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

Abstract

Conjugated 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 Gαq, by the phospholipase C (PLC) inhibitor U73122, by the inositol trisphosphate (IP3) receptor inhibitor 2-APB, by the calcium/calmodulin-dependent protein kinase kinase α (CaMKK) inhibitor STO-609 and by the intracellular Ca2+ chelator BAPTA-AM. This suggests that t10,c12-CLA may exert its apoptotic effect by stimulating GPCR through Gαq signaling, activation of phosphatidylinositol-PLC, followed by binding of the PLC-generated IP3 to its receptor on the ER, triggering Ca2+ 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.

Oleic Acid Attenuates trans‐10,cis‐12 Conjugated Linoleic Acid‐Mediated Inflammatory Gene Expression in Human Adipocytes

“…GPR40, 84, 119, and 120 are classically activated by long chain FFA, and GPR41 and 43 by short chain FFA. Importantly, 1) cell surface, FFA receptors [30–32] and putative GPCR [33–35] activated by FFA impact on cell signaling, 2) CLA reduces FFA transport in tumors and white adipose tissue by activating specific GPCR [36, 37], 3) CLA increased pancreatic insulin release via islet GRP40 [38], and 4) we found that impairing coupling between GPCR and Gi/o with pertusis toxin blocked 10,12 CLA’s suppression of PPARγ target gene expression and lipid metabolism in adipocytes [15]. …”

Mechanism of All-trans-retinal Toxicity with Implications for Stargardt Disease and Age-related Macular Degeneration

“…Pharmacological interventions targeting these mechanisms can provide novel therapeutic strategies for treating blinding retinal disorders such as Stargardt disease and age-related macular degeneration. Note Added in Proof-During the review of our manuscript, we came upon a recently published paper (59), which indicates that unsaturated fatty acids activate PLC/IP 3 /Ca 2ϩ signaling through GPCR activation and induce ROS overproduction in TM4t mouse mammary tumor cells. This complex mechanism highlights the effect of unsaturated fatty acids on apoptosis.…”

A Novel Initiation Mechanism of Death in Streptococcus pneumoniae Induced by the Human Milk Protein-Lipid Complex HAMLET and Activated during Physiological Death

“…Ca 2ϩ -induced kinase activation has also been recently described for conjugated linoleic acid (48), which is a fatty acid that can complex with ␣-lactalbumin equally as well as oleic acid and yield similar lethal effects (49). To evaluate the potential role of kinase activity in HAMLET-induced pneumococcal death, we measured the bactericidal activity of HAM-LET in the presence of the pan-kinase inhibitor staurosporine, using a concentration range that has previously been reported to be effective in bacterial systems (20 M (50)).…”