Five novelSLC7A7 variants and y+L gene-expression pattern in cultured lymphoblasts from Japanese patients with lysinuric protein intolerance

Abstract

Two distinct human light subunits of the heteromeric amino acid transporter, y+LAT-1 coded by SLC7A7 and y+LAT-2 coded by SLC7A6, are both known to induce transport system y+L activity. SLC7A7 has already been identified as the gene responsible for lysinuric protein intolerance (LPI). We successfully identified five novel SLC7A7 variants (S238F, S489P, 1630delC, 1673delG, and IVS3-IVS5del9.7kb) in Japanese patients with LPI by PCR amplification and direct DNA sequencing. In addition, we performed a semi-quantitative expression analysis of SLC7A7 and SLC7A6 in human tissue. In normal tissue, the gene-expression ratio of SLC7A6 to SLC7A7 was high in the brain, muscle, and cultured skin fibroblasts; low in the kidneys and small intestine; and at an intermediate level in peripheral blood leukocytes, the lungs, and cultured lymphoblasts. The gene-expression ratio of SLC7A6 to SLC7A7 in cultured lymphoblasts was significantly different between normal subjects and LPI patients with R410X and/or S238F, where the relative amount of SLC7A7 mRNA was significantly lower and the relative amount of SLC7A6 mRNA was statistically higher in affected lymphoblasts than in normal cells. Expression of SLC7A7 and SLC7A6 may thus be interrelated in cultured lymphoblasts.

A y+LAT-1 mutant protein interferes with y+LAT-2 activity: implications for the molecular pathogenesis of lysinuric protein intolerance

“…In other tissues, such as the small intestine and kidney, where both SLC7A6 and SLC7A7 are expressed, y þ LAT-1 mutants might interfere with the activity of the [4F2hc/y þ LAT-2] complex. This interference can explain why the compensatory mechanism, that is, an increased expression of SLC7A6 as seen in lymphoblasts from LPI patients, 11 may not be sufficient to restore the y þ L system activity.…”

“…In fact, an increased expression of SLC7A6 was found in lymphoblasts from LPI patients. 11 Here we report the results of functional studies of two mutations of SLC7A7, which provide further insight into the molecular pathogenesis of LPI: a putative multiheteromeric structure of both [4F2hc/y þ LAT-1] and [4F2hc/ y þ LAT-2], and the interference between y þ LAT-1 and y þ LAT-2 proteins.…”

Lysinuric protein intolerance: update and extended mutation analysis of theSLC7A7 gene

“…LPI is more prevalent in Finland (1/76,000 births) but clusters of LPI families are also known in southern Italy and Japan, and sporadic cases have been described worldwide Shoji et al, 2002;Norio, 2003]. Major symptoms include vomiting, diarrhea, failure to thrive, hepatosplenomegaly, bone marrow abnormalities, osteoporosis, episodes of coma, mental retardation, lung involvement (mainly as alveolar proteinosis), altered immune response and chronic renal disease [Palacin et al, 2001;Simell, 2001].…”

Lysinuric protein intolerance: one gene, many problems

“…Both transporters export cationic amino acids from the cell in exchange for neutral amino acids. Due to the low expression levels of y ϩ LAT2 in the intestine and kidney, it cannot replace the function of y ϩ LAT1 (11). LPI is more frequent in Finland than in other countries.…”