role of laccase in prostaglandin production by Cryptococcus neoformans

Recently, it has been demonstrated that the opportunistic fungal pathogen Cryptococcus neoformans can synthesize authentic immunomodulatory prostaglandins. The mechanism by which this takes place is unclear as there is no cyclooxygenase homologue in the cryptococcal genome. In this study, we show that cryptococcal production of both PGE₂ and PGF₂α can be chemically inhibited by caffeic acid, resveratrol and nordihydroguaiaretic acid. These polyphenolic molecules are frequently used as inhibitors of lipoxygenase enzymes; however, blast searches of the cryptococcal genome were unable to identify any homologues of mammalian, plant or fungal lipoxygenases. Next we investigated cryptococcal laccase, an enzyme known to bind polyphenols, and found that either antibody depletion or genetic deletion of the primary cryptococcal laccase (lac1Δ) resulted in a loss of cryptococcal prostaglandin production. To determine how laccase is involved, we tested recombinant laccase activity on the prostaglandin precursors, arachidonic acid (AA), PGG₂ and PGH₂. Using mass spectroscopy we determined that recombinant Lac1 does not modify AA or PGH₂, but does have a marked activity toward PGG₂ converting it to PGE₂ and 15-keto-PGE₂. These data demonstrate a critical role for laccase in cryptococcal prostaglandin production, and provides insight into a new and unique fungal prostaglandin pathway.