppressor Fhit protein is defective or absent in many tumor cells due to methylation, mutation or deletion of the FHIT gene. Despite numerous attempts to unravel the functions of Fhit, the mechanisms by which the function and expression of Fhit are regulated remain poorly understood. We have recently shown that activated Gαq subunits interact directly with Fhit and enhance its inhibitory effect on cell growth. Here we investigated the regulation of Fhit expression by Gq. Our results showed that Fhit was up-regulated specifically by activating Gα subunits of the Gq subfamily but not by those of the other G protein subfamilies. This up-regulation effect was mediated by a PKC/MEK pathway independent of Src-mediated Fhit Tyr(114) phosphorylation. We further demonstrated that elevated Fhit expression was due to the specific regulation of Fhit protein synthesis in the ribosome by activated Gαq, where the regulations of cap-dependent protein synthesis were apparently not required. Moreover, we showed that activated Gαq could increase cell-cell adhesion through Fhit. These findings provide a possible handle to modulate the level of the Fhit tumor suppressor by manipulating the activity of Gq-coupled receptors.

Activation state-dependent interaction between Gαq subunits and the Fhit tumor suppressor

Background

The FHIT tumor suppressor gene is arguably the most commonly altered gene in cancer since it is inactivated in about 60% of human tumors. The Fhit protein is a member of the ubiquitous histidine triad proteins which hydrolyze dinucleoside polyphosphates such as Ap₃A. Despite the fact that Fhit functions as a tumor suppressor, the pathway through which Fhit inhibits growth of cancer cells remains largely unknown. Phosphorylation by Src tyrosine kinases provides a linkage between Fhit and growth factor signaling. Since many G proteins can regulate cell proliferation through multiple signaling components including Src, we explored the relationship between Gα subunits and Fhit.

Results

Several members of the Gα_q subfamily (Gα₁₆, Gα₁₄, and Gα_q) were found to co-immunoprecipitate with Fhit in their GTP-bound active state in HEK293 cells. The binding of activated Gα_q members to Fhit appeared to be direct and was detectable in native DLD-1 colon carcinoma cells. The use of Gα_16/z chimeras further enabled the mapping of the Fhit-interacting domain to the α2-β4 region of Gα₁₆. However, Gα_q/Fhit did not affect either Ap₃A binding and hydrolysis by Fhit, or the ability of Gα_q/16 to regulate downstream effectors including phospholipase Cβ, Ras, ERK, STAT3, and IKK. Functional mutants of Fhit including the H96D, Y114F, L25W and L25W/I10W showed comparable abilities to associate with Gα_q. Despite the lack of functional regulation of G_q signaling by Fhit, stimulation of G_q-coupled receptors in HEK293 and H1299 cells stably overexpressing Fhit led to reduced cell proliferation, as opposed to an enhanced cell proliferation typically seen with parental cells.

Conclusions

Activated Gα_q members interact with Fhit through their α2-β4 region which may result in enhancement of the growth inhibitory effect of Fhit, thus providing a possible avenue for G protein-coupled receptors to modulate tumor suppression.

Amino-acyl tRNA synthetases generate dinucleotide polyphosphates as second messengers: functional implications

In this chapter we describe aminoacyl-tRNA synthetase (aaRS) production of dinucleotide polyphosphate in response to stimuli, their interaction with various signaling pathways, and the role of diadenosine tetraphosphate and diadenosine triphosphate as second messengers. The primary role of aaRS is to mediate aminoacylation of cognate tRNAs, thereby providing a central role for the decoding of genetic code during protein translation. However, recent studies suggest that during evolution, "moonlighting" or non-canonical roles were acquired through incorporation of additional domains, leading to regulation by aaRSs of a spectrum of important biological processes, including cell cycle control, tissue differentiation, cellular chemotaxis, and inflammation. In addition to aminoacylation of tRNA, most aaRSs can also produce dinucleotide polyphosphates in a variety of physiological conditions. The dinucleotide polyphosphates produced by aaRS are biologically active both extra- and intra-cellularly, and seem to function as important signaling molecules. Recent findings established the role of dinucleotide polyphosphates as second messengers.

Src family kinases and paclitaxel sensitivity

Src-family Kinases (SFKs) participate in the regulation of proliferation, differentiation, apoptosis, autophagy, adhesion, migration, invasion and angiogenesis in normal and cancer cells. Abnormal expression of SFKs has been documented in cancers that arise in breast, colon, ovary, melanocyte, gastric mucosa, head and neck, pancreas, lung, and brain. Targeting SFKs in cancer cells has been shown to be a promising therapeutic strategy in solid tumors, particularly in ovarian, colon and breast cancers. Paclitaxel is one of most widely used chemotherapeutic agents for the management of ovarian, breast, lung and head/neck cancers. As a microtubule-stabilizing agent, paclitaxel possesses both mitosis-dependent and mitosis-independent activities against cancer cells. A variety of mechanisms such as deregulation of P-glycoprotein, alteration of tubulin isotypes, alteration of microtubule-regulatory proteins, deregulation of apoptotic signaling pathways, mutation of tubulins and overexpression of copper transporters have been implicated in the development of primary or secondary resistance to paclitaxel. By affecting cancer cell survival, proliferation, autophagy, microtubule stability, motility, and/or angiogenesis, SFKs interact with mechanisms that regulate paclitaxel sensitivity. Inhibition of SFKs can potentiate the anti-tumor activity of paclitaxel by enhancing apoptosis, autophagy and microtubule stability. Based on pre-clinical observations, administration of SFK inhibitors in combination with paclitaxel could improve treatment for ovarian, breast, lung and head/neck cancers. Identification and validation of predictive biomarkers could also permit personalization of the therapy.

Integrated preclinical and clinical development of mTOR inhibitors in pancreatic cancer

BACKGROUND

The purpose of this work was to determine the efficacy of inhibiting mammalian target of rapamycin (mTOR) in pancreatic cancer preclinical models and translate preclinical observations to the clinic.

METHODS

Temsirolimus (20 mg Kg(-1) daily) was administered to freshly generated pancreatic cancer xenografts. Tumour growth inhibition was determined after 28 days. Xenografts were characterised at baseline by gene expression and comparative genomic hybridisation. Patients with advanced, gemcitabine-resistant pancreatic cancer were treated with sirolimus (5 mg daily). The primary end point was 6-month survival rate (6mSR). Correlative studies included immunohistochemistry assessment of pathway expression in baseline tumours, drug pharmacokinetics (PKs), response assessment by FDG-PET and pharmacodynamic effects in peripheral-blood mononuclear cells (PBMCs).

RESULTS

In all, 4 of 17 xenografts (23%) responded to treatment. Sensitive tumours were characterised by gene copy number variations and overexpression of genes leading to activation of the PI3K/Akt/mTOR pathway. Activation of p70S6K correlated with drug activity in the preclinical studies. Sirolimus was well tolerated in the clinic, showed predictable PKs, exerted pathway inhibition in post-treatment PBMCs and resulted in a 6mSR of 26%. No correlation, however, was found between activated p70S6K in tumour tissues and anti-tumour effects.

CONCLUSION

Sirolimus activity in pancreatic cancer was marginal and not predicted by the selected biomarker.

Fhit regulates invasion of lung tumor cells

In many types of cancers, the fragile histidine triad (Fhit) gene is frequently targeted by genomic alterations leading to a decrease or loss of gene and protein expression. Fhit has been described as a tumor suppressor gene because of its ability to induce apoptosis and to inhibit proliferation of tumor cells. Moreover, several studies have shown a correlation between the lack of Fhit expression and tumor aggressiveness, thus suggesting that Fhit could be involved in tumor progression. In this study, we explored the potential role of Fhit during tumor cell invasion. We first showed that a low Fhit expression is associated with in vivo and in vitro invasiveness of tumor cells. Then, we showed that Fhit overexpression in Fhit-negative highly invasive NCI-H1299 cells by transfection of Fhit cDNA and Fhit inhibition in Fhit-positive poorly invasive HBE4-E6/E7 cells by transfection of Fhit small interfering RNA induce, respectively, a decrease and an increase in migratory/invasive capacities. These changes in cell behavior were associated with a reorganization of tight and adherens junction molecules and a regulation of matrix metalloproteinase and vimentin expression. These results show that Fhit controls the invasive phenotype of lung tumor cells by regulating the expression of genes associated with epithelial-mesenchymal transition.

Survivin as a global target of intrinsic tumor suppression networks

Despite the constant exposure to genomic insults that may lead to malignancy, cancer is surprisingly a relatively rare occurrence, and this is largely credited to an elaborate network of endogenous tumor suppression. Many effectors of tumor suppression have been identified, and their functions when activated in damaged cells have in large part been elucidated. What is less clear is whether there are common target gene(s) of tumor suppression, whose expression must be ablated in order to block transformation and preserve cellular homeostasis. Fresh experimental evidence suggests that silencing of the mitotic regulator and cell death inhibitor, survivin, is a universal requirement for successful tumor suppression in humans.

Fragile gene product, Fhit, in oxidative and replicative stress responses

Though the fragile histidine triad gene product, Fhit, was discovered and characterized as a tumor suppressor 13 years ago, its sequence, structure, and cellular location did not provide clues to aid discovery of its mechanisms of suppression. Recently, using chemical cross-linkers and immunoprecipitation, a Fhit protein complex was identified that includes Hsp60 and Hsp10 which may mediate Fhit stability and mitochondrial localization, where Fhit binds and stabilizes ferredoxin reductase (Fdxr); when Fdxr is overexpressed, it can lead to production of reactive oxygen species (ROS) that induce apoptosis. Cancer cells expressing endogenous or exogenous Fhit, when exposed to H(2)O(2), an oxidative stress, produce higher levels of apoptosis-inducing ROS than matched, Fhit-negative cells; the Fhit-negative cancer cells survive, carrying DNA damage. In addition to this mitochondrial function, Fhit-overexpression in cancer cells exposed to replicative stress-inducing agents leads to enhanced caspase 3 activation and apoptosis, due to defective Chk1 activation. Thus, damage to the fragile FHIT locus leads to reduced expression of Fhit protein, and makes a two-pronged contribution to development of preneoplastic clonal expansion: (1) absence or reduction of Fhit leads to reduced expression of Fdxr and reduced ROS-induced apoptosis; (2) cells that escape ROS- or replicative stress-induced apoptosis can carry misrepaired DNA damage. The aberrant DNA damage response checkpoint in Fhit-deficient preneoplasias and cancers may make these lesions targets for inhibitors of proteins such as Parp1 and Chk1 with important roles in checkpoint responses, as observed for BRCA1-deficient cancer cells that also exhibit DNA damage repair deficiencies.

Crystallization and preliminary X-ray crystallographic analysis of SMU.412c protein from the caries pathogen Streptococcus mutans

The smu.412c gene encodes a putative histidine triad-like protein (SMU.412c) with 139 residues that is involved in cell-cycle regulation in Streptococcus mutans. The gene was cloned into the expression vector pET28a and subsequently expressed in Escherichia coli strain BL21 (DE3) to give a substantially soluble form of SMU.412c with a His(6) tag at its N-terminus. The recombinant protein was purified to homogeneity in a two-step procedure involving Ni(2+)-chelating and size-exclusion chromatography. Crystals suitable for X-ray diffraction were obtained using the sitting-drop vapour-diffusion method and diffracted to 1.8 A resolution on beamline BL6A at Photon Factory, Tsukuba, Japan. The crystal belonged to space group P4(1)2(1)2, with unit-cell parameters a = b = 53.5, c = 141.1 A.

Fhit tumor suppressor: guardian of the preneoplastic genome

Environmental agents induce intragenic alterations in the FRA3B/FHIT chromosome fragile site, resulting in fragile FHIT allele loss early in cancer development. Fhit knockout mice are predisposed to tumor development and Fhit gene therapy reduces tumor burden. Repair-deficient cancers are likely to be Fhit-deficient and Fhit-deficient cells show enhanced resistance to ultraviolet C, mitomycin C, camptothecin and oxidative stress-induced cell killing. Loss of Fhit leads to alterations in the DNA damage response checkpoint and contributes to DNA instability. Hsp60/Hsp10 are Fhit interactors, suggesting a direct role for Fhit in stress responses. Fhit also interacts with and stabilizes ferrodoxin reductase (Fdxr), a mitochondrial flavoprotein that transfers electrons from NADPH to cytochrome P450, suggesting a role for Fhit in the modulation of reactive oxygen species production and of genomic damage.

Correlation of fragile histidine triad (Fhit) protein structural features with effector interactions and biological functions

We have previously shown that Fhit tumor suppressor protein interacts with Hsp60 chaperone machinery and ferredoxin reductase (Fdxr) protein. Fhit-effector interactions are associated with a Fhit-dependent increase in Fdxr stability, followed by generation of reactive oxygen species and apoptosis induction under conditions of oxidative stress. To define Fhit structural features that affect interactions, downstream signaling, and biological outcomes, we used cancer cells expressing Fhit mutants with amino acid substitutions that alter enzymatic activity, enzyme substrate binding, or phosphorylation at tyrosine 114. Gastric cancer cell clones stably expressing mutants that do not bind substrate or cannot be phosphorylated showed decreased binding to Hsp60 and Fdxr and reduced mitochondrial localization. Expression of Fhit or mutants that bind interactor proteins results in oxidative damage and accumulation of cells in G(2)/M or sub-G(1) fractions after peroxide treatment; noninteracting mutants are defective in these biological effects. Gastric cancer clones expressing noncomplexing Fhit mutants show reduction of Fhit tumor suppressor activity, confirming that substrate binding, interaction with heat shock proteins, mitochondrial localization, and interaction with Fdxr are important for Fhit tumor suppressor function.

Effect of exogenous FHIT gene expression on vincristine-induced apoptosis of human gastric cancer cells MKN-28

AIM: To investigate effect of exogenous fragile histidine triad (FHIT) gene expression on gastric cancer cells MKN-28 apoptosis induced by vincristine as well as its molecular mechanism.

METHODS: The recombinant FHIT gene was transfected into human gastric cancer cells MKN-28 through liposomes. The expression of exogenous FHIT gene was detected using western blot. The MKN-28-pRcCMV-FHIT, MKN-28-pRcCMV and MKN-28 cells were treated with vincristine of different concentrations. After treatment with vincristine, the inhibition rates of the cells in 3 groups were examined using MTT assay. The apoptosis of cells was determined by flow cytometry. The expressions of Bcl-2 and Bax were measured using Western blot.

RESULTS: The expression of FHIT protein was detected in MKN-28 cells after transfection with FHIT gene. After being treated with vincristine for 48 h, the apoptosis rates of the cells transfected with FHIT gene, the cells transfected with empty vector and the non-transfected cells were 30.967% ± 2.122%, 11.033% ± 1.724% and 10.733% ± 1.021%, respectively. The apoptosis of the cells transfected with FHIT gene was more obvious (F = 142.045, P < 0.05). The expression of Bcl-2 was down-regulated and that of Bax was up-regulated after treatment with vincristine.

CONCLUSION: The expression of exogenous FHIT gene can enhance the vincristine-induced apoptosis in gastric cancer cells, which may be related to the expressions of apoptosis-related protein Bcl-2 and Bax.

Inhibition of the Akt/survivin pathway synergizes the antileukemia effect of nutlin-3 in acute lymphoblastic leukemia cells

The phosphatidylinositol 3-kinase (PI3K)/Akt and p53 pathways play antiapoptotic and proapoptotic roles in cell death, respectively. Cancer cell growth and progression are associated with high levels of PI3K/Akt activation by loss of PTEN expression and the inactivation of p53 by MDM2 overexpression. We report that inhibition of PI3K/Akt, either by the PI3K inhibitor Ly294002 or by expression of PTEN, synergized the ability of the MDM2 antagonist nutlin-3 to induce apoptosis in acute lymphoblastic leukemia (ALL). We used a set of ALL cell lines with wild-type p53 and MDM2 overexpression, but different status of PTEN expression/PI3K/Akt activation, to test the ability of nutlin-3 to induce p53 and apoptosis. Nutlin-3 activated p53 in all the ALL cell lines; however, induction of apoptosis was dependent on PTEN status. Nutlin-3 induced potent apoptosis in cells with PTEN expression but not in those without PTEN, suggesting that PTEN/PI3K/Akt pathway may play a role in this process. Furthermore, nutlin-3 significantly down-regulated survivin expression in PTEN-positive cells but not in PTEN-negative cells. When these nutlin-3-resistant cells were either pretransfected with the PTEN gene or simultaneously treated with the PI3K inhibitor Ly294002, survivin was down-regulated and sensitivity to nutlin-3 was increased. Furthermore, direct silencing of survivin by small interfering RNA also increased the proapoptotic effect of nutlin-3 on the PTEN-negative, nutlin-3-resistant ALL cells. Our results suggest that Akt-mediated survivin up-regulation in PTEN-negative ALL cells may counteract the proapoptotic effect of nutlin-3, and indicate that a combination of MDM2 antagonist and PI3K/Akt inhibitor may be a promising approach for treating refractory ALL.

Role of the WWOX gene, encompassing fragile region FRA16D, in suppression of pancreatic carcinoma cells

The WW-domain-containing oxidoreductase (WWOX) gene spans the common chromosomal fragile site FRA16D (16q23.2) and is believed to be a tumor suppressor in various human malignancies. We have previously shown frequent down-modulation of Wwox expression in pancreatic carcinoma (PC); however, biological function of Wwox in pancreatic duct carcinogenesis remains unknown. In PANC-1 (Wwox-negative) PC-derived cells, restoration of recombinant WWOX gene expression with adenoviral gene delivery (Ad-WWOX) effectively increased the number of cells with subG(1) DNA contents in a multiplicity of infection-dependent manners: Ad-WWOX infection up-regulated caspase-3 activity and reduced procaspase-3 and procaspase-8 levels. We also confirmed that restoration of WWOX gene suppressed cell growth in vitro and tumorigenicity in vivo. In addition, transduction of wild-type WWOX-expressing vector inhibited PANC-1 colony formation; however, substitution of Y33 of Wwox with arginine did not lead to inhibition of colony formation, suggesting the biological significance of the WW1 domain of Wwox for its tumor-suppressing activity. In PC tissue samples, abundant cytoplasmic Wwox expression was detected in the normal pancreatic duct epithelium, whereas Wwox expression was frequently reduced not only in a large fraction of PC but also in precancerous lesions in accord with the pancreatic intraepithelial neoplasia (PanIN) grade, which was closely correlated with patients' poorer outcome. Interestingly, the existence of Wwox expression was associated with elevated mothers against decapentaplegic homolog 4 (Smad4) protein levels in vitro and in vivo. These findings suggest that down-modulation of Wwox expression is an early event and may be associated with the down-regulation of Smad4 protein levels during pancreatic duct carcinogenesis.

Hypermethylation of the 5'CpG island of the FHIT gene in clear cell renal carcinomas

FHIT is a tumour suppressor gene which is frequently inactivated in different types of cancer. Both genetic (mutations, deletions, chromosomal rearrangements) and epigenetic (aberrant methylation of the 5'CpG island) alterations of the FHIT gene have been reported in various malignancies. Yet little is known about the mechanism of FHIT inactivation in clear cell renal carcinomas. Since genetic alterations were not frequently observed in DNA corresponding to the FHIT gene in renal tumours, to elucidate the mechanism of FHIT gene silencing we examined 22 paired samples of clear cell renal carcinoma and non-malignant renal tissue for the methylation of the FHIT 5'CpG island by methylation-specific PCR. Hypermethylation of the FHIT 5'CpG island was detected in 54.5% (12/22) of clear cell renal carcinomas. Bisulfite sequencing of the FHIT 5'CpG island confirmed the results obtained by methylation-specific PCR for selected samples. We showed here that expression of the FHIT gene is inversely correlated with hypermethylation of the FHIT 5'CpG island in the selected samples. Our results suggest that hypermethylation of the FHIT 5'CpG island may be responsible for inactivation of the FHIT gene in clear cell renal carcinomas.

Inhibitor of apoptosis proteins and apoptosis

Apoptosis is a physiological cell death process that plays a critical role in development, homeostasis, and immune defense of multicellular animals. Inhibitor of apoptosis proteins (IAPs) constitute a family of proteins that possess between one and three baculovirus IAP repeats. Some of them also have a really interesting new gene finger domain, and can prevent cell death by binding and inhibiting active caspases, but are regulated by IAP antagonists. Some evidence also indicates that IAP can modulate the cell cycle and signal transduction. The three main factors, IAPs, IAP antagonists, and caspases, are involved in regulating the progress of apoptosis in many species. Many studies and assumptions have been focused on the anfractuous interactions between these three main factors to explore their real functional model in order to develop potential anticancer drugs. In this review, we describe the classification, molecular structures, and properties of IAPs and discuss the mechanisms of apoptosis. We also discuss the promising significance of clinical applications of IAPs in the diagnosis and treatment of malignancy.

Restoration of fragile histidine triad expression restores Chk2 activity in response to ionizing radiation in oral squamous cell carcinoma cells

Early in tumorigenesis, a DNA damage-response network is activated in preneoplastic cells that delays or prevents cancer. Activation of the Chk2 G(2)/M checkpoint kinase and loss of fragile histidine triad (Fhit) tumor suppressor expression increase cellular susceptibility to DNA-damaging 'oncogenic' stressors, particularly in precursor or precancerous lesions. To understand the mechanism of oral carcinogenesis, we assessed the association between phosphorylated Chk2 (pChk2) and Fhit expression in oral squamous cell carcinoma. Loss of Fhit expression was an early event during oral carcinogenesis, whereas a decrease in the number of pChk2-positive cells was associated with tumor progression. Although tyrosine 114 is known to be essential to Fhit's tumor-suppressing activity, both wild-type and tyrosine 114 mutant Fhit increased the population of subG(1) DNA-containing HSC-3 OSCC cells with elevated pChk2 levels. In particular, when cells were exposed to ionizing radiation, pChk2 levels were upregulated dramatically, as were those of its downstream target Cdc25C. Knockdown of Fhit with FHIT small interfering RNA diminished the ionizing radiation-induced Chk2 phosphorylation in HEK293 cells. Furthermore, Fhit-deficient mice demonstrated a decrease in the number of pChk2-positive cells not only in dysplastic lesions but also in N-nitrosobenzylamine-induced papilloma of the forestomach, suggesting that lack of Fhit expression and the resultant defects of the ataxia telangiectasia mutated-Chk2 pathway can cause a difference in the incidence of N-nitrosobenzylamine-induced forestomach lesions. These findings suggest that Fhit plays a key role in the regulation of the ataxia telangiectasia mutated-Chk2 DNA damage response during oral carcinogenesis.

Survivin, cancer networks and pathway-directed drug discovery

Although there is no shortage of potential targets for cancer therapeutics, we know of only a handful of molecules that are differentially expressed in cancer and intersect multiple pathways required for tumour maintenance. Survivin embodies these properties, and orchestrates integrated cellular networks that are essential for tumour cell proliferation and viability. Pursuing the nodal functions of survivin in cancer might lead to the development of global pathway inhibitors with unique therapeutic potential.

The tumor suppressor Fhit acts as a repressor of beta-catenin transcriptional activity

The Fra3B locus on chromosome 3p14.2 targeting the fragile histidine triad (Fhit) gene represents one of the most common fragile sites of the human genome and is associated with early preneoplastic and malignant disorders in multiple human tumors. Fhit was classified as a tumor suppressor; however, the molecular mechanisms of its function are not well established. Here, we report that Fhit associates with the lymphoid enhancer-binding factor 1/T cell factor/beta-catenin complex by directly binding to beta-catenin, a major player in the canonical Wnt pathway that is deregulated in numerous forms of human cancer. In binding to the beta-catenin C-terminal domain, Fhit represses transcription of target genes such as cyclin D1, axin2, MMP-14, and survivin. Knockdown of Fhit reversed this effect, whereas this reversal was not detectable when beta-catenin was knocked down simultaneously. The Fhit enzymatic activity as a diadenosine-polyphosphate hydrolase is not required for the down-regulation of beta-catenin-mediated transcription as examined with an enzymatic inactive Fhit-H96N protein. ChIPs revealed recruitment of Fhit/beta-catenin complexes to target gene promoters. In soft agar assays Fhit and beta-catenin are involved in regulation of anchorage-independent growth. These observations assign to the tumor suppressor Fhit an unexpected role in the regulation of beta-catenin-mediated gene transcription.

Correlation of intracellular diadenosine triphosphate (Ap3A) with apoptosis in Fhit-positive HEK293 cells

The pro-apoptotic Fhit tumor suppressor protein binds and hydrolyses diadenosine triphosphate (Ap3A) and diadenosine tetraphosphate (Ap4A) in vitro. We have measured the level of both these nucleotides in Fhit-positive HEK293 cells exposed to various apoptosis inducers. Cold shock, anti-Fas, cadmium ions and etoposide all increased the basal level of Ap4A of 0.500pmol/10(6)cells by about 50%. However, the corresponding increases in Ap3A from a basal 0.079pmol/10(6)cells correlated closely with the degree of apoptosis produced, up to a maximum of 0.510pmol/10(6)cells with etoposide. These results support the view that Ap3A is the in vivo Fhit ligand and that an inhibition of Fhit activity is a key element in Fhit-mediated apoptosis.

Multifaceted targeting in cancer: the recent cell death players meet the usual oncogene suspects

Recent complicated advances towards the blueprinting of the altered molecular networks that lie behind cancer development have paved the way for targeted therapy in cancer. This directed a significant part of the research community to the development of specialized targeted agents, many of which are already available or in clinical trials. The prospect of patient-tailored therapeutic strategies, although very close to becoming a reality also raises the level of complexity of the therapeutic approach. This review summarizes the functions, in vivo expression patterns and aberrations of factors presently targeted or representing potential targets by therapeutic agents, focusing on those implicated in death receptor-induced apoptosis. The authors overview the regulation of these factors and death receptor-induced apoptosis by classical oncogenes (e.g., RAS, MYC, HER2) and their effectors/regulators, most of which are also being targeted. In addition, the importance of orthologic systemic approaches in future patient-tailored therapies are discussed.

Fhit Modulates the DNA Damage Checkpoint Response

In preneoplastic lesions, the DNA damage checkpoint is induced and loss of heterozygosity at the FRA3B/FHIT common chromosome fragile region precedes or is coincident with activation of the checkpoint response in these early stages. Introduction of exogenous Fhit into cells in vitro led to modulation of expression of checkpoint proteins Hus1 and Chk1 at mid-S checkpoint, a modulation that led to induction of apoptosis in esophageal cancer cells but not in noncancerous primary cultures. Mutation of the conserved Fhit tyrosine 114 resulted in failure of this function, confirming the importance of this residue. The results suggest that the DNA damage-susceptible FRA3B/FHIT chromosome fragile region, paradoxically, encodes a protein that is necessary for protecting cells from accumulation of DNA damage through its role in modulation of checkpoint proteins, and inactivation of Fhit contributes to accumulation of abnormal checkpoint phenotypes in cancer development.