Truncated Forms of the Dual Function Human ASCT2 Neutral Amino Acid Transporter/Retroviral Receptor Are Translationally Initiated at Multiple Alternative CUG and GUG Codons

Chetankumar S. Tailor, Mariana Marin, Ali Nouri, Michael P. Kavanaugh, David Kabat

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

The sodium-dependent neutral amino acid transporter type 2 (ASCT2) was recently identified as a cell surface receptor for endogenously inherited retroviruses of cats, baboons, and humans as well as for horizontally transmitted type-D simian retroviruses. By functional cloning, we obtained 10 full-length 2.9-kilobase pair (kbp) cDNAs and two smaller identical 2.1-kbp cDNAs that conferred susceptibility to these viruses. Compared with the 2.9-kbp cDNA, the 2.1-kbp cDNA contains exonic deletions in its 3′ noncoding region and a 627-bp 5′ truncation that eliminates sequences encoding the amino-terminal portion of the full-length ASCT2 protein. Although expression of the truncated mRNA caused enhanced amino acid transport and viral receptor activities, the AUG codon nearest to its 5′ end is flanked by nucleotides that are incompatible with translational initiation and the next in-frame AUG codon is far downstream toward the end of the protein coding sequence. Interestingly, the 5′ region of the truncated ASCT2 mRNA contains a closely linked series of CUG(Leu) and GUG(Val) codons in optimal consensus contexts for translational initiation. By deletion and site-directed mutagenesis, cell-free translation, and analyses of epitope-tagged ASCT2 proteins synthesized intracellularly, we determined that the truncated mRNA encodes multiple ASCT2 isoforms with distinct amino termini that are translationally initiated by a leaky scanning mechanism at these CUG and GUG codons. Although the full-length ASCT2 mRNA contains a 5′-situated AUG initiation codon, a significant degree of leaky scanning also occurred in its translation. ASCT2 isoforms with relatively short truncations were active in both amino acid transport and viral reception, whereas an isoform with a 79-amino acid truncation that lacked the first transmembrane sequence was active only in viral reception. We conclude that ASCT2 isoforms with truncated amino termini are synthesized in mammalian cells by a leaky scanning mechanism that employs multiple alternative CUG and GUG initiation codons.

Original languageEnglish (US)
Pages (from-to)27221-27230
Number of pages10
JournalJournal of Biological Chemistry
Volume276
Issue number29
DOIs
StatePublished - Jul 20 2001

Fingerprint

Neutral Amino Acid Transport Systems
Codon
Protein Isoforms
Complementary DNA
Messenger RNA
Initiator Codon
Scanning
Amino Acids
Simian Retroviruses
Mutagenesis
Proteins
Papio
Cloning
Cell Surface Receptors
Retroviridae
Site-Directed Mutagenesis
Viruses
Organism Cloning
Epitopes
Cats

ASJC Scopus subject areas

  • Biochemistry

Cite this

Truncated Forms of the Dual Function Human ASCT2 Neutral Amino Acid Transporter/Retroviral Receptor Are Translationally Initiated at Multiple Alternative CUG and GUG Codons. / Tailor, Chetankumar S.; Marin, Mariana; Nouri, Ali; Kavanaugh, Michael P.; Kabat, David.

In: Journal of Biological Chemistry, Vol. 276, No. 29, 20.07.2001, p. 27221-27230.

Research output: Contribution to journalArticle

Tailor, Chetankumar S. ; Marin, Mariana ; Nouri, Ali ; Kavanaugh, Michael P. ; Kabat, David. / Truncated Forms of the Dual Function Human ASCT2 Neutral Amino Acid Transporter/Retroviral Receptor Are Translationally Initiated at Multiple Alternative CUG and GUG Codons. In: Journal of Biological Chemistry. 2001 ; Vol. 276, No. 29. pp. 27221-27230.
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