Inhibition of mTORC2 enhances UVB-induced apoptosis in keratinocytes through a mechanism dependent on the FOXO3a transcriptional target NOXA but independent of TRAIL

mTORC2: A neglected player in aging regulation

Mammalian target of rapamycin (mTOR) is a serine/threonine kinase that plays a pivotal role in various biological processes, through integrating external and internal signals, facilitating gene transcription and protein translation, as well as by regulating mitochondria and autophagy functions. mTOR kinase operates within two distinct protein complexes known as mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), which engage separate downstream signaling pathways impacting diverse cellular processes. Although mTORC1 has been extensively studied as a pro-proliferative factor and a pro-aging hub if activated aberrantly, mTORC2 received less attention, particularly regarding its implication in aging regulation. However, recent studies brought increasing evidence or clues for us, which implies the associations of mTORC2 with aging, as the genetic elimination of unique subunits of mTORC2, such as RICTOR, has been shown to alleviate aging progression in comparison to mTORC1 inhibition. In this review, we first summarized the basic characteristics of mTORC2, including its protein architecture and signaling network. We then focused on reviewing the molecular signaling regulation of mTORC2 in cellular senescence and organismal aging, and proposed the multifaceted regulatory characteristics under senescent and nonsenescent contexts. Next, we outlined the research progress of mTOR inhibitors in the field of antiaging and discussed future prospects and challenges. It is our pleasure if this review article could provide meaningful information for our readers and call forth more investigations working on this topic.

Loss of mutant p53 in HaCaT keratinocytes promotes cadmium-induced keratin 17 expression and cell death

BACKGROUND

Cadmium exposure induces dermatotoxicity and epidermal barrier disruption and leads to the development of various pathologies. HaCaT cells are immortalized human keratinocytes that are widely used as alternatives to primary human keratinocytes, particularly for evaluating cadmium toxicity. HaCaT cells bear two gain-of-function (GOF) mutations in the TP53 gene, which strongly affect p53 function. Mutant forms of p53 are known to correlate with increased resistance to various stimuli, including exposure to cytotoxic substances. In addition, keratin 17 (KRT17) was recently shown to be highly expressed in HaCaT cells in response to genotoxic stress. Moreover, p53 is a direct transcriptional repressor of KRT17. However, the impact of TP53 mutations in HaCaT cells on the regulation of cell death and keratin 17 expression is unclear. In this study, we aimed to evaluate the impact of p53 on the response to Cd-induced cytotoxicity.

METHODS AND RESULTS

Employing the MTT assay and Annexin V/propidium iodide staining, we demonstrated that knockout of TP53 leads to a decrease in the sensitivity of HaCaT cells to the cytotoxic effects of cadmium. Specifically, HaCaT cells with TP53 knockout (TP53 KO HaCaT) exhibited cell death at a cadmium concentration of 10 μM or higher, whereas wild-type cells displayed cell death at a concentration of 30 μM. Furthermore, apoptotic cells were consistently detected in TP53 KO HaCaT cells upon exposure to low concentrations of cadmium (10 and 20 μM) but not in wild-type cells. Our findings also indicate that cadmium cytotoxicity is mediated by reactive oxygen species (ROS), which were significantly increased only in TP53 knockout cells treated with 30 μM cadmium. An examination of proteomic data revealed that TP53 knockout in HaCaT cells resulted in the upregulation of proteins involved in the regulation of apoptosis, redox systems, and DNA repair. Moreover, RT‒qPCR and immunoblotting showed that cadmium toxicity leads to dose-dependent induction of keratin 17 in p53-deficient cells but not in wild-type cells.

CONCLUSIONS

The connection between mutant p53 in HaCaT keratinocytes and increased resistance to cadmium toxicity was demonstrated for the first time. Proteomic profiling revealed that TP53 knockout in HaCaT cells led to the activation of apoptosis regulatory circuits, redox systems, and DNA repair. In addition, our data support the involvement of keratin 17 in the regulation of DNA repair and cell death. Apparently, the induction of keratin 17 is p53-independent but may be inhibited by mutant p53.

Natural bioactive compounds and FOXO3a in cancer therapeutics: An update

Forkhead box protein 3a (FOXO3a) is a transcription factor that regulates various downstream targets upon its activation, leading to the upregulation of tumor suppressor and apoptotic pathways. Hence, targeting FOXO3a is an emerging strategy for cancer prevention and treatment. Recently, Natural Bioactive Compounds (NBCs) have been used in drug discovery for treating various disorders including cancer. Notably, several NBCs have been shown as potent FOXO3a activators. NBCs upregulate FOXO3a expressions through PI3K/Akt, MEK/ERK, AMPK, and IκB signaling pathways. FOXO3a promotes its anticancer effects by upregulating the levels of its downstream targets, including Bim, FasL, and Bax, leading to apoptosis. This review focuses on the dysregulation of FOXO3a in carcinogenesis and explores the potent FOXO3a activating NBCs for cancer prevention and treatment. Additionally, the review evaluates the safety and efficacy of NBCs. Looking ahead, NBCs are anticipated to become a cost-effective, potent, and safer therapeutic option for cancer, making them a focal point of research in the field of cancer prevention and treatment.

Therapeutic strategies targeting FOXO transcription factors

FOXO proteins are transcription factors that are involved in numerous physiological processes and in various pathological conditions, including cardiovascular disease, cancer, diabetes and chronic neurological diseases. For example, FOXO proteins are context-dependent tumour suppressors that are frequently inactivated in human cancers, and FOXO3 is the second most replicated gene associated with extreme human longevity. Therefore, pharmacological manipulation of FOXO proteins is a promising approach to developing therapeutics for cancer and for healthy ageing. In this Review, we overview the role of FOXO proteins in health and disease and discuss the pharmacological approaches to modulate FOXO function.

Sex-specific differences in patients with nonmelanoma skin cancer of the pinna

Background

Generally, it is known that men are affected more frequently by nonmelanoma skin cancer (NMSC) than women. The aim of our study was to investigate the effect of sex on the characteristics of NMSCs of the pinna at the population that our center serves and to compare it with the international data.

Methods

We analyzed retrospectively the data of 225 patients with NMSC of the pinna. Sex‐specific differences were investigated for basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC) subgroups.

Results

The ratio of BCC to cSCC was determined in male patients at 1:1.3, in contrast in females it was identified at 4:1 (P = .001).

Conclusion

In our study, a new aspect of the sex‐dependent distribution of cSCC and BCC of the pinna was demonstrated. Women are affected four times more frequently by BCC than by cSCC, whereas in men this ratio is approximately equal.

BH3 mimetic ABT-263 enhances the anticancer effects of apigenin in tumor cells with activating EGFR mutation

Background

Mutated epidermal growth factor receptor (EGFR) is one of the most successful targets in cancer targeted therapy. While this treatment has benefited many patients with an activating EGFR mutation (EGFRm), almost all those who initially benefited will eventually develop acquired drug resistance (ADR) after a certain period of time. New therapeutic strategies need to be explored to treat EGFRm tumors and overcome or minimize this recurring ADR.

Results

Our data showed that apigenin alone has only mild inhibitory effects on EGFRm tumor cells. By drug screening, we found that ABT-263 can significantly enhance the antitumor activities of apigenin in tumor cells harbouring an activating EGFR mutation and AZD9291-resistant H1975 cells. Mechanistically, apigenin upregulated the expression of Noxa in EGFRm tumor cells by targeting the AKT-FoxO3a pathway, thereby synergizing with ABT-263 to suppress tumor cell growth and proliferation in vitro and in vivo.

Conclusions

Our study provides a rationale for the clinical application of the combination treatment of apigenin and BH3 mimetics in the treatment of EGFRm tumors.

Electronic supplementary material

The online version of this article (10.1186/s13578-019-0322-y) contains supplementary material, which is available to authorized users.

Knocking down raptor in human keratinocytes affects ornithine decarboxylase in a post-transcriptional Manner following ultraviolet B exposure

Non-melanoma skin cancer (NMSC) is the most common form of cancer. Ultraviolet-B (UVB) radiation has been shown to be a complete carcinogen in the development of NMSC. The mammalian target of rapamycin complex 1 (mTORC1) is upregulated by UVB. Ornithine decarboxylase (ODC), the first enzyme of the polyamine biosynthetic pathway, is also upregulated in response to UVB. However, the interplay between these two pathways after UVB exposure remains unclear. The studies described here compare mRNA stability between normal human keratinocytes (HaCaT cells) and HaCaT cells with low levels of raptor to investigate whether the induction of ODC by UVB is dependent on mTORC1. We show that the knockdown of mTORC1 activity led to decreased levels of ODC protein both before and after exposure to 20 mJ/cm² UVB. ODC mRNA was less stable in cells with decreased mTORC1 activity. Polysome profiles revealed that the initiation of ODC mRNA translation did not change in UVB-treated cells. We have shown that the ODC transcript is stabilized by the RNA-binding protein human antigen R (HuR). To expand these studies, we investigated whether HuR functions to regulate ODC mRNA stability in human keratinocytes exposed to UVB. We show an increased cytoplasmic localization of HuR after UVB exposure in wild-type cells. The ablation of HuR via CRISPR/Cas9 did not alter the stability of the ODC message, suggesting the involvement of other trans-acting factors. These data suggest that in human keratinocytes, ODC mRNA stability is regulated, in part, by an mTORC1-dependent mechanism after UVB exposure.