Sunlight UV-induced skin cancer relies upon activation of the p38α signaling pathway

Phosphorylation of PBK at Thr9 by CDK5 correlates with invasion of prolactinomas

CONTEXT

Prolactinomas are the most prevalent functional pituitary neuroendocrine tumors (PitNETs), and they are invasive to surrounding anatomic structures. The detailed mechanisms of invasion are not yet clear.

OBJECTIVE

We explored the role of PBK phosphorylation in the proliferation and invasion of prolactinomas and its possible mechanism.

RESULTS

We report that PBK directly binds to and is phosphorylated at Thr9 by cyclin-dependent kinase 5 (CDK5), which promotes GH3 cell EMT progression and proliferation. Phosphorylation of PBK at Thr9 (pPBK-T9) by CDK5 enhances the stability of PBK. p38 is one of the downstream targets of PBK, and its phosphorylation is reduced as pPBK-T9 increases in vivo and in vitro. Furthermore, we found that pPBK-T9 is highly expressed in invasive PitNETs and was significantly correlated with invasion by univariate and multivariate analyses.

CONCLUSIONS

Phosphorylation of PBK at Thr9 by CDK5 promotes cell proliferation and EMT progression in prolactinomas.

Inducible Keratinocyte Specific FGFR2 Deficiency Inhibits UVB-Induced Signaling, Proliferation, Inflammation, and Skin Carcinogenesis

A potential role for fibroblast growth factor receptor 2 (FGFR2) in cutaneous squamous cell carcinoma (cSCC) has been reported. To demonstrate the specific role of FGFR2 in UVB-induced skin carcinogenesis and development of cSCC, we generated a keratinocyte specific, tamoxifen inducible mouse model of FGFR2 deficiency. In this mouse model, topical application of 4-hydroxy tamoxifen led to the induction of Cre recombinase to delete FGFR2 in epidermal keratinocytes of both male and female transgenic mice. Analysis of epidermal protein lysates isolated from FGFR2 deficient mice exposed to UVB showed significant reductions of phospho-FGFR (pFGFR; Y653/654) and phospho-fibroblast growth factor receptor substrate 2α as well as downstream effectors of mTORC1 signaling. Phosphorylation of signal transducer and activators of transcription 1/3 was significantly reduced as well as levels of IRF-1, DUSP6, early growth response 1, and PD-L1 compared to the control groups. Keratinocyte-specific ablation of FGFR2 also significantly inhibited epidermal hyperproliferation, hyperplasia, and inflammation after exposure to UVB. Finally, keratinocyte-specific deletion of FGFR2 significantly inhibited UVB-induced cSCC formation. Collectively, the current data demonstrate an important role of FGFR2 in UVB-induced oncogenic signaling as well as development of cSCC. In addition, the current preclinical findings suggest that inhibition of FGFR2 signaling may provide a previously unreported strategy to prevent and/or treat UVB-induced cSCC.

Synthesis, in silico modelling, and in vitro biological evaluation of substituted pyrazole derivatives as potential anti-skin cancer, anti-tyrosinase, and antioxidant agents

Twenty-five azole compounds (P1-P25) were synthesised using regioselective base-metal catalysed and microwave-assisted approaches, fully characterised by high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR), and infrared spectra (IR) analyses, and evaluated for anticancer, anti-tyrosinase, and anti-oxidant activities in silico and in vitro. P25 exhibited potent anticancer activity against cells of four skin cancer (SC) lines, with selectivity for melanoma (A375, SK-Mel-28) or non-melanoma (A431, SCC-12) SC cells over non-cancerous HaCaT-keratinocytes. Clonogenic, scratch-wound, and immunoblotting assay data were consistent with anti-proliferative results, expression profiling therewith implicating intrinsic and extrinsic apoptosis activation. In a mushroom tyrosinase inhibition assay, P14 was most potent among the compounds (half-maximal inhibitory concentration where 50% of cells are dead, IC50 15.9 μM), with activity greater than arbutin and kojic acid. Also, P6 exhibited noteworthy free radical-scavenging activity. Furthermore, in silico docking and absorption, distribution, metabolism, excretion, and toxicity (ADMET) simulations predicted prominent-phenotypic actives to engage diverse cancer/hyperpigmentation-related targets with relatively high affinities. Altogether, promising early-stage hits were identified - some with multiple activities - warranting further hit-to-lead optimisation chemistry with further biological evaluations, towards identifying new skin-cancer and skin-pigmentation renormalising agents.

Therapeutic Implications of Caffeic Acid in Cancer and Neurological Diseases

Caffeic acid (CA) is found abundantly in fruits, vegetables, tea, coffee, oils, and more. CA and its derivatives have been used for many centuries due to their natural healing and medicinal properties. CA possesses various biological and pharmacological activities, including antioxidant, anti-inflammatory, anticancer, and neuroprotective effects. The potential therapeutic effects of CA are mediated via repression and inhibition of transcription and growth factors. CA possesses potential anticancer and neuroprotective effects in human cell cultures and animal models. However, the biomolecular interactions and pathways of CA have been described highlighting the target binding proteins and signaling molecules. The current review focuses on CA’s chemical, physical, and pharmacological properties, including antioxidant, anti-inflammatory, anticancer, and neuroprotective effects. We further described CA’s characteristics and therapeutic potential and its future directions.

BRD4 drives esophageal squamous cell carcinoma growth by promoting RCC2 expression

The low survival rate of esophageal squamous cell carcinoma patients is primarily attributed to technical limitations and a lack of insight regarding the molecular mechanisms contributing to its progression. Alterations in epigenetic modulators are critical to cancer development and prognosis. BRD4, a chromatin reader protein, plays an essential role in regulating oncogene expression. Here, we investigated the contributing role of BRD4 and its related mechanisms in the context of ESCC tumor progression. Our observations showed that BRD4 transcript and protein expression levels are significantly increased in ESCC patient tissues. Genetic or pharmacological inhibition of BRD4 suppressed ESCC cell proliferation in vitro and in vivo. Proteomic and transcriptomic analyses were subsequently used to deduce the potential targets of BRD4. Mechanistic studies showed that RCC2 is a downstream target of BRD4. Inhibition of either BRD4 or RCC2 resulted in decreased ESCC cell proliferation. The BRD4-TP73 interaction facilitated the binding of BRD4 complex to the promoter region of RCC2, and subsequently modulated RCC2 transcription. Furthermore, targeting BRD4 with inhibitors significantly decreased tumor volume in ESCC PDX models, indicating that BRD4 expression may contribute to tumor progression. Collectively, these findings suggest that BRD4 inhibition could be a promising strategy to treat ESCC by downregulating RCC2.

Ultraviolet Radiation and Basal Cell Carcinoma: An Environmental Perspective

Ultraviolet radiation (UVR) is a known carcinogen participated for the development of skin cancers. Solar UVR exposure, particularly ultraviolet B (UVB), is the mostly significant environmental risk factor for the occurrence and progress of basal cell carcinoma(BCC). Both cumulative and intermittent high-grade UVR exposure could promote the uncontrolled replication of skin cells. There are also exsiting other contributing environmental factors that combine with the UVR exposure to promote the development of BCC. DNA damage in formation of skin cancers is considered to be a result of UVR toxicity. It is UVR that could activate a series of oncogenes simultaneously inactivating tumor suppressor genes and aberrant proliferation and survival of keratinocytes that repair these damages. Furthermore, mounting evidence demonstrates that inflammatory responses of immune cells in the tumor microenvironment plays crucial role in the skin tumorigenesis as well. In this chapter, we will follow the function of UVR in the onset and development of BCC. We describe the factors that influence BCC induced by UVR, and also review the recent advances of pathogenesis of BCC induced by UVR from the genetic and inflammatory aspects.

Bestatin Cream Impairs Solar Simulated Light‒Driven Skin Inflammation and Skin Carcinogenesis in Mice

Leukotriene A4 hydrolase (LTA4H) is an enzyme that catalyzes the production of the inflammatory mediator leukotriene B4, which is involved in inflammatory responses mediated through the leukotriene B4/leukotriene B4 receptor type 1 (BLT1) signaling pathway. In this study, we investigated whether bestatin, an LTA4H inhibitor, could suppress skin acute inflammation and carcinogenesis. In the clinical sample, BLT1 was significantly induced in human skin tissues after acute solar simulated light (SSL) exposure. BLT1 and NF-κB p65 expressions were also increased in acute SSL‒induced mouse skin tissue. Furthermore, LTA4H and BLT1 were highly expressed in skin chronic inflammation and squamous cell carcinomas. More importantly, topical administration of bestatin cream dramatically inhibited BLT1 expression in acute SSL‒induced human skin tissues. BLT1 and NF-κB p65 expressions were also suppressed in acute SSL‒induced Lta4h-knockout and bestatin-treated mice skin tissues. Moreover, we conducted long-term prevention and therapeutic studies, which showed that bestatin significantly attenuated SSL-induced skin carcinogenesis. Mechanistic studies showed that bestatin inhibited skin carcinogenesis by suppressing cell proliferation and inducing cell apoptosis through LTA4H‒BLT1‒protein kinase B‒NF-κB p65 pathway. Overall, our results suggest that topical application of novel cream containing bestatin might open a helpful avenue for SSL-induced skin carcinogenesis.

Current status and future prospects of p38α/MAPK14 kinase and its inhibitors

P38α (which is also named MAPK14) plays a pivotal role in initiating different disease states such as inflammatory disorders, neurodegenerative diseases, cardiovascular cases, and cancer. Inhibitors of p38α can be utilized for treatment of these diseases. In this article, we reviewed the structural and biological characteristics of p38α, its relationship to the fore-mentioned disease states, as well as the recently reported inhibitors and classified them according to their chemical structures. We focused on the articles published in the literature during the last decade (2011-2020).

PBK phosphorylates MSL1 to elicit epigenetic modulation of CD276 in nasopharyngeal carcinoma

CD276 (also known as B7-H3, an immune checkpoint molecule) is aberrantly overexpressed in many cancers. However, the upregulation mechanism and in particular, whether oncogenic signaling has a role, is unclear. Here we demonstrate that a pro-oncogenic kinase PBK, the expression of which is associated with immune infiltration in nasopharyngeal carcinoma (NPC), stimulates the expression of CD276 epigenetically. Mechanistically, PBK phosphorylates MSL1 and enhances the interaction between MSL1 and MSL2, MSL3, and KAT8, the components of the MSL complex. As a consequence, PBK promotes the enrichment of MSL complex on CD276 promoter, leading to the increased histone H4 K16 acetylation and the activation of CD276 transcription. In addition, we show that CD276 is highly upregulated and associated with immune infiltrating levels in NPC. Collectively, our findings describe a novel PBK/MSL1/CD276 signaling axis, which may play an important role in immune evasion of NPC and may be targeted for cancer immunotherapy.

Ultraviolet irradiation-induced inhibition of histone deacetylase 4 increases the expression of matrix metalloproteinase-1 but decreases that of type I procollagen via activating JNK in human dermal fibroblasts

BACKGROUND

Ultraviolet (UV) irradiation is the main contributing factor for skin aging. UV irradiation induces epigenetic changes in skin. It increases the activity of histone acetylases (HATs) but decreases that of histone deacetylases (HDACs).

OBJECTIVE

We aimed to investigate alterations in all classes of HDACs and sirtuins (SIRTs) in response to UV irradiation, and determine the HDACs regulating the expressions of matrix metalloproteinase 1 (MMP-1) and type I procollagen.

METHODS

Primary human dermal fibroblasts were UV irradiated. HDAC4 was knocked-down or overexpressed to investigate its effect on the expression of MMP-1 and type I procollagen. The mRNA and protein levels were analyzed by quantitative real-time polymerase chain reaction and western blotting.

RESULTS

Among 11 HDACs and 7 SIRTs, we found that the expression of HDAC4, HDAC5, HDAC6, HDAC7, HDAC8, HDAC11, SIRT2, and SIRT3 were significantly and consistently reduced by UV at both mRNA and protein levels. Among these, the reduction of HDAC4 was responsible for the basal and UV-induced increase in the expression of MMP-1 and decrease in that of type I procollagen. Furthermore, the reduced HDAC4 could activate c-Jun N-terminal kinase (JNK), resulting in an increase in MMP-1 and decrease in type I procollagen.

CONCLUSIONS

UV treatment decreases the expression of HDACs and SIRTs in dermal fibroblasts; in particular, the UV-induced reduction in the expression of HDAC4 might play an important role in regulating the expression of MMP-1 and type I procollagen.

Evaluating antitumor activity of antiglypican-3 therapy in experimentally induced skin cancer in mice

Glypican-3 (GPC3) is considered as a cell surface heparan sulfate proteoglycan. It is overexpressed in skin cancer and promotes tumor progression and pathogenicity. Therefore, we aimed to find out the therapeutic effects of immuno-suppressing GPC3 in skin cancer experimentally induced in mice as well as to underline molecular mechanisms especially inflammatory and apoptotic pathways. Skin cancer was experimentally induced in mice by repeated rubbing of mice skin with 7,12-dimethylbenz (a) anthracene. Mice were injected with anti-GPC3. Skin samples were isolated to investigate the gene and protein expression of GPC3, Wnt-1, NFκB, TNF-α, IGF-1, p38 MAPK and caspase-3 using PCR, Western blot and ELISA. Moreover, skin sections were stained with hematoxylin and eosin. Treating skin cancer mice with anti-GPC3 significantly blocked GPC3, which is accompanied by amelioration of skin cancer-induced increase in the numbers of tumors and scratching behavior. Moreover, anti-GPC3 attenuated skin cancer-induced increase in the expression of Wnt-1, NFκB, TNF-α, IGF-1, p38 MAPK and caspase-3. In parallel, anti-GPC3 reduced degeneration of melanocyte cells and reduced phagocytic cells epidermal hyperplasia and dysplasia in skin sections stained with hematoxylin and eosin stain. In conclusion, anti-GPC3 produced anti-tumor effects against skin cancer, which can be explained by reduction in both inflammatory and apoptotic pathways. Targeting GPC3 is a promising therapeutic approach for skin cancer.

Copper/Zinc Superoxide Dismutase in Human Skin: Current Knowledge

Superoxide dismutase is widespread in the human body, including skin and its appendages. Here, we focus on human skin copper/zinc superoxide dismutase, the enzyme that protects skin and its appendages against reactive oxygen species. Human skin copper/zinc superoxide dismutase resides in the cytoplasm of keratinocytes, where up to 90% of cellular reactive oxygen species is produced. Factors other than cell type, such as gender, age and diseased state influence its location in skin tissues. We review current knowledge of skin copper/zinc superoxide dismutase including recent studies in an attempt to contribute to solving the question of its remaining unexplained functions. The research described here may be applicable to pathologies associated with oxidative stress. However, recent studies on copper/zinc superoxide dismutase in yeast reveal that its predominant function may be in signaling pathways rather than in scavenging superoxide ions. If confirmed in the skin, novel approaches might be developed to unravel the enzyme's remaining mysteries.

Suppression of the solar ultraviolet-induced skin carcinogenesis by TOPK inhibitor HI-TOPK-032

Nonmelanoma skin cancer (NMSC) such as cutaneous squamous cell carcinoma (cSCC) is caused by solar ultraviolet (SUV) exposure and is the most common cancer in the United States. T-LAK cell-originated protein kinase (TOPK), a serine-threonine kinase is activated by SUV irradiation and involved in skin carcinogenesis. Strategies with research focusing on the TOPK signaling pathway and targeted therapy in skin carcinogenesis may helpful for the discovery of additional treatments against skin cancer. In this study, we found that TOPK can directly bind to and phosphorylate c-Jun (as one of the core member of AP-1) at Ser63 and Ser73 after SSL exposure in a JNKs-independent manner. TOPK knocking down, or HI-TOPK-032 (TOPK specific inhibitor) attenuated colony formation and cell proliferation of skin cancer cells. Phosphorylated levels of c-Jun were overexpressed in human AK and cSCC compared with normal skin tissues, and HI-TOPK-032 inhibited the phosphorylation of c-Jun in SCC cell line in a dose-dependent manner. Furthermore, HI-TOPK-032 decreased SSL-induced AP-1 transactivation activity. Moreover, acute SSL-induced inflammation was attenuated by the topical application of HI-TOPK-032 in SKH1 hairless mice. Importantly, HI-TOPK-032 suppressed chronic SSL-induced skin carcinogenesis and c-Jun phosphorylation levels in SKH1 hairless mice. Our results demonstrate that TOPK can phosphorylate and activate c-Jun at Ser63 and Ser73 in the process of skin carcinogenesis and HI-TOPK-032 could be used as a potential chemopreventive drug against cSCC development.

Gossypetin Inhibits Solar-UV Induced Cutaneous Basal Cell Carcinoma Through Direct Inhibiting PBK/TOPK Protein Kinase

BACKGROUND

Skin photoaging, skin inflammation and skin cancer are related with excessive exposure to solar UV. PDZ-binding kinase/T-LAK cell-originated protein kinase (PBK/TOPK), a member of the serine/threonine protein kinase, which regulates the signaling cascades of p38 mitogen-activated protein kinase (p38 MAPK) and extracellular signal regulated kinase 1/2 (ERK1/2). PBK/TOPK plays a significant role in solar-UV-induced cutaneous basal cell carcinoma (BCC), and targeting PBK/TOPK can be supposed to treat and prevent cutaneous BCC.

METHODS

The pathological feature and the expression level of PBK/TOPK in cutaneous BCC tissues of human were studied in clinical samples. SUV-induced the phosphorylation of p38 MAPK and ERK1/2 were demonstrated ex vivo. Moreover, the interaction between Gossypetin and PBK/TOPK were detected by in vitro kinase assay and Microscale thermophoresis (MST) assay. Furthermore, the effect of Gossypetin to solar UV-induced the activity of PBK/TOPK were detected ex vivo and in vivo.

RESULTS

The clinical samples showed that the expression levels of PBK/TOPK, phosphor-p38 MAPK and phosphor- ERK1/2 were up-regulated in cutaneous BCC tissues of human. The expression of phosphor-p38 MAPK or phosphor-ERK1/2 increased in a dose and time dependent manner after solar UV treatment in HaCaT cells. MTT cytotoxicity assay results showed that Gossypetin has no effect on HaCaT cells. In vitro kinase assay and MST assay results showed that Gossypetin bound with PBK/TOPK and suppressed PBK/TOPK activity. Ex vivo results showed Gossypetin inhibited solar UV-induced phosphorylation of PBK/TOPK, p38 MAPK, ERK1/2 and H2AX by suppressing PBK/TOPK activity. In vivo test results indicated that Gossypetin suppressed solar UV-induced increase of PBK/TOPK, phosphor-p38 MAPK, phosphor-ERK1/2 and phosphor- H2AX in SKH-1 hairless mice.

CONCLUSION

Our data demonstrated that Gossypetin can alleviate solar-UV-induced cutaneous BCC by blocking PBK/TOPK, and Gossypetin could be a remarkable agent for treating solar-UV induced cutaneous basal cell carcinoma.

Requirement for epithelial p38α in KRAS-driven lung tumor progression

Malignant transformation entails important changes in the control of cell proliferation through the rewiring of selected signaling pathways. Cancer cells then become very dependent on the proper function of those pathways, and their inhibition offers therapeutic opportunities. Here we identify the stress kinase p38α as a nononcogenic signaling molecule that enables the progression of Kras^G12V-driven lung cancer. We demonstrate in vivo that, despite acting as a tumor suppressor in healthy alveolar progenitor cells, p38α contributes to the proliferation and malignization of lung cancer epithelial cells. We show that high expression levels of p38α correlate with poor survival in lung adenocarcinoma patients, and that genetic or chemical inhibition of p38α halts tumor growth in lung cancer mouse models. Moreover, we reveal a lung cancer epithelial cell-autonomous function for p38α promoting the expression of TIMP-1, which in turn stimulates cell proliferation in an autocrine manner. Altogether, our results suggest that epithelial p38α promotes Kras^G12V-driven lung cancer progression via maintenance of cellular self-growth stimulatory signals.

Photoprotection of maqui berry against ultraviolet B-induced photodamage in vitro and in vivo

Maqui berry extracts could ameliorate oxidative stress, cellular DNA damage, and inflammation induced by UVB-irradiation in vitro and in vivo.

Ornithine decarboxylase inhibition downregulates multiple pathways involved in the formation of precancerous lesions of esophageal squamous cell cancer

The high incidence and mortality of esophageal squamous cell cancer (ESCC) is a major health problem worldwide. Precancerous lesions of ESCC may either progress to cancer or revert to normal epithelium with appropriate interventions; the bidirectional instability of the precancerous lesions of ESCC provides opportunities for intervention. Reports suggest that the upregulation of ornithine decarboxylase (ODC) is closely related to carcinogenesis. In this study, we investigated whether ODC may act as a target for chemoprevention in ESCC. Immunohistochemistry (IHC) assays indicate that ODC expression is higher in esophageal precancerous lesions compared with normal tissue controls. Its overexpression promotes cell proliferation and transformation of normal esophageal epithelial cells, and its activity is increased after N-nitrosomethylbenzylamine (NMBA) induction in Shantou human embryonic esophageal cell line (SHEE) and human immortalized cells (Het1A) cells. In addition, p38 α, extracellular regulated kinase (ERK1/2) in the mitogen-activated protein kinase pathway and protein kinase B (AKT)/mammalian target of rapamycin (mTOR)/ribosomal protein S6 kinase (p70S6K) pathways are activated in response to NMBA treatment. Difluoromethylornithine (DFMO) is an ODC inhibitor, which inhibits NMBA-induced activation of p38 α, ERK1/2 and AKT/mTOR/p70S6K pathways; this has been verified by Western blotting. DFMO was also found to suppress the development of esophageal precancerous lesions in an NMBA-induced rat model; IHC demonstrated p38 α, ERK1/2, and AKT/mTOR/p70S6K pathways to be downregulated in these rats. These findings indicate the mechanisms by which ODC inhibition suppresses the development of esophageal precancerous lesions by downregulating p38 α, ERK1/2, and AKT/mTOR/p70S6k signaling pathways, ODC may be a potential target for chemoprevention in ESCC.

Roles of p38α and p38β mitogen‑activated protein kinase isoforms in human malignant melanoma A375 cells

Skin cancer is one of the most common cancers worldwide. Melanoma accounts for ~5% of skin cancers but causes the large majority of skin cancer‑related deaths. Recent discoveries have shown that the mitogen‑activated protein kinase (MAPK) signaling pathway is critical for melanoma development and progression. Many oncogenic pathways that cause melanoma tumorigenesis have been identified, most of which are due to RAF/MEK/ERK (MAPK) pathway activation. However, the precise role of p38 remains unclear. Using specific short hairpin (sh) RNA to silence p38α and p38β, the present findings demonstrated that p38α was a crucial factor in regulating cell migration in the A375 melanoma cell line. Silencing p38α downregulated the expression of epithelial‑mesenchymal transition markers, such as matrix metallopeptidase (MMP) 2, MMP9, twist family bHLH transcription factor 1, snail family transcriptional repressor 1 and vimentin, while mesenchymal‑epithelial transition markers, such as E‑cadherin, were upregulated. Of note, the results also demonstrated that p38α silencing impaired vascular endothelial growth factor expression, which regulates tumor angiogenesis. Furthermore, p38α knockdown inhibited cell proliferation in melanoma cells. In addition, silencing p38α induced senescence‑like features, but not cell cycle arrest. Expression of the senescence markers p16, p21, p53 and β‑galactosidase was upregulated, and an increase in the number of senescence‑associated β‑galactosidase‑positive cells was observed in a p38α knockdown stable clone. However, no significant difference was found between control and p38β stable knockdown cells. Taken together, the present results suggested that p38α knockdown impaired migration and proliferation, and increased senescence, in A375 melanoma cells. However, p38β may not be involved in melanoma tumorigenesis. Therefore, targeting p38α may be a valuable approach towards inhibiting tumor growth and metastasis in patients with melanoma.

Heat shock proteins in the physiology and pathophysiology of epidermal keratinocytes

Heat shock proteins (HSPs), a large group of highly evolutionary conserved proteins, are considered to be main elements of the cellular proteoprotection system. HSPs are encoded by genes activated during the exposure of cells to proteotoxic factors, as well as by genes that are expressed constitutively under physiological conditions. HSPs, having properties of molecular chaperones, are involved in controlling/modulation of multiple cellular and physiological processes. In the presented review, we summarize the current knowledge on HSPs in the biology of epidermis, the outer skin layer composed of stratified squamous epithelium. This tissue has a vital barrier function preventing from dehydratation due to passive diffusion of water out of the skin, and protecting from infection and other environmental insults. We focused on HSPB1 (HSP27), HSPA1 (HSP70), HSPA2, and HSPC (HSP90), because only these HSPs have been studied in the context of physiology and pathophysiology of the epidermis. The analysis of literature data shows that HSPB1 plays a role in the regulation of final steps of keratinization; HSPA1 is involved in the cytoprotection, HSPA2 contributes to the early steps of keratinocyte differentiation, while HSPC is essential in the re-epithelialization process. Since HSPs have diverse functions in various types of somatic tissues, in spite of multiple investigations, open questions still remain about detailed roles of a particular HSP isoform in the biology of epidermal keratinocytes.

1,2-Bis[(3-Methoxyphenyl)Methyl]Ethane-1,2-Dicarboxylic Acid Reduces UVB-Induced Photodamage In Vitro and In Vivo

This study investigated the effects and mechanisms of 1,2-bis[(3-methoxyphenyl)methyl]ethane-1,2-dicarboxylic acid (S4), a sesamin derivative, on anti-inflammation and antiphotoaging in vitro and in vivo. Human skin fibroblasts were treated with S4 and did not show cytotoxicity under concentrations of 5–50 µM. In addition, S4 also reduced ultraviolet (UV)B-induced intracellular reactive oxygen species (ROS) production. Additionally, S4 inhibited UVB-induced phosphorylation of mitogen-activated protein (MAP) kinases, activator protein-1 (AP-1), and matrix metalloproteinases (MMPs) overexpression. Furthermore, S4 also inhibited UVB-induced Smad7 protein expression and elevated total collagen content in human dermal fibroblasts. For anti-inflammatory activity, S4 inhibited UVB-induced nitric oxide synthase (i-NOS) and cyclooxygenase (COX)-2 protein expression and inhibited nuclear factor-kappaB (NF-ĸB) translocation into the nucleus. S4 ameliorated UVB-induced erythema and wrinkle formation in hairless mice. On histological observation, S4 also ameliorated UVB-induced epidermal hyperplasia and collagen degradation. S4 reduced UVB-induced MMP-1, interleukin (IL)-6, and NF-ĸB expression in the mouse skin. The results indicated that S4 had antiphotoaging and anti-inflammatory activities, protecting skin from premature aging.

Protective Effects of Sesamin against UVB-Induced Skin Inflammation and Photodamage In Vitro and In Vivo

Ultraviolet (UV) exposure has been demonstrated as the most critical factor causing extrinsic skin aging and inflammation. This study explored the protective effects and mechanisms of sesamin against skin photodamage. Sesamin reduced intracellular reactive oxygen species production after UVB irradiation in human dermal fibroblasts. The sesamin treatment attenuated mitogen-activated protein (MAP) kinase phosphorylation and matrix metalloproteinase (MMPs) overexpression induced by UVB exposure, and it significantly enhanced the tissue inhibitor of metalloproteinase-1 protein expression. Sesamin also elevated the total collagen content in human fibroblasts by inhibiting UVB-induced mothers against decapentaplegic homolog 7 (Smad7) protein expression. Sesamin reduced UVB-induced inducible nitric oxide synthase (i-NOS) and cyclooxygenase-2 (COX-2) overexpression and inhibited nuclear factor-kappa B (NF-κB) translocation. Moreover, sesamin may regulate the c-Jun N-terminal kinases (JNK) and p38 MAP kinase pathways, which inhibit COX-2 expression. Sesamin could reduce UVB-induced inflammation, epidermal hyperplasia, collagen degradation, and wrinkle formation in hairless mice. It also reduced MMP-1, interleukin (IL-1), i-NOS, and NF-κB in the mouse skin. These results demonstrate that sesamin had antiphotodamage and anti-inflammatory activities. Sesamin has potential for use as a skin protection agent in antiphotodamage and skin care products.

The effects of HSP27 against UVB-induced photoaging in rat skin

Skin photoaging refers to the phenomenon of skin aging or accelerated aging as a result of long-term UV exposure. Ultraviolet radiation can lead to DNA damage, cell apoptosis, cell growth inhibition and carcinogenic effects. Evidence suggests that hsp27 can protect cells from apoptosis induced by various stimuli in vivo and in vitro. However, modulation in hsp27 expression toward skin protection against UVB treatment has not been investigated clearly. In this study, we aimed to investigate the effects of hsp27 against UVB-induced photoaging in rat skin and to explore the underlying mechanisms. In the present study, we identified that the level of hsp27 increased after UVB irradiation induced chronic photoaging rat model. In order to investigate the function of hsp27 in UVB-induced skin photoaging, we used adeno-associated virus (AAV) to specificity reduce the expression of hsp27 in rat skin. In contrast to UVB group, we found that collagen fibers were disorganized and elastic fibers were thickened and twisted in UVB-AAV group. In the UVB-AAV group, reduced hsp27 enhanced the oxidative stress. Aging markers (SA-β-Gal staining and the protein levels of p16, p53, p21) were significantly changed in the hsp27 decreased group. However, in hsp27 deletion group, the expression of antiapoptotic factor bcl-2 was decreased, while the apoptosis factor bax was increased after UVB irradiation. These findings suggested that hsp27 was involved in oxidative stress, aging and apoptosis of skin after UV exposure. Management the expression of hsp27 can be used as a potential intervention method to alleviate UVB-induced skin damage.

The protein kinase p38α destabilizes p63 to limit epidermal stem cell frequency and tumorigenic potential

The molecular circuitry directing tissue development and homeostasis is hardwired by genetic programs but may also be subject to fine-tuning or major modification by environmental conditions. It remains unclear whether such malleability is at work-particularly in tissues directly in contact with the environment-and contributes to their optimal maintenance and resilience. The protein kinase p38α is activated by physiological cues that signal tissue damage and neoplastic transformation. Here, we found that p38α phosphorylated and thereby destabilized p63, a transcription factor essential for epidermal development. Through this regulatory mechanism, p38α limited the frequency of keratinocytes with stem cell properties and tumorigenic potential. Correspondingly, epidermal loss of p38α expression or activity promoted or correlated with carcinogenesis in mouse and human skin, respectively. Genetic mouse models revealed a tumorigenic mechanism from p38α loss through p63-mediated suppression of the matrix metalloprotease MMP13. These findings illustrate a previously uncharacterized epidermal tumor-suppressive mechanism in which stress-activated signaling induces the contraction of stem cell-like keratinocyte pools.

Bakuchiol suppresses proliferation of skin cancer cells by directly targeting Hck, Blk, and p38 MAP kinase

Bakuchiol is a meroterpene present in the medicinal plant Psoralea corylifolia, which has been traditionally used in China, India, Japan and Korea for the treatment of premature ejaculation, knee pain, alopecia spermatorrhea, enuresis, backache, pollakiuria, vitiligo, callus, and psoriasis. Here, we report the chemopreventive properties of bakuchiol, which acts by inhibiting epidermal growth factor (EGF)-induced neoplastic cell transformation. Bakuchiol also decreased viability and inhibited anchorage-independent growth of A431 human epithelial carcinoma cells. Bakuchiol reduced A431 xenograft tumor growth in an in vivo mouse model. Using kinase profiling, we identified Hck, Blk and p38 mitogen activated protein kinase (MAPK) as targets of bakuchiol, which directly bound to each kinase in an ATP-competitive manner. Bakuchiol also inhibited EGF-induced signaling pathways downstream of Hck, Blk and p38 MAPK, including the MEK/ERKs, p38 MAPK/MSK1 and AKT/p70S6K pathways. This report is the first mechanistic study identifying molecular targets for the anticancer activity of bakuchiol and our findings indicate that bakuchiol exhibits potent anticancer activity by targeting Hck, Blk and p38 MAPK.

Astragalin Attenuates UVB Radiation-induced Actinic Keratosis Formation

BACKGROUND

Actinic Keratosis (AK), is the most common precancerous skin lesion induced by the excessive Ultraviolet B (UVB) and is a significant threat to the public health. UVB exposure causes oxidative DNA damage and is considered to be a significant contributor to AK and subsequent development of skin cancer. Besides, activation of p38 MAPK also plays a significant role in the development of AK.

OBJECTIVE

This study aimed at the development of a nature compound which can inhibit UVB-induced AK.

METHOD

MTS Cell Proliferation Assay Kit was used to detect the toxicity of astragalin. HE-staining, Immunohistochemical, Western blot and Enzyme Linked Immunosorbent Assay were applied to examine the clinicopathologic feature of AK and the change of p38 MAPK signal pathway treated with astraglin under the condition of UVB in vitro and in vivo. Results：In our clinical findings revealed that p38 MAPK, phospho-MSK1, and γ -H2AX were significantly highly expressed in human AK tissue than the normal healthy skin tissue. Moreover, in vitro studies showed that UVB induced the phospho-MSK1 and γ-H2AX in a time- and dose-dependent manner in HaCaT cells. Further, in vitro kinase assay demonstrated that astragalin could directly bind to p38 MAPK and suppress p38 MAPK activity. Furthermore, astragalin exhibited no toxicity and suppressed the UVB-induced expression of phospho- MSK1 and γ -H2AX by suppressing p38 MAPK activity in a time-dependent and dose-dependent manner in HaCaT cells. The in vivo studies with animal UV model demonstrated that astragalin inhibited UVB-induced expression of phospho-MSK1 and γ-H2AX in Babl/c mice.

CONCLUSION

These results suggested that p38 MAPK is a direct valid molecular target of astragalin for the attenuation of UVB-induced AK. Furthermore, astragalin could be a potential promising novel natural therapeutic agent for the prevention and management of UVB-induced AK with high target specificity and low toxicity.

Cefradine blocks solar-ultraviolet induced skin inflammation through direct inhibition of T-LAK cell-originated protein kinase

Skin inflammation, and skin cancer induced by excessive solar ultraviolet (SUV) is a great threat to human health. SUV induced skin inflammation through activating p38 mitogen-activated protein kinase (p38) and c-Jun N-termeinal kinases (JNKs). T-LAK cell-originated protein kinase (TOPK) plays an important role in this process. Herein, the clinical data showed TOPK, phospho-p38, phospho-JNKs were highly expressed in human solar dermatitis. Ex vivo studies showed that SUV induced the phosphorylation of p38 and JNKs in HaCat and JB6 cells in a dose and time dependent manner. Molecule docking model indicated cefradine, an FDA-approved cephalosporin antibiotic, directly binds with TOPK. The result of in vitro binding assay verified cefradine can directly bind with TOPK. In vitro kinase results showed cefradine can inhibit TOPK activity. Ex vivo studies further showed cefradine inhibited SUV-induced the phosphorylation level of p38, JNKs and H2AX through inhibiting TOPK activity in a dose and time dependent manner, and cefradine inhibited the secretion of IL6 and TNF-α in HaCat and JB6 cells. In vivo studies showed that cefradine down-regulated SUV-induced the phosphorylation of p38, JNKs and H2AX and inhibited the secretion of IL6 and TNF-α in Babl/c mice. These results indicated that cefradine can inhibit SUV-induced skin inflammation by blocking TOPK signaling pathway, and TOPK is an effective target for suppressing inflammation induced by SUV irradiation.

Monitoring UV-induced signalling pathways in an ex vivo skin organ culture model using phospho-antibody array

We investigated UV-induced signalling in an ex vivo skin organ culture model using phospho-antibody array. Phosphorylation modulations were analysed in time-course experiments following exposure to solar-simulated UV and validated by Western blot analyses. We found that UV induced P-p38 and its substrates, P-ERK1/2 and P-AKT, which were previously shown to be upregulated by UV in cultured keratinocytes and in vivo human skin. This indicates that phospho-antibody array applied to ex vivo skin organ culture is a relevant experimental system to investigate signalling events following perturbations. As the identified proteins are components of pathways implicated in skin tumorigenesis, UV-exposed skin organ culture model could be used to investigate the effect on these pathways of NMSC cancer drug candidates. In addition, we found that phospho-HCK is induced upon UV exposure, producing a new candidate for future studies investigating its role in the skin response to UV and UV-induced carcinogenesis.

Metformin inhibits esophageal squamous cell carcinoma-induced angiogenesis by suppressing JAK/STAT3 signaling pathway

Although it has been known that the tumor microenvironment affects angiogenesis, the precise mechanism remains unclear. In this study, we simulated the microenvironment of human esophageal squamous cell carcinoma (ESCC) by tumor conditioned medium (TCM) to assess the influence on normal endothelial cells (NECs). We found that the TCM-induced NECs showed enhanced angiogenic properties, such as migration, invasion and tube formation. Moreover, the TCM-induced NECs expressed tumor endothelial cells (TECs) markers at higher levels, which indicated that TCM probably promoted tumor angiogenesis by coercing NECs to change toward TECs. The microarray gene expression analysis indicated that TCM induced great changes in the genome of NECs and altered many regulatory networks, especially c-MYC and JAK/STAT3 signaling pathway. More importantly, we investigated the anti-angiogenic effect of metformin, and found that metformin abrogated the ESCC microenvironment-induced transition of NECs toward TECs by inhibiting JAK/STAT3/c-MYC signaling pathway. Furthermore, we verified the anti-angiogenic activity of metformin in vivo by a human ESCC patient-derived xenograft (PDX) mouse model for the first time. Taken together, our research provides a novel mechanism for the anti-angiogenic effect of metformin, and sets an experimental basis for the development of new anti-angiogenic drugs by blocking the transition of NECs toward TECs, which possibly open new avenues for targeted treatment of cancer.

ADA-07 Suppresses Solar Ultraviolet-Induced Skin Carcinogenesis by Directly Inhibiting TOPK

Cumulative exposure to solar ultraviolet (SUV) irradiation is regarded as the major etiologic factor in the development of skin cancer. The activation of the MAPK cascades occurs rapidly and is vital in the regulation of SUV-induced cellular responses. The T-LAK cell-originated protein kinase (TOPK), an upstream activator of MAPKs, is heavily involved in inflammation, DNA damage, and tumor development. However, the chemopreventive and therapeutic effects of specific TOPK inhibitors in SUV-induced skin cancer have not yet been elucidated. In the current study, ADA-07, a novel TOPK inhibitor, was synthesized and characterized. Pull-down assay results, ATP competition, and in vitro kinase assay data revealed that ADA-07 interacted with TOPK at the ATP-binding pocket and inhibited its kinase activity. Western blot analysis showed that ADA-07 suppressed SUV-induced phosphorylation of ERK1/2, p38, and JNKs and subsequently inhibited AP-1 activity. Importantly, topical treatment with ADA-07 dramatically attenuated tumor incidence, multiplicity, and volume in SKH-1 hairless mice exposed to chronic SUV. Our findings suggest that ADA-07 is a promising chemopreventive or potential therapeutic agent against SUV-induced skin carcinogenesis that acts by specifically targeting TOPK. Mol Cancer Ther; 16(9); 1843-54. ©2017 AACR.

Phytochemicals for the Prevention of Photocarcinogenesis

Ultraviolet (UV) exposure has an array of damaging effects and is the main cause of skin cancer in humans. Nonmelanoma skin cancer (NMSC), including basal cell carcinoma and squamous cell carcinoma, is the most common type of cancer. Incidence of NMSC has increased due to greater UV radiation, increased life expectancy and other changes in lifestyle; the annual cost of skin cancer treatment in the United States has increased concurrently to around eight billion dollars. Because of these trends, novel approaches to skin cancer prevention have become an important area of research to decrease skin cancer morbidity and defray the costs associated with treatment. Chemoprevention aims to prevent or delay the development of skin cancer through the use of phytochemicals. Use of phytochemicals as chemopreventive agents has gained attention due to their low toxicity and anticarcinogenic properties. Phytochemicals also exhibit antioxidant, anti-inflammatory and antiproliferative effects which support their use as chemopreventive agents, particularly for skin cancer. Preclinical and human studies have shown that phytochemicals decrease UV-induced skin damage and photocarcinogenesis. In this review article, we discuss the selected phytochemicals that may prevent or delay UV-induced carcinogenesis and highlight their potential use for skin protection.

Diet phytochemicals and cutaneous carcinoma chemoprevention: A review

Cutaneous carcinoma, which has occupied a peculiar place among worldwide populations, is commonly responsible for the considerably increasing morbidity and mortality rates. Currently available medical procedures fail to completely avoid cutaneous carcinoma development or to prevent mortality. Cancer chemoprevention, as an alternative strategy, is being considered to reduce the incidence and burden of cancers through chemical agents. Derived from dietary foods, phytochemicals have become safe and reliable compounds for the chemoprevention of cutaneous carcinoma by relieving multiple pathological processes, including oxidative damage, epigenetic alteration, chronic inflammation, angiogenesis, etc. In this review, we presented comprehensive knowledges, main molecular mechanisms for the initiation and development of cutaneous carcinoma as well as effects of various diet phytochemicals on chemoprevention.

TRAF1 Is Critical for DMBA/Solar UVR-Induced Skin Carcinogenesis

TRAF1 is a member of the TRAF protein family, which regulates the canonical and noncanonical NF-κB signaling cascades. Although aberrant TRAF1 expression in tumors has been reported, the role of TRAF1 remains elusive. Here, we report that TRAF1 is required for solar UV-induced skin carcinogenesis. Immunohistochemical analysis showed that TRAF1 expression is up-regulated in human actinic keratosis and squamous cell carcinoma. In vivo studies indicated that TRAF1 expression levels in mouse skin are induced by short-term solar UV irradiation, and a long-term skin carcinogenesis study showed that deletion of TRAF1 in mice results in a significant inhibition of skin tumor formation. Moreover, we show that TRAF1 is required for solar UV-induced extracellular signal-regulated kinase-5 (ERK5) phosphorylation and the expression of AP-1 family members (c-Fos/c-Jun). Mechanistic studies showed that TRAF1 expression enhances the ubiquitination of ERK5 on lysine 184, which is necessary for its kinase activity and AP-1 activation. Overall, our results suggest that TRAF1 mediates ERK5 activity by regulating the upstream effectors of ERK5 and also by modulating its ubiquitination status. Targeting TRAF1 function might lead to strategies for preventing and treating skin cancer.

Trends in Regenerative Medicine: Repigmentation in Vitiligo Through Melanocyte Stem Cell Mobilization

Vitiligo is the most frequent human pigmentary disorder, characterized by progressive autoimmune destruction of mature epidermal melanocytes. Of the current treatments offering partial and temporary relief, ultraviolet (UV) light is the most effective, coordinating an intricate network of keratinocyte and melanocyte factors that control numerous cellular and molecular signaling pathways. This UV-activated process is a classic example of regenerative medicine, inducing functional melanocyte stem cell populations in the hair follicle to divide, migrate, and differentiate into mature melanocytes that regenerate the epidermis through a complex process involving melanocytes and other cell lineages in the skin. Using an in-depth correlative analysis of multiple experimental and clinical data sets, we generated a modern molecular research platform that can be used as a working model for further research of vitiligo repigmentation. Our analysis emphasizes the active participation of defined molecular pathways that regulate the balance between stemness and differentiation states of melanocytes and keratinocytes: p53 and its downstream effectors controlling melanogenesis; Wnt/β-catenin with proliferative, migratory, and differentiation roles in different pigmentation systems; integrins, cadherins, tetraspanins, and metalloproteinases, with promigratory effects on melanocytes; TGF-β and its effector PAX3, which control differentiation. Our long-term goal is to design pharmacological compounds that can specifically activate melanocyte precursors in the hair follicle in order to obtain faster, better, and durable repigmentation.

Ultra-Porous Nanoparticle Networks: A Biomimetic Coating Morphology for Enhanced Cellular Response and Infiltration

Orthopedic treatments are amongst the most common cause of surgery and are responsible for a large share of global healthcare expenditures. Engineering materials that can hasten bone integration will improve the quality of life of millions of patients per year and reduce associated medical costs. Here, we present a novel hierarchical biomimetic coating that mimics the inorganic constituent of mammalian bones with the aim of improving osseointegration of metallic implants. We exploit the thermally-driven self-organization of metastable core-shell nanoparticles during their aerosol self-assembly to rapidly fabricate robust, ultra-porous nanoparticle networks (UNN) of crystalline hydroxyapatite (HAp). Comparative analysis of the response of osteoblast cells to the ultra-porous nanostructured HAp surfaces and to the spin coated HAp surfaces revealed superior osseointegrative properties of the UNN coatings with significant cell and filopodia infiltration. This flexible synthesis approach for the engineering of UNN HAp coatings on titanium implants provides a platform technology to study the bone-implant interface for improved osseointegration and osteoconduction.

Nucleotide Excision Repair and Vitamin D--Relevance for Skin Cancer Therapy

Ultraviolet (UV) radiation is involved in almost all skin cancer cases, but on the other hand, it stimulates the production of pre-vitamin D3, whose active metabolite, 1,25-dihydroxyvitamin D3 (1,25VD3), plays important physiological functions on binding with its receptor (vitamin D receptor, VDR). UV-induced DNA damages in the form of cyclobutane pyrimidine dimers or (6-4)-pyrimidine-pyrimidone photoproducts are frequently found in skin cancer and its precursors. Therefore, removing these lesions is essential for the prevention of skin cancer. As UV-induced DNA damages are repaired by nucleotide excision repair (NER), the interaction of 1,25VD3 with NER components can be important for skin cancer transformation. Several studies show that 1,25VD3 protects DNA against damage induced by UV, but the exact mechanism of this protection is not completely clear. 1,25VD3 was also shown to affect cell cycle regulation and apoptosis in several signaling pathways, so it can be considered as a potential modulator of the cellular DNA damage response, which is crucial for mutagenesis and cancer transformation. 1,25VD3 was shown to affect DNA repair and potentially NER through decreasing nitrosylation of DNA repair enzymes by NO overproduction by UV, but other mechanisms of the interaction between 1,25VD3 and NER machinery also are suggested. Therefore, the array of NER gene functioning could be analyzed and an appropriate amount of 1.25VD3 could be recommended to decrease UV-induced DNA damage important for skin cancer transformation.

Inhibition of Akt Enhances the Chemopreventive Effects of Topical Rapamycin in Mouse Skin

The PI3Kinase/Akt/mTOR pathway has important roles in cancer development for multiple tumor types, including UV-induced nonmelanoma skin cancer. Immunosuppressed populations are at increased risk of aggressive cutaneous squamous cell carcinoma (SCC). Individuals who are treated with rapamycin (sirolimus, a classical mTOR inhibitor) have significantly decreased rates of developing new cutaneous SCCs compared with those that receive traditional immunosuppression. However, systemic rapamycin use can lead to significant adverse events. Here, we explored the use of topical rapamycin as a chemopreventive agent in the context of solar-simulated light (SSL)-induced skin carcinogenesis. In SKH-1 mice, topical rapamycin treatment decreased tumor yields when applied after completion of 15 weeks of SSL exposure compared with controls. However, applying rapamycin during SSL exposure for 15 weeks, and continuing for 10 weeks after UV treatment, increased tumor yields. We also examined whether a combinatorial approach might result in more significant tumor suppression by rapamycin. We validated that rapamycin causes increased Akt (S473) phosphorylation in the epidermis after SSL, and show for the first time that this dysregulation can be inhibited in vivo by a selective PDK1/Akt inhibitor, PHT-427. Combining rapamycin with PHT-427 on tumor prone skin additively caused a significant reduction of tumor multiplicity compared with vehicle controls. Our findings indicate that patients taking rapamycin should avoid sun exposure, and that combining topical mTOR inhibitors and Akt inhibitors may be a viable chemoprevention option for individuals at high risk for cutaneous SCC.

Fyn is a redox sensor involved in solar ultraviolet light-induced signal transduction in skin carcinogenesis

Solar ultraviolet (UV) light is a major etiological factor in skin carcinogenesis, with solar UV-stimulated signal transduction inducing pathological changes and skin damage. The primary sensor of solar UV-induced cellular signaling has not been identified. We use an experimental system of solar simulated light (SSL) to mimic solar UV and we demonstrate that Fyn is a primary redox sensor involved in SSL-induced signal transduction. Reactive oxygen species (ROS) generated by SSL exposure directly oxidize Cys488 of Fyn, resulting in increased Fyn kinase activity. Fyn oxidation was increased in mouse skin after SSL exposure, and Fyn knockout (Fyn^−/−) mice formed larger and more tumors compared to Fyn wildtype mice when exposed to SSL for an extended period of time. Murine embryonic fibroblasts (MEFs) lacking Fyn as well as cells in which Fyn expression was knocked down were resistant to SSL-induced apoptosis. Furthermore, cells expressing mutant Fyn (C448A) were resistant to SSL-induced apoptosis. These findings suggest that Fyn acts as a regulatory nexus between solar UV, ROS and signal transduction during skin carcinogenesis.

Mitogen-activated protein kinase kinase 3 induces cell cycle arrest via p38 activation mediated Bmi-1 downregulation in hepatocellular carcinoma

The underlying molecular pathogenesis of hepatocellular carcinoma (HCC) remains poorly understood. Mitogen-activated protein kinase kinase 3 (MKK3), has been reported as a novel tumor suppressor in breast cancer. However, its potential suppressive role in HCC has not been evaluated. In the current study, the biologic functions of MKK3 in HCC were investigated and a previously unreported cell cycle regulation mechanism was observed. MKK3 overexpression suppressed HepG2 and PLC‑PRF‑5 cell proliferation and induced cell cycle arrest in the two cell lines. In addition, MKK3 overexpression upregulated the cyclin-dependent kinase inhibitors, p16 INK4A and p15 INK4B in HCC cells. Their negative regulator, Bim‑1, was downregulated following MKK3 overexpression. Moreover, MKK3 activated p38 in HCC cells and SB203580, a p38 inhibitor, reversed the tumor suppressive effect of MKK3. In conclusion, the results identify MKK3 as a tumor suppressor and highlighted the significance of p38 pathway aberration in HCC.

Activation of the PI3K/Akt/mTOR and MAPK Signaling Pathways in Response to Acute Solar-Simulated Light Exposure of Human Skin

The incidence of skin cancer is higher than all other cancers and continues to increase, with an average annual cost over $8 billion in the United States. As a result, identifying molecular pathway alterations that occur with UV exposure to strategize more effective preventive and therapeutic approaches is essential. To that end, we evaluated phosphorylation of proteins within the PI3K/Akt and MAPK pathways by immunohistochemistry in sun-protected skin after acute doses of physiologically relevant solar-simulated ultraviolet light (SSL) in 24 volunteers. Biopsies were performed at baseline, 5 minutes, 1, 5, and 24 hours after SSL irradiation. Within the PI3K/Akt pathway, we found activation of Akt (serine 473) to be significantly increased at 5 hours while mTOR (serine 2448) was strongly activated early and was sustained over 24 hours after SSL. Downstream, we observed a marked and sustained increase in phospho-S6 (serine 235/S236), whereas phospho-4E-BP1 (threonines 37/46) was increased only at 24 hours. Within the MAPK pathway, SSL-induced expression of phospho-p38 (threonine 180/tyrosine 182) peaked at 1 to 5 hours. ERK 1/2 was observed to be immediate and sustained after SSL irradiation. Phosphorylation of histone H3 (serine 10), a core structural protein of the nucleosome, peaked at 5 hours after SSL irradiation. The expression of both p53 and COX-2 was increased at 5 hours and was maximal at 24 hours after SSL irradiation. Apoptosis was significantly increased at 24 hours as expected and indicative of a sunburn-type response to SSL. Understanding the timing of key protein expression changes in response to SSL will aid in development of mechanistic-based approaches for the prevention and control of skin cancers.

In vivo gene manipulation reveals the impact of stress-responsive MAPK pathways on tumor progression

It has been widely accepted that tumor cells and normal stromal cells in the host environment coordinately modulate tumor progression. Mitogen-activated protein kinase pathways are the representative stress-responsive cascades that exert proper cellular responses to divergent environmental stimuli. Genetically engineered mouse models and chemically induced tumorigenesis models have revealed that components of the MAPK pathway not only regulate the behavior of tumor cells themselves but also that of surrounding normal stromal cells in the host environment during cancer pathogenesis. The individual functions of MAPK pathway components in tumor initiation and progression vary depending on the stimuli and the stromal cell types involved in tumor progression, in addition to the molecular isoforms of the components and the origins of the tumor. Recent studies have indicated that MAPK pathway components synergize with environmental factors (e.g. tobacco smoke and diet) to affect tumor initiation and progression. Moreover, some components play distinct roles in the course of tumor progression, such as before and after the establishment of tumors. Hence, a comprehensive understanding of the multifaceted functions of MAPK pathway components in tumor initiation and progression is essential for the improvement of cancer therapy. In this review, we focus on the reports that utilized knockout, conditional knockout, and transgenic mice of MAPK pathway components to investigate the effects of MAPK pathway components on tumor initiation and progression in the host environment.

Chemopreventive efficacy of menthol on carcinogen-induced cutaneous carcinoma through inhibition of inflammation and oxidative stress in mice

Inflammation and oxidative stress have been implicated in various pathological processes including skin tumorigenesis. Skin cancer is the most common form of cancer responsible for considerable morbidity and mortality, the treatment progress of which remains slow though. Therefore, chemoprevention and other strategies are being considered. Menthol has shown high anticancer activity against various human cancers, but its effect on skin cancer has never been evaluated. We herein investigated the chemopreventive potential of menthol against 9,10-dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation, oxidative stress and skin carcinogenesis in female ICR mice. Pretreatment with menthol at various doses significantly suppressed tumor formation and growth, and markedly reduced tumor incidence and volume. Moreover, menthol inhibited TPA-induced skin hyperplasia and inflammation, and significantly suppressed the expression of cyclooxygenase-2 (COX-2). Furthermore, pretreatment with menthol inhibited the formation of reactive oxygen species and affected the activities of a battery of antioxidant enzymes in the skin. The expressions of NF-κB, Erk and p38 were down-regulated by menthol administration. Thus, inflammation and oxidative stress collectively played a crucial role in the chemopreventive efficacy of menthol on the murine skin tumorigenesis.

REGγ is critical for skin carcinogenesis by modulating the Wnt/β-catenin pathway

Here we report that mice deficient for the proteasome activator, REGγ, exhibit a marked resistance to TPA (12-O-tetradecanoyl-phorbol-13-acetate)-induced keratinocyte proliferation, epidermal hyperplasia and onset of papillomas compared with wild-type counterparts. Interestingly, a massive increase of REGγ in skin tissues or cells resulting from TPA induces activation of p38 mitogen-activated protein kinase (MAPK/p38). Blocking p38 MAPK activation prevents REGγ elevation in HaCaT cells with TPA treatment. AP-1, the downstream effector of MAPK/p38, directly binds to the REGγ promoter and activates its transcription in response to TPA stimulation. Furthermore, we find that REGγ activates Wnt/β-catenin signalling by degrading GSK-3β in vitro and in cells, increasing levels of CyclinD1 and c-Myc, the downstream targets of β-catenin. Conversely, MAPK/p38 inactivation or REGγ deletion prevents the increase of cyclinD1 and c-Myc by TPA. This study demonstrates that REGγ acts in skin tumorigenesis mediating MAPK/p38 activation of the Wnt/β-catenin pathway.

Roles of p38α mitogen-activated protein kinase in mouse models of inflammatory diseases and cancer

The p38α mitogen‐activated protein kinase pathway not only regulates the production of inflammatory mediators, but also controls processes related to tissue homeostasis, such as cell proliferation, differentiation and survival, which are often disrupted during malignant transformation. The versatility of this signaling pathway allows for the regulation of many specific functions depending on the cell type and context. Here, we discuss mouse models that have been used to identify in vivo functions of p38α signaling in the pathogenesis of inflammatory diseases and cancer. Experiments using genetically modified mice and pharmacological inhibitors support that targeting the p38α pathway could be therapeutically useful for some inflammatory diseases and tumor types.

Ultraviolet radiation-induced non-melanoma skin cancer: Regulation of DNA damage repair and inflammation

Exposure to ultraviolet (UV) radiation is associated with approximately 65% of melanoma cases, and 90% of non-melanoma skin cancers (NMSC), including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). While the incidence of most other malignancies has either stabilized or declined, that of NMSC has increased and is developing even in younger age groups. NMSCs account for nearly 15,000 deaths, 3.5 million new cases, and more than 3 billion dollars a year in medical costs in the United States alone, representing a major public health concern. As sun protection efforts have not been proven effective, targeted chemoprevention strategies are much needed. Skin carcinogenesis by DNA damage is considered a predominant paradigm for UV toxicity. Exposure to UV radiation can activate various oncogenes while inactivating tumor suppressor genes, resulting in inappropriate survival and proliferation of keratinocytes that harbor these damages. Moreover, increasing evidence demonstrate that inflammatory responses by the immune cells within the tumor microenvironment also contribute significantly to skin tumorigenesis. Initiation and progression of skin carcinogenesis mediated by UV radiation involve complex pathways, including those of apoptosis, proliferation, autophagy, DNA repair, checkpoint signaling, metabolism, and inflammation. In this review, we highlight the recent advances in two of these key molecular processes that result in UV-mediated skin carcinogenesis. In particular, we discuss 1) pathways that regulate DNA damage repair and 2) the regulation of the inflammatory process its crosstalk with DNA repair potentially leading to non-melanoma skin carcinogenesis.

Kaempferol targets RSK2 and MSK1 to suppress UV radiation-induced skin cancer

Solar UV (SUV) irradiation is a major factor in skin carcinogenesis, the most common form of cancer in the United States. The MAPK cascades are activated by SUV irradiation. The 90 kDa ribosomal S6 kinase (RSK) and mitogen and stress-activated protein kinase (MSK) proteins constitute a family of protein kinases that mediate signal transduction downstream of the MAPK cascades. In this study, phosphorylation of RSK and MSK1 was upregulated in human squamous cell carcinoma (SCC) and SUV-treated mouse skin. Kaempferol, a natural flavonol, found in tea, broccoli, grapes, apples, and other plant sources, is known to have anticancer activity, but its mechanisms and direct target(s) in cancer chemoprevention are unclear. Kinase array results revealed that kaempferol inhibited RSK2 and MSK1. Pull-down assay results, ATP competition, and in vitro kinase assay data revealed that kaempferol interacts with RSK2 and MSK1 at the ATP-binding pocket and inhibits their respective kinase activities. Mechanistic investigations showed that kaempferol suppresses RSK2 and MSK1 kinase activities to attenuate SUV-induced phosphorylation of cAMP-responsive element binding protein (CREB) and histone H3 in mouse skin cells. Kaempferol was a potent inhibitor of SUV-induced mouse skin carcinogenesis. Further analysis showed that skin from the kaempferol-treated group exhibited a substantial reduction in SUV-induced phosphorylation of CREB, c-Fos, and histone H3. Overall, our results identify kaempferol as a safe and novel chemopreventive agent against SUV-induced skin carcinogenesis that acts by targeting RSK2 and MSK1.

Inhibition of p38 MAPK signaling augments skin tumorigenesis via NOX2 driven ROS generation

p38 mitogen-activated protein kinases (MAPKs) respond to a wide range of extracellular stimuli. While the inhibition of p38 signaling is implicated in the impaired capacity to repair ultraviolet (UV)-induced DNA damage—a primary risk factor for human skin cancers—its mechanism of action in skin carcinogenesis remains unclear, as both anti-proliferative and survival functions have been previously described. In this study, we utilized cultured keratinocytes, murine tumorigenesis models, and human cutaneous squamous cell carcinoma (SCC) specimens to assess the effect of p38 in this regard. UV irradiation of normal human keratinocytes increased the expression of all four p38 isoforms (α/β/γ/δ); whereas irradiation of p53-deficient A431 keratinocytes derived from a human SCC selectively decreased p38α, without affecting other isoforms. p38α levels are decreased in the majority of human cutaneous SCCs assessed by tissue microarray, suggesting a tumor-suppressive effect of p38α in SCC pathogenesis. Genetic and pharmacological inhibition of p38α and in A431 cells increased cell proliferation, which was in turn associated with increases in NAPDH oxidase (NOX2) activity as well as intracellular reactive oxygen species (ROS). These changes led to enhanced invasiveness of A431 cells as assessed by the matrigel invasion assay. Chronic treatment of p53^-/-/SKH-1 mice with the p38 inhibitor SB203580 accelerated UV-induced SCC carcinogenesis and increased the expression of NOX2. NOX2 knockdown suppressed the augmented growth of A431 xenografts treated with SB203580. These findings indicate that in the absence of p53, p38α deficiency drives SCC growth and progression that is associated with enhanced NOX2 expression and ROS formation.