2D; different letters indicate significance, P < 0.05). PBA treatment significantly reduced ER stress–induced formation of apoB-GFP-LC3–positive cells and number of apoB-GFP-LC3 puncta (Fig. 2B, and analysis data shown in Fig. 2C; P < 0.05), and decreased apoB-GFP-LC3-II conversion (Fig. 2D; P < 0.05). Furthermore, PBA treatment markedly inhibited ER stress based on reduced cellular levels of GRP78 and phosphorylated eIF-2α (Fig. 2D). PBA treatment also prevented the loss of newly synthesized cellular and secreted apoB-100 (Fig. 2E) following TM and GLS treatment (different letters indicate significance, P < 0.05). These results strongly indicate that the induction of ER stress

augments autophagic degradation of apoB, whereas suppression of ER stress blocks apoB autophagy. We next assessed whether autophagic degradation

of apoB also occurs in primary hepatocytes. Small Molecule Compound Library Primary rat hepatocytes were transiently transfected with GFP-LC3 cDNA for 40 hours, and then treated with TM (5 μg/mL) or GLS (5 mM) for 4 hours in the presence or absence of PBA (1 mM). Treatment with TM or glucosamine resulted in substantially increased colocalization of apoB with GFP-LC3 and increased number of apoB-GFP-LC3 puncta (Fig. 3A, panels f and i; analysis of data shown in Fig. 3C; *P < 0.05 versus corresponding control). Similar results were obtained when colocalization of apoB and endogenous LC3 was examined in nontransfected cells (Supporting Fig. 2). Increased apoB-GFP-LC3 MCE puncta were observed together with elevated endogenous this website LC3-II conversion (Fig. 3D; *P < 0.05). Importantly, treatment with TM and glucosamine decreased [35S]-labeled

cellular and secreted apoB100 (Fig. 3E,F; different letters indicate significance, P < 0.05), apoB48 was also slightly reduced but this change did not reach statistical significance suggesting that ER stress induces autophagy of apoB100 in primary rat hepatocytes. Importantly, PBA treatment inhibited colocalization of apoB with GFP-LC3 (Fig. 3B, panels f and i; analysis of data shown in Fig. 3C), reduced the endogenous LC3-II conversion (Fig. 3D; different letters indicate significance, P < 0.05), and led to a significantly increased recovery of [35S]-labeled cellular or secreted apoB100 (Fig. 3E,F; different letters indicate significance, P < 0.05), suggesting that blocking ER stress prevents apoB autophagy. Interestingly, PBA was also found to significantly block colocalization of apoB with GFP-LC3 in primary rat hepatocytes under basal conditions (Fig. 3C; top panel, *P < 0.05 versus corresponding control). However, under basal conditions, PBA did not significantly alter the number of apoB-GFL-LC3 puncta in positive cells (Fig. 3C, bottom panel), or endogenous LC3-II conversion (Fig. 3D).