SECRETION OF APOLIPOPROTEIN B-CONTAINING LIPOPROTEINS FROM HELA-CELLSIS DEPENDENT ON EXPRESSION OF THE MICROSOMAL TRIGLYCERIDE TRANSFER PROTEIN AND IS REGULATED BY LIPID AVAILABILITY

To elucidate the role of the microsomal triglyceride transfer protein (MTP) in lipoprotein assembly, MTP and apolipoprotein B-53 (apoB 53; t he N-terminal 53% of apoB) were expressed in HeLa cells. The results s howed that apoB-53 could be expressed in HeLa cells with or without ex pression of MTP. In contrast, efficient secretion of apoB-53 required expression of MTP. Ultracentrifugal density flotation analysis showed that apoB-53 was secreted predominantly as a particle with the density of high density lipoprotein. An essentially identical apoB-53 particl e density distribution was obtained after transient expression of apoB -53 in McArdle RH-7777 rat hepatoma cells. The mass of apoB-53 secrete d was greater, and the flotation density was lower, from cells fed lip id, suggesting that apoB secretion in HeLa cells was regulated by lipi d availability, similar to what has been described for lipoprotein-pro ducing cell lines. These results indicate that MTP is necessary and su fficient to direct the regulated secretion of apoB-53 in HeLa cells.