Inhibitory effect of c-Myc on p53-induced apoptosis in leukemia cells. Microarray analysis reveals defective induction of p53 target genes and upregulation of chaperone genes

PERP-ing into diverse mechanisms of cancer pathogenesis: Regulation and role of the p53/p63 effector PERP

The tetraspan plasma membrane protein PERP (p53 apoptosis effector related to PMP22) is a lesser-known transcriptional target of p53 and p63. A member of the PMP22/GAS3/EMP membrane protein family, PERP was originally identified as a p53 target specifically trans-activated during apoptosis, but not during cell-cycle arrest. Several studies have since shown downregulation of PERP expression in numerous cancers, suggesting that PERP is a tumour suppressor protein. This review focusses on the important advances made in elucidating the mechanisms regulating PERP expression and its function as a tumour suppressor in diverse human cancers, including breast cancer and squamous cell carcinoma. Investigating PERP's role in clinically-aggressive uveal melanoma has revealed that PERP engages a positive-feedback loop with p53 to regulate its own expression, and that p63 is required beside p53 to achieve pro-apoptotic levels of PERP in this cancer. Furthermore, the recent discovery of the apoptosis-mediating interaction of PERP with SERCA2b at the plasma membrane-endoplasmic reticulum interface demonstrates a novel mechanism of PERP stabilisation, and how PERP can mediate Ca²⁺ signalling to facilitate apoptosis. The multi-faceted role of PERP in cancer, involving well-documented functions in mediating apoptosis and cell-cell adhesion is discussed, alongside PERP's emerging roles in epithelial-mesenchymal transition, and PERP crosstalk with inflammation signalling pathways, and other signalling pathways. The potential for restoring PERP expression as a means of cancer therapy is also considered.

RNA-Binding Proteins in Acute Leukemias

Acute leukemias are genetic diseases caused by translocations or mutations, which dysregulate hematopoiesis towards malignant transformation. However, the molecular mode of action is highly versatile and ranges from direct transcriptional to post-transcriptional control, which includes RNA-binding proteins (RBPs) as crucial regulators of cell fate. RBPs coordinate RNA dynamics, including subcellular localization, translational efficiency and metabolism, by binding to their target messenger RNAs (mRNAs), thereby controlling the expression of the encoded proteins. In view of the growing interest in these regulators, this review summarizes recent research regarding the most influential RBPs relevant in acute leukemias in particular. The reported RBPs, either dysregulated or as components of fusion proteins, are described with respect to their functional domains, the pathways they affect, and clinical aspects associated with their dysregulation or altered functions.

Advantage of HSP110 (T17) marker inclusion for microsatellite instability (MSI) detection in colorectal cancer patients

Colorectal cancer (CRC) is a leading cause of cancer death worldwide. Microsatellite instability (MSI) is a genetic pathway leading to CRC, associated with particular clinicopathological features, and recently a major biomarker of immunotherapy response. There is little information the frequency MSI among Brazilian CRC patients, and it is still debatable the ideal methodology for MSI screening in countries with limited resources. We proposed to evaluate MSI by molecular and immunohistochemistry (IHC) methods, to compare both methodologies and also to assess the inclusion of a novel microsatellite marker, HSP110 (T17). The molecular MSI evaluation was performed using a PCR-multiplex panel in a total of 1013 CRC patients. Mismatch repair (MMR) proteins (MLH1, MSH2, MSH6 and PMS2) expression were evaluated by IHC. HSP110 (T17) marker was analyzed by fragment analysis. Molecularly, 89.5% of cases were MSI-negative and 10.5% were MSI-positive. The IHC showed that 88.9% of cases exhibited MMR-proficient status, 10.2% were MMR-deficient and 0.9% was inconclusive. Genotyping of the HSP110 (T17) in 106 MSI-positive and 215 MSI-negative cases showed its alteration only among the MSI-positive cases. We observed agreement (0.956, Kappa Test) between both molecular and IHC methodologies, with only eight discordant results, and in this subset of cases the HSP110 (T17) corroborate the molecular findings. This study suggests the use of molecular assays over IHC for MSI analysis and proposes the inclusion HSP110 (T17) marker as a complementary analysis in discordant cases.

A highly sensitive trap vector system for isolating reporter cells and identification of responsive genes

We devised a versatile vector system for efficient isolation of reporter cells responding to a certain condition of interest. This system combines nontoxic GAL4-UAS and piggyBac transposon systems, allowing application to mammalian cells and improved expression of a fluorescent reporter protein for cell sorting. Case studies under conditions of c-MYC gene induction or endoplasmic reticulum (ER) stress with thapsigargin on mouse or human cell lines confirmed easy and efficient isolation of responsive reporter cells. Sequence analyses of the integrated loci of the thapsigargin-responsive clones identified responsive genes including BiP and OSBPL9. OSBPL9 is a novel ER stress-responsive gene and we confirmed that endogenous mRNA expression of OSBPL9 is upregulated by thapsigargin, and is repressed by IRE1α inhibitors, 4μ8C and toyocamycin, but not significantly by a PERK inhibitor, GSK2656157. These results demonstrate that this approach can be used to discover novel genes regulated by any stimuli without the need for microarray analysis, and that it can concomitantly produce reporter cells without identification of stimuli-responsive promoter/enhancer elements. Therefore, this system has a variety of benefits for basic and clinical research.

Molecular cloning and characterization of PTEN in the orange-spotted grouper (Epinephelus coioides)

PTEN is a key tumor suppressor gene that can play a regulatory role in the cellular proliferation, survival and apoptosis. In this study, the full-length PTEN (EcPTEN) was obtained, containing a 5'UTR of 745 bp, an ORF of 1269 bp and a 3'UTR of 106 bp. The EcPTEN gene encoded a polypeptide of 422 amino acids with an estimated molecular mass of 49.14 KDa and a predicted isoelectric point (pI) of 6.34. The deduced amino acid sequence analysis showed that EcPTEN comprised the conserved residues and the characteristic domains known to the critical functionality of PTEN. qRT-PCR analysis revealed that EcPTEN mRNA was broadly expressed in all the examined tissues, while the highest expression level was observed in liver, followed by the expression in blood, kidney, spleen, heart, gill, muscle and intestine. The groupers challenged with Vibrio alginolyticus showed a sharp increase of EcPTEN mRNA expression in immune tissues. In addition, western blotting analysis confirmed that the up-regulation of EcPTEN protein expression was steadily induced in liver. Subcellular localization analysis indicated that EcPTEN was localized in both nucleus and cytoplasm. Overexpression of EcPTEN can activate the apoptotic cascade and abrogate NF-kB, AP-1, Stat3 and Myc promoter activity in Hela cells. These results indicated that EcPTEN harboring highly-conserved domains with a close sequence similarity to those of PTP superfamily may disrupt the mammalian signalings and play a regulatory role in the apoptotic process.

NUMB inactivation confers resistance to imatinib in chronic myeloid leukemia cells

Chronic myeloid leukemia (CML) progresses from a chronic to a blastic phase, where the leukemic cells are proliferative and undifferentiated. The CML is nowadays successfully treated with BCR-ABL kinase inhibitors as imatinib and its derivatives. NUMB is an evolutionary well-conserved protein initially described as a functional antagonist of NOTCH function. NUMB is an endocytic protein associated with receptor internalization, involved in multiple cellular functions. It has been reported that MSI2 protein, a NUMB inhibitor, is upregulated in CML blast crisis, whereas NUMB itself is downregulated. This suggest that NUMB plays a role in the malignant progression of CML. Here we have generated K562 cells (derived from CML in blast crisis) constitutively expressing a dominant negative form of NUMB (dnNUMB). We show that dnNUMB expression confers a high proliferative phenotype to the cells. Importantly, dnNUMB triggers a partial resistance to imatinib in these cells, antagonizing the apoptosis mediated by the drug. Interestingly, imatinib resistance is not linked to p53 status or NOTCH signaling, as K562 lack p53 and imatinib resistance is reproduced in the presence of NOTCH inhibitors. Taken together, our data support the hypothesis that NUMB activation could be a new therapeutic target in CML.

The dosage of Patz1 modulates reprogramming process

The acquisition of pluripotent cells can be achieved by combined overexpression of transcription factors Oct4, Klf4, Sox2 and c-Myc in somatic cells. This cellular reprogramming process overcomes various barriers to re-activate pluripotency genes and re-acquire the highly dynamic pluripotent chromatin status. Many genetic and epigenetic factors are essentially involved in the reprogramming process. We previously reported that Patz1 is required for maintenance of ES cell identity. Here we report that Patz1 plays an inhibitory role in OKSM-induced reprogramming process since more iPS colonies can be induced from Patz1^+/− MEFs than wild type MEFs; while the addition of Patz1 significantly repressed reprogramming efficiency. Patz1^+/− MEFs can surpass the senescence barrier of Ink4a/Arf locus, thus enhancing iPS colonies formation. Moreover, Patz1^+/− MEFs displayed higher levels of acetylated histone H3, H3K4me2, H3K4me3, H3K36me3 and lower levels of histone H3K9me3 and HP1α, indicating that heterozygous knockout of Patz1 results in a globally open chromatin which is more accessible for transcriptional activation. However, Patz1^−/− MEFs gave the lowest reprogramming efficiency which may result from cell senescence trigged by up-regulated Ink4a/Arf locus. Together, we have demonstrated that the dosage of Patz1 modulates reprogramming process via significantly influencing cell senescence, proliferation and chromatin structure.

Systems analysis of the prostate tumor suppressor NKX3.1 supports roles in DNA repair and luminal cell differentiation

NKX3.1 is a homeobox transcription factor whose function as a prostate tumor suppressor remains insufficiently understood because neither the transcriptional program governed by NKX3.1, nor its interacting proteins have been fully revealed. Using affinity purification and mass spectrometry, we have established an extensive NKX3.1 interactome which contains the DNA repair proteins Ku70, Ku80, and PARP, thus providing a molecular underpinning to previous reports implicating NKX3.1 in DNA repair. Transcriptomic profiling of NKX3.1-negative prostate epithelial cells acutely expressing NKX3.1 revealed a rapid and complex response that is a near mirror image of the gene expression signature of human prostatic intraepithelial neoplasia (PIN). Pathway and network analyses suggested that NKX3.1 actuates a cellular reprogramming toward luminal cell differentiation characterized by suppression of pro-oncogenic c-MYC and interferon-STAT signaling and activation of tumor suppressor pathways. Consistently, ectopic expression of NKX3.1 conferred a growth arrest depending on TNFα and JNK signaling. We propose that the tumor suppressor function of NKX3.1 entails a transcriptional program that maintains the differentiation state of secretory luminal cells and that disruption of NKX3.1 contributes to prostate tumorigenesis by permitting luminal cell de-differentiation potentially augmented by defects in DNA repair.

MYC and the art of microRNA maintenance

MYC is a noncanonical transcription factor that binds to thousands of genomic loci and affects >15% of the human transcriptome, with surprisingly little overlap between MYC-bound and -regulated genes. This discordance raises the question whether MYC chooses its targets based on their individual biological effects ("a la carte") or by virtue of belonging to a certain group of genes (on a "prix fixe" basis). This review presents evidence for a prix fixe, posttranscriptional model whereby MYC initially deregulates a select number of microRNAs. These microRNAs then target a broad spectrum of genes based solely on the presence in their 3' UTRs (untranslated regions) of distinct "seed" sequences. Existing evidence suggests that there are significant microRNA components to all key MYC-driven phenotypes, including cell-cycle progression, apoptosis, metabolism, angiogenesis, metastasis, stemness, and hematopoiesis. Furthermore, each of these cell-intrinsic and -extrinsic phenotypes is likely attributable to deregulation of multiple microRNA targets acting in different, yet frequently overlapping, pathways. The habitual targeting of multiple genes within the same pathway might account for the robustness and persistence of MYC-induced phenotypes.

miR-375 activates p21 and suppresses telomerase activity by coordinately regulating HPV E6/E7, E6AP, CIP2A, and 14-3-3ζ

Background

While microRNAs (miRNAs) are extensively studied in post-transcriptional regulation of gene expressions in many biological processes, cellular miRNA-mediated regulation of viral genes remains unclear. In particular, the interplay between human papillomavirus (HPV) genes and miRNAs and how these interactions contribute to HPV-associated cancers remain elusive.

Methods

Transient transfection of miR-375-mimic was used to compensate the loss-of-function of miR-375 in HPV-positive cancer. Regulation of oncogenic molecules and their downstream molecules via miR-375 in HPV-positive cancer was investigated using qRT-PCR, western blot, dual luciferase assay, indirect immunofluorescence analysis. All experiments were conducted at least three times to achieve statistical significance determined by Student t-test.

Results

In this study, we demonstrated how miR-375 negatively regulates HPV16 and 18 transcripts. We also found a cellular protein, E6-associated protein (E6AP), directly regulated by miR-375. miR-375-mediated repression of HPV transcripts and E6AP elevated major tumor suppressors p53, p21, and retinoblastoma protein 1 (RB). Cooperative regulation of miR-375 targets along with the increase of tumor suppressors led to ~60% reduction of telomerase reverse transcriptase (TERT) transcription followed by ~35% decrease of telomerase activity. Furthermore, miR-375-mediated regulation of 14-3-3ζ contributes to decrease telomerase activity by altering nuclear translocation of TERT.

Conclusion

Taken together, miR-375-mediated suppression of multiple oncogenic components in HPV-associated carcinogenesis generates a cumulative biological response to rescue key tumor suppressors and diminish telomerase activity, which results in cell cycle arrest and cell proliferation inhibition.

Diminished origin-licensing capacity specifically sensitizes tumor cells to replication stress

Previous studies have shown that dormant licensed replication origins can be exploited to enhance recovery from replication stress. Since tumor cells express high levels of origin-licensing proteins, we examined whether depletion of such factors might specifically sensitize tumor versus nontumor cells. Consistent with previous findings, we observed that three tumor-derived cell lines overexpress ORC1, a licensing component, compared with four nontumor cell lines and that a greater level of ORC1 was required to maintain viability in the tumor cells. We determined siRNA-mediated knockdown conditions for each line that maximally reduced ORC1 but did not impact upon viability, which we considered would optimally deplete dormant origins. ORC1 depletion hypersensitized the tumor-derived cells to hydroxyurea and H202 but did not affect the sensitivity of the nontumor lines. Similar results were observed following depletion of ORC6 or CDC6. Furthermore, codepletion of p53 and ORC1 modestly impaired viability of 1BR3hTERT nontumor fibroblasts and more dramatically caused hypersensitivity to hydroxyurea. Finally, overexpression of the c-Myc oncogene combined with ORC1 depletion in nontumor BJhTERT cells diminished viability. Collectively, these findings suggest that tumor cells may have a reliance on origin-licensing capacity, suggesting that licensing factors could represent a target for drug-based cancer therapy.

The myc road to hearing restoration

Current treatments for hearing loss, the most common neurosensory disorder, do not restore perfect hearing. Regeneration of lost organ of Corti hair cells through forced cell cycle re-entry of supporting cells or through manipulation of stem cells, both avenues towards a permanent cure, require a more complete understanding of normal inner ear development, specifically the balance of proliferation and differentiation required to form and to maintain hair cells. Direct successful alterations to the cell cycle result in cell death whereas regulation of upstream genes is insufficient to permanently alter cell cycle dynamics. The Myc gene family is uniquely situated to synergize upstream pathways into downstream cell cycle control. There are three Mycs that are embedded within the Myc/Max/Mad network to regulate proliferation. The function of the two ear expressed Mycs, N-Myc and L-Myc were unknown less than two years ago and their therapeutic potentials remain speculative. In this review, we discuss the roles the Mycs play in the body and what led us to choose them to be our candidate gene for inner ear therapies. We will summarize the recently published work describing the early and late effects of N-Myc and L-Myc on hair cell formation and maintenance. Lastly, we detail the translational significance of our findings and what future work must be performed to make the ultimate hearing aid: the regeneration of the organ of Corti.

FAK deletion promotes p53-mediated induction of p21, DNA-damage responses and radio-resistance in advanced squamous cancer cells

Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that is elevated in a variety of human cancers. While FAK is implicated in many cellular processes that are perturbed in cancer, including proliferation, actin and adhesion dynamics, polarisation and invasion, there is only some limited information regarding the role of FAK in radiation survival. We have evaluated whether FAK is a general radio-sensitising target, as has been suggested by previous reports. We used a clean genetic system in which FAK was deleted from mouse squamous cell carcinoma (SCC) cells (FAK -/-), and reconstituted with exogenous FAK wild type (wt). Surprisingly, the absence of FAK was associated with increased radio-resistance in advanced SCC cells. FAK re-expression inhibited p53-mediated transcriptional up-regulation of p21, and a sub-set of other p53 target genes involved in DNA repair, after treatment with ionizing radiation. Moreover, p21 depletion promoted radio-sensitisation, implying that FAK-mediated inhibition of p21 induction is responsible for the relative radio-sensitivity of FAK-proficient SCC cells. Our work adds to a growing body of evidence that there is a close functional relationship between integrin/FAK signalling and the p53/p21 pathway, but demonstrates that FAK's role in survival after stress is context-dependent, at least in cancer cells. We suggest that there should be caution when considering inhibiting FAK in combination with radiation, as this may not always be clinically advantageous.

The human papillomavirus type 16 E7 oncoprotein targets Myc-interacting zinc-finger protein-1

We demonstrate that HPV-16 E7 forms a complex with Miz-1. UV-induced expression of the CDK-inhibitor p21^Cip1 and subsequent cell cycle arrest depends upon endogenous Miz-1 in HPV-negative C33A cervical cancer cells containing mutated p53. Transient expression of E7 in C33A inhibits UV-induced expression of p21^Cip1 and overcomes Miz-1-induced G1-phase arrest. The C-terminal E7Δ79LEDLL83-mutant with reduced Miz-1-binding capacity was impaired in its capability to repress p21^Cip1 expression; whereas the pRB-binding-deficient E7C24G-mutant inhibited p21^Cip1 expression similar to wild-type E7. Using ChIP, we demonstrate that endogenous E7 is bound to the endogenous p21^Cip1 core-promoter in CaSki cells and RNAi-mediated knock down of Miz-1 abrogates E7-binding to the p21^Cip1 promoter. Co-expression of E7 with Miz-1 inhibited Miz-1-induced p21^Cip1 expression from the minimal-promoter via Miz-1 DNA-binding sites. Co-expression of E7Δ79LEDLL83 did not inhibit Miz-1-induced p21^Cip1 expression. E7C24G retained E7-wild-type capability to inhibit Miz-1-dependent transactivation. These findings suggest that HPV-16 E7 can repress Miz-1-induced p21^Cip1 gene expression.

Expression of a mutant HSP110 sensitizes colorectal cancer cells to chemotherapy and improves disease prognosis

Heat shock proteins (HSPs) are necessary for cancer cell survival. We identified a mutant of HSP110 (HSP110ΔE9) in colorectal cancer showing microsatellite instability (MSI CRC), generated from an aberrantly spliced mRNA and lacking the HSP110 substrate-binding domain. This mutant was expressed at variable levels in almost all MSI CRC cell lines and primary tumors tested. HSP110ΔE9 impaired both the normal cellular localization of HSP110 and its interaction with other HSPs, thus abrogating the chaperone activity and antiapoptotic function of HSP110 in a dominant-negative manner. HSP110ΔE9 overexpression caused the sensitization of cells to anticancer agents such as oxaliplatin and 5-fluorouracil, which are routinely prescribed in the adjuvant treatment of people with CRC. The survival and response to chemotherapy of subjects with MSI CRCs was associated with the tumor expression level of HSP110ΔE9. HSP110 may thus constitute a major determinant for both prognosis and treatment response in CRC.

MYC in chronic myeloid leukemia: induction of aberrant DNA synthesis and association with poor response to imatinib

Untreated chronic myeloid leukemia (CML) progresses from chronic phase to blastic crisis (BC). Increased genomic instability, deregulated proliferation, and loss of differentiation appear associated to BC, but the molecular alterations underlying the progression of CML are poorly characterized. MYC oncogene is frequently deregulated in human cancer, often associated with tumor progression. Genomic instability and induction of aberrant DNA replication are described as effects of MYC. In this report, we studied MYC activities in CML cell lines with conditional MYC expression with and without exposure to imatinib, the front-line drug in CML therapy. In cells with conditional MYC expression, MYC did not rescue the proliferation arrest mediated by imatinib but provoked aberrant DNA synthesis and accumulation of cells with 4C content. We studied MYC mRNA expression in 66 CML patients at different phases of the disease, and we found that MYC expression was higher in CML patients at diagnosis than control bone marrows or in patients responding to imatinib. Further, high MYC levels at diagnosis correlated with a poor response to imatinib. MYC expression did not directly correlate with BCR-ABL levels in patients treated with imatinib. Overall our study suggests that, as in other tumor models, MYC-induced aberrant DNA synthesis in CML cells is consistent with MYC overexpression in untreated CML patients and nonresponding patients and supports a role for MYC in CML progression, possibly through promotion of genomic instability.

Determination of genes and microRNAs involved in the resistance to fludarabine in vivo in chronic lymphocytic leukemia

BACKGROUND

Chronic lymphocytic leukemia (CLL) cells are often affected by genomic aberrations targeting key regulatory genes. Although fludarabine is the standard first line therapy to treat CLL, only few data are available about the resistance of B cells to this purine nucleoside analog in vivo. Here we sought to increase our understanding of fludarabine action and describe the mechanisms leading to resistance in vivo. We performed an analysis of genomic aberrations, gene expression profiles, and microRNAs expression in CLL blood B lymphocytes isolated during the course of patients' treatment with fludarabine.

RESULTS

In sensitive patients, the differentially expressed genes we identified were mainly involved in p53 signaling, DNA damage response, cell cycle and cell death. In resistant patients, uncommon genomic abnormalities were observed and the resistance toward fludarabine could be characterized based on the expression profiles of genes implicated in lymphocyte proliferation, DNA repair, and cell growth and survival. Of particular interest in some patients was the amplification of MYC (8q) observed both at the gene and transcript levels, together with alterations of myc-transcriptional targets, including genes and miRNAs involved in the regulation of cell cycle and proliferation. Differential expression of the sulfatase SULF2 and of miR-29a, -181a, and -221 was also observed between resistant and sensitive patients before treatment. These observations were further confirmed on a validation cohort of CLL patients treated with fludarabine in vitro.

CONCLUSION

In the present study we identified genes and miRNAs that may predict clinical resistance of CLL to fludarabine, and describe an interesting oncogenic mechanism in CLL patients resistant to fludarabine by which the complete MYC-specific regulatory network was altered (DNA and RNA levels, and transcriptional targets). These results should prove useful for understanding and overcoming refractoriness to fludarabine and also for predicting the clinical outcome of CLL patients before or early during their treatment.

Selenium and vitamin E: cell type- and intervention-specific tissue effects in prostate cancer

BACKGROUND

Secondary analyses of two randomized, controlled phase III trials demonstrated that selenium and vitamin E could reduce prostate cancer incidence. To characterize pharmacodynamic and gene expression effects associated with use of selenium and vitamin E, we undertook a randomized, placebo-controlled phase IIA study of prostate cancer patients before prostatectomy and created a preoperative model for prostatectomy tissue interrogation.

METHODS

Thirty-nine men with prostate cancer were randomly assigned to treatment with 200 microg of selenium, 400 IU of vitamin E, both, or placebo. Laser capture microdissection of prostatectomy biopsy specimens was used to isolate normal, stromal, and tumor cells. Gene expression in each cell type was studied with microarray analysis and validated with a real-time polymerase chain reaction (PCR) and immunohistochemistry. An analysis of variance model was fit to identify genes differentially expressed between treatments and cell types. A beta-uniform mixture model was used to analyze differential expression of genes and to assess the false discovery rate. All statistical tests were two-sided.

RESULTS

The highest numbers of differentially expressed genes by treatment were 1329 (63%) of 2109 genes in normal epithelial cells after selenium treatment, 1354 (66%) of 2051 genes in stromal cells after vitamin E treatment, and 329 (56%) of 587 genes in tumor cells after combination treatment (false discovery rate = 2%). Validation of 21 representative genes across all treatments and all cell types yielded Spearman correlation coefficients between the microarray analysis and the PCR validation ranging from 0.64 (95% confidence interval [CI] = 0.31 to 0.79) for the vitamin E group to 0.87 (95% CI = 0.53 to 0.99) for the selenium group. The increase in the mean percentage of p53-positive tumor cells in the selenium-treated group (26.3%), compared with that in the placebo-treated group (5%), showed borderline statistical significance (difference = 21.3%; 95% CI = 0.7 to 41.8; P = .051).

CONCLUSIONS

We have demonstrated the feasibility and efficiency of the preoperative model and its power as a hypothesis-generating engine. We have also identified cell type- and zone-specific tissue effects of interventions with selenium and vitamin E that may have clinical implications.

Knockdown of TFIIS by RNA silencing inhibits cancer cell proliferation and induces apoptosis

Background

A common element among cancer cells is the presence of improperly controlled transcription. In these cells, the degree of specific activation of some genes is abnormal, and altering the aberrant transcription may therefore directly target cancer. TFIIS is a transcription elongation factor, which directly binds the transcription motor, RNA Polymerase II and allows it to read through various transcription arrest sites. We report on RNA interference of TFIIS, a transcription elongation factor, and its affect on proliferation of cancer cells in culture.

Methods

RNA interference was performed by transfecting siRNA to specifically knock down TFIIS expression in MCF7, MCF10A, PL45 and A549 cells. Levels of TFIIS expression were determined by the Quantigene method, and relative protein levels of TFIIS, c-myc and p53 were determined by C-ELISA. Induction of apoptosis was determined by an enzymatic Caspase 3/7 assay, as well as a non-enzymatic assay detecting cytoplasmic mono- and oligonucleosomes. A gene array analysis was conducted for effects of TFIIS siRNA on MCF7 and MCF10A cell lines.

Results

Knockdown of TFIIS reduced cancer cell proliferation in breast, lung and pancreatic cancer cell lines. More specifically, TFIIS knockdown in the MCF7 breast cancer cell line induced cancer cell death and increased c-myc and p53 expression whereas TFIIS knockdown in the non-cancerous breast cell line MCF10A was less affected. Differential effects of TFIIS knockdown in MCF7 and MCF10A cells included the estrogenic, c-myc and p53 pathways, as observed by C-ELISA and gene array, and were likely involved in MCF7 cell-death.

Conclusion

Although transcription is a fundamental process, targeting select core transcription factors may provide for a new and potent avenue for cancer therapeutics. In the present study, knockdown of TFIIS inhibited cancer cell proliferation, suggesting that TFIIS could be studied as a potential cancer target within the transcription machinery.

RNA interference of LRRK2-microarray expression analysis of a Parkinson's disease key player

The protein leucine-rich repeat kinase 2 (LRRK2) is a key player in the pathogenesis of Parkinson's disease (PD). Mutations in the LRRK2 gene account for up to 10% of all autosomal dominant forms of familiar and for approximately 1-3% of sporadic PD patients. Although the LRRK2 protein has many functional domains like a leucine-rich repeat domain, a Roc-GTPase domain, a kinase domain of the tyrosine kinase-like subfamily and multiple protein interaction domains (armadillo, ankyrin, WD40), the exact biological role of LRRK2 in the human brain is elusive. To gain more insight into the biological function of this protein, we monitored the changes in the expression profiles of SH-SY5Y cells, a dopaminergic neuroblastoma cell line, induced by a depletion of LRRK2 levels by RNA interference (RNAi) with Affymetrix U133 Plus 2.0 microarrays. A total of 187 genes were differentially regulated by at least a 1.5-fold change with 94 transcripts being upregulated and 93 transcripts being downregulated compared to scrambled control siRNA transfected cells. Key players of the interaction networks were independently verified by qRT-PCR. The differentially expressed gene products are involved in axonal guidance, nervous system development, cell cycle, cell growth, cell differentiation, cell communication, MAPKKK cascade, and Ras protein signal transduction. Defined gene expression networks will now serve to look more closely for candidates affected by LRRK2 reduction and how they might be altered in other forms of familial or sporadic PD.

Altered adenosine-to-inosine RNA editing in human cancer

Adenosine-to-inosine (A-to-I) RNA editing was recently shown to be abundant in the human transcriptome, affecting thousands of genes. Employing a bioinformatic approach, we identified significant global hypoediting of Alu repetitive elements in brain, prostate, lung, kidney, and testis tumors. Experimental validation confirmed this finding, showing significantly reduced editing in Alu sequences within MED13 transcripts in brain tissues. Looking at editing of specific recoding and noncoding sites, including in cancer-related genes, a more complex picture emerged, with a gene-specific editing pattern in tumors vs. normal tissues. Additionally, we found reduced RNA levels of all three editing mediating enzymes, ADAR, ADARB1, and ADARB2, in brain tumors. The reduction of ADARB2 correlated with the grade of malignancy of glioblastoma multiforme, the most aggressive of brain tumors, displaying a 99% decrease in ADARB2 RNA levels. Consistently, overexpression of ADAR and ADARB1 in the U87 glioblastoma multiforme cell line resulted in decreased proliferation rate, suggesting that reduced A-to-I editing in brain tumors is involved in the pathogenesis of cancer. Altered epigenetic control was recently shown to play a central role in oncogenesis. We suggest that A-to-I RNA editing may serve as an additional epigenetic mechanism relevant to cancer development and progression.

γ-Glutamylcysteine Synthetase Mediates the c-Myc-Dependent Response to Antineoplastic Agents in Melanoma Cells

This study aims to investigate the role of gamma-glutamylcysteine synthetase (gamma-GCS), the rate-limiting enzyme for glutathione (GSH) synthesis, in the c-Myc-dependent response to antineoplastic agents. We found that specific c-Myc inhibition depleted cells of GSH by directly reducing the gene expression of both heavy and light subunits of the gamma-GCS enzyme and increased their susceptibility to antineoplastic drugs with different mechanisms of action, such as cisplatin (CDDP), staurosporine (STR), and 5-fluorouracil (5-FU). The effect caused by c-Myc inhibition on CDDP and STR response, but not to 5-FU treatment, is directly linked to the impairment of the gamma-GCS expression, because up-regulation of gamma-GCS reverted drug sensitivity, whereas the interference of GSH synthesis increased drug susceptibility as much as after c-Myc down-regulation. The role of gamma-GCS in the c-Myc-directed drug response depends on the capacity of drugs to trigger reactive oxygen species (ROS) production. Indeed, although 5-FU exposure did not induce any ROS, CDDP- and STR-induced oxidative stress enhanced the recruitment of c-Myc on both gamma-GCS promoters, thus stimulating GSH neosynthesis and allowing cells to recover from ROS-induced drug damage. In conclusion, our data demonstrate that the gamma-GCS gene is the downstream target of c-Myc oncoprotein, driving the response to ROS-inducing drugs. Thus, gamma-GCS impairment might specifically sensitize high c-Myc tumor cells to chemotherapy.

Apoptosis induced by proteasome inhibition in cancer cells: predominant role of the p53/PUMA pathway

The proteasome has emerged as a novel target for antineoplastic treatment of hematological malignancies and solid tumors, including those of the central nervous system. To identify cell death pathways activated in response to inhibition of the proteasome system in cancer cells, we treated human SH-SY5Y neuroblastoma cells with the selective proteasome inhibitor (PI) epoxomicin (Epoxo). Prolonged exposure to Epoxo was associated with increased levels of poly-ubiquitinylated proteins and p53, release of cytochrome c from the mitochondria, and activation of caspases. Analysis of global gene expression using high-density oligonucleotide microarrays revealed that Epoxo triggered transcriptional activation of the two Bcl-2-homology domain-3-only (BH3-only) genes p53 upregulated modulator of apoptosis (PUMA) and Bim. Subsequent studies in PUMA- and Bim-deficient cells indicated that Epoxo-induced caspase activation and apoptosis was predominantly PUMA-dependent. Further characterization of the transcriptional response to Epoxo in HCT116 human colon cancer cells demonstrated that PUMA induction was p53-dependent; with deficiency in either p53 or PUMA significantly protected HCT116 cells against Epoxo-induced apoptosis. Our data suggest that p53 activation and the transcriptional induction of its target gene PUMA play an important role in the sensitivity of cancer cells to apoptosis induced by proteasome inhibition, and imply that antineoplastic therapies with PIs might be especially useful in cancers with functional p53.

Cancer diagnosis marker extraction for soft tissue sarcomas based on gene expression profiling data by using projective adaptive resonance theory (PART) filtering method

Background

Recent advances in genome technologies have provided an excellent opportunity to determine the complete biological characteristics of neoplastic tissues, resulting in improved diagnosis and selection of treatment. To accomplish this objective, it is important to establish a sophisticated algorithm that can deal with large quantities of data such as gene expression profiles obtained by DNA microarray analysis.

Results

Previously, we developed the projective adaptive resonance theory (PART) filtering method as a gene filtering method. This is one of the clustering methods that can select specific genes for each subtype. In this study, we applied the PART filtering method to analyze microarray data that were obtained from soft tissue sarcoma (STS) patients for the extraction of subtype-specific genes. The performance of the filtering method was evaluated by comparison with other widely used methods, such as signal-to-noise, significance analysis of microarrays, and nearest shrunken centroids. In addition, various combinations of filtering and modeling methods were used to extract essential subtype-specific genes. The combination of the PART filtering method and boosting – the PART-BFCS method – showed the highest accuracy. Seven genes among the 15 genes that are frequently selected by this method – MIF, CYFIP2, HSPCB, TIMP3, LDHA, ABR, and RGS3 – are known prognostic marker genes for other tumors. These genes are candidate marker genes for the diagnosis of STS. Correlation analysis was performed to extract marker genes that were not selected by PART-BFCS. Sixteen genes among those extracted are also known prognostic marker genes for other tumors, and they could be candidate marker genes for the diagnosis of STS.

Conclusion

The procedure that consisted of two steps, such as the PART-BFCS and the correlation analysis, was proposed. The results suggest that novel diagnostic and therapeutic targets for STS can be extracted by a procedure that includes the PART filtering method.

Essential dosage-dependent functions of the transcription factor yin yang 1 in late embryonic development and cell cycle progression

Constitutive ablation of the Yin Yang 1 (YY1) transcription factor in mice results in peri-implantation lethality. In this study, we used homologous recombination to generate knockout mice carrying yy1 alleles expressing various amounts of YY1. Phenotypic analysis of yy1 mutant embryos expressing approximately 75%, approximately 50%, and approximately 25% of the normal complement of YY1 identified a dosage-dependent requirement for YY1 during late embryogenesis. Indeed, reduction of YY1 levels impairs embryonic growth and viability in a dose-dependent manner. Analysis of the corresponding mouse embryonic fibroblast cells also revealed a tight correlation between YY1 dosage and cell proliferation, with a complete ablation of YY1 inducing cytokinesis failure and cell cycle arrest. Consistently, RNA interference-mediated inhibition of YY1 in HeLa cells prevents cytokinesis, causes proliferative arrest, and increases cellular sensitivity to various apoptotic agents. Genome-wide expression profiling identified a plethora of YY1 target genes that have been implicated in cell growth, proliferation, cytokinesis, apoptosis, development, and differentiation, suggesting that YY1 coordinates multiple essential biological processes through a complex transcriptional network. These data not only shed new light on the molecular basis for YY1 developmental roles and cellular functions, but also provide insight into the general mechanisms controlling eukaryotic cell proliferation, apoptosis, and differentiation.

c-Myc phosphorylation is required for cellular response to oxidative stress

Aside from the well-established roles of c-Myc in the regulation of cell cycle, differentiation, and apoptosis, a recent picture is beginning to emerge linking c-Myc to the regulation of metabolic pathways. Here, we define a further function for c-Myc in determining cellular redox balance, identifying glutathione (GSH) as the leading molecule mediating this process. The link between c-Myc and GSH is gamma-glutamyl-cysteine synthetase (gamma-GCS), the rate-limiting enzyme catalyzing GSH biosynthesis. Indeed, c-Myc transcriptionally regulates gamma-GCS by binding and activating the promoters of both gamma-GCS heavy and light subunits. Exposure to H2O2 enhances c-Myc recruitment to gamma-GCS regulatory regions through ERK-dependent phosphorylation. Phosphorylation at Ser-62 is required for c-Myc recruitment to gamma-GCS promoters and determines the cellular response to oxidative stress induced by different stimuli. Thus, the c-Myc phosphorylation-dependent activation of the GSH-directed survival pathway can contribute to oxidative stress resistance in tumor cells, which generally exhibit deregulated c-Myc expression.