SUMMARY Highly proliferating cells are particularly dependent on glucose and glutamine for bioenergetics and macromolecule biosynthesis. The signals that respond to nutrient fluctuations to maintain metabolic homeostasis remain poorly understood. Here, we found that mTORC2 is activated by nutrient deprivation due to decreasing glutamine catabolites. We elucidate how mTORC2 modulates a glutamine-requiring biosynthetic pathway, the hexosamine biosynthesis pathway (HBP) via regulation of expression of GFAT1 (glutamine:fructose-6-phosphate amidotransferase 1), the rate-limiting enzyme of the HBP. GFAT1 expression is dependent on sufficient amounts of glutaminolysis catabolites particularly α-ketoglutarate, which are generated in an mTORC2-dependent manner. Additionally, mTORC2 is essential for proper expression and nuclear accumulation of the GFAT1 transcriptional regulator, Xbp1s. Thus, while mTORC1 senses amino acid abundance to promote anabolism, mTORC2 responds to declining glutamine catabolites in order to restore metabolic homeostasis. Our findings uncover the role of mTORC2 in metabolic reprogramming and have implications for understanding insulin resistance and tumorigenesis.

Nijmegen breakage syndrome (NBS) is a chromosomal instability syndrome associated with cancer predisposition, radiosensitivity, microcephaly, and growth retardation. The NBS gene product, NBS1 (p95) or nibrin, is a part of the hMre11 complex, a central player associated with double strand break repair. We previously demonstrated that c-Myc directly activates NBS1 expression. Here we have shown that constitutive expression of NBS1 in Rat1a and HeLa cells induces/enhances their transformation. Repression of endogenous NBS1 levels using short interference RNA reduces the transformation activity of two tumor cell lines. Increased NBS1 expression is observed in 40 -52% of non-small cell lung carcinoma, hepatoma, and esophageal cancer samples. NBS1 overexpression stimulates phosphatidylinositol (PI) 3-kinase activity, leading to increased phosphorylation levels of Akt and its downstream targets such as glycogen synthase kinase 3␤ and mammalian target of rapamycin in different cell lines and tumor samples. Transformation induced by NBS1 overexpression can be inhibited by a PI3-kinase inhibitor (LY294002). Repression of endogenous Akt expression by short interference RNA decreases the transformation activity of Rat1a cells overexpressing NBS1. These results indicate that overexpression of NBS1 is an oncogenic event that contributes to transformation through the activation of PI3-kinase/Akt. Nijmegen breakage syndrome (NBS)3 is an autosomal recessive hereditary disorder characterized by microcephaly, a "bird-like" facial appearance, growth retardation, immunodeficiency, radiosensitivity, chromosomal instability, and predisposition to tumor formation (1-3). The gene defective in NBS has been cloned, and the gene product, NBS1 (p95, nibrin), is a member of the DNA double strand break repair complex (hMre11 complex) including hMre11, hRad50, and NBS1 (1, 3). Increased radiation sensitivity and radioresistant DNA synthesis of NBS fibroblasts are similar to the cellular features of AT (ataxia-telangiectasis) cells (2, 4), demonstrated by the recent results that ATM (ataxiatelangiectasis-mutated) protein phosphorylates NBS1 (5-7), linking these two proteins in the same pathway. NBS1 is a putative tumor suppressor gene as shown by the existence of NBS patients and some mutations discovered in different tumors (1, 2). However, NBS1 is expressed in highly proliferating tissues developmentally (8) and is located at sites of DNA synthesis through interaction with E2F (9). In addition, Mre11 complex is able to prevent double strand break accumulation during chromosomal DNA synthesis to ensure cell cycle progression (10). Nbs1 knock out in mouse embryonic stem cells shows the phenotype of diminished expansion of the inner cell mass of mutant blastocysts (Nbs1 null) (11, 12). Cellular proliferation defects are shown in Nbs1 m/m mouse embryonic fibroblasts (13). Obviously, the roles of NBS1 are multiple, and some of them are still subject to intensive investigation.Phosphatidylinositol (PI) 3-kinase is a major signaling component downs...

Low-molecular-weight hyaluronic acid (LMWHA) was integrated with superparamagnetic Fe3O4 nanoparticles (Fe3O4 NPs). The size distribution, zeta potential, viscosity, thermogravimetric and paramagnetic properties of the LMWHA-Fe3O4 NPs were systematically examined. For cellular experiments, MCF7 breast cancer cell line was carried out. In addition, the cell targeting ability and characteristics of the LMWHA-Fe3O4 NPs for MCF7 breast cancer cells were analyzed using the thiocyanate method and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The experimental results showed that the LMWHA-Fe3O4 NPs were not only easily injectable due to their low viscosity, but also exhibited a significant superparamagnetic property. Furthermore, the in vitro assay results showed that the NPs had negligible cytotoxicity and exhibited a good cancer cell targeting ability. Overall, the results therefore suggest that the LMWHA-Fe3O4 NPs have considerable potential as an injectable agent for enhanced magnetic resonance imaging (MRI) and/or hyperthermia treatment in breast cancer therapy.