Sakai J, Duncan E A, Rawson R B, Hua X, Brown M S, Goldstein J L
Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA.
Cell. 1996 Jun 28;85(7):1037-46. doi: 10.1016/s0092-8674(00)81304-5.
Sterol regulatory element binding proteins (SREBPs) are transcription factors attached to the endoplasmic reticulum. The NH2-segment, which activates transcription, is connected to membranes by a hairpin anchor formed by two transmembrane sequences and a short lumenal loop. Using H-Ras-SREBP-2 fusion proteins, we show that the NH2-segment is released from membranes by two sequential cleavages. The first, regulated by sterols, occurs in the lumenal loop. The second, not regulated by sterols, occurs within the first transmembrane domain. The liberated NH2-segment enters the nucleus and activates genes controlling cholesterol synthesis and uptake. Certain mutant Chinese hamster ovary cells are auxotrophic for cholesterol because they fail to carry out the second cleavage; the NH2-segment remains membrane-bound and transcription is not activated.
固醇调节元件结合蛋白（SREBPs）是附着在内质网上的转录因子。激活转录的NH2片段通过由两个跨膜序列和一个短腔内环形成的发夹锚定与膜相连。使用H-Ras-SREBP-2融合蛋白，我们发现NH2片段通过两次连续切割从膜上释放。第一次切割受固醇调节，发生在腔内环。第二次切割不受固醇调节，发生在第一个跨膜结构域内。释放的NH2片段进入细胞核并激活控制胆固醇合成和摄取的基因。某些突变的中国仓鼠卵巢细胞对胆固醇营养缺陷，因为它们无法进行第二次切割；NH2片段仍然与膜结合，转录未被激活。
