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H. Ma, M. Shih, E. Nakajima, C. Fukiage, M. Azuma, T.R. Shearer; Different Expression Patterns for Human Css1 and Css2 During Lens Maturation . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1236.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Typical calpains are heterodimeric cystenine proteases, which have distinct large catalytic subunits (80 kDa) but share a common small regulatory subunit (30 kDa; css1). Recently, a novel human small subunit of calpains (css2) has been reported. The amino acid sequence of css2 displays 73% identity within the Ca-binding region but lacks two oligo-Gly stretches in the N-terminal domain of the conventional small subunit (css1). To identify the function of css2, the present work described the expression of transcripts for css1 and css2 during normal lens maturation.Methods:The expression patterns of css1 and css2 mRNAs in various tissues of rats and in human lenses of various ages were determined by the relative quantitative RT-PCR using 18 S rRNA as an endogenous standard. Results:Quantitative RT-PCR indicated that appreciable mRNA levels for css2 were found only in specific tissues of young rats including brain, liver, lung, stomach, retina and lens. In contrast, mRNA of css1 was found to be expressed in all tissues examined so far. Lens contained relatively high mRNA levels for css2, and the highest amount was in the outer region of the lens epithelium. This expression pattern was similar to the css1 as well as to the large subunit of calpain 2 in the lens. Moreover, levels of css1 and css2 mRNAs changed during the lens maturation. Young human lenses also showed a high level of mRNA for css1, while aging lenses showed a decrease. In contrast, mRNA level for css2 in aged human lenses was much higher than in young lenses. Computer-based homology modeling revealed similar interactions between the large subunit of calpain 2 with css2 or css1.Conclusions:These results suggested calpain small subunit 2(css2) might substitute for age-related loss of small subunit 1(css1) in the lens during development and maturation. They also suggested that css2 may interact with the large subunit of calpains and regulate the activity of the large subunit in vivo.
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