D'Souza C A, Alspaugh J A, Yue C, Harashima T, Cox G M, Perfect J R, Heitman J
Departments of Genetics, Duke University Medical Center, Durham, North Carolina 27710, USA.
Mol Cell Biol. 2001 May;21(9):3179-91. doi: 10.1128/MCB.21.9.3179-3191.2001.
Cryptococcus neoformans is an opportunistic fungal pathogen that infects the human central nervous system. This pathogen elaborates two specialized virulence factors: the antioxidant melanin and an antiphagocytic immunosuppressive polysaccharide capsule. A signaling cascade controlling mating and virulence was identified. The PKA1 gene encoding the major cyclic AMP (cAMP)-dependent protein kinase catalytic subunit was identified and disrupted. pka1 mutant strains were sterile, failed to produce melanin or capsule, and were avirulent. The PKR1 gene encoding the protein kinase A (PKA) regulatory subunit was also identified and disrupted. pkr1 mutant strains overproduced capsule and were hypervirulent in animal models of cryptococcosis. pkr1 pka1 double mutant strains exhibited phenotypes similar to that of pka1 mutants, providing epistasis evidence that the Pka1 catalytic subunit functions downstream of the Pkr1 regulatory subunit. The PKA pathway was also shown to function downstream of the Galpha protein Gpa1 and to regulate cAMP production by feedback inhibition. These findings define a Galpha protein-cAMP-PKA signaling pathway regulating differentiation and virulence of a human fungal pathogen.
新型隐球菌是一种感染人类中枢神经系统的机会性真菌病原体。这种病原体产生两种特殊的毒力因子：抗氧化剂黑色素和抗吞噬免疫抑制多糖荚膜。已鉴定出一种控制交配和毒力的信号级联反应。鉴定并破坏了编码主要环磷酸腺苷（cAMP）依赖性蛋白激酶催化亚基的PKA1基因。pka1突变株不育，不产生黑色素或荚膜，且无毒力。还鉴定并破坏了编码蛋白激酶A（PKA）调节亚基的PKR1基因。pkr1突变株荚膜产生过多，在隐球菌病动物模型中具有高毒力。pkr1 pka1双突变株表现出与pka1突变株相似的表型，提供了上位性证据，表明Pka1催化亚基在Pkr1调节亚基的下游发挥作用。PKA途径也被证明在Gα蛋白Gpa1的下游发挥作用，并通过反馈抑制调节cAMP的产生。这些发现定义了一种调节人类真菌病原体分化和毒力的Gα蛋白-cAMP-PKA信号通路。
