Poly(A)+ RNA from rabbit intestinal mucosa induces b0,+ and y+ amino acid transport activities in Xenopus laevis oocytes

Abstract

Injection of poly(A)+ RNA (mRNA) isolated from rabbit intestinal mucosa into Xenopus laevis oocytes results in an increase in sodium-independent uptake of L-[3H]leucine, L-[35S]cystine, and L-[3H]arginine. This uptake activity is related to an mRNA species corresponding to the recently isolated rabbit kidney cortex cDNA clone rBAT (related to b0,+ amino acid transporter; Bertran, J., Werner, A., Stange, G., Markovich, D., Moore, M. L., Biber, J., Testar, X., Zorzano, A., Palacin, M., and Murer, H. (1992) Proc. Natl. Acad. Sci. U.S.A. 281, 717-723) and to a protein involved in amino acid transport via system y+. This conclusion is based on the following observations: 1) mRNA isolated from mucosa of duodenum, jejunum, and ileum, but not from colon, induces sodium-independent uptake of L-leucine, L-cystine, and L-arginine. 2) In Northern blot analysis, mRNA isolated from mucosa of duodenum, jejunum, and ileum, but not from colon, hybridizes to an rBAT cDNA probe, with signals of 2.2-2.3 kilobases and 3.7-3.9 kilobases. 3) mRNA isolated from mucosa of jejunum induces sodium-independent uptake of L-leucine and L-cysteine which shows an inhibition pattern corresponding to system b0,+; the inhibition pattern of mRNA-induced uptake of L-arginine is compatible with the contribution of system b0,+ and y+. 4) Hybrid depletion with an rBAT antisense oligonucleotide greatly prevents the mRNA-dependent induction of uptake of L-cystine (greater than 90%) and of L-leucine (approximately 75%); it reduces to about 50% the induction of L-arginine uptake. 5) After separation of mRNA on a sucrose density gradient, the fractions resulting in expression of b0,+ transport activity were also those hybridizing with rBAT cDNA; induction of transport activity from these fractions was also sensitive to hybrid depletion. 6) The mRNA-induced component of L-arginine uptake which is resistant to rBAT hybrid depletion is inhibited by L-homoserine, only in the presence of sodium; thus, it is related to a system y(+)-like activity.