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

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 RNA-mediated 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. (C) 2012 AACR.