Ma H, Shih M, Throneberg D B, David L L, Shearer T R
Department of Oral Molecular Biology, Oregon Health Sciences University, Portland 97201, USA.
Exp Eye Res. 1997 Mar;64(3):437-45. doi: 10.1006/exer.1996.0229.
The purpose of these experiments was to describe the expression of mRNA for calpain II proteolytic enzyme (EC 3.4.22.17) during normal maturation of rat lens and in cataract formation. Quantitative RT-PCR indicated that the concentration of mRNA for calpain II in whole lens was 3-24 times higher than in age-matched rat liver, kidney, lung and brain, and it was at least five times higher than in young human lens. mRNA levels for calpain II were highest in the outer regions of young rat lens at 5 x 10(6) copies microgram-1 total RNA. Early-stage experimental cataract caused increased calpain II mRNA, while mature nuclear cataract showed a 64% loss. In contrast, mRNA levels for GAPDH, beta-actin, and lens-specific structural protein beta A4 remained constant during experimental cataract formation. Unlike the lower and constant levels in rat liver, kidney and lung; calpain II mRNA levels in whole rat lens decreased with age. These data help explain the high enzymatic activity of calpain II in young rat lens, susceptibility of young rat lens to a variety of cataracts showing increased calcium and calpain-induced proteolysis, and low calpain enzyme activity in human lens. Since the up-regulation of calpain II mRNA was more dynamic than either the amounts of calpain II enzyme or proteolysis of crystallins in cortex, resulting proteolytic activity against the bulk of lens proteins seems to be regulated by post-translational factors, such as increased calcium. The precise role of the up-regulation of calpain II mRNA is unknown, but we hypothesize that it may be associated with the initial cataractogenic response in the epithelial cells or peripheral cortical fibers.
这些实验的目的是描述钙蛋白酶II（EC 3.4.22.17）的mRNA在大鼠晶状体正常成熟过程及白内障形成过程中的表达情况。定量逆转录聚合酶链反应表明，整个晶状体中钙蛋白酶II的mRNA浓度比年龄匹配的大鼠肝脏、肾脏、肺和大脑中的浓度高3至24倍，且至少比年轻人类晶状体中的浓度高五倍。在5×10⁶拷贝/微克总RNA时，年轻大鼠晶状体外部区域的钙蛋白酶II的mRNA水平最高。早期实验性白内障导致钙蛋白酶II的mRNA增加，而成熟核性白内障则显示出64%的减少。相比之下，在实验性白内障形成过程中，甘油醛-3-磷酸脱氢酶（GAPDH）、β-肌动蛋白和晶状体特异性结构蛋白βA4的mRNA水平保持恒定。与大鼠肝脏、肾脏和肺中较低且恒定的水平不同；整个大鼠晶状体中钙蛋白酶II的mRNA水平随年龄下降。这些数据有助于解释钙蛋白酶II在年轻大鼠晶状体中的高酶活性、年轻大鼠晶状体对各种显示钙增加和钙蛋白酶诱导的蛋白水解的白内障的易感性以及人类晶状体中低钙蛋白酶酶活性。由于钙蛋白酶II的mRNA上调比皮质中钙蛋白酶II酶的量或晶状体蛋白的蛋白水解更具动态性，因此针对大部分晶状体蛋白的蛋白水解活性似乎受翻译后因素调节，如钙增加。钙蛋白酶II的mRNA上调的确切作用尚不清楚，但我们推测它可能与上皮细胞或周边皮质纤维中的初始致白内障反应有关。
