ATP Citrate Lyase Knockdown Induces Growth Arrest and Apoptosis through Different Cell- and Environment-Dependent Mechanisms

Abstract

ATP citrate lyase (ACLY) is a cytosolic enzyme that catalyzes generation of acetyl-CoA, which is a vital building block for fatty acid, cholesterol, and isoprenoid biosynthesis. ACLY is upregulated in several types of cancer, and its inhibition induces proliferation arrest in certain cancer cells. As ACLY is involved in several pathways, its downregulation may affect multiple processes. Here, we have shown that short hairpin RNAmediated ACLY silencing in cell lines derived from different types of cancers induces proliferation, cell-cycle arrest, and apoptosis. However, this antiproliferative effect of ACLY knockdown was observed only when cells were cultivated under lipid-reduced growth conditions. Proliferation arrest induced by ACLY silencing was partially rescued by supplementing the media with fatty acids and/or cholesterol. This indicates that the ACLY knockdown-mediated growth arrest might be the result of either fatty acid or cholesterol starvation or both. In the absence of ACLY, the cancer cells displayed elevated expression of sterol regulatory element binding protein-regulated downstream genes involved in de novo fatty acid and cholesterol biosynthesis. Furthermore, ACLY suppression resulted in elevated expression of acyl-CoA synthetase short-chain family member 2 (ACSS2), an enzyme that also produces acetyl-CoA using acetate as a substrate. Acetate supplementation partially rescued the cancer cells from ACLY suppression-induced proliferation arrest. We also observed that the absence of ACLY enhanced ACSS2-dependent lipid synthesis. These findings provide new insights into the role of ACLY in cancer cell growth and give critical information about the effects of ACLY silencing on different pathways. This information is crucial in understanding the possible application of ACLY inhibition in cancer therapeutics. Mol Cancer Ther; 11(9); 1925-35. Ó2012 AACR.

Silencing of solute carrier family 13 member 5 disrupts energy homeostasis and inhibits proliferation of human hepatocarcinoma cells

“…Increased de novo lipogenesis is a key characteristic of rapidly proliferating cancer cells, in which conversion of cytosolic citrate into acetyl-CoA and oxaloacetate by ACLY represents the initial and rate-limiting step for the biosynthesis of long-chain fatty acids and cholesterol as building blocks for cell growth (29,30). In the liver, the level of cytosolic citrate is well-maintained through CIC-mediated export from the TCA cycle in mitochondria and SLC13A5-mediated uptake from the circulation (24,31).…”

Cullin3–KLHL25 ubiquitin ligase targets ACLY for degradation to inhibit lipid synthesis and tumor progression

“…CUL3 inhibits the proliferation and anchorageindependent growth of lung cancer cells through negative regulation of ACLY ACLY plays a critical role in promoting cancer cell proliferation, and targeting ACLY by RNAi or specific small molecule inhibitors such as SB-204990 inhibits proliferation of cancer cells in vitro and in vivo Hatzivassiliou et al 2005;Migita et al 2008;Zaidi et al 2012a). Here, we investigated whether CUL3 inhibits proliferation of lung cancer cells through negative regulation of ACLY in different lung cancer cells as well as normal lung NHBE cells in vitro by MTT assays.…”

“…Promoting lipid synthesis is critical for the role of ACLY in tumor progression Hatzivassiliou et al 2005;Migita et al 2008;Zaidi et al 2012a). It has been reported that supplementation of cells with metabolites from the fatty acid synthesis pathway (e.g., oleic acid and palmitic acid) and the mevalonate pathway (e.g., mevalonate and cholesterol) rescued the growth inhibition of cancer cells caused by inhibition of lipid synthesis, including ACLY knockdown (Nakakuki et al 2007;Zaidi et al 2012a;Young et al 2013).…”

Lipid Metabolism, Metabolic Syndrome, and Cancer

“…Both ACC and ACL have been found to be over-expressed in many cancers such as breast, liver, lung, ovarian, prostate and leukemia cancers [132,133]. Inhibition of either ACL or ACC induces growth arrest and apoptosis in several cancer cell lines [134][135][136]. The potential mechanism of ACL overexpression in tumorigenesis is through PI3K/AKT and MAPK signaling pathway [135,137].…”