The cells were then treated as indicated and the luciferase activity was measured using a Dual-Luciferase Reporter Assay System (Promega, E1960) based on the protocol provided

The cells were then treated as indicated and the luciferase activity was measured using a Dual-Luciferase Reporter Assay System (Promega, E1960) based on the protocol provided. Increased nuclear translocation of FOXO1 was observed following AKT inactivation, leading to increased transcription of genes involved in the autophagic process. Thetsc2/MEFs were also more susceptible to apoptosis induced by SCD1 inhibition and blockage of autophagy sensitized the cell death response. These results revealed a novel function of SCD1 on regulation of autophagy via lipogenesis and the lipid rafts-AKT-FOXO1 pathway. Keywords: SCD1, autophagy, TSC2, AKT, FOXO1, lipogenesis, lipid rafts == Introduction == The MTOR (mechanistic target of rapamycin) protein is a serine/threonine kinase that makes up the catalytic subunit of 2 distinct complexes in cells named MTOR complex 1 (MTORC1) and MTOR complex 2 (MTORC2). The distinct protein components of MTORC1 include RPTOR (regulatory-associated protein of MTOR, complex 1) and PRAS40, while RICTOR (RPTOR-independent companion of MTOR, complex 2) and MAPKAP1/SIN1 (mitogen-activated protein kinase associated protein 1) are specifically found in MTORC2. 1Tuberous sclerosis complex is a dominant genetic disorder that is characterized by the growth of benign tumors in multiple organs due to loss-of-function mutations in the gene encoding either TSC1 (tuberous sclerosis 1/hamartin) or TSC2 (tuberous sclerosis 2/tuberin). 2The TCS1-TSC2 complex is a heterodimer formed by these BGLAP 2 proteins and acts as a GTPase-activating protein, inhibiting the activity of the GTPase protein RHEB (Ras homolog enriched in brain), 3, 4which is an upstream activator of MTORC1. Cells without the functional TSC1-TSC2 complex have a constitutively activated MTORC1 signaling pathway independent of growth factors regulation. 1MTORC1 acts as the key sensor and convergent point of nutrients, growth factors, and energy and stress inputs in the cells, 5and controls numerous metabolic processes such as energy production, protein and lipid synthesis, and autophagy. As a result, deregulation of signaling pathways that results in hyperactivation of MTORC1 is also frequently observed in cancer and other metabolic diseases. 1, 5, 6 Deregulated cellular metabolism in cancer cells has emerged as one of the important hallmarks of cancer Treprostinil and also an area of great interest in cancer research. 7One of the metabolic changes that has been well characterized in cancer cells is the increase in de novo fatty acid synthesis to produce large quantity of fatty acids to satisfy the increased demand for lipids that are required for membrane Treprostinil biogenesis during cell growth and proliferation. 8MTORC1 has been identified as Treprostinil the main regulator of lipogenesis as it can initiate lipogenesis in cells through the activation of SREBF1 (sterol regulatory element binding transcription factor 1). 9-12SREBF1 is one of the transcription factors in mammalian cells that increases the expression of enzymes involved in fatty acid synthesis including FASN (fatty acid synthase), SCD1, and ACLY (ATP citrate lyase) when activated and thus leads to increased levels of de novo lipid synthesis in the cells. 9-11Although FASN has been proposed as a potential oncogene and therapeutic target in cancer, 13, 14relatively little is known about SCD1 and its oncogenic properties. SCD1 is an endoplasmic reticulum-bound enzyme that catalyzes the formation of the first double bond at the cis-9 position by converting palmitoyl-CoA Treprostinil (16C: 0) and stearoyl-CoA (18C: 0) to palmitoleoyl-CoA (16C: 1) and oleoyl-CoA (18C: 1), Treprostinil respectively. Oleic acid (18C: 1) is the major MUFA found in cells and SCD1 thus plays an important role in regulating the fatty acid composition of membrane and in maintaining membrane fluidity and lipid homeostasis. 15The importance of SCD1 activity in malignant cell transformation and subsequent proliferation is beginning to emerge. Some studies have shown that the loss of SCD1 enzymatic activity can inhibit the transformation and proliferation of malignant cells. 16, 17Inhibition of SCD1 activity induces cell death in various cancer cell lines and in mice xenograft models, 18-21suggesting that SCD1 could be a potential therapeutic target.

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