Wright Lesley C, Santangelo Rosemary M, Ganendren Ranjini, Payne Jackie, Djordjevic Julianne T, Sorrell Tania C
Centre for Infectious Diseases and Microbiology, Level 3, ICPMR Building, Westmead Hospital, Westmead NSW 2145, Australia.
Eukaryot Cell. 2007 Jan;6(1):37-47. doi: 10.1128/EC.00262-06. Epub 2006 Nov 10.
Cryptococci survive and replicate within macrophages and can use exogenous arachidonic acid for the production of eicosanoids. Phospholipase B1 (PLB1) has a putative, but uninvestigated, role in these processes. We have shown that uptake and esterification of radiolabeled arachidonic, palmitic, and oleic acids by the Cryptococcus neoformans var. grubii H99 wild-type strain and its PLB1 deletion mutant strain (the Deltaplb1 strain) are independent of PLB1, except under hyperosmolar stress. Similarly, PLB1 was required for metabolism of 1-palmitoyl lysophosphatidylcholine (LysoPC), which is toxic to eukaryotic cell membranes, under hyperosmolar conditions. During both logarithmic and stationary phases of growth, the physiologically relevant phospholipids, dipalmitoyl phosphatidylcholine (DPPC) and dioleoyl phosphatidylcholine, were taken up and metabolized via PLB1. Exogenous DPPC did not enhance growth in the presence of glucose as a carbon source but could support it for at least 24 h in glucose-free medium. Detoxification of LysoPC by reacylation occurred in both the H99 wild-type and the Deltaplb1 strains in the presence of glucose, but PLB1 was required when LysoPC was the sole carbon source. This indicates that both energy-independent (via PLB1) and energy-dependent transacylation pathways are active in cryptococci. Phospholipase A(1) activity was identified by PLB1-independent degradation of 1-palmitoyl-2-arachidonoyl phosphatidylcholine, but the arachidonoyl LysoPC formed was not detoxified by reacylation. Using the human macrophage-like cell line THP-1, we demonstrated the PLB1-dependent incorporation of macrophage-derived arachidonic acid into cryptococcal lipids during cryptococcus-phagocyte interaction. This pool of arachidonate can be sequestered for eicosanoid production by the fungus and/or suppression of host phagocytic activity, thus diminishing the immune response.
隐球菌可在巨噬细胞内存活并复制，且能够利用外源性花生四烯酸来合成类二十烷酸。磷脂酶B1（PLB1）在这些过程中可能发挥作用，但尚未得到研究。我们已经表明，新型隐球菌变种格鲁比H99野生型菌株及其PLB1缺失突变株（Δplb1菌株）对放射性标记的花生四烯酸、棕榈酸和油酸的摄取及酯化作用不依赖于PLB1，但在高渗应激条件下除外。同样，在高渗条件下，1-棕榈酰溶血磷脂酰胆碱（LysoPC）（对真核细胞膜有毒性）的代谢需要PLB1。在对数生长期和稳定期，生理相关磷脂二棕榈酰磷脂酰胆碱（DPPC）和二油酰磷脂酰胆碱通过PLB1被摄取和代谢。在外源DPPC存在下，以葡萄糖作为碳源时其并不能促进生长，但在无葡萄糖培养基中它至少能维持生长24小时。在有葡萄糖存在的情况下，H99野生型菌株和Δplb1菌株中LysoPC通过再酰化作用进行解毒，但当LysoPC是唯一碳源时则需要PLB1。这表明在隐球菌中，能量非依赖型（通过PLB1）和能量依赖型转酰基途径均具有活性。通过不依赖PLB1的1-棕榈酰-2-花生四烯酰磷脂酰胆碱降解鉴定出磷脂酶A(1)活性，但形成的花生四烯酰LysoPC不能通过再酰化作用解毒。利用人巨噬细胞样细胞系THP-1，我们证明了在隐球菌与吞噬细胞相互作用过程中，PLB1依赖的巨噬细胞衍生花生四烯酸掺入隐球菌脂质中。这部分花生四烯酸可被真菌截留用于合成类二十烷酸和/或抑制宿主吞噬活性，从而削弱免疫反应。
