Inhibition of translocation of nascent apolipoprotein B across the endoplasmic reticulum membrane is associated with selective inhibition of the synthesis of apolipoprotein B

In HepG2 cells, inhibition of apolipoprotein B100 (apoB) translocation acro ss the endoplasmic reticulum by an microsomal triglyceride transfer protein (MTP) inhibitor (CP-10447) in the presence of N-acetyl-leucinyl-norleucina l, a proteasomal inhibitor, results in accumulation of newly synthesized ap oB in the translocation channel. Here we demonstrated that such accumulatio n led to a specific reduction of apoB synthesis. ApoB mRNA levels remained unchanged, but we observed reduced rates of elongation of nascent apoB in p uromycin-synchronized cells pretreated with MTP inhibitor. This observation was consistent with a longer half-ribosome transit time for the synthesis of apoB in MTP-inhibited cells. Initiation of translation of apoB mRNA was not impaired by MTP inhibition. Overall, these findings suggest that transl ocation arrest of apoB in the endoplasmic reticulum channel can exert a sel ective and negative effect on the synthesis of apoB at the stage of elongat ion.