Coordination of the leucine-sensing Rag GTPase cycle by leucyl-tRNA synthetase in the mTORC1 signaling pathway

Modulation of autophagy in human diseases strategies to foster strengths and circumvent weaknesses

Autophagy is central to the maintenance of intracellular homeostasis across species. Accordingly, autophagy disorders are linked to a variety of diseases from the embryonic stage until death, and the role of autophagy as a therapeutic target has been widely recognized. However, autophagy-associated therapy for human diseases is still in its infancy and is supported by limited evidence. In this review, we summarize the landscape of autophagy-associated diseases and current autophagy modulators. Furthermore, we investigate the existing autophagy-associated clinical trials, analyze the obstacles that limit their progress, offer tactics that may allow barriers to be overcome along the way and then discuss the therapeutic potential of autophagy modulators in clinical applications.

Investigation of Urinary Sestrin2 in Patients with Obstructive Sleep Apnea

Background

Obstructive sleep apnea (OSA) is a disease seriously threatening individual health, which results in serious complications such as hypertension and stroke. These complications are associated with oxidative stress triggered by intermittent hypoxia in OSA. Sestrin2 is a crucial factor involved in oxidative stress. The goal of this study was to investigate if a relationship exists between OSA and Sestrin2.

Methods

We prospectively enrolled 71 subjects, and 16 patients of them with severe OSA completed 4 weeks of nasal continuous positive airway pressure (nCPAP) therapy. We measured and compared the concentration of Sestrin2 in the urine of all subjects, as well as the changes between before and after nCPAP treatment. Additionally, the correlation between Sestrin2 and sleep parameters was analyzed, and the multiple linear regression analysis with stepwise selection was performed to explore the relationship between Sestrin2 and various factors.

Results

A total of 71 subjects were enrolled and divided into two groups: OSA group (n = 41), control group (n = 30). The level of urinary Sestrin2 in OSA patients was significantly higher than that of the control group, and increased with the severity of OSA, while it reduced after nCPAP treatment. Additionally, Sestrin2 was positively correlated with apnea/hypopnea index (AHI), oxygen desaturation index, oxygen saturation < 90% percentage of recording time spent (PRTS) and high-density lipoprotein (HDL), while negatively correlated with the lowest oxygen saturation. Importantly, Sestrin2 was independently associated with AHI, oxygen saturation < 90% PRTS and HDL.

Conclusions

Urinary Sestrin2 is involved in OSA, and is a paramount marker of OSA severity.

Regulation of Autophagy by mTOR Signaling Pathway

Autophagy plays a crucial role in maintaining cellular homeostasis, and is closely related to the occurrence of variety of human diseases. It is known that autophagy occurs in response to various environmental stresses such as nutrient deficiency, growth factor deficiency, and hypoxia. Induced autophagy eliminates the damage caused by these stresses and returns to normal levels when the stresses are relieved. To comprehend the induction of autophagy under various stress conditions and the effects of autophagy on the life processes of cells, it is necessary to understand how autophagy is regulated. Many studies have shown that a number of signal transduction pathways are involved in the regulation of autophagy. Among these pathways, some pathways converge at the target of rapamycin (TOR), a highly conserved kinase important for autophagy regulation. This review will focus on the role of TOR signaling pathway in the regulation of autophagy.

BCAT1 promotes proliferation of endometrial cancer cells through reprogrammed BCAA metabolism

Branched-chain amino acid aminotransferase 1 (BCAT1) enzyme is an aminotransferase of glutamate and branched-chain amino acids (BCAAs), which is required for survival of various cancers. However, the role of BCAT1 in human endometrial cancer (EC) remains unknown. We analyzed the expression of BCAT1 in endometrial lesions using IHC. After BCAT1 gene knockdown and activity inhibition, cell proliferation, apoptosis, and metabolism were detected using CCK-8 assay, flow cytometry, and LC-MS/MS analysis. We analyzed molecular signature characteristics to understand how BCAT1 promotes cell proliferation. In this study, we demonstrated a significant increase in BCAT1 expression from normal endometrium to atypical endometrial hyperplasia (AEH) and then to EC, and the expression of BCAT1 in EC samples was related to tumor grade, FIGO stage and lymph node metastasis. Next, cell proliferation was markedly inhibited by lentiviral BCAT1 knockdown or Gbp treatment, but this had little effect on apoptosis rate. Further, BCAT1 knockdown resulted in 31.2% and 33.3% decreases in the amount of intracellular isoleucine and leucine produced, respectively, relative to a control. BCAT1 knockdown or activity inhibition resulted in a decrease of pS6K, a downstream target kinase of mTORC1. In conclusion, our study showed that BCAT1 is essential for EC progression and to increase EC cell proliferation through the production of BCAAs to activate the mTORC1 pathway, providing ideas for clinicians to identify metabolism-based targeted approaches for patients with EC.

mTOR Complexes as a Nutrient Sensor for Driving Cancer Progression

Recent advancement in the field of molecular cancer research has clearly revealed that abnormality of oncogenes or tumor suppressor genes causes tumor progression thorough the promotion of intracellular metabolism. Metabolic reprogramming is one of the strategies for cancer cells to ensure their survival by enabling cancer cells to obtain the macromolecular precursors and energy needed for the rapid growth. However, an orchestration of appropriate metabolic reactions for the cancer cell survival requires the precise mechanism to sense and harness the nutrient in the microenvironment. Mammalian/mechanistic target of rapamycin (mTOR) complexes are known downstream effectors of many cancer-causing mutations, which are thought to regulate cancer cell survival and growth. Recent studies demonstrate the intriguing role of mTOR to achieve the feat through metabolic reprogramming in cancer. Importantly, not only mTORC1, a well-known regulator of metabolism both in normal and cancer cell, but mTORC2, an essential partner of mTORC1 downstream of growth factor receptor signaling, controls cooperatively specific metabolism, which nominates them as an essential regulator of cancer metabolism as well as a promising candidate to garner and convey the nutrient information from the surrounding environment. In this article, we depict the recent findings on the role of mTOR complexes in cancer as a master regulator of cancer metabolism and a potential sensor of nutrients, especially focusing on glucose and amino acid sensing in cancer. Novel and detailed molecular mechanisms that amino acids activate mTOR complexes signaling have been identified. We would also like to mention the intricate crosstalk between glucose and amino acid metabolism that ensures the survival of cancer cells, but at the same time it could be exploitable for the novel intervention to target the metabolic vulnerabilities of cancer cells.

The Regulation and Function of the L-Type Amino Acid Transporter 1 (LAT1) in Cancer

The progression of cancer is associated with increases in amino acid uptake by cancer cells. Upon their entry into cells through specific transporters, exogenous amino acids are used to synthesize proteins, nucleic acids and lipids and to generate ATP. The essential amino acid leucine is also important for maintaining cancer-associated signaling pathways. By upregulating amino acid transporters, cancer cells gain greater access to exogenous amino acids to support chronic proliferation, maintain metabolic pathways, and to enhance certain signal transduction pathways. Suppressing cancer growth by targeting amino acid transporters will require an in-depth understanding of how cancer cells acquire amino acids, in particular, the transporters involved and which cancer pathways are most sensitive to amino acid deprivation. L-Type Amino Acid Transporter 1 (LAT1) mediates the uptake of essential amino acids and its expression is upregulated during the progression of several cancers. We will review the upstream regulators of LAT1 and the downstream effects caused by the overexpression of LAT1 in cancer cells.