FIGURE 1.

Sar1A and Sar1B have opposite effects on apoB48- and apoB100-containing lipoprotein secretion. A and B, McArdle-RH7777 cells were labeled with l-[³⁵S]methionine for 60 min and chased for 120 min. The l-³⁵S-labeled apoB in the cell media was immunoprecipitated, analyzed by SDS-PAGE, and visualized by phosphorimaging. Data (mean ± S.E.) are from four independent experiments.****, p < 0.0001 versus cells with empty vector control. ***, p < 0.001 versus cells with empty vector control. **, p < 0.01 versus cells with empty vector control. C and D, densities of fractions containing secreted l-³⁵S-labeled apoB48-containing (C) and l-³⁵S-labeled apoB100-containing (D) lipoproteins were determined gravimetrically. Data (mean ± S.E.) are from three independent experiments. E, secreted l-³⁵S-labeled apoB from two independent Sar1A-FLAG cell lines, quantified as in A and B. ****, p < 0.0001 versus cells with empty vector control. **, p < 0.01 versus apoB100 lipoproteins. F, total l-[³⁵S]methionine in secreted protein fraction. Data (mean ± S.E.) are from five independent experiments. ****, p < 0.0001 versus cells with empty vector control.