Age-related decrease of IF5/BTG4 in oral and respiratory cavities in mice.

An IF5 cDNA was isolated by expression cloning from a mouse oocyte cDNA library. It encoded a protein of 250 amino acids, and the region of it encoding amino acids 1-137 showed 86.8% alignment with the anti-proliferative domain of BTG/TOB family genes. This gene is also termed BTG4 or PC3B. Transiently expressed IF5/BTG4 induced alkaline phosphatase activity in human embryonic kidney (HEK293T) and 2T3 cells. IF5/BTG4 mRNA was detected by reverse transcription polymerase chain reaction in pharynx, larynx, trachea, oviduct, ovary, caput epididymis, and testis, but not in lung, intestine, or liver. Immunohistochemistry showed the IF5/BTG4 protein to be present in epithelial cells of the tongue, palate, pharynx, internal nose, and trachea. Both protein and mRNA levels of IF5/BTG4 were reduced by aging when comparing 4-week-old mice with 48-week-old mice. Our findings suggest that IF5/BTG4 may be an aging-related gene in epithelial cells.

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