Autophagy induced by silibinin protects human epidermoid carcinoma A431 cells from UVB-induced apoptosis

RhFGF21 Protects Epidermal Cells against UVB-Induced Apoptosis through Activating AMPK-Mediated Autophagy

Ultraviolet irradiation, especially ultraviolet B (UVB) irradiation, increases the risks of various skin diseases, such as sunburn, photo-aging and cancer. However, few drugs are available to treat skin lesions. Therefore, the discovery of drugs to improve the health of irradiated skin is urgently needed. Fibroblast growth factor 21 (FGF21) is a metabolic factor that plays an important role in the protection and repair of various types of pathological damage. The effects of FGF21 on skin injury caused by UVB-irradiation were the focus of this study. We found that UVB irradiation promoted the expression of FGF21 protein in mouse epidermal cells, and exogenous recombinant human FGF21 (rhFGF21) protected mouse skin tissue against UVB-induced injury. RhFGF21 inhibited the inflammatory responses and epidermal cell apoptosis as well as promotion of autophagy in UVB-irradiated mice. Moreover, we found that rhFGF21 protected HaCaT cells against UVB-induced apoptosis, and the protective effect was enhanced by treatment with an autophagy activator (rapamycin) but was inhibited by treatment with an autophagy inhibitor (3-methyladenine, 3MA). AMP-activated protein kinase (AMPK), as a cellular energy sensor, regulates autophagy. RhFGF21 increased the expression of p-AMPK protein in epidermal cells irradiated with UVB in vivo and in vitro. Moreover, rhFGF21 increased autophagy levels and the viability were diminished by treatment with an AMPK inhibitor (compound C). RhFGF21 protects epidermal cells against UVB-induced apoptosis by inducing AMPK-mediated autophagy.

Effect of Autophagy Inhibitors on Radiosensitivity in DNA Repair-Proficient and -Deficient Glioma Cells

Background and Objectives: The development of radioresistance is a fundamental barrier to successful glioblastoma therapy. Autophagy is thought to play a role in facilitating the DNA repair of DNA damage foci in radiation-exposed tumor cells, thus, potentially contributing to their restoration of proliferative capacity and development of resistance in vitro. However, the effect of autophagy inhibitors on DNA damage repair is not fully clear and requires further investigation. Materials and Methods: In this work, we utilized M059K (DNA-PKcs proficient) and M059J (DNA-PKcs deficient) glioma cell lines to investigate the role of autophagy inhibitors in the DNA repair of radiation-induced DNA damage. Cell viability following radiation was determined by trypan blue exclusion in both cell lines. Cell death and autophagy assays were performed to evaluate radiation-induced cell stress responses. DNA damage was measured as based on the intensity of phosphorylated γ-H2AX, a DNA double-stranded breaks (DSBs) marker, in the presence or absence of autophagy inhibitors. Results: The cell viability assay showed that M059J cells were more sensitive to the same dose of radiation (4 Gy) than M059K cells. This observation was accompanied by an elevation in γ-H2AX formation in M059J but not in M059K cells. In addition, the DAPI/TUNEL and Senescence-associated β-galactosidase (SA-β-gal) staining assays did not reveal significant differences in apoptosis and/or senescence induction in response to radiation, respectively, in either cell line. However, acridine orange staining demonstrated clear promotion of acidic vesicular organelles (AVOs) in both cell lines in response to 4 Gy radiation. Moreover, DNA damage marker levels were found to be elevated 72 h post-radiation when autophagy was inhibited by the lysosomotropic agent bafilomycin A1 (BafA1) or the PI3K inhibitor 3-methyl adenine (3-MA) in M059K cells. Conclusions: The extent of the DNA damage response remained high in the DNA-PKcs deficient cells following exposure to radiation, indicating their inability to repair the newly formed DNA-DSBs. On the other hand, radioresistant M059K cells showed more DNA damage response only when autophagy inhibitors were used with radiation, suggesting that the combination of autophagy inhibitors with radiation may interfere with DNA repair efficiency.

Gypenosides regulate autophagy through Sirt1 pathway and the anti-inflammatory mechanism of mitochondrial autophagy in systemic lupus erythematosus

To study the mechanism of gynostemma pentaphyllum saponins (GpS) regulating mitochondrial autophagy and anti-inflammatory through Sirtuin 1 (Sirt1) pathway in systemic lupus erythematosus (SLE). JURKAT cells were cultured in vitro, RT-PCR and western blotting (WB) were utilized to identify the expression of related-proteins in Sirt1 pathway and global autophagy and mitochondrial autophagy markers in JURKAT before and after GpS treatment induced by ultraviolet B (UVB), and the related-mechanism of GpS regulation of autophagy was analyzed. The SLE model was established to analyze the alleviating effects of GpS on various symptoms of lupus mice. Sirt1/AMPK/mTOR pathway was activated in UVB induced JURKAT cells. After the addition of GpS, WB revealed that the phosphorylation of AMPK decreased, the phosphorylation of mTOR increased, the expression of Sirt1 protein decreased, and the activation of the pathway was inhibited. Moreover, autophagy of JURKAT cells wasinhibited. In order to further verify the role of Sirt1 pathway, we activated Sirt1 expression in cells by constructing lentiviral vectors, and the therapeutic effect of GpS was significantly reduced. These results indicate GpS can exert autophagy regulation by inhibiting the activity of Sirt1 pathway. To treat SLE. GpS can significantly reduce the level of autoantibodies, kidney inflammation, immune complex deposition and urinary protein excretion, improve kidney function in lupus-prone mice. GpS can regulate autophagy and mitochondrial autophagy through Sirt1 pathway, which may be a potential mechanism for GpS to reduce the level of autoantibodies, kidney inflammation, immune complex deposition and urinary protein excretion, improve kidney function in lupus-prone mice.

Plant Polyphenols for Aging Health: Implication from Their Autophagy Modulating Properties in Age-Associated Diseases

Polyphenols are a family of naturally occurring organic compounds, majorly present in fruits, vegetables, and cereals, characterised by multiple phenol units, including flavonoids, tannic acid, and ellagitannin. Some well-known polyphenols include resveratrol, quercetin, curcumin, epigallocatechin gallate, catechin, hesperetin, cyanidin, procyanidin, caffeic acid, and genistein. They can modulate different pathways inside the host, thereby inducing various health benefits. Autophagy is a conserved process that maintains cellular homeostasis by clearing the damaged cellular components and balancing cellular survival and overall health. Polyphenols could maintain autophagic equilibrium, thereby providing various health benefits in mediating neuroprotection and exhibiting anticancer and antidiabetic properties. They could limit brain damage by dismantling misfolded proteins and dysfunctional mitochondria, thereby activating autophagy and eliciting neuroprotection. An anticarcinogenic mechanism is stimulated by modulating canonical and non-canonical signalling pathways. Polyphenols could also decrease insulin resistance and inhibit loss of pancreatic islet β-cell mass and function from inducing antidiabetic activity. Polyphenols are usually included in the diet and may not cause significant side effects that could be effectively used to prevent and treat major diseases and ailments.

The Multifaceted Role of Flavonoids in Cancer Therapy: Leveraging Autophagy with a Double-Edged Sword

Flavonoids are considered as pleiotropic, safe, and readily obtainable molecules. A large number of recent studies have proposed that flavonoids have potential in the treatment of tumors by the modulation of autophagy. In many cases, flavonoids suppress cancer by stimulating excessive autophagy or impairing autophagy flux especially in apoptosis-resistant cancer cells. However, the anti-cancer activity of flavonoids may be attenuated due to the simultaneous induction of protective autophagy. Notably, flavonoids-triggered protective autophagy is becoming a trend for preventing cancer in the clinical setting or for protecting patients from conventional therapeutic side effects in normal tissues. In this review, focusing on the underlying autophagic mechanisms of flavonoids, we hope to provide a new perspective for clinical application of flavonoids in cancer therapy. In addition, we highlight new research ideas for the development of new dosage forms of flavonoids to improve their various pharmacological effects, establishing flavonoids as ideal candidates for cancer prevention and therapy in the clinic.

Silibinin treatment protects human skin cells from UVB injury through upregulation of estrogen receptors

Ultraviolet B (UVB) from the sunlight is a major environmental cause for human skin damages, inducing cell death, inflammation, senescence and even carcinogenesis. The natural flavonoid silibinin, clinically used as liver protectant, has protective effects against UVB-caused skin injury in vivo and in vitro. Silibinin is often classified as a phytoestrogen, because it modulates the activation of estrogen receptors (ERs). However, whether silibinin's estrogenic effect contributes to the skin protection against UVB injury remains to be elucidated. The issue was explored in this study by using the human foreskin dermal fibroblasts (HFF) and human non-malignant immortalized keratinocytes (HaCaT). In HFF, pre-treatment with silibinin rescued UVB-irradiated cells from apoptosis. Interestingly, silibinin increased the whole cellular and nuclear levels of ERα and ERβ in UVB-irradiated cells. Activation of ERs by treatment with estradiol elevated the cell survival and reduced apoptosis in UVB-treated cells. ERα agonist increased cell survival, while its antagonist decreased it. ERβ agonist also increased cell survival, but the antagonist had no effect on cell survival. Transfection of the cells with the small interfering RNAs (si-RNAs) to ERα or ERβ diminished the protective effect of silibinin on UVB-irradiated cells. In UVB-treated HaCaT cells, both ERα and ERβ were increased by silibinin treatment. Inhibition of activation and expression of ERα or ERβ by specific antagonists and si-RNAs, respectively, reduced cell survival in UVB-treated HaCaT cells regardless of silibinin treatment. Taken together, it is summarized that silibinin up-regulates both ERα and ERβ pathways in UVB-treated dermal HFF cells and epidermal HaCaT cells, leading to protection of skin from UVB-damage.

Polyphyllin VII induces apoptotic cell death via inhibition of the PI3K/Akt and NF‑κB pathways in A549 human lung cancer cells

Polyphyllin VII is an active compound isolated from Paris polyphylla, which is termed Chonglou in China. The present study was designed to investigate the underlying mechanisms of the antitumor effect of Polyphyllin VII in lung cancer cells. The cytotoxic effect of Polyphyllin VII in human lung cancer A549 cells was analyzed; the results revealed an IC₅₀ value of 0.41±0.10 µM at 24 h. The associated mechanisms were investigated by phase-contrast microscopy, fluorescence microscopy, flow cytometry and western blot analysis. Exposure of A549 cells to Polyphyllin VII resulted in apoptosis. Pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-κB, and wortmannin, an inhibitor of PI3K, both decreased the proportion of viable A549 cells in the presence of Polyphyllin VII. The ratio of apoptotic cells increased in the presence of wortmannin and PDTC. Western blot analysis revealed that PI3K, phosphorylated (p)-PI3K, Akt, p-Akt, NF-κB and p-NF-κB were downregulated following treatment with Polyphyllin VII. Increased caspase-3 activity, increased poly-(ADP-ribose) polymerase cleavage and a downregulation of inhibitor of caspase-activated DNase were observed following treatment with Polyphyllin VII, and these effects were enhanced by either wortmannin or PDTC. The present results revealed that Polyphyllin VII was able to induce apoptotic cell death in A549 human lung cancer cells via inhibition of the PI3K/Akt and NF-κB pathways.

Naturally occurring anti-cancer compounds: shining from Chinese herbal medicine

Numerous natural products originated from Chinese herbal medicine exhibit anti-cancer activities, including anti-proliferative, pro-apoptotic, anti-metastatic, anti-angiogenic effects, as well as regulate autophagy, reverse multidrug resistance, balance immunity, and enhance chemotherapy in vitro and in vivo. To provide new insights into the critical path ahead, we systemically reviewed the most recent advances (reported since 2011) on the key compounds with anti-cancer effects derived from Chinese herbal medicine (curcumin, epigallocatechin gallate, berberine, artemisinin, ginsenoside Rg3, ursolic acid, silibinin, emodin, triptolide, cucurbitacin B, tanshinone I, oridonin, shikonin, gambogic acid, artesunate, wogonin, β-elemene, and cepharanthine) in scientific databases (PubMed, Web of Science, Medline, Scopus, and Clinical Trials). With a broader perspective, we focused on their recently discovered and/or investigated pharmacological effects, novel mechanism of action, relevant clinical studies, and their innovative applications in combined therapy and immunomodulation. In addition, the present review has extended to describe other promising compounds including dihydroartemisinin, ginsenoside Rh2, compound K, cucurbitacins D, E, I, tanshinone IIA and cryptotanshinone in view of their potentials in cancer therapy. Up to now, the evidence about the immunomodulatory effects and clinical trials of natural anti-cancer compounds from Chinese herbal medicine is very limited, and further research is needed to monitor their immunoregulatory effects and explore their mechanisms of action as modulators of immune checkpoints.

Upregulation of autophagy by Ginsenoside Rg2 in MCF-7 cells

Autophagy is a major intracellular degradation process that plays an important role in cell survival, stress responses, nutrient sensing and development. Our previous studies have shown that Rg2, a triterpenoid saponin contained in ginseng, protects cells against UVB-induced genotoxicity by increasing DNA repair, in possible association with modulation of protein levels involved in p53 pathway. In this study, we determined an upregulation of autophagy by Rg2. Rg2 treatment for 24 h in MCF-7, a breast cancer cell, did not show cytotoxicity up to 200 μM. Rg2 also upregulated the level of p-p53, p-AMPK, p-ACC, Atg-7 and LC3-II and decreased the level of p62 in concentration-dependent manners. We also determined the level of p53, AMPK, p62, Atg-7 and LC3 after UVB exposure and subsequent incubation in growth medium for 24 h. UVB increased the level of p-p53, p-AMPK, p-ACC and decreased the levels of p62, Atg-7 and LC3-II. Interestingly, Rg2 treatment for 24 h after UVB exposure increased the levels of p-p53, p-AMPK, p-ACC, Atg-7 and LC3-II and decreased the level of cyclobutane pyrimidine dimer, a UVB-induced DNA damage in concentration-dependent manners. All these results suggest that Rg2 increased autophagy and decreased UVB-induced DNA damage, in possible association with the modulation of protein levels in p53- and autophagic pathways.

Deoxynivalenol induces structural alterations in epidermoid carcinoma cells A431 and impairs the response to biomechanical stimulation

Morphology together with the capability to respond to surrounding stimuli are key elements governing the spatial interaction of living cells with the environment. In this respect, biomechanical stimulation can trigger significant physiological cascades that can potentially modulate toxicity. Deoxynivalenol (DON, vomitoxin) is one of the most prevalent mycotoxins produced by Fusarium spp. and it was used to explore the delicate interaction between biomechanical stimulation and cytotoxicity in A431 cells. In fact, in addition of being a food contaminant, DON is a relevant toxin for several organ systems. The combination between biomechanical stimulation and the mycotoxin revealed how DON can impair crucial functions affecting cellular morphology, tubulin and lysosomes at concentrations even below those known to be cytotoxic in routine toxicity studies. Sub-toxic concentrations of DON (0.1-1 μM) impaired the capability of A431 cells to respond to a biomechanical stimulation that normally sustains trophic effects in these cells. Moreover, the effects of DON (0.1-10 μM) were partially modulated by the application of uniaxial stretching (0.5 Hz, 24 h, 15% deformation). Ultimately, proteomic analysis revealed the potential of DON to alter several proteins necessary for cell adhesion and cytoskeletal modulation suggesting a molecular link between biomechanics and the cytotoxic potential of the mycotoxin.

Skin Protective Nutraceuticals: The Current Evidence in Brief

Nutraceuticals are important for healthy skin maintenance. Probiotics, phenolics, and vitamins are just a few of the nutraceuticals meant to potentially prevent and assist medical management of dermatologic conditions. Among these, probiotics, vitamin E, and green tea catechins may offer the broadest array of skin protective mechanisms with probiotics having the greatest clinical range. Probiotics’ amelioration of atopic dermatitis and opportunistic infections of skin burns has been targeted in recent research efforts. This includes the improvement of Scoring Atopic Dermatitis index scores, p = 0.02, with intact Lactobacillus rhamnosus Goldin and Gorbach (LGG) in comparison to heat inactivated LGG or placebo. Lactobacillus reuteri used prior to or concurrently with Staphylococcus aureus infection can increase epidermal keratinocyte survival, p < 0.01. Phenolics may not have been extensively studied for atopic dermatitis or skin burns. However, phenolics do have a role in photoprotection. The phenolic rutin increases ultraviolet B radiation filter reactive oxygen species scavenging at 75%, p < 0.002, and peak wavelength absorption, p < 0.001. While oral and topical probiotics have untapped potential for atopic dermatitis amelioration and skin infection prevention, phenolics will be increasingly used for photoprotection. With optimized bioavailability, dosage, and formulation, nutraceuticals will become crucial for healthy skin maintenance.

Silibinin Induced Human Glioblastoma Cell Apoptosis Concomitant with Autophagy through Simultaneous Inhibition of mTOR and YAP

Silibinin, also known as silybin, is the major flavonolignan isolated from Silybum marianum. Although previous reports demonstrated that silibinin exhibits significant tumor suppressor activities in various cancers by promoting cell apoptosis, it was also shown to trigger autophagy to counteract apoptosis induced by exogenous stresses in several types of cells. However, there is no report to address the role of silibinin induced autophagy in human A172 and SR glioblastoma cells. Our study showed that silibinin treatment not only inhibited the metabolic activities of glioblastoma cells but also promoted their apoptosis through the regulation of caspase 3 and PARP-1 in concentration- and time-dependent manners. Meanwhile, silibinin induced autophagy through upregulation of microtubule-associated protein a light chain 3- (LC3-) II. And autophagy inhibition with chloroquine, a lysosomotropic agent, significantly enhanced silibinin induced glioblastoma cell apoptosis. Moreover, silibinin dose-dependently downregulated the phosphorylation levels of mTOR at Ser-2448, p70S6K at Thr-389, and 4E-BP1 at Thr-37/46. Furthermore, the expression of YAP, the downstream effector of Hippo signal pathway, was also suppressed by silibinin. These results suggested that silibinin induced glioblastoma cell apoptosis concomitant with autophagy which might be due to simultaneous inhibition of mTOR and YAP and silibinin induced autophagy exerted a protective role against cell apoptosis in both A172 and SR cells.

Autophagy-inducing effect of pterostilbene: A prospective therapeutic/preventive option for skin diseases

Pterostilbene is a naturally occurring analog of resveratrol with many health benefits. These health benefits are associated with its antioxidant activity, anti-inflammatory effects, and chemopreventive effects attributed to its unique structure. The skin cancer chemopreventive potential of pterostilbene is supported by a variety of mechanistic studies confirming the anti-inflammatory effects in skin cancer models. Molecular biological studies have identified that pterostilbene targets pleotropic signaling pathways, including those involved in mitogenesis, cell cycle regulation, and apoptosis. Recently, pterostilbene has been reported to induce autophagy in cancer and normal cells. Through autophagy induction, the inflammatory-related skin diseases can be attenuated. This finding suggests the potential use of pterostilbene in the treatment and prevention of skin disorders via alleviating inflammatory responses by autophagy induction. This review summarizes the protective and therapeutic benefits of pterostilbene in skin diseases from the viewpoint of its antioxidant, anti-inflammatory, and autophagy-inducing effects. Novel underlying mechanisms regarding these effects are discussed. We proposed that pterostilbene, a promising natural product, can be used as a preventive and therapeutic agent for inflammation-related skin disorders through induction of autophagy.

Autophagy induction by silibinin positively contributes to its anti-metastatic capacity via AMPK/mTOR pathway in renal cell carcinoma

Silibinin, a dietary cancer chemopreventive flavonoid from the seeds of milk thistle, has been reported to exhibit anti-metastatic effects on renal cell carcinoma (RCC), but the mechanism underlying this phenomenon is not fully understood. The present study aimed at examining the potential role of autophagy in regulating silibinin-induced anti-metastatic effects on RCC cells. Using RCC ACHN and 786-O cells as a model system in vitro, we found that silibinin treatment increased the expression of LC3-II, resulted in the formation of autophagolysosome vacuoles, and caused a punctate fluorescence pattern with the monomeric red fluorescence protein-enhanced green fluorescence protein-LC3 (mRFP-EGFP-LC3) protein, which all are markers for cellular autophagy. Autophagy flux was induced by silibinin in RCC cells, as determined by LC3 turnover assay. Mechanically, the adenosine 5'-monophosphate activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway was identified as involved in regulation of silibinin-induced autophagy. Furthermore, autophagy induction was demonstrated to positively contribute to silibinin-induced anti-metastatic effects on RCC cells in vitro. Activation of autophagy enhanced silibinin-induced inhibition of migration and invasion of RCC cells, while inhibition of autophagy attenuated it. These findings thus provide new information about the potential link between autophagy and metastasis inhibition induced by silibinin, and the induction of autophagy may shed some light into future treatment strategies for metastatic RCC.

An Overview of Ultraviolet B Radiation-Induced Skin Cancer Chemoprevention by Silibinin

Skin cancer incidences are rising worldwide, and one of the major causative factors is excessive exposure to solar ultraviolet radiation (UVR). Annually, ~5 million skin cancer patients are treated in United States, mostly with nonmelanoma skin cancer (NMSC), which is also frequent in other Western countries. As sunscreens do not provide adequate protection against deleterious effects of UVR, additional and alternative chemoprevention strategies are urgently needed to reduce skin cancer burden. Over the last couple of decades, extensive research has been conducted to understand the molecular basis of skin carcinogenesis, and to identifying novel agents which could be useful in the chemoprevention of skin cancer. In this regard, several natural non-toxic compounds have shown promising efficacy in preventing skin carcinogenesis at initiation, promotion and progression stages, and are considered important in better management of skin cancer. Consistent with this, we and others have studied and established the notable efficacy of natural flavonolignan silibinin against UVB-induced skin carcinogenesis. Extensive pre-clinical animal and cell culture studies report strong anti-inflammatory, anti-oxidant, DNA damage repair, immune-modulatory and anti-proliferative properties of silibinin. Molecular studies have identified that silibinin targets pleotropic signaling pathways including mitogenic, cell cycle, apoptosis, autophagy, p53, NF-κB, etc. Overall, the skin cancer chemopreventive potential of silibinin is well supported by comprehensive mechanistic studies, suggesting its greater use against UV-induced cellular damages and photocarcinogenesis.

Posttranslational protein modifications by reactive nitrogen and chlorine species and strategies for their prevention and elimination

Proteins are subject to various posttranslational modifications, some of them being undesired from the point of view of metabolic efficiency. Prevention of such modifications is expected to provide new means of therapy of diseases and decelerate the process of aging. In this review, modifications of proteins by reactive nitrogen species and reactive halogen species, is briefly presented and means of prevention of these modifications and their sequelae are discussed, including the denitrase activity and inhibitors of myeloperoxidase.

New Therapeutic Potentials of Milk Thistle (Silybum marianum)

Silymarin is a bioflavonoid complex extract derived from dry seeds of Milk thistle [( Silybum marianum(L.) Gaernt. (Fam. Asteraceae/Compositaceae)] whose hepatoprotective effect has clinically been proved. Low toxicity, favorable pharmacokinetics, powerful antioxidant, detoxifying, preventive, protective and regenerative effects and side effects similar to placebo make silymarin extremely attractive and safe for therapeutic use. The medicinal properties of silymarin and its main component silibinin have been studied in the treatment of Alzheimer's disease, Parkinson's disease, sepsis, burns, osteoporosis, diabetes, cholestasis and hypercholesterolemia. Owing to its apoptotic effect, without cytotoxic effects, silymarin possesses potential applications in the treatment of various cancers. Silymarin is being examined as a neuro-, nephro- and cardio-protective in the damage of different etiologies due to its strong antioxidant potentials. Furthermore, it has fetoprotective (against the influence of alcohol) and prolactin effects and is safe to be used during pregnancy and lactation. Finally, the cosmetics industry is examining the antioxidant and UV-protective effects of silymarin. Further clinical studies and scientific evidence that silymarin and silibinin are effective in the therapy of various pathologies are indispensable in order to confirm their different flavonolignan pharmacological effects.

Crosstalk between apoptosis and autophagy: molecular mechanisms and therapeutic strategies in cancer

Both apoptosis and autophagy are highly conserved processes that besides their role in the maintenance of the organismal and cellular homeostasis serve as a main target of tumor therapeutics. Although their important roles in the modulation of tumor therapeutic strategies have been widely reported, the molecular actions of both apoptosis and autophagy are counteracted by cancer protective mechanisms. While apoptosis is a tightly regulated process that is implicated in the removal of damaged or unwanted cells, autophagy is a cellular catabolic pathway that is involved in lysosomal degradation and recycling of proteins and organelles, and thereby is considered an important survival/protective mechanism for cancer cells in response to metabolic stress or chemotherapy. Although the relationship between autophagy and cell death is very complicated and has not been characterized in detail, the molecular mechanisms that control this relationship are considered to be a relevant target for the development of a therapeutic strategy for tumor treatment. In this review, we focus on the molecular mechanisms of apoptosis, autophagy, and those of the crosstalk between apoptosis and autophagy in order to provide insight into the molecular mechanisms that may be essential for the balance between cell survival and death as well as their role as targets for the development of novel therapeutic approaches.

Silibinin protects murine fibroblast L929 cells from UVB-induced apoptosis through the simultaneous inhibition of ATM-p53 pathway and autophagy

Ultraviolet B (UVB) is a major cause of skin inflammation, leading to skin damage. Our previous in vivo study revealed that a natural flavonoid silibinin had marked anti-inflammatory effect on UVB-exposed murine skin. UVB exposure caused reduced autophagy in epidermis while it promoted autophagy in dermis. Nevertheless, silibinin inhibited the inflammatory flux in the skin epidermis as well as dermis through the modulation of autophagy. In order to elucidate the underlying protective mechanisms of silibinin for UVB damage on skin, separate studies on epidermis and dermis are helpful. Derived from the normal tissue of the mouse, L929 cells are capable of representing some characteristics of dermal cells. UVB irradiation caused L929 cell apoptosis in a time- and dose-dependent manner. Ataxia-telangiectasia-mutated (ATM) protein and p53 were activated to cause cell apoptosis, accompanying upregulation of the autophagic flux. The pharmacological inhibition of ATM, p53 and autophagy or the transfection with autophagy-associated protein-targeted small interfering RNAs showed that the UVB-activated ATM-p53 axis and autophagy formed a positive feedback loop, which synergistically promoted cell apoptosis. Silibinin treatment simultaneously repressed the activation of ATM-p53 and autophagy and thereby protected UVB-irradiated L929 cells from apoptotic death.