Regulatory mechanism of peroxisome biogenesis by ubiquitination

过氧化物酶体是普遍存在的单膜结合细胞器，其含有约100种不同的酶，催化各种代谢途径，如脂肪酸β-氧化和醚甘油脂合成。过氧化物酶体是通过翻译后输入新合成的过氧化物酶体基质和膜蛋白后，预先存在的过氧化物酶体的生长和分裂形成的。两种不同的信号，过氧化物酶体靶向信号类型1（PTS 1）和PTS 2，指导蛋白质的过氧化物酶体基质。PEX 5和PEX 7分别编码PTS 1和PTS 2的胞质受体。然而，泛素对Pex 7 p的功能调节仍不清楚。为了解决泛素化对Pex 7 p的调节（如果有的话），我们首先研究了Pex 7 p是否被细胞中的蛋白酶体泛素化和降解。在细胞培养物中加入蛋白酶体抑制剂MG 132延迟了Pex 7 p的降解。或者，我们还试图分离参与Pex 7 p降解系统的任何潜在的Pex 7 p结合蛋白。从稳定表达FLAG-Pex 7 p的细胞系中，我们分离出几种Pex 7 p结合蛋白，称为P7 BPs：Pex 7 p结合蛋白。通过RNAi抑制P7 BP 1导致Pex 7 p降解延迟，如在MG 132处理的细胞中观察到的，因此暗示P7 BP 1在Pex 7 p泛素化中起作用。

Peroxisomes are ubiquitous single membrane-bound organelles that contain about 100 different enzymes catalyzing various metabolic pathways such as fatty-acid β-oxidation and etherglycerolipid synthesis. Peroxisomes are formed by growth and division of preexisting peroxisomes after posttranslational import of newly synthesized peroxisomal matrix and membrane proteins. Two distinct signals, peroxisomal targeting signal type 1 (PTS1) and PTS2, direct proteins to the peroxisomal matrix. PEX5 and PEX7 encode the cytosolic receptors for PTS1 and PTS2, respectively. However, functional regulation of Pex7p by ubiquitin remains undefined.To address the regulation, if any, of Pex7p by ubiquitination, we first investigated whether or not Pex7p is ubiquitinated and degraded by proteasomes in cells. Addition of a proteasome inhibitor, MG132 to cell culture delayed Pex7p degradation. Alternatively, we also attempted to isolate any potential Pex7p-binding proteins involved in the degradation system of Pex7p. From a cell line stably expressing FLAG-Pex7p, we isolated several Pex7p-binding proteins, termed P7BPs : Pex7p binding proteins. Suppression of P7BP1 by RNAi resulted in a delay of Pex7p degradation, as observed in the MG132-treated cells, hence implying that P7BP1 plays a role in Pex7p ubiquitination.