Berger J J, Eisenhauer D A, Taylor A
Laboratory for Nutrition and Cataract Research, USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts 02111.
In Vitro Cell Dev Biol. 1988 Oct;24(10):990-4. doi: 10.1007/BF02620871.
Although several proteases have been identified in homogenates of cultured epithelial cells of the eye lens and in lens tissues, there is little information regarding intracellular protein degradation in intact lens cells in vitro. Cultured lens cells may be useful in the study of intracellular protein degradation in the lens, a tissue with a wide range of protein half-lives. This is of interest because alterations in protein turnover in the lens have been implicated in cataract formation. This study examines intracellular protein degradation in cultured bovine lens epithelial cells (BLEC). Cell cultures were incubated with radiolabeled leucine to label intracellular proteins. Protein degradation was measured by monitoring the release of trichloroacetic-acid-soluble radioactivity into the culture medium. The average half-life of long-lived proteins (half-life greater than 50 h) was typically about 57 h in serum-supplemented medium. Average rates of degradation of long-lived proteins increased by up to 73% when fetal bovine serum was withdrawn from the culture medium. Serum had no effect on the degradation of short-lived proteins (half-life less than 10 h). Degradation of long-lived proteins in the presence and absence of serum was further studied in cultured BLEC from population doubling level (PDL) 2 to 43. Average half-life of proteins in serum-supplemented medium was 52 to 58 h and did not vary significantly as a function of PDL. Degradation rates in serum-free medium increased approximately twofold up to PDL 7, but returned by PDL 25 to original levels, which were maintained through PDL 43.
尽管在培养的晶状体上皮细胞匀浆和晶状体组织中已鉴定出几种蛋白酶，但关于体外完整晶状体细胞内蛋白质降解的信息却很少。培养的晶状体细胞可能有助于研究晶状体中的细胞内蛋白质降解，晶状体是一种蛋白质半衰期范围很广的组织。这一点很重要，因为晶状体中蛋白质周转的改变与白内障的形成有关。本研究检测了培养的牛晶状体上皮细胞（BLEC）中的细胞内蛋白质降解。细胞培养物与放射性标记的亮氨酸一起孵育以标记细胞内蛋白质。通过监测三氯乙酸可溶性放射性物质释放到培养基中来测量蛋白质降解。在补充血清的培养基中，长寿命蛋白质（半衰期大于50小时）的平均半衰期通常约为57小时。当从培养基中去除胎牛血清时，长寿命蛋白质的平均降解率增加高达73%。血清对短寿命蛋白质（半衰期小于10小时）的降解没有影响。在从群体倍增水平（PDL）2到43的培养的BLEC中，进一步研究了有无血清时的长寿命蛋白质降解。补充血清的培养基中蛋白质的平均半衰期为52至58小时，并且不会随PDL显著变化。无血清培养基中的降解率在PDL 7之前增加了约两倍，但在PDL 25时恢复到原始水平，并一直维持到PDL 43。
