Molecular Sites of Regulation of Expression of the Rat Cationic Amino Acid Transporter Gene

Self Cite

107

The cationic amino acid transporter, Cat-1, is a high affinity transporter of the essential amino acids, arginine and lysine. Expression of the cat-1 gene increases during nutritional stress as part of the adaptive response to starvation. Amino acid limitation induces coordinate increases in stability and translation of the cat-1 mRNA, at a time when global protein synthesis decreases. It is shown here that increased cat-1 mRNA stability requires an 11 nucleotide AU-rich element within the distal 217 bases of the 3-untranslated region. When this 217-nucleotide nutrient sensor AU-rich element (NS-ARE) is present in a chimeric mRNA it confers mRNA stabilization during amino acid starvation. HuR is a member of the ELAV family of RNA-binding proteins that has been implicated in regulating the stability of ARE-containing mRNAs. We show here that the cytoplasmic concentration of HuR increases during amino acid starvation, at a time when total cellular HuR levels decrease. In addition, RNA gel shift experiments in vitro demonstrated that HuR binds to the NS-ARE and binding was dependent on the 11 residue AU-rich element. Moreover, HuR binding to the NS-ARE in extracts from amino acid-starved cells increased in parallel with the accumulation of cytoplasmic HuR. It is proposed that an adaptive response of cells to nutritional stress results in increased mRNA stability mediated by HuR binding to the NS-ARE.

mentioning

confidence: 71%

Nutritional Control of mRNA Stability Is Mediated by a Conserved AU-rich Element That Binds the Cytoplasmic Shuttling Protein HuR

Yaman¹,

Fernandez²,

Sarkar³

et al. 2002

Self Cite

107

“…In brain astrocytes, lipopolysaccharide/interferon ␥ induced CAT2 but not CAT1 (20). Various signals that cause transition of cells from the resting state to the proliferating state appear to activate CAT1 expression (35)(36)(37).…”

Section: Discussionmentioning

confidence: 99%

A New Member of the Cationic Amino Acid Transporter Family Is Preferentially Expressed in Adult Mouse Brain

Ito

Groudine

1997

105

We have isolated and characterized a novel member (CAT3) of the cationic amino acid transporter (CAT) family. In oocyte injection assays, CAT3 cRNA exhibited a saturable, sodium ion-independent transport activity with high affinity for L-arginine and L-lysine (K m ‫؍‬ 40 -60 and 115-165 M, respectively). Transport of L-arginine was effectively competed only by cationic amino acids in L-form: arginine, lysine, ornithine, and 2,4-diamino-n-butyric acid but not by 2,3-diaminopropionic acid. The presence of L-arginine in the incubation medium stimulated the efflux rate of L-arginine, indicating that CAT3 is subject to trans-stimulation. All these results are consistent with the idea that CAT3, along with CAT1 and CAT2, constitutes the transport activity originally assigned to system y ؉ . Like CAT2, but unlike CAT1, the expression of CAT3 is regulated in a highly tissue-specific manner; when various adult tissues were examined, significant levels of CAT3 transcript were detectable only in brain. In situ hybridization on brain sections revealed that CAT3 transcripts were localized predominantly along the midbrain-thalamus-hypothalamus axis, whereas neither CAT1 nor CAT2 transcripts demonstrated a similar localization. In contrast to its highly localized expression during the primitive streak stage and in the adult stage, CAT3 expression was detected more widely in 13.5 day post-coitum mouse embryos.

“…Characterization of the Promoter Regulatory Region of the cat-1 Gene-Rat genomic DNA clones were isolated by PCR screening of a P1 phage genomic library using oligonucleotides from the 5Ј-end of the available cat-1 cDNA (27). We obtained three clones that cover this region with inserts of ϳ70 kb each.…”

Section: Induction Of Cat-1 Gene Expression By Amino Acid Starvation-mentioning

confidence: 99%

Transcriptional Control of the Arginine/Lysine Transporter, Cat-1, by Physiological Stress

Fernandez¹,

Lopez²,

Wang³

et al. 2003

Cells respond to physiological stress by phosphorylating the ␣ subunit of the translation initiation factor eIF2. This adaptive response inhibits protein synthesis and up-regulates genes essential for cell survival. Cat-1, the transporter for the essential amino acids, arginine and lysine, is one of the up-regulated genes. We previously showed that stress increases cat-1 expression by coordinated stabilization of the mRNA and increased mRNA translation. This induction is triggered by amino acid depletion and the unfolded protein response (UPR), which is caused by unfolded proteins in the endoplasmic reticulum. We show here that cat-1 gene transcription is also increased by cellular stress. Our studies demonstrate that the cat-1 gene promoter/regulatory region is TATA-less and is located in a region that includes 94 bases of the first exon. Transcription from this promoter is stimulated 8-fold by cellular stress. An amino acid response element within the first exon is shown to be required for the response to amino acid depletion but not to the UPR. The stimulation of transcription by amino acid depletion requires activation of GCN2 kinase, which phosphorylates eIF2␣. This phosphorylation also induces translation of the cat-1 mRNA, demonstrating that stress-induced transcriptional and translational control of cat-1 are downstream targets of a signaling pathway initiating with eIF2␣ phosphorylation. Our studies show that the increase in cat-1 gene expression by cellular stress involves at least three types of coordinate regulation: regulation of transcription, regulation of mRNA stability, and regulation of mRNA translation.