DAG
The sphingolipid biosynthetic pathway generates bioactive
molecules crucial to the regulation of mammalian and fungal physiological and pathobiological processes. In previous studies, we
demonstrated that an enzyme of the fungal sphingolipid
pathway, inositol-phosphoryl ceramide
synthase 1 (Ipc1), regulates melanin, a pigment
required for the pathogenic fungus Cryptococcus neoformans
to cause disease. In this study, we investigated the mechanism by which Ipc1
regulates melanin production. Since Ipc1 also catalyzes the production of diacylglycerol (DAG), a physiological activator of the
classical and novel isoforms of mammalian protein kinase C (PKC), and since it has been suggested that PKC is
required for melanogenesis in mammalian cells, we
investigated whether Ipc1 regulates melanin in C. neoformans
through the production of DAG and the subsequent activation of Pkc1, the fungal
homolog of mammalian PKC. The results show that modulation of Ipc1 regulates
the levels of DAG in C. neoformans cells. Next, we
demonstrate that C. neoformans Pkc1 is a
DAG-activated serine-threonine kinase, and that the C1
domain of Pkc1 is necessary for this activation. Finally, through both
pharmacological and genetic approaches, we find that inhibition of Pkc1
abolishes melanin formation in C. neoformans. This
study identifies a novel signaling pathway in which the C. neoformans
Ipc1 plays a key role in the activation of Pkc1 through the formation of DAG.
Importantly, this pathway is essential for melanin production with implications
for the pathogenicity of C. neoformans.
PMID: 15014071 [PubMed - as supplied by publisher]