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lüll Conjugated linoleic acid-induced apoptosis in mouse mammary tumor cells is mediated by both G protein coupled receptor-dependent activation of the AMP-activated protein kinase pathway and by oxidative stress Hsu YC; Ip MMCell Signal 2011[Dec]; 23 (12): 2013-20Conjugated linoleic acid (CLA) has shown chemopreventive activity in several tumorigenesis models, in part through induction of apoptosis. We previously demonstrated that the t10,c12 isomer of CLA induced apoptosis of TM4t mouse mammary tumor cells through both mitochondrial and endoplasmic reticulum (ER) stress pathways, and that the AMP-activated protein kinase (AMPK) played a critical role in the apoptotic effect. In the current study, we focused on the upstream pathways by which AMPK was activated, and additionally evaluated the contributing role of oxidative stress to apoptosis. CLA-induced activation of AMPK and/or induction of apoptosis were inhibited by infection of TM4t cells with an adenovirus expressing a peptide which blocks the interaction between the G protein coupled receptor (GPCR) and Galpha(q), by the phospholipase C (PLC) inhibitor U73122, by the inositol trisphosphate (IP(3)) receptor inhibitor 2-APB, by the calcium/calmodulin-dependent protein kinase kinase alpha (CaMKK) inhibitor STO-609 and by the intracellular Ca(2+) chelator BAPTA-AM. This suggests that t10,c12-CLA may exert its apoptotic effect by stimulating GPCR through Galpha(q) signaling, activation of phosphatidylinositol-PLC, followed by binding of the PLC-generated IP(3) to its receptor on the ER, triggering Ca(2+) release from the ER and finally stimulating the CaMKK-AMPK pathway. t10,c12-CLA also increased oxidative stress and lipid peroxidation, and antioxidants blocked its apoptotic effect, as well as the CLA-induced activation of p38 MAPK, a downstream effector of AMPK. Together these data elucidate two major pathways by which t10,c12-CLA induces apoptosis, and suggest a point of intersection of the two pathways both upstream and downstream of AMPK.|*Signal Transduction[MESH]|AMP-Activated Protein Kinases/*metabolism[MESH]|Acetylcysteine/pharmacology[MESH]|Animals[MESH]|Antioxidants/pharmacology[MESH]|Apoptosis Regulatory Proteins/metabolism[MESH]|Apoptosis/*drug effects[MESH]|Benzimidazoles/pharmacology[MESH]|Calcium Signaling/drug effects[MESH]|Calcium-Calmodulin-Dependent Protein Kinase Kinase/antagonists & inhibitors[MESH]|Cell Line, Tumor[MESH]|Cell Survival[MESH]|Chelating Agents/pharmacology[MESH]|Egtazic Acid/analogs & derivatives/pharmacology[MESH]|Endoplasmic Reticulum/drug effects/metabolism[MESH]|Enzyme Activation[MESH]|Female[MESH]|GTP-Binding Protein alpha Subunits, Gq-G11/metabolism[MESH]|Linoleic Acids, Conjugated/*pharmacology[MESH]|Lipid Peroxidation[MESH]|Mammary Neoplasms, Animal[MESH]|Mice[MESH]|Naphthalimides/pharmacology[MESH]|Oxidants/*pharmacology[MESH]|Oxidative Stress[MESH]|Phosphorylation[MESH]|Poly (ADP-Ribose) Polymerase-1[MESH]|Poly(ADP-ribose) Polymerases/metabolism[MESH]|Receptors, G-Protein-Coupled/*metabolism[MESH]|Transcription Factor CHOP/metabolism[MESH]|Type C Phospholipases/metabolism[MESH] |