E1a is an exogenous in vivo tumour suppressor

MAPK11 (p38β) is a major determinant of cellular radiosensitivity by controlling ionizing radiation-associated senescence: An in vitro study

Background and purpose

MAPKs are among the most relevant signalling pathways involved in coordinating cell responses to different stimuli. This group includes p38MAPKs, constituted by 4 different proteins with a high sequence homology: MAPK14 (p38α), MAPK11 (p38β), MAPK12 (p38γ) and MAPK13 (p38δ). Despite their high similarity, each member shows unique expression patterns and even exclusive functions. Thus, analysing protein-specific functions of MAPK members is necessary to unequivocally uncover the roles of this signalling pathway. Here, we investigate the possible role of MAPK11 in the cell response to ionizing radiation (IR).

Materials and methods

We developed MAPK11/14 knockdown through shRNA and CRISPR interference gene perturbation approaches and analysed the downstream effects on cell responses to ionizing radiation in A549, HCT-116 and MCF-7 cancer cell lines. Specifically, we assessed IR toxicity by clonogenic assays; DNA damage response activity by immunocytochemistry; apoptosis and cell cycle by flow cytometry (Annexin V and propidium iodide, respectively); DNA repair by comet assay; and senescence induction by both X-Gal staining and gene expression of senescence-associated genes by RT-qPCR.

Results

Our findings demonstrate a critical role of MAPK11 in the cellular response to IR by controlling the associated senescent phenotype, and without observable effects on DNA damage response, apoptosis, cell cycle or DNA damage repair.

Conclusion

Our results highlight MAPK11 as a novel mediator of the cellular response to ionizing radiation through the control exerted onto IR-associated senescence.

Tilting MYC toward cancer cell death

MYC oncoprotein promotes cell proliferation and serves as the key driver in many human cancers; therefore, considerable effort has been expended to develop reliable pharmacological methods to suppress its expression or function. Despite impressive progress, MYC-targeting drugs have not reached the clinic. Recent advances suggest that within a limited expression range unique to each tumor, MYC oncoprotein can have a paradoxical, proapoptotic function. Here we introduce a counterintuitive idea that modestly and transiently elevating MYC levels could aid chemotherapy-induced apoptosis and thus benefit the patients as much, if not more than MYC inhibition.

Shedding more light on the role of Midkine in hepatocellular carcinoma: New perspectives on diagnosis and therapy

One of the most common malignant tumors is hepatocellular carcinoma (HCC). Progression of HCC mainly results from highly complex molecular and pathological pathways. Midkine (MDK) is a growth factor that impacts viability, migration, and other cell activities. Since MDK has been involved in the inflammatory responses, it has been claimed that MDK has a crucial role in HCC. MDK acts as an anti-apoptotic factor, which mediates tumor cell viability. In addition, MDK blocks anoikis to promote metastasis. There is also evidence that MDK is involved in angiogenesis. It has been shown that the application of anti-MDK approaches might be promising in the treatment of HCC. Besides, due to the elevated expression in HCC, MDK has been proposed as a biomarker in the prognosis and diagnosis of HCC. In this review, we will discuss the role of MDK in HCC. It is hoped that the development of new strategies concerning MDK-based therapies will be promising in HCC management.

Analysis of E1A domains involved in the enhancement of CDK2 activity

E1A is an adenoviral protein which is expressed at the early phase after viral infection and contains four conserved regions (CR1, CR2, CR3 and CR4). Our previous work suggests that E1A facilitates the formation of cyclin A-CDK2 complex and thereby enhances CDK2 activity. However, the molecular function of E1A in CDK2 activation has been unclear. Here, we studied the mechanism of enhancement of CDK2 activity by E1A, using the E1A variant forms which selectively contain CR domains. We isolated four E1A variant forms, i.e. 13S (containing CR1, CR2, CR3, CR4), 12S (CR1, CR2, CR4), 10S (CR2, CR4) and 9S (CR4), derived from HEK293 cells which express E1A. 13S promoted G2/M-phase arrest, upon CDK2 hyper-activation by co-expressing a stabilized cyclin A mutant, most strongly among those E1A variant forms. Concomitantly, the specific activity of the 13S-associated CDK2 was highest among them. 10S exhibited lower affinity for CDK2 than the 13S while the affinity for CDK2 was comparable between 13S and 12S. Nonetheless, 12S did not enhance the CDK2 specific activity. On the other hand, a mutation in CR2 domain, which is essential for binding to p107, suppressed both the binding and activation of CDK2. These results suggest that CR1 domain, in addition to CR2 domain via p107 interaction, is important for binding to CycA-CDK2 complex while CR3 domain facilitates CDK2 activation. Since the function of CR3 in cell cycle regulation has been relatively unknown, we propose the enhancement of CDK2 activity as a novel function of CR3 domain.

Structural Determinants within the Adenovirus Early Region 1A Protein Spacer Region Necessary for Tumorigenesis

It has long been established that group A human adenoviruses (HAdV-A12, -A18, and -A31) can cause tumors in newborn rodents, with tumorigenicity related to the presence of a unique spacer region located between conserved regions 2 and 3 within the HAdV-A12 early region 1A (E1A) protein. Group B adenoviruses are weakly oncogenic, whereas most of the remaining human adenoviruses are nononcogenic. In an attempt to understand better the relationship between the structure of the AdE1A spacer region and oncogenicity of HAdVs, the structures of synthetic peptides identical or very similar to the adenovirus 12 E1A spacer region were determined and found to be α-helical using nuclear magnetic resonance (NMR) spectroscopy. This contrasts significantly with some previous suggestions that this region is unstructured. Using available predictive algorithms, the structures of spacer regions from other E1As were also examined, and the extent of the predicted α-helix was found to correlate reasonably well with the tumorigenicity of the respective virus. We suggest that this may represent an as-yet-unknown binding site for a partner protein required for tumorigenesis.IMPORTANCE This research analyzed small peptides equivalent to a region within the human adenovirus early region 1A protein that confers, in part, tumor-inducing properties to various degrees on several viral strains in rats and mice. The oncogenic spacer region is α-helical, which contrasts with previous suggestions that this region is unstructured. The helix is characterized by a stretch of amino acids rich in alanine residues that are organized into a hydrophobic, or "water-hating," surface that is considered to form a major site of interaction with cellular protein targets that mediate tumor formation. The extent of α-helix in E1A from other adenovirus species can be correlated to a limited degree to the tumorigenicity of that virus. Some serotypes show significant differences in predicted structural propensity, suggesting that the amino acid type and physicochemical properties are also of importance.

Polyethylenimine (PEI)-Mediated E1A Increases the Sensitivity of Hepatocellular Carcinoma Cells to Chemotherapy

BACKGROUND The aim of this study was to assess the ability of polyethylenimine (PEI) as an E1A plasmid vector to transfect hepatocellular carcinoma SMMC-7721 cells and to analyze the sensitization effect of E1A on various anti-tumor drugs. MATERIAL AND METHODS PEI-mediated recombinant plasmid psv-E1A with high expression of the E1A gene was introduced into hepatocellular carcinoma SMMC-7721 cells, and the effective transfection of E1A gene was determined by RT-PCR and Western blot analysis. The CCK8 method was used to detect the proliferation inhibition of docetaxel, epirubicin, gemcitabine, and 5-fluorouracil on SMMC-7721 cells before and after the transfection of the E1A gene. RESULTS RT-PCR and Western blot analysis showed that PEI could transfect plasmid psv-E1A with stable expression. After the transfection of E1A gene, the sensitivity of SMMC-7721 cells to docetaxel, epirubicin, gemcitabine, and 5-fluorouracil was increased (P<0.05), and the sensitivity to docetaxel was significantly improved (P<0.01). CONCLUSIONS PEI can transfect plasmid psv-E1A. The E1A gene can increase the sensitivity of hepatocellular carcinoma cells to chemotherapeutic drugs. The mechanism may be related to the increased ability of the E1A gene to inhibit proliferation of hepatocellular carcinoma cells and altering the cell cycle of hepatocellular carcinoma cells.

P53 pathway is a major determinant in the radiosensitizing effect of Palbociclib: Implication in cancer therapy

Targeting cell cycle has become one of the major challenges in cancer therapy, being Palbociclib, a CDK4/6 inhibitor, an excellent example. Recently, it has been reported that Palbociclib could be a novel radiosensitizer agent. In an attempt to clarify the molecular basis of this effect we have used cell lines from colorectal (HT29, HCT116) lung (A549, H1299) and breast cancer (MCF-7). Our results indicate that the presence of a p53 wild type is strictly required for Palbociclib to exert its radiosensitizing effect, independently of the inhibitory effect exerted on CDK4/6. In fact, abrogation of p53 in cells with functional p53 blocks the radiosensitizing effect of Palbociclib. Moreover, no radiosensitizing effect is observed in cells with non-functional p53, but restoration of p53 function promotes radiosensitivity associated to Palbociclib. Furthermore, the presence of Palbociclib blocks the transcriptional activity of p53 in an ATM-dependent-fashion after ionizing radiation exposure, as the blockage of p21/WAF1 expression demonstrates. These observations are a proof of concept for a more selective therapy, based on the combination of CDK4/6 inhibition and radiotherapy, which would only benefit to those patients with a functional p53 pathway.