Thomas C F, Anders R A, Gustafson M P, Leof E B, Limper A H
Division of Pulmonary, Critical Care and Internal Medicine, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
Am J Respir Cell Mol Biol. 1998 Mar;18(3):297-306. doi: 10.1165/ajrcmb.18.3.3122.
Pneumocystis carinii causes life-threatening pneumonia in immunocompromised patients. The inability to culture P. carinii has hampered basic investigations of the organism's life cycle, limiting the development of new therapies directed against it. Recent investigations indicate that P. carinii is a fungus phylogenetically related to other ascomycetes such as Schizosaccharomyces pombe. The cell cycles of S. pombe and homologous fungi are carefully regulated by cell-division-cycle molecules (cdc), particularly cell-division-cycle 2 (Cdc2), a serine-threonine kinase with essential activity at the G1 restriction point and for entry into mitosis. Antibodies to the proline-serine-threonine-alanine-isoleucine-arginine (PSTAIR) amino-acid sequence conserved in Cdc2 proteins specifically precipitated, from P. carinii extracts, a molecule with kinase activity consistent with a Cdc2-like protein. Cdc2 molecules exhibit differential activity throughout the life cycle of the organisms in which they occur. In accord with this, the P. carinii Cdc2 showed greater specific activity in P. carinii trophic forms (trophozoites) than in spore-case forms (cysts). In addition, complete genomic and complementary DNA (cDNA) sequences of P. carinii Cdc2 were cloned and found to be most closely homologus to the corresponding sequences of other pathogenic fungi. The function of P. carinii cdc2 cDNA was further documented through its ability to complement the DNA of mutant strains of S. pombe with temperature-sensitive deficiencies in Cdc2 activity. The P. carinii cdc2 cDNA restored normal Cdc2 function in these mutant strains of S. pombe, and promoted fungal proliferation. These studies represent the first molecular analysis of the cell-cycle-regulatory machinery in P. carinii. Further understanding of P. carinii's life cycle promises novel insights for preventing and treating the intractable infection it causes in immunocompromised patients.
卡氏肺孢子菌可在免疫功能低下的患者中引发危及生命的肺炎。由于无法培养卡氏肺孢子菌，对该生物体生命周期的基础研究受到了阻碍，限制了针对它的新疗法的开发。最近的研究表明，卡氏肺孢子菌是一种在系统发育上与其他子囊菌（如粟酒裂殖酵母）相关的真菌。粟酒裂殖酵母和同源真菌的细胞周期受到细胞分裂周期分子（cdc）的严格调控，特别是细胞分裂周期2（Cdc2），一种丝氨酸 - 苏氨酸激酶，在G1限制点和进入有丝分裂时具有重要活性。针对Cdc2蛋白中保守的脯氨酸 - 丝氨酸 - 苏氨酸 - 丙氨酸 - 异亮氨酸 - 精氨酸（PSTAIR）氨基酸序列的抗体，从卡氏肺孢子菌提取物中特异性沉淀出一种具有激酶活性的分子，该分子与类似Cdc2的蛋白一致。Cdc2分子在其所在生物体的整个生命周期中表现出不同的活性。与此一致的是，卡氏肺孢子菌的Cdc2在卡氏肺孢子菌的营养型（滋养体）中比在孢子囊型（包囊）中表现出更高的比活性。此外，克隆了卡氏肺孢子菌Cdc2的完整基因组和互补DNA（cDNA）序列，发现它们与其他致病真菌的相应序列最为同源。通过其补充Cdc2活性存在温度敏感性缺陷的粟酒裂殖酵母突变株DNA的能力，进一步证明了卡氏肺孢子菌cdc2 cDNA的功能。卡氏肺孢子菌cdc2 cDNA在这些粟酒裂殖酵母突变株中恢复了正常的Cdc2功能，并促进了真菌增殖。这些研究代表了对卡氏肺孢子菌细胞周期调控机制的首次分子分析。对卡氏肺孢子菌生命周期的进一步了解有望为预防和治疗其在免疫功能低下患者中引起的难治性感染带来新的见解。
