Abstract
Mpv17-like protein (M-LP) has been identified as a new protein that shows high sequence homology with Mpv17 protein, a peroxisomal membrane protein involved in the development of early onset glomerulosclerosis. We previously showed that the originally identified M-LP isoform, designated M-LP L, is, like Mpv17, localized in peroxisomes, and that transfection with M-LP L up-regulates expression of the manganese superoxide dismutase (SOD2) gene [R. Iida, T. Yasuda, E. Tsubota, H. Takatsuka, M. Masuyama, T. Matsuki, K. Kishi, M-LP, Mpv17-like protein, has a peroxisomal membrane targeting signal comprising a transmembrane domain and a positively charged loop and up-regulates expression of the manganese superoxide dismutase gene. J. Biol. Chem. 278 (2003) 6301–6306.]. We report here the identification of a novel alternative splicing product of the M-LP gene, designated M-LP S. A comparison of the genomic sequence with the cDNA sequences and an analysis of 5'-flanking regions revealed that the two isoforms are generated by alternative usage of two promoters. M-LP S consists of the C-terminal half of M-LP L (90 amino acids) and therefore lacks the peroxisome targeting signal of membrane protein that exists near the N-terminus of M-LP L. Expression of green fluorescent protein-tagged M-LP S in COS-7 cells demonstrated that M-LP S localizes in the cytosol. In mice, M-LP S is expressed exclusively in kidneys after the age of 6 weeks. Moreover, quantitative real-time PCR analysis revealed that transfection with M-LP S up-regulates expression of the SOD2 gene and down-regulates expression of the cellular glutathione peroxidase (Gpx1) and plasma glutathione peroxidase (Gpx3) genes. Taken together, these results suggest different functional attributes of the two M-LP isoforms during aging and development.
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