Wójcik C, Tanaka K, Paweletz N, Naab U, Wilk S
Department of Pharmacology, Mount Sinai School of Medicine, New York, NY, USA.
Eur J Cell Biol. 1998 Oct;77(2):151-60. doi: 10.1016/s0171-9335(98)80083-6.
The catalytic activity of the 20S proteasome can be modulated by endogenous proteins. A proteasome activator protein termed PA28 or 11S regulator, composed of two homologous subunits (alpha and beta) and a separate but related protein termed Ki antigen or PA28gamma have been characterized. To explore the functional relationship of these proteins, NT2 clone D1 human neuronal precursor cells, as well as HeLa S3 cells were labeled by immunofluorescence and immunoelectron microscopy with three different antisera directed against peptides derived from their sequences. It was found that both PA28alpha and PA28beta antisera label the cytoplasm and the nucleoli. In contrast, the PA28gamma antiserum labels the nucleus but not the nucleoli while in the cytoplasm it labels two different classes of structures identified as microtubular-like extensions and inclusion bodies that are most likely autophagosomes. The latter do not contain proteasome delta subunit antigen. The microtubular-like structures colocalize with beta-tubulin, are dispersed by nocodazole and are not affected by brefeldin A treatment. PA28alpha and PA28beta are co-localized in the cell whereas PA28gamma has a different distribution. PA28gamma complexed with the proteasome may serve a function other than or in addition to activation and may also have a proteasome-independent function.
20S蛋白酶体的催化活性可受内源性蛋白质的调节。一种被称为PA28或11S调节因子的蛋白酶体激活蛋白，由两个同源亚基（α和β）组成，还有一种单独但相关的蛋白被称为Ki抗原或PA28γ，它们的特性已得到表征。为了探究这些蛋白质之间的功能关系，利用针对源自它们序列的肽段的三种不同抗血清，通过免疫荧光和免疫电子显微镜对NT2克隆D1人神经前体细胞以及HeLa S3细胞进行标记。结果发现，PA28α和PA28β抗血清均标记细胞质和核仁。相比之下，PA28γ抗血清标记细胞核但不标记核仁，而在细胞质中它标记两类不同的结构，被鉴定为微管样延伸和最有可能是自噬体的包涵体。后者不含有蛋白酶体δ亚基抗原。微管样结构与β-微管蛋白共定位，可被诺考达唑分散，且不受布雷菲德菌素A处理的影响。PA28α和PA28β在细胞中共定位，而PA28γ具有不同的分布。与蛋白酶体复合的PA28γ可能具有除激活之外的其他功能，或者除激活功能之外还具有其他功能，并且可能还具有不依赖蛋白酶体的功能。
