Translational control of an intestinal microvillar enzyme

Abstract

The rates of biosynthesis of adult and foetal pig small-intestinal aminopeptidase N (EC 3.4.11.2) were compared to determine at which level the expression of the microvillar enzyme is developmentally controlled. In organ-cultured explants, the rate of biosynthesis of foetal aminopeptidase N is only about 3% of the adult rate. The small amount synthesized occurs in a high-mannose-glycosylated, membrane-bound, form that is processed to the mature, complex-glycosylated, form at a markedly slower rate than that of the adult enzyme. Extracts of total RNA from adult and foetal intestine contained comparable amounts of aminopeptidase N mRNA, encoding gel-electrophoretically identical primary translation products. Together, these data indicate that the expression of aminopeptidase N is controlled at a translational level.

Developmental control over vitamin-D-induced calbindin gene expression during early differentiation of chicken jejunal enterocytes

“…A similar observation has already been reported for villin [2]. Many other proteins, including those whose synthesis is now thought to be controlled at the translational level [3,6,191, might show similar inefficient translation of mRNA during structural differentiation of enterocytes.…”

“…Enterocyte differentiation takes place in two stages, initial completion of microvillus elongation and expression of microvillus digestive enzymes being followed by late expression of absorptive function [21,22]. Developmental control over the expression of one of these digestive enzymes, sucraseisomaltase, appears to be by transcription in neonatal rabbits and humans [17,181 and adult rats [Ill. Developmental control over lactase [6, 191 and aminopeptidase N [3] expression appears, however, to be at the level of translation. These results showing regulation of * To whom offprint requests should be sent digestive enzyme expression have all been obtained by analysing homogenates prepared from different intestinal tissues.…”

Regulation of the ovine intestinal Na+/glucose co-transporter (SGLT1) is dissociated from mRNA abundance

“…The disparity in the relative changes in mRNA levels and enzyme activities may be due to enhanced biosynthesis, alterations in protein half-life or recruitment of intracellular proteins to their functional site. In the case of aminopeptidase N and sucrase-isomaltase, the disparity is attributed to differences in translational processing (Danielsen et al, 1986;Hoffman and Chang, 1991). Hoffman and Chang (1991) determined that a large proportion of jejunal sucroseisomaltase mRNA was associated with membrane-bound polyribosomes, which could account for the 3-4-fold difference in enzyme expression along the longitudinal axis of the gut in the absence of any difference in mRNA levels.…”

The Prenatal Development and Glucocorticoid Control of Brush-Border Hydrolases in the Pig Small Intestine

“…In the newborn pig, changes in the fundamental biochemistry of existing enterocytes rather than cell replacement are likely to account for the age-and glucocort icoid-related enzymatic changes (11,39). There is now substantial evidence that ageand glucocor ticoid-related increases in the biosynthesis of enzyme protein are regulated at the transcriptional level, although changes in posttranslatio nal modifications may also occur during development (7,8,(40)(41)(42)(43). The observa tions in the present study and other studies showi ng that glucocort icoids affect only some enzymes and only in certain parts of the intestine certainly indicate a more sophisticated regulatory mechanism than that of a genera l increase in the mucosal cell proliferation rate or enterocyte biosynt hetic capacity.…”