Ionizing radiation increases primary cilia incidence and induces multiciliation in C2C12 myoblasts

YAP/Aurora A-mediated ciliogenesis regulates ionizing radiation-induced senescence via Hedgehog pathway in tumor cells

Primary cilia are antenna-like organelles that play critical roles in sensing and responding to various signals. Nevertheless, the function of primary cilia in cellular response to ionizing radiation (IR) in tumor cells remains unclear. Here, we show that primary cilia are frequently expressed in tumor cells and tissues. Notably, IR promotes cilia formation and elongation in time- and dose-dependent manners. Mechanistic study shows that the suppression of YAP/Aurora A pathway contributes to IR-induced ciliogenesis, which is diminished by Aurora A overexpression. The ciliated tumor cells undergo senescence but not apoptosis in response to IR and the abrogation of cilia formation is sufficient to elevate the lethal effect of IR. Furthermore, we show that IR-induced ciliogenesis leads to the activation of Hedgehog signaling pathway to drive senescence and resist apoptosis, and its blockage enhances cellular radiosensitivity by switching senescence to apoptosis. In summary, this work shows evidence of primary cilia in coordinating cellular response to IR in tumor cells, which may help to supply a novel sensitizing target to improve the outcome of radiotherapy.

Primary cilium participates in radiation-induced bystander effects through TGF-β1 signaling

Many studies have indicated that tumor growth factor-beta (TGF-β) signaling mediates radiation-induced bystander effects (RIBEs). The primary cilium (PC) coordinates several signaling pathways including TGF-β signaling to regulate diverse cellular processes. But whether the PC participates in TGF-β induced RIBEs remains unclear. The cellular levels of TGF-β1 were detected by western blot analysis and the secretion of TGF-β1 was measured by ELISA kit. The ciliogenesis was altered by CytoD treatment, STIL siRNA transfection, IFT88 siRNA transfection, or KIF3a siRNA transfection, separately, and was detected by western blot analysis and immunofluorescence staining. G0 /G1 phase cells were arrested by serum starvation and S phase cells were induced by double thymidine block. The TGF-β1 signaling was interfered by LY2109761, a TGF-β receptor 1 (TβR1) inhibitor, or TGF-β1 neutral antibody. The DNA damages were induced by TGF-β1 or radiated conditional medium (RCM) from irradiated cells and were reflected by p21 expression, 53BP1 foci, and γH2AX foci. Compared with unirradiated control, both A549 and Beas-2B cells expressed and secreted more TGF-β1 after carbon ion beam or X-ray irradiation. RCM collected from irradiated cells or TGF-β1 treatment caused an increase of DNA damage in cocultured unirradiated Beas-2B cells while blockage of TGF-β signaling by TβR1 inhibitor or TGF-β1 neutral antibody alleviates this phenomenon. IFT88 siRNA or KIF3a siRNA impaired PC formation resulted in an aggravated DNA damage in bystander cells, while elevated PC formation by CytoD or STIL siRNA resulted in a decrease of DNA damage. Furthermore, TGF-β1 induced more DNA damages in S phases cells which showed lower PC formation rate and less DNA damages in G0 /G1 phase cells which showed higher PC formation rate. This study demonstrates the particular role of primary cilia during RCM induced DNA damages through TGF-β1 signaling restriction and thereby provides a functional link between primary cilia and RIBEs.

Racgap1 knockdown results in cells with multiple cilia due to cytokinesis failure

Most mammalian cells have a single primary cilium that acts as a signalling hub in mediating cellular functions. However, little is known about the mechanisms that result in aberrant supernumerary primary cilia per cell. In this study, we re-analysed a previously published whole-genome siRNA-based reverse genetic screen for genes mediating ciliogenesis to identify knockdowns that permit multi-ciliation. We identified siRNA knockdowns that caused significant formation of supernumerary cilia, validated candidate hits in different cell-lines and confirmed that RACGAP1, a component of the centralspindlin complex, was the strongest candidate hit at the whole-genome level. Following loss of RACGAP1, mother centrioles were specified correctly prior to ciliogenesis and the cilia appeared normal. Live cell imaging revealed that increased cilia incidence was caused by cytokinesis failure which led to the formation of multinucleate cells with supernumerary cilia. This suggests that the signalling mechanisms for ciliogenesis are unable to identify supernumerary centrosomes and therefore allow ciliation of duplicated centrosomes as if they were in a new diploid daughter cell. These results, demonstrating that aberrant ciliogenesis is de-coupled from cell cycle regulation, have functional implications in diseases marked by centrosomal amplification.

Black Ginseng Ameliorates Cellular Senescence via p53-p21/p16 Pathway in Aged Mice

Simple Summary

The goal of this study was to examine if BG impacts the aging process, specifically cellular senescence, using in vitro and aged mouse models. Primary mouse embryonic fibroblasts (MEFs) and aged mice (18 months old) showed that BG supplementation retarded cellular senescence. Of note, BG-supplemented aged mice had remarkedly altered hepatic genes involved in the aging process as it caused less activation of the canonical senescence pathway. These observations demonstrated that BG positively impacts the age-related phenotype by controlling the expression of cellular senescence in the liver and other metabolic organs such as skeletal muscle and white adipose tissue.

Abstract

Cellular senescence, one of the hallmarks of aging, refers to permanent cell cycle arrest and is accelerated during the aging process. Black ginseng (BG), prepared by a repeated steaming and drying process nine times from fresh ginseng (Panax ginseng C.A. Meyer), is garnering attention for herbal medicine due to its physiological benefits against reactive oxygen species (ROS), inflammation, and oncogenesis, which are common cues to induce aging. However, which key nodules in the cellular senescence process are regulated by BG supplementation has not been elucidated yet. In this study, we investigated the effects of BG on cellular senescence using in vitro and aged mouse models. BG-treated primary mouse embryonic fibroblasts (MEFs) in which senescence was triggered by ionizing radiation (IR) expressed less senescence-associated β-galactosidase (SA-β-gal)-positive stained cells. In our aged mice (18 months old) study, BG supplementation (300 mg/kg) for 4 weeks altered hepatic genes involved in the aging process. Furthermore, we found BG supplementation downregulated age-related inflammatory genes, especially in the complement system. Based on this observation, we demonstrated that BG supplementation led to less activation of the canonical senescence pathway, p53-dependent p21 and p16, in multiple metabolic organs such as liver, skeletal muscle and white adipose tissue. Thus, we suggest that BG is a potential senolytic candidate that retards cellular senescence.

Microgravity and space radiation inhibit autophagy in human capillary endothelial cells, through either opposite or synergistic effects on specific molecular pathways

Microgravity and space radiation (SR) are two highly influential factors affecting humans in space flight (SF). Many health problems reported by astronauts derive from endothelial dysfunction and impaired homeostasis. Here, we describe the adaptive response of human, capillary endothelial cells to SF. Reference samples on the ground and at 1g onboard permitted discrimination between the contribution of microgravity and SR within the combined responses to SF. Cell softening and reduced motility occurred in SF cells, with a loss of actin stress fibers and a broader distribution of microtubules and intermediate filaments within the cytoplasm than in control cells. Furthermore, in space the number of primary cilia per cell increased and DNA repair mechanisms were found to be activated. Transcriptomics revealed the opposing effects of microgravity from SR for specific molecular pathways: SR, unlike microgravity, stimulated pathways for endothelial activation, such as hypoxia and inflammation, DNA repair and apoptosis, inhibiting autophagic flux and promoting an aged-like phenotype. Conversely, microgravity, unlike SR, activated pathways for metabolism and a pro-proliferative phenotype. Therefore, we suggest microgravity and SR should be considered separately to tailor effective countermeasures to protect astronauts' health.

Primary Cilia Enhance Osteogenic Response of Jaw Mesenchymal Stem Cells to Hypoxia and Bisphosphonate

PURPOSE

Primary cilia play a significant role in mesenchymal stem cell (MSC) lineage commitment, skeletal development, and bone homeostasis. MSC responsiveness to metabolic stress is associated with radiation and drug-induced jaw osteonecrosis. Therefore, we hypothesize that orofacial MSCs (OFMSCs) osteogenic commitment in response to cellular stressors hypoxia and bisphosphonates is a survival response coupled to primary cilia biogenesis.

MATERIALS AND METHODS

Human OFMSCs were subjected to cellular stress using severe hypoxia, nitrogen-containing bisphosphonate (pamidronate) and low serum starvation. OFMSC primary cilia formation, as well as cell survival and proliferation, were detected using immunofluorescence, CellTitre-Glo, and WST-1 assays respectively. OFMSC differentiation was tested using Alizarin Red S staining. OFMSCs survival and osteogenic markers were assessed by western blotting relative to primary cilia number and associated acetylated tubulin levels.

RESULTS

Baseline OFMSC proliferation was stable under short-term severe hypoxia and pamidronate treatments whether combined with or without serum starvation. Hypoxia and pamidronate decreased the number of OFMSCs positive for primary cilia that was consistent with increased HIF-1α and caspase 3 but decreased cyclin D1. Combined effects of hypoxia and pamidronate on OFMSCs significantly reduced ciliation but did not completely abrogate it. Combination of serum deprivation, hypoxia, and pamidronate promoted OFMSCs osteogenic differentiation that was consistent with upregulated HIF-1α levels.

CONCLUSIONS

Partial rather than complete loss of OFMSC ciliation and enhanced osteogenic commitment represent adaptive survival response of OFMSCs to severe hypoxia and pamidronate-induced metabolic stress. Hypoxia and drug-induced OFMSC stress may be significant events governing the pathogenesis and clinical outcomes of jaw osteonecrosis.

The toxic effect of cytostatics on primary cilia frequency and multiciliation

The primary cilium is considered as a key component of morphological cellular stability. However, cancer cells are notorious for lacking primary cilia in most cases, depending upon the tumour type. Previous reports have shown the effect of starvation and cytostatics on ciliogenesis in normal and cancer cells although with limited success, especially when concerning the latter. In this study, we evaluated the presence and frequency of primary cilia in breast fibroblasts and in triple-negative breast cancer cells after treatment with cytostatics finding that, in the case of breast fibroblasts, primary cilia were detected at their highest incidence 72 hours after treatment with 120 nM doxorubicin. Further, multiciliated cells were also detected after treatment with 80 nM doxorubicin. On the other hand, treatment with taxol increased the number of ciliated cells only at low concentrations (1.25 and 3.25 nM) and did not induce multiciliation. Interestingly, triple-negative breast cancer cells did not present primary cilia after treatment with either doxorubicin or taxol. This is the first study reporting the presence of multiple primary cilia in breast fibroblasts induced by doxorubicin. However, the null effect of these cytostatics on primary cilia incidence in the evaluated triple negative breast carcinomas cell lines requires further research.