NR2F1 and IRE1β Suppress Microsomal Triglyceride Transfer Protein Expression and Lipoprotein Assembly in Undifferentiated Intestinal Epithelial Cells

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Abstract
Objective— Our aim was to elucidate mechanisms involved in the acquisition of lipid transport properties during enterocyte differentiation. Methods and Results— We show that lipid mobilization via apolipoprotein B lipoproteins is dependent on the expression of microsomal triglyceride transfer protein (MTP) during differentiation of Caco-2 cells into enterocyte-like cells. Mechanistic studies showed that binding of the nuclear receptor family 2 group F member 1 (NR2F1) to the DR1 element in the MTTP promoter suppresses MTTP expression in undifferentiated cells. During cellular differentiation, NR2F1 expression and its binding to MTTP promoter decline and MTP induction ensues. Moreover, undifferentiated cells express inositol-requiring enzyme 1β (IRE1β), a protein that posttranscriptionally degrades MTP mRNA, and its expression substantially decreases during differentiation, contributing to MTP induction. Immunohistochemical studies revealed a significant negative relationship between the expressions of MTP and NR2F1/IRE1β in undifferentiated and differentiated Caco-2 cells, as well as in crypt–villus and jejunum–colon axes of mouse intestine. Conclusion— We propose that transcriptional and posttranscriptional mechanisms involving NR2F1 and IRE1β ensure low MTP expression in undifferentiated intestinal cells and avoid apolipoprotein B lipoprotein biosynthesis.