E2F1 and E2F3 activate ATM through distinct mechanisms to promote E1A-induced apoptosis

Deubiquitinase USP47-stabilized splicing factor IK regulates the splicing of ATM pre-mRNA

IK depletion leads to an aberrant mitotic entry because of chromosomal misalignment through the enhancement of Aurora B activity at the interphase. Here, we demonstrate that IK, a spliceosomal component, plays a crucial role in the proper splicing of the ATM pre-mRNA among other genes related with the DNA Damage Response (DDR). Intron 1 in the ATM pre-mRNA, having lengths <200 bp, was not spliced in the IK-depleted cells and led to a deficiency of the ATM protein. Subsequently, the IK depletion-induced ATM protein deficiency impaired the ability to repair the damaged DNA. Because the absence of SMU1 results in IK degradation, the mechanism underlying IK degradation was exploited. IK was ubiquitinated in the absence of SMU1 and then subjected to proteolysis through the 26S proteasome. To prevent the proteolytic degradation of IK, a deubiquitinating enzyme, USP47, directly interacted with IK and stabilized it through deubiquitination. Collectively, our results suggest that IK is required for proper splicing of the ATM pre-mRNA and USP47 contributes toward the stabilization of IK.

The broken cycle: E2F dysfunction in cancer

The cyclin-dependent kinase (CDK)-RB-E2F axis forms the core transcriptional machinery driving cell cycle progression, dictating the timing and fidelity of genome replication and ensuring genetic material is accurately passed through each cell division cycle. The ultimate effectors of this axis are members of a family of eight distinct E2F genes encoding transcriptional activators and repressors. E2F transcriptional activity is tightly regulated throughout the cell cycle via transcriptional and translational regulation, post-translational modifications, protein degradation, binding to cofactors and subcellular localization. Alterations in one or more key components of this axis (CDKs, cyclins, CDK inhibitors and the RB family of proteins) occur in virtually all cancers and result in heightened oncogenic E2F activity, leading to uncontrolled proliferation. In this Review, we discuss the activities of E2F proteins with an emphasis on the newest atypical E2F family members, the specific and redundant functions of E2F proteins, how misexpression of E2F transcriptional targets promotes cancer and both current and developing therapeutic strategies being used to target this oncogenic pathway.

Mesenchymal Stem Cells from Cervix and Age: New Insights into CIN Regression Rate

Cervical intraepithelial neoplasia (CIN) is a precancerous lesion of the uterine cervix that can regress or progress to cervical cancer; interestingly, it has been noted that young women generally seem to have higher rates of spontaneous regression and remission, suggesting a correlation between the patient's age and regression/progression rates of CIN. Even if the underlying mechanisms are still unclear, inflammation seems to play a pivotal role in CIN fate and inflammatory processes are often driven by mesenchymal stem cells (MSCs). This study was aimed at evaluating if age affects the behavior of MSCs from the cervix (C-MSCs) that in turn may modulate inflammation and, finally, regression rate. Fourteen samples of the human cervix were recovered from two groups of patients, "young" (mean age 28 ± 2) and "old" (mean age 45 ± 3), during treatment using the loop electrosurgical excision procedure (LEEP) technique. Progenitor cells were isolated, deeply characterized, and divided into young (yC-MSCs) and old cervixes (oC-MSCs); the senescence, expression/secretion of selected cytokines related to inflammation, and the effects of indirect cocultures with HeLa cells were analyzed. Our results show that isolated cells satisfy the fixed criteria for stemness and display age-related properties; yC-MSCs express a higher level of cytokines related to acute inflammation than oC-MSCs. Finally, in the crosstalk with HeLa cells, MSCs derived from the cervixes of young patients play a stronger antitumoral role than oC-MSCs. In conclusion, the immunobiology of MSCs derived from the cervix is affected by the age of donors and this can correlate with the regression rate of CIN by influencing their paracrine effect. In addition, MSCs from a young cervix drives an antitumoral effect by sustaining an acute inflammatory environment.

Identity, proliferation capacity, genomic stability and novel senescence markers of mesenchymal stem cells isolated from low volume of human bone marrow

Human bone marrow mesenchymal stem cells (hBM-MSCs) hold promise for treating incurable diseases and repairing of damaged tissues. However, hBM-MSCs face the disadvantages of painful invasive isolation and limited cell numbers. In this study we assessed characteristics of MSCs isolated from residual human bone marrow transplantation material and expanded to clinically relevant numbers at passages 3-4 and 6-7. Results indicated that early passage hBM-MSCs are genomically stable and retain identity and high proliferation capacity. Despite the chromosomal stability, the cells became senescent at late passages, paralleling the slower proliferation, altered morphology and immunophenotype. By qRT-PCR array profiling, we revealed 13 genes and 33 miRNAs significantly differentially expressed in late passage cells, among which 8 genes and 30 miRNAs emerged as potential novel biomarkers of hBM-MSC aging. Functional analysis of genes with altered expression showed strong association with biological processes causing cellular senescence. Altogether, this study revives hBM as convenient source for cellular therapy. Potential novel markers provide new details for better understanding the hBM-MSC senescence mechanisms, contributing to basic science, facilitating the development of cellular therapy quality control, and providing new clues for human disease processes since senescence phenotype of the hematological patient hBM-MSCs only very recently has been revealed.

E1A enhances cellular sensitivity to DNA-damage-induced apoptosis through PIDD-dependent caspase-2 activation

Expression of the adenoviral protein, E1A, sensitizes mammalian cells to a wide variety of apoptosis-inducing agents through multiple cellular pathways. For example, E1A sensitizes cells to apoptosis induced by TNF-superfamily members by inhibiting NF-kappa B (NF-κB)-dependent gene expression. In contrast, E1A sensitization to nitric oxide, an inducer of the intrinsic apoptotic pathway, is not dependent upon repression of NF-κB-dependent transcription but rather is dependent upon caspase-2 activation. The latter observation suggested that E1A-induced enhancement of caspase-2 activation might be a critical factor in cellular sensitization to other intrinsic apoptosis pathway-inducing agents. Etoposide and gemcitabine are two DNA damaging agents that induce intrinsic apoptosis. Here we report that E1A-induced sensitization to both of these agents, like NO, is independent of NF-κB activation but dependent on caspase-2 activation. The results show that caspase-2 is a key mitochondrial-injuring caspase during etoposide and gemcitabine-induced apoptosis of E1A-positive cells, and that caspase-2 is required for induction of caspase-3 activity by both chemotherapeutic agents. Expression of PIDD was required for caspase-2 activation, mitochondrial injury and enhanced apoptotic cell death. Furthermore, E1A-enhanced sensitivity to injury-induced apoptosis required PIDD cleavage to PIDD-CC. These results define the PIDD/caspase-2 pathway as a key apical, mitochondrial-injuring mechanism in E1A-induced sensitivity of mammalian cells to chemotherapeutic agents.

E1a promotes c-Myc-dependent replicative stress: implications in glioblastoma radiosensitization

The E1a gene from adenovirus is known to be a potent inducer of chemo/radiosensitivity in a wide range of tumors. However, the molecular bases of its radiosensitizer properties are still poorly understood. In an attempt to study this effect, U87MG cells, derived from a radio-resistant tumor as glioblastoma, where infected with lentivirus carrying E1a gene developing an acute sensitivity to ionizing radiation. The induction of radiosensitivity correlated with a marked G 2/M phase accumulation and a potent apoptotic response. Our findings demonstrate that c-Myc plays a pivotal role in E1a-associated radiosensitivity through the induction of a replicative stress situation, as our data support by genetic approaches, based in interference and overexpression in U87MG cells. In fact, we present evidence showing that Chk1 is a novel transcriptional target of E1a gene through the effect exerted by this adenoviral protein onto c-Myc. Moreover, c-Myc upregulation also explains the marked phosphorylation of H2AX associated to E1a expression in the absence of DNA damage. Indeed, all these observations were applicable to other experimental models, such as T98G, LN-405 and A172, rendering the same pattern in terms of radiosensitivity, cell cycle distribution, upregulation of Chk1, c-Myc, and phosphorylation pattern of H2AX. In summary, our data propose a novel mechanism to explain how E1a mediates radiosensitivity through the signaling axis E1a→c-Myc→ replicative stress situation. This novel mechanism of E1a-mediated radiosensitivity could be the key to open new possibilities in the current therapy of glioblastoma.

miR-210 has an antiapoptotic effect in pulmonary artery smooth muscle cells during hypoxia

MicroRNAs (miRNAs) were recently reported to play an important role in the pathogenesis of pulmonary arterial hypertension (PAH), but it is not clear which miRNAs are important or what pathways are involved in the process. Because hypoxia is an important stimulus for human pulmonary artery smooth muscle cell (HPASMC) proliferation and PAH, we performed miRNA microarray assays in hypoxia-treated and control HPASMC. We found that miR-210 is the predominant miRNA induced by hypoxia in HPASMC. Induction of miR-210 was also observed in whole lungs of mice with chronic hypoxia-induced PAH. We found that transcriptional induction of miR-210 in HPASMC is hypoxia-inducible factor-1α dependent. Inhibition of miR-210 in HPASMC caused a significant decrease in cell number due to increased apoptosis. We found that miR-210 appears to mediate its antiapoptotic effects via the regulation of transcription factor E2F3, a direct target of miR-210. Our results have identified miR-210 as a hypoxia-inducible miRNA both in vitro and in vivo, which inhibits pulmonary vascular smooth muscle cell apoptosis in hypoxia by specifically repressing E2F3 expression.

Noise induced changes in the expression of p38/MAPK signaling proteins in the sensory epithelium of the inner ear

Noise exposure is a major cause of hearing loss. Classical methods of studying protein involvement have provided a basis for understanding signaling pathways that mediate hearing loss and damage repair but do not lend themselves to studying large networks of proteins that are likely to increase or decrease during noise trauma. To address this issue, antibody microarrays were used to quantify the very early changes in protein expression in three distinct regions of the chinchilla cochlea 2h after exposure to a 0.5-8 kHz band of noise for 2h at 112 dB SPL. The noise exposure caused significant functional impairment 2h post-exposure which only partially recovered. Distortion product otoacoustic emissions were abolished 2h after the exposure, but at 4 weeks post-exposure, otoacoustic emissions were present, but still greatly depressed. Cochleograms obtained 4 weeks post-exposure demonstrated significant loss of outer hair cells in the basal 60% of the cochlea corresponding to frequencies in the noise spectrum. A comparative analysis of the very early (2h post-exposure) noise-induced proteomic changes indicated that the sensory epithelium, lateral wall and modiolus differ in their biological response to noise. Bioinformatic analysis of the cochlear protein profile using "The Database for Annotation, Visualization and Integrated Discovery 2008" (DAVID - http://david.abcc. ncifcrf.gov) revealed the initiation of the cell death process in sensory epithelium and modiolus. An increase in Fas and phosphorylation of FAK and p38/MAPK in the sensory epithelium suggest that noise-induced stress signals at the cell membrane are transmitted to the nucleus by Fas and focal adhesion signaling through the p38/MAPK signaling pathway. Up-regulation of downstream nuclear proteins E2F3 and WSTF in immunoblots and microarrays along with their immunolocalization in the outer hair cells supported the pivotal role of p38/MAPK signaling in the mechanism underlying noise-induced hearing loss.

Transcription factor NF-Y induces apoptosis in cells expressing wild-type p53 through E2F1 upregulation and p53 activation

The CCAAT-binding transcription factor NF-Y plays a central role in regulating cellular proliferation by controlling the expression of genes required for cell-cycle progression such as cyclin A, cyclin B1, cyclin B2, cdc25A, cdc25C, and cdk1. Here we show that unrestricted NF-Y activity leads to apoptosis in an E2F1- and wild-type p53 (wtp53)-dependent manner. Unrestricted NF-Y activity induced an increase in E2F1 mRNA and protein levels. Furthermore, NF-Y directly bound the E2F1 promoter and this correlated with the appearance of open chromatin marks. The ability of NF-Y to induce apoptosis was impaired in cells lacking E2F1 and wtp53. Moreover, NF-Y overexpression elicited phosphorylation of wt p53Ser18 in an E2F1-dependent manner. Our findings establish that NF-Y acts upstream of E2F1 in p53-mediated apoptosis.

A truncated minimal-E1a gene with potency to support adenoviral replication mediates antitumor activity by down-regulating Neu expression and preserving Rb function

Oncolytic adenovirus is capable of infecting, replicating in and lysing cancer cells. In adenovirus infection and replication, the wild type E1a gene (wE1a) mediates various genetic events to facilitate viral replication and exert antitumor effect. To enhance its antitumor efficacy and optimize its safety, we manipulated the wE1a gene and designed a 720-bp truncated minimal-E1a (mE1a) by deletions and mutations of amino acid residues. The mE1a gene was incorporated in an adenovirus under the control of hTERT promoter, giving the vector AdDC315-mE1a. A variety of cancer cell lines infected with the virus expressed the mE1a protein and showed considerable down-regulation in Neu protein expression as compared to normal cell lines. mE1a also had a lower binding affinity to the Rb protein, preserving the Rb tumor suppressive function. The mE1a expression allowed efficient adenovirus replication with high and stable replication ratios in cancer cells (about 125- to 8500-fold higher at 48 h and 180- to 10,900-fold higher at 96 h post-infection). Further, the mE1a-supported oncolytic adenovirus induced higher cancer cell apoptosis, stronger cell cycle arrest and more effective antitumor efficacy in hepatocarcinoma xenografts in nude mice. In conclusion, the truncated minimal mE1a can act as a tumor inhibitor gene, and may be used to construct oncolytic adenovirus vectors for use in gene therapy of a variety of cancers.

Implications of endoplasmic reticulum stress, the unfolded protein response and apoptosis for molecular cancer therapy. Part I: targeting p53, Mdm2, GADD153/CHOP, GRP78/BiP and heat shock proteins

BACKGROUND

In eukaryotes, endoplasmic reticulum stress (ERS) and the unfolded protein response (UPR) are coordinately regulated to maintain steady-state levels and activities of various cellular proteins to ensure cell survival.

OBJECTIVE

This review (Part I of II) focuses on specific ERS and UPR signalling regulators, their expression in the cancer phenotype and apoptosis, and proposes how their implication in these processes can be rationalised into proteasome inhibition, apoptosis induction and the development of more efficacious targeted molecular cancer therapies.

METHOD

In this review, we contextualise many ERS and UPR client proteins that are deregulated or mutated in cancers and show links between ERS and the UPR, their implication in oncogenic transformation, tumour progression and escape from immune surveillance, apoptosis inhibition, angiogenesis, metastasis, acquired drug resistance and poor cancer prognosis.

CONCLUSION

Evasion of programmed cell death or apoptosis is a hallmark of cancer that enables tumour cells to proliferate uncontrollably. Successful eradication of cancer cells through targeting ERS- and UPR-associated proteins to induce apoptosis is currently being pursued as a central tenet of anticancer drug discovery.

miR-17 and miR-20a temper an E2F1-induced G1 checkpoint to regulate cell cycle progression

The stringent regulation of cell cycle progression helps to maintain genetic stability in cells. MicroRNAs (miRNAs) are critical regulators of gene expression in diverse cellular pathways, including developmental patterning, hematopoietic differentiation and antiviral defense. Here, we show that two c-Myc-regulated miRNAs, miR-17 and miR-20a, govern the transition through G1 in normal diploid human cells. Inhibition of these miRNAs leads to a G1 checkpoint due to an accumulation of DNA double-strand breaks, resulting from premature temporal accumulation of the E2F1 transcription factor. Surprisingly, gross changes in E2F1 levels were not required to initiate the DNA damage response and checkpoint, as these responses could occur with a less than twofold change in E2F1 protein levels. Instead, our findings indicate that the precise timing of E2F1 expression dictates S-phase entry and that accurate timing of E2F1 accumulation requires converging signals from the Rb/E2F pathway and the c-Myc-regulated miR-17 and miR-20a miRNAs to circumvent a G1 checkpoint arising from the untimely accumulation of E2F1. These data provide a mechanistic view of miRNA-based regulation of E2F1 in the context of the emerging model that miRNAs coordinate the timing of cell cycle progression.