Gruszynski Amy E, van Deursen Frederick J, Albareda Maria C, Best Alexander, Chaudhary Kshitiz, Cliffe Laura J, del Rio Laura, Dunn Joe Dan, Ellis Louise, Evans Krystal J, Figueiredo Juliana M, Malmquist Nicholas A, Omosun Yusuf, Palenchar Jennifer B, Prickett Sara, Punkosdy George A, van Dooren Giel, Wang Qian, Menon Anant K, Matthews Keith R, Bangs James D
Department of Biomolecular Chemistry, University of Wisonsin-Madison, 1300 University Avenue, Madison, WI 53706, USA.
Mol Biochem Parasitol. 2006 Jun;147(2):211-23. doi: 10.1016/j.molbiopara.2006.02.013. Epub 2006 Mar 9.
African trypanosomes (Trypanosoma brucei) have a digenetic lifecycle that alternates between the mammalian bloodstream and the tsetse fly vector. In the bloodstream, replicating long slender parasites transform into non-dividing short stumpy forms. Upon transmission into the fly midgut, short stumpy cells differentiate into actively dividing procyclics. A hallmark of this process is the replacement of the bloodstream-stage surface coat composed of variant surface glycoprotein (VSG) with a new coat composed of procyclin. Pre-existing VSG is shed by a zinc metalloprotease activity (MSP-B) and glycosylphosphatidylinositol-specific phospholipase C (GPI-PLC). We now provide a detailed analysis of the coordinate and inverse regulation of these activities during synchronous differentiation. MSP-B mRNA and protein levels are upregulated during differentiation at the same time as proteolysis whereas GPI-PLC levels decrease. When transcription or translation is inhibited, VSG release is incomplete and a substantial amount of protein stays cell-associated. Both modes of release are still evident under these conditions, but GPI hydrolysis plays a quantitatively minor role during normal differentiation. Nevertheless, GPI biosynthesis shifts early in differentiation from a GPI-PLC sensitive structure to a resistant procyclic-type anchor. Translation inhibition also results in a marked increase in the mRNA levels of both MSP-B and GPI-PLC, consistent with negative regulation by labile protein factors. The relegation of short stumpy surface GPI-PLC to a secondary role in differentiation suggests that it may play a more important role as a virulence factor within the mammalian host.
非洲锥虫（布氏锥虫）具有双宿主生命周期，在哺乳动物血液和采采蝇载体之间交替。在血液中，进行复制的长形细长寄生虫转变为不分裂的短粗形。一旦传播到蝇中肠，短粗形细胞就分化为活跃分裂的前循环体。这一过程的一个标志是由可变表面糖蛋白（VSG）组成的血液阶段表面被膜被由前环素组成的新被膜所取代。预先存在的VSG通过锌金属蛋白酶活性（MSP-B）和糖基磷脂酰肌醇特异性磷脂酶C（GPI-PLC）脱落。我们现在对同步分化过程中这些活性的协同和反向调节进行了详细分析。在分化过程中，MSP-B的mRNA和蛋白质水平在蛋白水解的同时上调，而GPI-PLC水平下降。当转录或翻译受到抑制时，VSG释放不完全，大量蛋白质仍与细胞相关。在这些条件下，两种释放模式仍然明显，但在正常分化过程中，GPI水解在数量上起次要作用。然而，GPI生物合成在分化早期从对GPI-PLC敏感的结构转变为抗性前循环体类型的锚定。翻译抑制还导致MSP-B和GPI-PLC的mRNA水平显著增加，这与不稳定蛋白质因子的负调节一致。短粗形表面GPI-PLC在分化中退居次要地位，这表明它可能在哺乳动物宿主内作为一种毒力因子发挥更重要的作用。
