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J Bertran

Publications and source records attributed to J Bertran.

10 recordsLinked to original sources
PubMed1992

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

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.

Amino Acids↗
PubMed1992

Expression cloning of a cDNA from rabbit kidney cortex that induces a single transport system for cystine and dibasic and neutral amino acids.

We have isolated a cDNA clone by screening a rabbit kidney cortex cDNA library for expression of sodium-independent transport of L-arginine and L-alanine in Xenopus laevis oocytes. Expressed uptake relates to a single component of sodium-independent transport for dibasic and neutral amino acids. This transport activity resembles the functionally defined system b0,+ and carries cystine and dibasic amino acids with high affinity. The rBAT (b0,+ amino acid transporter-related) mRNA is found mainly in kidney and intestinal mucosa. It encodes a predicted 77.8-kDa protein with only one putative transmembrane domain and seven potential N-glycosylation sites. This protein could either be a constitutive element or a specific activator of system b0,+.

Amino Acid Sequence↗
PubMed1992

Stimulation of system y(+)-like amino acid transport by the heavy chain of human 4F2 surface antigen in Xenopus laevis oocytes.

A kidney cortex cDNA clone (rBAT) has recently been isolated, which upon in vitro transcription and capping complementary RNA (cRNA) and injection into Xenopus laevis oocytes induces a system b0,(+)-like amino acid transport activity. This cDNA encodes a type II membrane glycoprotein that shows significant homology to another type II membrane glycoprotein, the heavy chain of the human and mouse 4F2 surface antigen (4F2hc). Here we demonstrate that injection of human 4F2hc cRNA into oocytes results in the activation of a cation-preferring amino acid transport system that appears to be identical to the y(+)-like transport already present in the oocyte. This is based on the following results: (i) Injection of in vitro transcripts from 4F2hc cDNA (4F2hc cRNA) into oocytes stimulates up to 10-fold the sodium-independent uptake of L-arginine and up to 4.1-fold the sodium-dependent uptake of L-leucine. In contrast, 4F2hc cRNA does not increase the basal sodium-independent uptake of L-leucine. (ii) Basal and 4F2hc cRNA-stimulated sodium-independent uptake of L-arginine is completely inhibited by L-leucine in the presence of sodium. Similarly, the basal and 4F2hc cRNA-stimulated sodium-dependent uptake of L-leucine is entirely inhibited by L-arginine. (iii) The stimulation of sodium-independent uptake of L-arginine and the stimulation of sodium-dependent uptake of L-leucine induced by injection of 4F2hc cRNA are both completely inhibited by dibasic L amino acids and to a lesser extent by D-ornithine. (iv) Both basal and 4F2hc cRNA-stimulated sodium-independent uptake of L-arginine show two additional characteristics of the system y+ transport activity: inhibition of L-arginine uptake by L-homoserine only in the presence of sodium and an increase in the inhibition exerted by L-histidine as the extracellular pH decreased. Our results allow us to propose that an additional family of type II membrane glycoproteins (composed by rBAT and 4F2hc) is involved in amino acid transport, either as specific activators or as components of amino acid transport systems.

Amino Acid Sequence↗
PubMed1992

Expression of Na(+)-independent amino acid transport in Xenopus laevis oocytes by injection of rabbit kidney cortex mRNA.

Poly(A)+ mRNA was isolated from rabbit kidney cortex and injected into Xenopus laevis oocytes. Injection of mRNA resulted in a time- and dose-dependent increase in Na(+)-independent uptake of L-[3H]alanine and L-[3H]arginine. L-Alanine uptake was stimulated about 3-fold and L-arginine uptake was stimulated about 8-fold after injection of mRNA (25-50 ng, after 3-6 days) as compared with water-injected oocytes. T.I.C. of oocyte extracts suggested that the increased uptake actually represented an increase in the oocyte content of labelled L-alanine and L-arginine. The expressed L-alanine uptake, obtained by subtracting the uptake in water-injected oocytes from that in mRNA-injected oocytes, showed saturability and was inhibited completely by 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) and L-arginine. The expressed L-arginine uptake in mRNA-injected oocytes also showed saturability, being completely inhibited by L-dibasic amino acids) and partially inhibited by BCH. Expression of both L-alanine and L-arginine uptake showed clear cis-inhibition by cationic (e.g. L-arginine) and neutral (e.g. L-leucine) amino acids. In all, this points to the expression of a Na(+)-independent transport system with broad specificity (i.e. b degree, (+)-like). In addition, part of the expressed uptake of L-arginine could be due to a system y(+)-like transporter. After size fractionation through a sucrose density gradient, the mRNA species encoding these increased transport activities (Na(+)-independent transport of L-alanine and of L-arginine) were found in fractions of an average mRNA chain-length of 1.8-2.4 kb. On the basis of these results, we conclude that Na(+)-independent transport system(s) for L-alanine and L-arginine from rabbit renal cortical tissues, most likely proximal tubules, are expressed in Xenopus laevis oocytes. These observations may represent the first steps towards expression and cloning of these transport pathways.

Alanine↗
PubMed1991

Modification of system A amino acid carrier by diethyl pyrocarbonate.

Sodium-dependent alanine transport in plasma membrane vesicles from rat liver was inactivated in a time- and concentration-dependent fashion by prior treatment of membranes with the acylating reagent diethyl pyrocarbonate (DEPC). Both components of Na+/alanine cotransport (systems A and ASC) were inhibited. Exposure of vesicles to p-bromophenacyl bromide and methyl p-nitrobenzenesulfonate, which share with DEPC reactivity against histidine residues, also led to inhibition of alanine transport through systems A and ASC. The presence of Na+ (100 mM NaCl) and L-alanine (10 mM) during exposure to vesicles to DEPC protected against inactivation of system A (but not system ASC) transport activity. This protective effect was specific and required the presence of L-alanine since the presence of L-phenylalanine alone (10 mM) or L-phenylalanine plus Na+ (100 mM NaCl) did not cause any detectable protection. This overall pattern of protection is opposite to that previously found against specific sulfhydryl reagents (i.e. N-ethylmaleimide), where protection of system ASC was nearly maximal. The pH profile for DEPC-dependent inhibition of system A transport activity suggests modification of amino acid residue(s) with a pKr of approximately 7, most likely histidine(s), in close parallel with the pH dependence of system A transport activity. Our results suggest the presence of critical histidine residues on the system A carrier that may be responsible for the pH dependence of system A transport activity.

Alanine↗
PubMed1990

Sensitivity of system A and ASC transport activities to thiol-group-modifying reagents in rat liver plasma-membrane vesicles. Evidence for a direct binding of N-ethylmaleimide and iodoacetamide on A and ASC carriers.

1. In the present study we have examined the sensitivity of A and ASC amino-acid-carrier activities in rat liver plasma-membrane vesicles to the thiol-group modifying reagents N-ethylmaleimide (NEM) and iodoacetamide (IA). To this end, the different Na(+)-dependent entities involved in alanine transport were assessed. 2. NEM inactivated Na(+)-dependent alanine transport as a result of the inhibition of both system A and ASC transport activities. The functional sensitivity of system A to NEM was greater than that of system ASC. 3. The presence of L-alanine (10 mM) during the exposure of vesicles to NEM afforded partial protection to system A, but not to the ASC, carrier. This effect was specific, since the presence of L-phenylalanine (10 mM) did not cause any protection. 4. Na+ did not protect A or ASC carriers against NEM inactivation; however, the presence of Na+ (100 mM-NaCl) and L-alanine (10 mM) during the exposure of the vesicles to NEM protected against inactivation of system A and ASC transport activities. The extent of protection was greater in the case of the system ASC transport activity than in the case of the A carrier. 5. IA also diminished Na(+)-dependent alanine transport by inhibition of A and ASC transport activities. Sodium and L-alanine afforded protection to both A and ASC transport activities from the inhibitory action of IA. The extent of protection induced by substrates was similar for both carriers. 6. It is concluded that there is one, or several, free thiol groups in A and ASC carriers, the integrity of which is essential for transport activity. Sensitivity to thiol-group-specific reagents and the pattern of protection with substrates against inactivation is different in A and ASC carriers. That suggests the existence of topological dissimilarities regarding the thiol-group containing site(s) in A and ASC amino acid carriers.

Alanine↗