High DEPTOR expression correlates with poor prognosis in patients with esophageal squamous cell carcinoma

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.

DEPTOR at the Nexus of Cancer, Metabolism, and Immunity

DEP domain-containing mechanistic target of rapamycin (mTOR)-interacting protein (DEPTOR) is an important modulator of mTOR, a kinase at the center of two important protein complexes named mTORC1 and mTORC2. These highly studied complexes play essential roles in regulating growth, metabolism, and immunity in response to mitogens, nutrients, and cytokines. Defects in mTOR signaling have been associated with the development of many diseases, including cancer and diabetes, and approaches aiming at modulating mTOR activity are envisioned as an attractive strategy to improve human health. DEPTOR interaction with mTOR represses its kinase activity and rewires the mTOR signaling pathway. Over the last years, several studies have revealed key roles for DEPTOR in numerous biological and pathological processes. Here, we provide the current state of the knowledge regarding the cellular and physiological functions of DEPTOR by focusing on its impact on the mTOR pathway and its role in promoting health and disease.

Prognostic and clinicopathological significance of DEPTOR expression in cancer patients: a meta-analysis

Background

DEP domain containing mammalian target of rapamycin (mTOR)-interacting protein (DEPTOR), a recently discovered endogenous inhibitor of mTOR, has been found to be abnormally expressed in various tumors. Recent studies have demonstrated that DEPTOR could serve as a potential prognostic biomarker in several kinds of cancer. However, the prognostic value of DEPTOR is still controversial so far.

Patients and methods

PubMed, Embase and Web of Science were systematically searched to obtain all relevant articles about the prognostic value of DEPTOR in cancer patients. ORs or HRs with corresponding 95% CIs were pooled to estimate the association between DEP-TOR expression and the clinicopathological characteristics or survival of cancer patients.

Results

A total of nine eligible studies with 974 cancer patients were included in our meta-analysis. Our results demonstrated that the expression of DEPTOR was not associated with the overall survival (OS) (pooled HR=0.795, 95% CI=0.252-2.509) and event-free survival (EFS) (pooled HR=1.244, 95% CI=0.543-2.848) in cancer patients. Furthermore, subgroup analysis divided by sample size, type of cancer, Newcastle-Ottawa Scale (NOS) score and evaluation of DEPTOR expression showed identical prognostic value. In addition, our analysis also revealed that there was no significant association between expression level of DEPTOR and clinicopathological characteristics, such as tumor stage, lymph node metastasis, differentiation grade and gender.

Conclusion

Our meta-analysis suggested that despite the fact that DEPTOR could be overexpressed or downregulated in cancer patients, it might not be a potential marker to predict the prognosis of cancer patients.

Celastrus orbiculatus extracts induce cell cycle arrest and apoptosis in human esophageal squamous carcinoma ECA-109 cells in vitro via the PI3K/AKT/mTOR signaling pathway

Recently, Celastrus orbiculatus ethyl acetate extracts (COE) have been investigated for their anticancer effects on digestive tract tumors. However, the therapeutic effects of COE on esophageal squamous carcinoma cells (ESCC) have not been investigated. In the present study, the effects of COE on the cell cycle and apoptosis of ESCCs were assessed in vitro, and it was revealed that COE treatment triggered G₀/G₁ cell cycle arrest, and induced DNA damage and apoptosis in a dose-dependent manner in ESCC. Activation of the phosphatidylinositol 3-kinase/protein kinase-B/mechanistic target of rapamycin (mTOR) pathway was also suppressed by COE. Additionally, the combined treatment with COE and rapamycin (an mTOR inhibitor) acted synergistically in ECA-109 cells compared with the treatment with COE or rapamycin alone. These findings extend the understanding of the action of COE and suggest that COE has potential as a treatment option for ESCC as a single treatment or in combination.

Deptor: not only a mTOR inhibitor

Deptor is an important protein that belongs to the mTORC1 and mTORC2 complexes, able to interact with mTOR and to inhibit its kinase activity. As a natural mTOR inhibitor, Deptor is involved in several molecular pathways, such as cell growth, apoptosis, autophagy and ER stress response. For this reason, Deptor seems to play an important role in controlling cellular homeostasis. Despite several recent insights characterizing Deptor functions and regulation, its complete role within cells has not yet been completely clarified. Indeed, quite recently, Deptor has been associated with chromatin, and it has been demonstrated having a role in transcriptional regulation, controlling in such way endoplasmatic reticulum activity.

From all these observations it is not surprising that Deptor can behave either as an oncogene or oncosuppressor, depending on the cell- or tissue-contexts. This review highlights recent progresses made in our understanding of the many activities of Deptor, describing its transcriptional and post-transcriptional regulation in different cancer cell types. Moreover, here we discuss the possibility of using compounds able to inhibit Deptor or to disrupt its interaction with mTOR as novel approaches for cancer therapy.

Identification of DEP domain-containing proteins by a machine learning method and experimental analysis of their expression in human HCC tissues

The Dishevelled/EGL-10/Pleckstrin (DEP) domain-containing (DEPDC) proteins have seven members. However, whether this superfamily can be distinguished from other proteins based only on the amino acid sequences, remains unknown. Here, we describe a computational method to segregate DEPDCs and non-DEPDCs. First, we examined the Pfam numbers of the known DEPDCs and used the longest sequences for each Pfam to construct a phylogenetic tree. Subsequently, we extracted 188-dimensional (188D) and 20D features of DEPDCs and non-DEPDCs and classified them with random forest classifier. We also mined the motifs of human DEPDCs to find the related domains. Finally, we designed experimental verification methods of human DEPDC expression at the mRNA level in hepatocellular carcinoma (HCC) and adjacent normal tissues. The phylogenetic analysis showed that the DEPDCs superfamily can be divided into three clusters. Moreover, the 188D and 20D features can both be used to effectively distinguish the two protein types. Motif analysis revealed that the DEP and RhoGAP domain was common in human DEPDCs, human HCC and the adjacent tissues that widely expressed DEPDCs. However, their regulation was not identical. In conclusion, we successfully constructed a binary classifier for DEPDCs and experimentally verified their expression in human HCC tissues.

PIM1 polymorphism and PIM1 expression as predisposing factors of esophageal squamous cell carcinoma in the Asian population

Our study aimed to identify the association between a PIM1 polymorphism and PIM1 expression levels with clinicopathological features of esophageal squamous cell carcinoma (ESCC). A total of 168 patients with ESCC were recruited as the case group, and 180 healthy individuals were included as the control group. Polymerase chain reaction-direct sequencing was employed to analyze all genotypes containing the PIM1 -1 882 A>T mutation. Immunohistochemistry was used to detect PIM1 expression. The distributions of genotype AA and allele A of PIM1 -1 882 A>T were higher in the case group than in the control group (both P<0.05). AT + TT carriers had a lower risk of ESCC than AA carriers (P<0.05). PIM1 polymorphism was related to the invasion depth, degree of differentiation, and lymphatic metastasis of ESCC (P<0.05). PIM1 expression was associated with lymphatic metastasis of ESCC and PIM1 polymorphism (both P<0.05). PIM1 -1 882 A>T and the overexpression of PIM1 were associated with the clinicopathological features of ESCC, and PIM1 -1 882 A>T may help to reduce the risk of ESCC in the Asian population.