RESUMEN
Heterodimeric amino acid transporters play crucial roles in epithelial transport, as well as in cellular nutrition. Among them, the heterodimer of a membrane protein b(0,+)AT/SLC7A9 and its auxiliary subunit rBAT/SLC3A1 is responsible for cystine reabsorption in renal proximal tubules. The mutations in either subunit cause cystinuria, an inherited amino aciduria with impaired renal reabsorption of cystine and dibasic amino acids. However, an unsolved paradox is that rBAT is highly expressed in the S3 segment, the late proximal tubules, whereas b(0,+)AT expression is highest in the S1 segment, the early proximal tubules, so that the presence of an unknown partner of rBAT in the S3 segment has been proposed. In this study, by means of coimmunoprecipitation followed by mass spectrometry, we have found that a membrane protein AGT1/SLC7A13 is the second partner of rBAT. AGT1 is localized in the apical membrane of the S3 segment, where it forms a heterodimer with rBAT. Depletion of rBAT in mice eliminates the expression of AGT1 in the renal apical membrane. We have reconstituted the purified AGT1-rBAT heterodimer into proteoliposomes and showed that AGT1 transports cystine, aspartate, and glutamate. In the apical membrane of the S3 segment, AGT1 is suggested to locate itself in close proximity to sodium-dependent acidic amino acid transporter EAAC1 for efficient functional coupling. EAAC1 is proposed to take up aspartate and glutamate released into luminal fluid by AGT1 due to its countertransport so that preventing the urinary loss of aspartate and glutamate. Taken all together, AGT1 is the long-postulated second cystine transporter in the S3 segment of proximal tubules and a possible candidate to be involved in isolated cystinuria.
Asunto(s)
Sistemas de Transporte de Aminoácidos Básicos/metabolismo , Sistemas de Transporte de Aminoácidos Neutros/metabolismo , Sistemas de Transporte de Aminoácidos/metabolismo , Membrana Celular/metabolismo , Cistinuria/metabolismo , Túbulos Renales Proximales/metabolismo , Secuencia de Aminoácidos , Sistemas de Transporte de Aminoácidos/química , Sistemas de Transporte de Aminoácidos/genética , Animales , Anticuerpos/metabolismo , Western Blotting , Transportador 3 de Aminoácidos Excitadores/metabolismo , Femenino , Células HEK293 , Humanos , Inmunohistoquímica , Hibridación in Situ , Riñón/metabolismo , Masculino , Ratones Endogámicos C57BL , Datos de Secuencia Molecular , Unión Proteica , Multimerización de Proteína , Proteolípidos/metabolismo , ARN Mensajero/genética , ARN Mensajero/metabolismo , Elementos de Respuesta/genéticaRESUMEN
Somatic cells can be reprogrammed to induced pluripotent stem cells (iPSCs) using oncogenic transcription factors. However, this method leads to genetic aberrations in iPSCs via unknown mechanisms, which may limit their clinical use. Here, we demonstrate that the supplementation of growth media with antioxidants reduces the genome instability of cells transduced with the reprogramming factors. Antioxidant supplementation did not affect transgene expression level or silencing kinetics. Importantly, iPSCs made with antioxidants had significantly fewer de novo copy number variations, but not fewer coding point mutations, than iPSCs made without antioxidants. Our results suggest that the quality and safety of human iPSCs might be enhanced by using antioxidants in the growth media during the generation and maintenance of iPSCs.