p53, caspase 8, and regulation of apoptosis after ionizing radiation

Sirtuin 5 alleviates apoptosis and autophagy stimulated by ammonium chloride in bovine mammary epithelial cells

Ammonia (NH3) is an irritating and harmful gas that affects cell apoptosis and autophagy. Sirtuin 5 (SIRT5) has multiple enzymatic activities and regulates NH3-induced autophagy in tumor cells. In order to determine whether SIRT5 regulates NH3-induced bovine mammary epithelial cell apoptosis and autophagy, cells with SIRT5 overexpression or knockdown were generated and in addition, bovine mammary epithelial cells were treated with SIRT5 inhibitors. The results showed that SIRT5 overexpression reduced the content of NH3 and glutamate in cells by inhibiting glutaminase activity in glutamine metabolism, and reduced the ratio of ADP/ATP. The results in the SIRT5 knockdown and inhibitor groups were comparable, including increased content of NH3 and glutamate in cells by activating glutaminase activity, and an elevated ratio of ADP/ATP. It was further confirmed that SIRT5 inhibited the apoptosis and autophagy of bovine mammary epithelial cells through reverse transcription-quantitative PCR, western blot, flow cytometry with Annexin V FITC/PI staining and transmission electron microscopy. In addition, it was also found that the addition of LY294002 or Rapamycin inhibited the PI3K/Akt or mTOR kinase signal, decreasing the apoptosis and autophagy activities of bovine mammary epithelial cells induced by SIRT5-inhibited NH3. In summary, the PI3K/Akt/mTOR signal involved in NH3-induced cell autophagy and apoptosis relies on the regulation of SIRT5. This study provides a new theory for the use of NH3 to regulate bovine mammary epithelial cell apoptosis and autophagy, and provides guidance for improving the health and production performance of dairy cows.

Mep50 is essential for embryonic development in medaka fish

Mep50 as a partner promotes the activity and substrate affinity of Prmt5. Prmt5 and Mep50 function together in multiple bioprocesses of the cells. Both Prmt5 and Mep50 are necessary for maintenance of the stem cells and are indispensable in the embryogenesis in the mammals. However, the role of Mep50 is rarely studied in fish. This study was to investigate the role of Mep50 in embryonic development of medaka. Medaka mep50 was mutated by genomic editing with CRISPR-Cas9 technology. Two mutants with a deletion of 22 and 46 bp separately in mep50 caused premature stopping of translation. The homozygotes of these mutant fish were obtained by self-crossing of the heterozygotes. These homozygotic mutants could reproduce embryos but the offspring were not viable. The apoptotic cells were significantly more in the mutant embryos than that in the wild type indicated by TUNEL assay. Quantitative RT-PCR showed that the expression of oct4 and sox2 were significantly decreased, but p53 was increased in the mutant embryos. These results suggest that disruption of mep50 severely interferes with embryogenesis and mep50 is necessary for embryonic development by maintaining stem cells and repression of apoptosis in medaka.

Inhibition of PI3K/Akt/mTOR pathway by ammonium chloride induced apoptosis and autophagy in MAC-T cell

Ammonia is a harmful gas with a pungent odor, participates in the regulation of a variety of apoptosis and autophagy, which in turn affects the growth and differentiation of cells. To test the regulation of NH₃ on the apoptosis and autophagy of mammary epithelial cells, we selected NH₄Cl as NH₃ donor in vitro model. MTT and CCK-8 assay kits were employed to detect cell activity. Real-time quantitative PCR and western blot methods were used to detect the abundance of inflammatory molecules, apoptosis markers, and autophagy genes. We selected TUNEL kit and the Annexin-FITC/PI method to detect apoptosis. TEM analysis was used to detect autophagic vesicles, and MDC stain evaluated the formation of autophagosome. The results indicated that NH₄Cl reduced cell viability in a concentration-dependent manner and promoted cell inflammatory response, apoptosis, and autophagy. NH₄Cl stimulation notable increased the autophagosomes number. Interestingly, we also detected that the addition of LY294002 and Rapamycin inhibited the PI3K/Akt pathway and the mTOR pathway, respectively, resulting in changes in both apoptosis and autophagy. Therefore, we draw a conclusion that NH₃ may regulate the apoptosis and autophagic response of bovine mammary epithelial cells through the PI3K/Akt/mTOR signaling pathway. Further investigations on ammonia's function in other physiological respects, will be critical to provide theoretical help for the improvement of production performance. It will be also helpful for controlling the harmful gas ammonia concentration in the livestock house to protect the health of dairy cows.

Lysyl oxidase inhibits TNF-α induced rat nucleus pulposus cell apoptosis via regulating Fas/FasL pathway and the p53 pathways

AIMS

Intervertebral disc degeneration (IVDD) has been regarded as the main cause of low back pain, which affects 80% of adults and still lack effective treatment. In IVDD, nucleus pulposus (NP) cell apoptosis has widely existed. Lysyl oxidase (LOX) has been demonstrated to protect chondrocyte against apoptosis in the TNF-α-treated human chondrocytes. Therefore, in this study, we investigated the anti-apoptosis effect of LOX on TNF-α-treated rat NP cells.

MAIN METHODS

Real-time quantitative reverse transcription-polymerase chain reaction (RT-qPCR) and western blot analyses were used to detect the expression of LOX in TNF-α-treated rat NP cells. Then, the toxicity of exogenous LOX and its protective effect was evaluated by Cell Counting kit-8 (CCK-8). NP cell apoptosis was evaluated by flow cytometry analysis and TUNEL assay. The regulatory effects of LOX on the expression of extracellular matrix (ECM) molecules in TNF-α-treated rat NP cells were measured by RT-qPCR, western blot, and ELISA analyses. The molecular mechanism of LOX in regulating NP cell apoptosis was investigated by RT-qPCR and western blot analyses.

KEY FINDINGS

The expression of LOX in TNF-α-treated rat NP cells was significantly decreased. Exogenous LOX preserved the cell viability, reduced the rate of apoptosis and improved the ECM secretion in TNF-α-treated rat NP cells. Further molecular mechanism investigation showed that LOX inhibited the Fas/FasL and p53 pathways.

SIGNIFICANCES

LOX played an anti-apoptotic role in TNF-α-treated rat NP cells which could be a promising reagent in IVDD treatment.

The NKL-code for innate lymphoid cells reveals deregulated expression of NKL homeobox genes HHEX and HLX in anaplastic large cell lymphoma (ALCL)

NKL homeobox genes encode developmental transcription factors and display an NKL-code according to their physiological expression pattern in hematopoiesis. Here, we analyzed public transcriptome data from primary innate lymphoid cells (ILCs) for NKL homeobox gene activities and found that ILC3 expressed exclusively HHEX while in ILC1 and ILC2 these genes were silenced. Deregulation of the NKL-code promotes hematopoietic malignancies, including anaplastic large cell lymphoma (ALCL) which reportedly may derive from ILC3. Accordingly, we analyzed NKL homeobox gene activities in ALCL cell lines and investigated their role in this malignancy. Transcriptome analyses demonstrated low expression levels of HHEX but powerfully activated HLX. Forced expression of HHEX in ALCL cell lines induced genes involved in apoptosis and ILC3 differentiation, indicating tumor suppressor activity. ALCL associated NPM1-ALK and JAK-STAT3-signalling drove enhanced expression of HLX while discounting HHEX. Genomic profiling revealed copy number gains at the loci of HLX and STAT3 in addition to genes encoding both STAT3 regulators (AURKA, BCL3, JAK3, KPNB1, NAMPT, NFAT5, PIM3, ROCK1, SIX1, TPX2, WWOX) and targets (BATF3, IRF4, miR135b, miR21, RORC). Transcriptome data of ALCL cell lines showed absence of STAT3 mutations while MGA was mutated and downregulated, encoding a novel potential STAT3 repressor. Furthermore, enhanced IL17F-signalling activated HLX while TGFbeta-signalling inhibited HHEX expression. Taken together, our data extend the scope of the NKL-code for ILCs and spotlight aberrant expression of NKL homeobox gene HLX in ALCL. HLX represents a direct target of ALCL hallmark factor STAT3 and deregulates cell survival and differentiation in this malignancy.

Effects of ammonia on apoptosis and oxidative stress in bovine mammary epithelial cells

Ammonia, produced mainly from the deamination of amino acids and glutamine, is one of the major toxic components in blood and tissues that may affect bovine health. However, the physiological and pathological roles of ammonia in the mammary glands are not understood clearly. In the present study, the bovine mammary epithelial cell line (MAC-T) was utilised as an in vitro model to determine the effects of ammonia on bovine mammary gland. We demonstrated that ammonia stimulated the production of intracellular reactive oxygen species, decreased mitochondrial membrane potential, interrupted intracellular calcium ion (Ca2+) homeostasis and induced cell apoptosis. Ammonia also significantly reduced cell viability and increased the proportion of apoptotic cells through enhancing the level of p53 phosphorylation and increasing the expressions of BAX, caspase 8, caspase 9, caspase 3. Interestingly, bumetanide, a specific Na+ K+ 2Cl--cotransporter inhibitor, dramatically abolished the damaging effects of ammonia on the cells. These data suggest that ammonia exposure induces apoptosis in bovine mammary epithelial cells via activation of the p53 pathway and the mitochondrial apoptotic pathway, and that these effects involved the Na+ K+ 2Cl--cotransporter.

MnSOD downregulation induced by extremely low 0.1 mGy single and fractionated X-rays and microgravity treatment in human neuroblastoma cell line, NB-1

A human neuroblastoma cell line, NB-1, was treated with 24 h of microgravity simulation by clinostat, or irradiated with extremely small X-ray doses of 0.1 or 1.0 mGy using single and 10 times fractionation regimes with 1 and 2 h time-intervals. A quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) examination was performed for apoptosis related factors (BAX, CYTC, APAF1, VDAC1–3, CASP3, CASP8, CASP9 P53, AIF, ANT1 and 2, BCL2, MnSOD, autophagy related BECN and necrosis related CYP-40. The qRT-PCR results revealed that microgravity did not result in significant changes except for a upregulation of proapoptotic VDAC2, and downregulations of proapoptotic CASP9 and antiapoptotic MnSOD. After 0.1 mGy fractionation irradiation, there was increased expression of proapoptotic APAF1 and downregulation of proapoptotic CYTC, VDAC2, VDAC3, CASP8, AIF, ANT1, and ANT2, as well as an increase in expression of antiapoptotic BCL2. There was also a decrease in MnSOD expression with 0.1 mGy fractionation irradiation. These results suggest that microgravity and low-dose radiation may decrease apoptosis but may potentially increase oxidative stress.

Environmental toxicity, oxidative stress and apoptosis: ménage à trois

Apoptosis is an evolutionary conserved homeostatic process involved in distinct physiological processes including organ and tissue morphogenesis, development and senescence. Its deregulation is also known to participate in the etiology of several human diseases including cancer, neurodegenerative and autoimmune disorders. Environmental stressors (cytotoxic agents, pollutants or toxicants) are well known to induce apoptotic cell death and to contribute to a variety of pathological conditions. Oxidative stress seems to be the central element in the regulation of the apoptotic pathways triggered by environmental stressors. In this work, we review the established mechanisms by which oxidative stress and environmental stressors regulate the apoptotic machinery with the aim to underscore the relevance of apoptosis as a component in environmental toxicity and human disease progression.

Study of the efficacy and mechanism of ALA-mediated photodynamic therapy on human hepatocellular carcinoma cell

OBJECTIVES

To examine the efficacy and mechanism of delta- or 5-aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT) on a human hepatocellular carcinoma cell line.

MATERIALS AND METHODS

The optimal uptake of photosensitizer ALA in HepG2 (p53 wild) cells was investigated by means of spectrometric measurement. Cell viability was determined by trypan blue exclusion assay. Morphological apoptotic changes in HepG2 cells before and after ALA-mediated PDT were determined by microscopic examination. Detection of apoptotic bodies was examined by DAPI staining. The changes in p53 expression were revealed by the immunostaining method.

RESULTS

ALA/protoporphyrin IX (PpIX) was mainly located in the cytoplasm of HepG2 cells. The maximal cellular uptake occurred after 18 h in vitro incubation. The photocytotoxic assay showed that ALA PDT induced 80% killing at 2 mM drug dose and 2 J/cm2 light intensity. Up to 70% of cells showed membrane blebbing and positive DAPI staining, indicating that ALA-PDT-mediated cell death was predominantly via apoptosis. In addition, p53 was upregulated after treatment, implying that p53 might evoke apoptotic cell death.

CONCLUSIONS

HepG2 cell line is sensitive to ALA-mediated PDT. ALA-PDT induces apoptosis in the HepG2 cell line that may be mediated by a p53-dependent pathway.

Autophagy for cancer therapy through inhibition of pro-apoptotic proteins and mammalian target of rapamycin signaling

Autophagy is an alternative cell death pathway that is induced by mammalian target of rapamycin (mTOR) inhibitors and up-regulated when apoptosis is defective. We investigated radiation-induced autophagy in the presence or absence of Bax/Bak with or without an mTOR inhibitor, Rad001. Two isogenic cell lines, wild type (WT) and Bak/Bak(-/-) mouse embryonic fibroblasts and tumor cell lines were used for this study. Irradiated Bak/Bak(-/-) cells had a decrease of Akt/mTOR signaling and a significant increase of pro-autophagic proteins ATG5-ATG12 COMPLEX and Beclin-1. These molecular events resulted in an up-regulation of autophagy. Bax/Bak(-/-) cells were defective in undergoing apoptosis but were more radiosensitive than the WT cells in autophagy. Both autophagy and sensitization of Bak/Bax(-/-) cells were further enhanced in the presence of Rad001. In contrast, inhibitors of autophagy rendered the Bak/Bax(-/-) cells radioresistant, whereas overexpression of ATG5 and Beclin-1 made the WT cells radiosensitive. When this novel concept of radiosensitization was tested in cancer models, small interfering RNAs against Bak/Bax also led to increased autophagy and sensitization of human breast and lung cancer cells to gamma radiation, which was further enhanced by Rad001. This is the first report to demonstrate that inhibition of pro-apoptotic proteins and induction of autophagy sensitizes cancer cells to therapy. Therapeutically targeting this novel pathway may yield significant benefits for cancer patients.

Tumor response to neoadjuvant chemoradiation therapy for rectal adenocarcinoma is mediated by p53-dependent and caspase 8-dependent apoptotic pathways

BACKGROUND

We tested the hypothesis that rectal tumors are most responsive to neoadjuvant therapy if they possess p53 and/or caspase 8 activity.

PATIENTS AND METHODS

Fifty patients diagnosed with biopsy-proven rectal cancer underwent neoadjuvant chemoradiation therapy consisting of 5-fluorouracil (300 mg/m(2) daily) and radiation (4,500 cGy). Endorectal ultrasonography was performed before and after neoadjuvant therapy along with digital rectal examination and/or sigmoidoscopy for staging purposes and to evaluate response to therapy. All patients underwent resection with specimens submitted for gross and microscopic review. Pretreatment biopsy specimens were subjected to immunohistochemical staining for mutated p53 and caspase 8 bioactivity.

RESULTS

The study population consisted of 32 men and 18 women. There were 17 complete responses (CRs; 34%), 17 partial responses (PRs; 34%), and 16 cases of no response (NR; 32%). There were 10 stage I tumors (20%), 22 stage II tumors (44%), and 18 stage III tumors (36%) in the cohort at the time of initial diagnosis. p53 protein staining (ie, mutated p53) was positive in 31 tumors (62%; CR, n = 8; PR, n = 11; NR, n = 12); caspase 8 positivity was apparent in 30 specimens (60%; CR, n = 13; PR, n = 13; NR, n = 4). In terms of pretreatment predictions, we scored 3 separate levels of response (CR, 3; PR, 2; NR, 1) and compared them with the expected responses (ie, p53 positivity and caspase 8 negativity should yield NR, whereas all other combinations should yield responses). Wilcoxon 2-sample tests yielded a 1-sided P value of 0.007.

CONCLUSION

The present study highlights a possible mechanism for tumor response to neoadjuvant manipulation, namely that dual mechanisms for apoptotic cell death are working in concert to cause tumor regression; one is p53 transcription-dependent, and the other is p53 transcription-independent.

1alpha,25-dihydroxyvitamin D(3) (calcitriol) and its analogue, 19-nor-1alpha,25(OH)(2)D(2), potentiate the effects of ionising radiation on human prostate cancer cells

Radiotherapy with external beam radiation or brachytherapy is an established therapeutic modality for prostate cancer. Approximately 30% of patients with localised prostate cancer relapse at the irradiated site. Secondary effects of ionising radiation (IR), for example, bowel and bladder complications, are common. Thus, the search for biological response modifiers that could potentiate the therapeutic effects of radiation and limit the occurrence of serious side effects is an important task in prostate cancer therapy. 1alpha,25-Dihydroxyvitamin D(3) (calcitriol), the active metabolite of vitamin D, and its analogues are under investigation for the treatment of several malignancies including prostate cancer. Here, we report that 1alpha,25-dihydroxyvitamin D(3) and its less calcaemic analogue 19-nor-1alpha,25-(OH)(2)D(2) (Zemplar) act synergistically with IR to inhibit the growth of the human prostate cancer cells in vitro. 1alpha,25-dihydroxyvitamin D(3) potentiated IR-induced apoptosis of LNCaP cells, and nanomolar doses of 1alpha,25-dihydroxyvitamin D(3) and 19-nor-1alpha,25-(OH)(2)D(2) showed synergistic inhibition of growth of LNCaP cells at radiobiologically relevant doses of IR (1-2 Gy). At higher doses of IR, the combination of 1alpha,25-dihydroxyvitamin D(3) and IR or 19-nor-1alpha,25-(OH)(2)D(2) and IR resulted in moderate antagonism. The synergistic effect at radiobiologically relevant doses of radiation suggests that a combination of 1alpha,25-dihydroxyvitamin D(3) or 19-nor-1alpha,25-(OH)(2)D(2) with IR could permit a reduction in the dose of radiation given clinically and thus potentially reduce treatment-related morbidity.

Decision making by p53: life, death and cancer

The p53 tumor-suppressor plays a critical role in the prevention of human cancer. In the absence of cellular stress, the p53 protein is maintained at low steady-state levels and exerts very little, if any, effect on cell fate. However, in response to various types of stress, p53 becomes activated; this is reflected in elevated protein levels, as well as augmented biochemical capabilities. As a consequence of p53 activation, cells can undergo marked phenotypic changes, ranging from increased DNA repair to senescence and apoptosis. This review deals with the mechanisms that underlie the apoptotic activities of p53, as well as the complex interactions between p53 and central regulatory signaling networks. In p53-mediated apoptosis, the major role is played by the ability of p53 to transactivate specific target genes. The choice of particular subsets of target genes, dictated by covalent p53 modifications and protein-protein interactions, can make the difference between life and apoptotic death of a cell. In addition, transcriptional repression of antiapoptotic genes, as well as transcription-independent activities of p53, can also contribute to the apoptotic effects of p53. Regarding the crosstalk between p53 and signaling networks, this review focuses on the interplay between p53 and two pivotal regulatory proteins: beta-catenin and Akt/PKB. Both proteins can regulate p53 as well as be regulated by it. In addition, p53 interacts with the GSK-3beta kinase, which serves as a link between Akt and beta-catenin. This review discusses how the functional balance between these different interactions might dictate the likelihood of a given cell to become cancerous or be eliminated from the replicative pool, resulting in suppression of cancer.

The apoptotic action of the retinoid CD437/AHPN: diverse effects, common basis

Retinoids, such as all-TRANS-retinoic acid (RA), have found applications in several different types of (cancer) therapies. The synthetic retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (CD437 or AHPN), an RA receptor (RAR)gamma agonist, not only induces RARgamma-dependent differentiation, but in contrast to RA, it also induces RARgamma-independent apoptosis in many tumor cells. This observation makes this and similar new retinoids very interesting from a clinical perspective. Several genes have been associated with CD437/AHPN-mediated apoptosis, but the multiple activities of this compound and the apparent cell-type-specific responses to treatment have made it difficult to discern a common biochemical basis for the mechanism of its apoptotic action. In this brief review, we present a model which links all CD437/AHPN-associated apoptotic effects. CD437/AHPN rapidly induces DNA adduct formation through an as-yet unknown reaction which is independent of cell type. This is followed by a cell-type-specific, largely p53-independent DNA damage response which can result in engagement of multiple cell death pathways and activation of caspases as a common endpoint. At the same time, the RARgamma-dependent pathway leads to regulation of differentiation-associated, cell-type-specific genes. CD437/AHPN, with its simultaneous differentiation and apoptosis-inducing activities, is a good prototype for new drugs which may be clinically more efficacious than those with a single activity.