Peturbation of PICALM Levels Alters Cellular Cholesterol Metabolism

PICALM (Phosphatidyl Inositol Clathrin Assembly Lymphoid Myeloid protein) is a ubiquitously expressed protein that plays a role in clathrin-mediated endocytosis. PICALM also affects the internalization of SNAREs and modulates macroautophagy. Chromosomal translocations that result in the fusion of PICALM to heterologous proteins cause leukemias, and genome-wide association studies have linked Single Nucleotide Polymorphisms (SNPs) of PICALM to Alzheimer’s disease. To obtain insight into the biological role of PICALM, we performed gene expression studies of PICALM-deficient and PICALM-expressing cells. Pathway analysis demonstrated that PICALM expression influences the expression of genes that encode proteins involved in cholesterol biosynthesis and lipoprotein uptake. GC-MS studies indicated that loss of PICALM increases total cholesterol pool size. Isotopic labeling studies revealed that loss of PICALM alters cholesterol homeostasis via increased scavenging of cholesterol. Measurement of LDL receptor endocytosis further showed that PICALM deficient cells express higher LDLR levels resulting in higher lipoprotein internalization. These findings suggest that PICALM is required for cellular cholesterol homeostasis and point to a novel mechanism by which PICALM alterations may contribute to disease. Total RNA was isolated (Qiagen RNeasy® Micro kit, Valencia, CA) from four replicates of PICALM knockout cells transfected with control vector, and from four replicates of PICALM knockout cells transfected with PICALM.