MAPK11 (p38ß) 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 (p38ß), 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.

p38ß (MAPK11) mediates gemcitabine-associated radiosensitivity in sarcoma experimental models.

BACKGROUND AND PURPOSE: Gemcitabine is an antitumour agent currently used in the treatment of several types of cancer with known properties as a radiosensitizer. p38MAPK signalling pathway has been shown to be a major determinant in the cellular response to gemcitabine in different experimental models. However, the molecular mechanism implicated in gemcitabine-associated radiosensitivity remains unknown. MATERIALS AND METHODS: The human sarcoma cell lines A673 and HT1080, and a mouse cell line derived from a 3-methylcholanthrene induced sarcoma were used as experimental models. Modulation of p38MAPKs was performed by pharmacological approaches (SB203580) and genetic interference using lentiviral vectors coding for specific shRNAs. Viability was assessed by MTT. Gene expression was evaluated by western blot and RT-qPCR. Induction of apoptosis was monitored by caspase 3/7 activity. Response to ionizing radiation was evaluated by clonogenic assays. RESULTS: Our data demonstrate that chemical inhibition of p38MAPK signalling pathway blocks gemcitabine radiosensitizing potential. Genetic interference of MAPK14 (p38α), the most abundantly expressed and best characterized p38MAPK, despite promoting resistance to gemcitabine, it does not affect its radiosensitizing potential. Interestingly, specific knockdown of MAPK11 (p38ß) induces a total loss of the radiosensitivity associated to gemcitabine, as well as a marked increase in the resistance to the drug. CONCLUSION: The present work identifies p38ß as a major determinant of the radiosensitizing potential of gemcitabine without implication of p38α, suggesting that p38ß status should be analysed in those cases in which gemcitabine is combined with ionizing radiation.

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.