Drolases have been reported to be critical for CE digestion in macrophage foam cells but their role in other cell types is not clear. Thus we are yet to examine the aforementioned possibility. We observed that the CHX-induced increase in CE and LDs also occurs in autophagy-deficient Atg5-null MEF, but this does not preclude the possibility that autophagy is involved in CE metabolism and LD turnover. In fact we found that significantly larger amounts of CE were observed in Atg5-deficient MEF than in wild-type MEF both before and after CHX treatment. Moreover, the seemingly complete suppression of the autophagic flow in cells treated with CHX and Torin1 caused a significantly higher increase of CE than in cells treated with CHX alone, in which a low level of autophagy was Maytansinol butyrate occurring. These results showed that autophagic suppression is not the main cause of the CE increase induced by CHX, but nonetheless they also indicated that autophagy is an important mechanism of CE degradation. LDs that consist predominantly of TG in white adipocytes are degraded effectively by the sequential action of ATGL, HSL, and monoacylglycerol lipase. To degrade LDs that are enriched with CE, however, lysosomal acid lipase, which has CE hydrolytic activity, may be involved, as it is for degradation of cholesterolloaded macrophages. For LDs containing CE and TG in comparable amounts, CE hydrolysis may be a prerequisite for effective TG degradation because CE may surround the TG core, forming concentric layers on the surface. In this context, it is notable that the deficiency of lysosomal acid lipase that characterizes Wolman disease manifests as an accumulation of CE as well as TG. It was surprising that, upon treatment with translation inhibitors, TIP47 was recruited to the CE-rich LDs even though the total ABT-267 amount of TIP47 decreased drastically. TIP47 was previously shown to be recruited to TG-rich LDs induced by unsaturated fatty acids, but in such cases the overall expression of TIP47 also increased. The present result indicates that TIP47 recruitment to LDs does not depend on the increased expression of TIP47 or on the composition of the lipid esters in LDs; rather, it is directly related to the increment of lipid esters. On the other hand, the increased recruitment of TIP47 to LDs
