Mammalian target of rapamycin (mTOR) inhibitors slow skin carcinogenesis, but impair wound healing

The application of a multi-component reaction peptide as a model regenerative active to enhance skin wound-healing postlaser procedure in a double-blinded placebo-controlled clinical trial

INTRODUCTION

Esthetic procedures are currently among the most effective options for consumers seeking to correct aging signs such as fine lines, wrinkles, and skin tone unevenness. Currently, there is a scientific need for an adjunct active to be paired with esthetic procedures to encourage wound recovery and address postprocedure pigmentation concerns.

OBJECTIVE

Toward that goal, this study assessed the efficacy of a peptide created from a multi-component reaction (multi-component peptide, MCP) as a model active for postprocedure care and evaluated its ability to promote skin healing in an ablative laser-induced wound model on the forearm.

METHODS

The mechanism of action of MCP was investigated using tubo assays, 2D melanocyte, and fibroblast cultures, reconstructed skin equivalents, and ex vivo skin explants. The MCP formula and the clinical benchmark formula of Aquaphor were assessed head-to-head by applying the products topically in an ablative laser-induced wound model (n = 20 subjects). The promotion of wound healing was evaluated by the investigator assessment of epithelial confluence, crusting or scabbing, general wound appearance, erythema, and edema.

RESULTS

MCP was determined to be beneficial to postprocedure skin recovery and healing by four main mechanisms of action: barrier repair as determined in an ex vivo tape-stripping model, reduction of inflammation and postinflammatory hyperpigmentation, reduction of elastase activity, and stimulation of fibroblast through the mTOR pathway. The formula containing 10% MCP enhanced the kinetics of epithelial confluence and improvement of the crusting or scabbing appearance of the laser-generated wounds in a laser-induced mini-zone wound healing study on the forearm.

CONCLUSION

This study demonstrates the use of MCP as a proof of concept regenerative active that when incorporated into an optimized postprocedure skincare formula can improve skin healing and enhance the appearance of skin after injury with relevance to ablative aesthetic procedures.

Risk factors for incisional hernia after liver transplantation in the era of mammalian target of rapamycin inhibitors use: a retrospective study of living donor liver transplantation dominant center in Korea

Purpose

Incisional hernia (IH) is a common complication after liver transplantation (LT) with an incidence rate of 5% to 46%. This retrospective study aimed to evaluate the risk factors for IH development after LT in the era of mammalian target of rapamycin (mTOR) inhibitors use.

Methods

Data on patients who underwent LT between 2015 and 2021 were retrospectively reviewed. The patients were divided into 2 groups (IH group and non-IH group) according to the postoperative occurrence of IH.

Results

We analyzed data from 878 patients during the study period, with 28 patients (3.2%) developing IH. According to multivariate analysis, body mass index exceeding 25 kg/m2 and the use of mTOR inhibitors within the first month after LT were the sole significant factors for both IH occurrence and the subsequent need for repair operations. Notably, a history of wound complications, a Model for End-stage Liver Disease score, and the timing of LT-whether conducted during regular hours or at night-did not emerge as significant risk factors for IH after LT.

Conclusion

Our study reveals a higher incidence of IH among obese patients following LT, often requiring surgical repair, particularly in cases involving mTOR inhibitor usage within the initial month after LT. Consequently, it is crucial to exercise increased vigilance, especially in obese patients, and exercise caution when considering early mTOR inhibitor administration after LT.

A review of heart transplant immunosuppressants and nonmelanoma skin cancer

Heart transplant recipients experience high rates of skin cancer, likely due to greater length or dosage of immunosuppression. We review the impact of immunosuppressive medications on development of nonmelanoma skin cancer (NMSC) in heart transplant recipients. The authors searched keywords "heart transplant" and "nonmelanoma skin cancer" on PubMed in October 2022 for eligible articles available in English. Articles were selected for inclusion based on relevance to heart transplantation and NMSC. If any cited articles within included articles were related to our search they were also included. Of the 29 identified articles, 18 met the inclusion criteria with a total of 11,699 patients. Two studies found that tacrolimus and azathioprine increased the risk of NMSC. Five studies demonstrated that tacrolimus, everolimus, sirolimus, azathioprine and mycophenolate mofetil decreased the risk of NMSC. Three studies described that cyclosporine, tacrolimus, everolimus, sirolimus, azathioprine, mycophenolate mofetil and prednisone had no significant association with the development in NMSC. Two studies did not specify the correlation between immunosuppressant use and NMSC development. Ten studies did not discuss the association of immunosuppressants use with the development of NMSC. Our review highlights the commonly used immunosuppressive drugs that can impact the development of NMSC in heart transplant recipients. A management strategy in immunosuppression-associated skin cancers may ultimately involve adjusting the immunosuppressive regimen. This review serves as a summary of the most commonly used immunosuppressive drugs in heart transplant patients and their tumorigenic mechanisms to guide recommendations for dermatologic follow-up in heart transplant recipients.

Local blockade of tacrolimus promotes T-cell-mediated tumor regression in systemically immunosuppressed hosts

BACKGROUND

Immunosuppressive drugs such as tacrolimus have revolutionized our ability to transplant organs between individuals. Tacrolimus acts systemically to suppress the activity of T-cells within and around transplanted organs. However, tacrolimus also suppresses T-cell function in the skin, contributing to a high incidence of skin cancer and associated mortality and morbidity in solid organ transplant recipients. Here, we aimed to identify a compound capable of re-establishing antitumor T-cell control in the skin despite the presence of tacrolimus.

METHODS

In this study, we performed time-resolved fluorescence resonance energy transfer to identify molecules capable of antagonizing the interaction between tacrolimus and FKBP12. The capacity of these molecules to rescue mouse and human T-cell function in the presence of tacrolimus was determined in vitro, and the antitumor effect of the lead compound, Q-2361, was assessed in "regressor" models of skin cancer in immunosuppressed mice. Systemic CD8 T-cell depletion and analyses of intratumoral T-cell activation markers and effector molecule production were performed to determine the mechanism of tumor rejection. Pharmacokinetic studies of topically applied Q-2361 were performed to assess skin and systemic drug exposure.

RESULTS

Q-2361 potently blocked the interaction between tacrolimus and FKBP12 and reversed the inhibition of the nuclear factor of activated T cells activation by tacrolimus following T-cell receptor engagement in human Jurkat cells. Q-2361 rescued T-cell function in the presence of tacrolimus, rapamycin, and everolimus. Intratumoral injection of Q-2361-induced tumor regression in mice systemically immune suppressed with tacrolimus. Mechanistically, Q-2361 treatment permitted T-cell activation, proliferation, and effector function within tumors. When CD8 T cells were depleted, Q-2361 could not induce tumor regression. A simple solution-based Q-2361 topical formulation achieved high and sustained residence in the skin with negligible drug in the blood.

CONCLUSIONS

Our findings demonstrate that the local application of Q-2361 permits T-cells to become activated driving tumor rejection in the presence of tacrolimus. The data presented here suggests that topically applied Q-2361 has great potential for the reactivation of T-cells in the skin but not systemically, and therefore represents a promising strategy to prevent or treat skin malignancies in immunosuppressed organ transplant recipients.

Astragalus Polysaccharides Promote Wound Healing in Diabetic Rats by Upregulating PETN and Inhibiting the mTOR Pathway

Objective. Presently, astragalus polysaccharide (APS) is being investigated for its therapeutic potential in various diseases; however, its underlying mechanism has not yet been clarified. This study was aimed at observing the effects of APS on wound healing in diabetic rats and at exploring its underlying mechanism. Methods. Streptozotocin was injected into the tail vein of SD rats to induce diabetic animal models, in which an incision on the back was made. Rats were treated with different dosages of APS to observe their wound healing. Additionally, RT-qPCR and Western blot assay were conducted to observe the expression levels of PTEN and mTOR pathway-associated factors. Results. Diabetic rats had a prolonged wound healing process, fewer blood vessels, and increased inflammatory response, in which decreased PTEN and elevated mTOR phosphorylation were also identified. APS effectively improved wound healing in a dose-dependent manner by inhibiting the release of inflammatory mediators and attenuating endothelial injuries. Suppression of PTEN could effectively increase the phosphorylation of mTOR and diminish the therapeutic functions of APS on wound healing in diabetic rats. Conclusion. This study highlighted that APS could promote wound healing in diabetic rats by upregulating PTEN and suppressing the mTOR pathway activation.

The regulation of skin homeostasis, repair and the pathogenesis of skin diseases by spatiotemporal activation of epidermal mTOR signaling

The epidermis, the outmost layer of the skin, is a stratified squamous epithelium that protects the body from the external world. The epidermis and its appendages need constantly renew themselves and replace the damaged tissues caused by environmental assaults. The mechanistic target of rapamycin (mTOR) signaling is a central controller of cell growth and metabolism that plays a critical role in development, homeostasis and diseases. Recent findings suggest that mTOR signaling is activated in a spatiotemporal and context-dependent manner in the epidermis, coordinating diverse skin homeostatic processes. Dysregulation of mTOR signaling underlies the pathogenesis of skin diseases, including psoriasis and skin cancer. In this review, we discuss the role of epidermal mTOR signaling activity and function in skin, with a focus on skin barrier formation, hair regeneration, wound repair, as well as skin pathological disorders. We propose that fine-tuned control of mTOR signaling is essential for epidermal structural and functional integrity.

Transferrin decorated-nanostructured lipid carriers (NLCs) are a promising delivery system for rapamycin in Alzheimer's disease: An in vivo study

Alzheimer's disease (AD), the most common neurodegenerative disorder, is characterized by progressive cognitive impairment and memory loss. The mammalian target of rapamycin (mTOR) signaling pathway could regulate learning and memory. The effect of rapamycin (Rapa) on mTOR activity could slow or prevent the progression of AD by affecting various essential cellular processes. Previously, we prepared transferrin (Tf) decorated-nanostructured lipid carriers (NLCs) for rapamycin (150 ± 9 nm) to protect the drug from chemical and enzymatic degradation and for brain targeted delivery of rapamycin. Herein, the effect of Tf-NLCs compared to untargeted anionic-NLCs and free rapamycin, were studied in amyloid beta (Aβ) induced rat model of AD. Behavioral test revealed that the Rapa Tf-NLCs were able to significantly improve the impaired spatial memory induced by Aβ. Histopathological studies of hippocampus also showed neural survival in Rapa Tf-NLCs treated group. The immunosuppressive, and delayed wound healing adverse effects in the rapamycin solution treated group were abolished by incorporating the drug into NLCs. The Aβ induced oxidative stress was also reduced by Rapa Tf-NLCs. Molecular studies on the level of Aβ, autophagy (LC3) and apoptotic (caspase-3) markers, and mTOR activity revealed that the Rapa Tf-NLCs decreased the Aβ level and suppressed the toxic effects of Aβ plaques by modulating the mTOR activity and autophagy, and decreasing the apoptosis level. As a conclusion, the designed Tf-NLCs could be an appropriate and a safe brain delivery system for rapamycin and make this drug more efficient in AD for improving memory and neuroprotection.

Divide and conquer: two stem cell populations in squamous epithelia, reserves and the active duty forces

Stem cells are of great interest to the scientific community due to their potential role in regenerative and rejuvenative medicine. However, their role in the aging process and carcinogenesis remains unclear. Because DNA replication in stem cells may contribute to the background mutation rate and thereby to cancer, reducing proliferation and establishing a relatively quiescent stem cell compartment has been hypothesized to limit DNA replication-associated mutagenesis. On the other hand, as the main function of stem cells is to provide daughter cells to build and maintain tissues, the idea of a quiescent stem cell compartment appears counterintuitive. Intriguing observations in mice have led to the idea of separated stem cell compartments that consist of cells with different proliferative activity. Some epithelia of short-lived rodents appear to lack quiescent stem cells. Comparing stem cells of different species and different organs (comparative stem cell biology) may allow us to elucidate the evolutionary pressures such as the balance between cancer and longevity that govern stem cell biology (evolutionary stem cell biology). The oral mucosa and its stem cells are an exciting model system to explore the characteristics of quiescent stem cells that have eluded biologists for decades.

Regulation of Wound Healing by the NRF2 Transcription Factor-More Than Cytoprotection

The nuclear factor-erythroid 2-related factor 2 (NRF2) transcription factor plays a central role in mediating the cellular stress response. Due to their antioxidant properties, compounds activating NRF2 have received much attention as potential medications for disease prevention, or even for therapy. Accumulating evidence suggests that activation of the NRF2 pathway also has a major impact on wound healing and may be beneficial in the treatment of chronic wounds, which remain a considerable health and economic burden. While NRF2 activation indeed shows promise, important considerations need to be made in light of corresponding evidence that also points towards pro-tumorigenic effects of NRF2. In this review, we discuss the evidence to date, highlighting recent advances using gain- and loss-of-function animal models and how these data fit with observations in humans.

Skin Cancer Following Solid Organ Transplantation: A Review of Risk Factors and Models of Care

The number of solid organ transplants has been increasing annually worldwide. Advances in transplantation surgery and community awareness of organ donation have been key contributors. Combined with increased understanding of immunosuppression, there are a growing number of solid organ transplant recipients in the community as a result of improved long-term outcomes. There remains a high incidence of deaths worldwide post-transplant due to non-melanoma skin cancer (NMSC), which has greater morbidity and mortality in this population than in the general community. Many transplant candidates are not screened prior to organ transplantation and not followed up dermatologically after transplant. After a comprehensive review of the MEDLINE database, we present an update of literature on risk factors for melanoma and non-melanoma skin cancer development in transplant recipients. Medications used by transplant recipients, including immunosuppressants and antibiotics, are discussed along with their respective risks of skin cancer development. We conclude with evidence-based recommendations for models of care, including patient education and dermatological review of transplant recipients.

Clinically-Relevant Rapamycin Treatment Regimens Enhance CD8+ Effector Memory T Cell Function In The Skin and Allow their Infiltration into Cutaneous Squamous Cell Carcinoma

Patients receiving immunosuppressive drugs to prevent organ transplant rejection exhibit a greatly increased risk of developing cutaneous squamous cell carcinoma (SCC). However, not all immunosuppressive drugs confer the same risk. Randomised, controlled trials demonstrate that switching renal transplant recipients receiving calcineurin inhibitor-based therapies to mammalian target of rapamycin (mTOR) inhibitors results in a reduced incidence of de novo SSC formation, and can even result in the regression of pre-existing premalignant lesions. However, the contribution played by residual immune function in this setting is unclear. We examined the hypotheses that mTOR inhibitors promote the enhanced differentiation and function of CD8⁺ memory T cells in the skin. Here, we demonstrate that the long-term oral administration of rapamycin to achieve clinically-relevant whole blood drug target thresholds, creates a "low rapamycin dose" environment in the skin. While both rapamycin and the calcineurin inhibitor tacrolimus elongated the survival of OVA-expressing skin grafts, and inhibited short-term antigen-specific CD8⁺ T cell responses, rapamycin but not tacrolimus permitted the statistically significant infiltration of CD8⁺ effector memory T cells into UV-induced SCC lesions. Furthermore, rapamycin uniquely enhanced the number and function of CD8⁺ effector and central memory T cells in a model of long-term contact hypersensitivity provided that rapamycin was present during the antigen sensitization phase. Thus, our findings suggest that patients switched to mTOR inhibitor regimens likely experience enhanced CD8⁺ memory T cell function to new antigen-challenges in their skin, which could contribute to their lower risk of de novo SSC formation and regression of pre-existing premalignant lesions.

The signaling involved in autophagy machinery in keratinocytes and therapeutic approaches for skin diseases

Autophagy is responsible for the lysosomal degradation of proteins, organelles, microorganisms and exogenous particles. Epidermis primarily consists of keratinocytes which functions as an extremely important barrier. Investigation on autophagy in keratinocytes has been continuously renewing, but is not so systematic due to the complexity of the autophagy machinery. Here we reviewed recent studies on the autophagy in keratinocyte with a focus on interplay between autophagy machinery and keratinocytes biology, and novel autophagy regulators identified in keratinocytes. In this review, we discussed the roles of autophagy in apoptosis, differentiation, immune response, survival and melanin metabolism, trying to reveal the possible involvement of autophagy in skin aging, skin disorders and skin color formation. Since autophagy routinely plays a double-edged sword role in various conditions, its functions in skin homeostasis and potential application as a therapeutic target for skin diseases remains to be clarified. Furthermore, more investigations are needed on optimizing designed strategies to inhibit or enhance autophagy for clinical efficacy.

mTORC1 loss impairs epidermal adhesion via TGF-β/Rho kinase activation

Despite its central position in oncogenic intracellular signaling networks, the role of mTORC1 in epithelial development has not been studied extensively in vivo. Here, we have used the epidermis as a model system to elucidate the cellular effects and signaling feedback sequelae of mTORC1 loss of function in epithelial tissue. In mice with conditional epidermal loss of the mTORC1 components Rheb or Rptor, mTORC1 loss of function unexpectedly resulted in a profound skin barrier defect with epidermal abrasions, blistering, and early postnatal lethality, due to a thinned epidermis with decreased desmosomal protein expression and incomplete biochemical differentiation. In mice with mTORC1 loss of function, we found that Rho kinase (ROCK) signaling was constitutively activated, resulting in increased cytoskeletal tension and impaired cell-cell adhesion. Inhibition or silencing of ROCK1 was sufficient to rescue keratinocyte adhesion and biochemical differentiation in these mice. mTORC1 loss of function also resulted in marked feedback upregulation of upstream TGF-β signaling, triggering ROCK activity and its downstream effects on desmosomal gene expression. These findings elucidate a role for mTORC1 in the regulation of epithelial barrier formation, cytoskeletal tension, and cell adhesion, underscoring the complexity of signaling feedback following mTORC1 inhibition.

Everolimus and Malignancy after Solid Organ Transplantation: A Clinical Update

Malignancy after solid organ transplantation remains a major cause of posttransplant mortality. The mammalian target of rapamycin (mTOR) inhibitor class of immunosuppressants exerts various antioncogenic effects, and the mTOR inhibitor everolimus is licensed for the treatment of several solid cancers. In kidney transplantation, evidence from registry studies indicates a lower rate of de novo malignancy under mTOR inhibition, with some potentially supportive data from randomized trials of everolimus. Case reports and small single-center series have suggested that switch to everolimus may be beneficial following diagnosis of posttransplant malignancy, particularly for Kaposi's sarcoma and nonmelanoma skin cancer, but prospective studies are lacking. A systematic review has shown mTOR inhibition to be associated with a significantly lower rate of hepatocellular carcinoma (HCC) recurrence versus standard calcineurin inhibitor therapy. One meta-analysis has concluded that patients with nontransplant HCC experience a low but significant survival benefit under everolimus monotherapy, so far unconfirmed in a transplant population. Data are limited in heart transplantation, although observational data and case reports have indicated that introduction of everolimus is helpful in reducing the recurrence of skin cancers. Overall, it can be concluded that, in certain settings, everolimus appears a promising option to lessen the toll of posttransplant malignancy.

Insulin and TOR signal in parallel through FOXO and S6K to promote epithelial wound healing

The TOR and Insulin/IGF signalling (IIS) network controls growth, metabolism and ageing. Although reducing TOR or insulin signalling can be beneficial for ageing, it can be detrimental for wound healing, but the reasons for this difference are unknown. Here we show that IIS is activated in the cells surrounding an epidermal wound in Drosophila melanogaster larvae, resulting in PI3K activation and redistribution of the transcription factor FOXO. Insulin and TOR signalling are independently necessary for normal wound healing, with FOXO and S6K as their respective effectors. IIS is specifically required in cells surrounding the wound, and the effect is independent of glycogen metabolism. Insulin signalling is needed for the efficient assembly of an actomyosin cable around the wound, and constitutively active myosin II regulatory light chain suppresses the effects of reduced IIS. These findings may have implications for the role of insulin signalling and FOXO activation in diabetic wound healing.

Nonfacial Reconstructive Techniques

BACKGROUND

Nonfacial reconstruction encompasses several anatomic locations with varied topography, skin quality, and tissue reservoirs. Patients also have varied mobility concerns and wound care needs when managing wounds in these areas.

MATERIALS AND METHODS

This article includes techniques and approaches from the dermatologic surgery, plastic surgery, and podiatric surgery literature in an effort to provide a comprehensive overview of the subject matter.

RESULTS AND CONCLUSION

Functionally and esthetically acceptable reconstructions of nonfacial surgical wounds can be accomplished with a variety of techniques based on the characteristics of the wound and unique needs of the patient.

[Delayed wound healing during therapy of cutaneous graft-versus-host disease with everolimus]

Graft-versus-host-disease (GvHD) is despite improvement in transplantation medicine the major cause for morbidity and mortality after allogeneic stem cell transplantation. We describe a patient with chronic cutaneous GvHD who developed massive skin ulcerations after changing the immunosuppressive therapy to a mammalian target of rapamycin (mTOR)-inhibitor.

Extracellular heat shock protein 90 signals through subdomain II and the NPVY motif of LRP-1 receptor to Akt1 and Akt2: a circuit essential for promoting skin cell migration in vitro and wound healing in vivo

Normal cells secrete heat shock protein 90 alpha (Hsp90α) in response to tissue injury. Tumor cells have managed to constitutively secrete Hsp90α during invasion and metastasis. The sole function of extracellular Hsp90α (eHsp90α) is to promote cell motility, a critical event for both wound healing and tumor progression. The mechanism of promotility action by eHsp90α, however, has remained elusive. A key issue is whether eHsp90α still acts as a chaperone outside the cells or is a new and bona fide signaling molecule. Here, we have provided evidence that eHsp90α utilizes a unique transmembrane signaling mechanism to promote cell motility and wound healing. First, subdomain II in the extracellular part of low-density lipoprotein receptor-related protein 1 (LRP-1) receives the eHsp90α signal. Then, the NPVY but not the NPTY motif in the cytoplasmic tail of LRP-1 connects eHsp90α signaling to serine 473 but not threonine 308 phosphorylation in Akt kinases. Individual knockdown of Akt1, Akt2, or Akt3 revealed the importance of Akt1 and Akt2 in eHsp90α-induced cell motility. Akt gene rescue experiments suggest that Akt1 and Akt2 work in concert, rather than independently, to mediate eHsp90α promotility signaling. Finally, Akt1 and Akt2 knockout mice showed impaired wound healing that cannot be corrected by topical application with the eHsp90α protein.

Islet transplantation in type 1 diabetes: ongoing challenges, refined procedures, and long-term outcome

Remarkable progress has been made in islet transplantation over a span of 40 years. Once just an experimental curiosity in mice, this therapy has moved forward, and can now provide robust therapy for highly selected patients with type 1 diabetes (T1D), refractory to stabilization by other means. This progress could not have occurred without extensive dynamic international collaboration. Currently, 1,085 patients have undergone islet transplantation at 40 international sites since the Edmonton Protocol was reported in 2000 (752 allografts, 333 autografts), according to the Collaborative Islet Transplant Registry. The long-term results of islet transplantation in selected centers now match registry data of pancreas-alone transplantation, with 6 sites reporting five-year insulin independence rates ≥50%. Islet transplantation has been criticized for the use of multiple donor pancreas organs, but progress has also occurred in single-donor success, with 10 sites reporting increased single-donor engraftment. The next wave of innovative clinical trial interventions will address instant blood-mediated inflammatory reaction (IBMIR), apoptosis, and inflammation, and will translate into further marked improvements in single-donor success. Effective control of auto- and alloimmunity is the key to long-term islet function, and high-resolution cellular and antibody-based assays will add considerable precision to this process. Advances in immunosuppression, with new antibody-based targeting of costimulatory blockade and other T-B cellular signaling, will have further profound impact on the safety record of immunotherapy. Clinical trials will move forward shortly to test out new human stem cell derived islets, and in parallel trials will move forward, testing pig islets for compatibility in patients. Induction of immunological tolerance to self-islet antigens and to allografts is a difficult challenge, but potentially within our grasp.

Smad4 disruption accelerates keratinocyte reepithelialization in murine cutaneous wound repair

Keratinocyte reepithelialization is a rate-limiting event in cutaneous wound repair, which involves the migration and proliferation of keratinocytes to cover the denuded dermal surface. Transforming growth factor-β1 (TGF-β1) has the ability to induce epithelial cell migration while inhibiting proliferation, and controversial results have been generated regarding the effect of TGF-β signaling on reepithelialization. In this study, full-thickness skin wounds were made in keratinocyte-specific Smad4 knockout and the control mice. The wound closure, reepithelialization, keratinocyte proliferation, myofibroblast numbers and collagen deposition of were assessed. The results showed that the proliferation of keratinocytes increased, which accelerated the reepithelialization, and led to faster wound repair in the epidermis of Smad4 mutant mice. Upregulation of keratin 17, 14-3-3 sigma and phosphorylated AKT in the hyperproliferative epidermis may be correlated with the accelerated reepithelialization. We conclude that Smad4 plays an inhibitory role in the keratinocyte-mediated reepithelialization of wound healing.

Resveratrol-mediated downregulation of Rictor attenuates autophagic process and suppresses UV-induced skin carcinogenesis

Macroautophagy is a cellular response to various environmental stresses that ensures lysosomal degradation of long-lived and damaged proteins and cellular organelles. It occurs through the formation of an autophagosome, which then fuses with a lysosome to form an autolysosome. Depending on the cellular context, autophagy may promote cancer cell survival or it may serve as a mechanism of tumor suppression. Herein, we show that resveratrol, a natural phytoalexin, induces premature senescence in human A431 SCC cells, and that resveratrol-induced premature senescence is associated with a blockade of autolysosome formation, as assessed by the absence of colocalization of LC3 and Lamp-2, markers for autophagosomes and lysosomes, respectively. Further, we show that resveratrol downregulates the level of Rictor, a component of mTORC2, leading to decreased RhoA-GTPase and altered actin cytoskeleton organization. Exogenous overexpression of Rictor restores RhoA-GTPase activity and actin cytoskeleton network, and decreases resveratrol-induced senescence-associated β-gal activity, indicating a direct role of Rictor in senescence induction. Rictor is overexpressed in UV-induced murine SCCs, whereas its expression is diminished by oral administration of resveratrol. These data indicate that resveratrol attenuates autophagic process via Rictor, and suggest that downregulation of Rictor may be a mechanism of tumor suppression associated with premature senescence.