Swiss Cheese, a Protein Involved in Progressive Neurodegeneration, Acts as a Noncanonical Regulatory Subunit for PKA-C3

Abstract

The Drosophila Swiss Cheese (SWS) protein and its vertebrate ortholog Neuropathy Target Esterase (NTE) are required for neuronal survival and glial integrity. In humans, NTE is the target of organophosphorous compounds which cause a paralyzing axonal degeneration and recently mutations in NTE have been shown to cause a Hereditary Spastic Paraplegia called NTE-related Motor-Neuron Disorder. SWS and NTE are concentrated in the endoplasmic reticulum and both have been shown to have an esterase function against an artificial substrate. However, the functional mechanisms and the pathways in which SWS/NTE are involved in are still widely unknown. Here, we show that SWS interacts specifically with the C3 catalytic subunit of cAMP activated protein kinase (PKA-C3), which together with orthologs in mouse (Pkare) and human (PrKX) forms a novel class of catalytic subunits of unknown function. This interaction requires a domain of SWS which shows homology to regulatory subunits of PKA and, like conventional regulatory subunits, the binding of SWS to the PKA-C3 inhibits its function. Consistent with this result, expression of additional PKA-C3 induces degeneration and enhances the neurodegenerative phenotype in sws mutants. We also show that the complex formation with the membrane-bound SWS tethers PKA-C3 to membranes. We therefore propose a model in which SWS acts as a noncanonical subunit for PKA-C3, whereby the complex formation regulates the localization and kinase activity of PKA-C3, and that disruption of this regulation can induce neurodegeneration.

Motor neuron disease due to neuropathy target esterase mutation: Enzyme analysis of fibroblasts from human subjects yields insights into pathogenesis

“…For example, recent work has shown that the Drosophila NTE homologue SWS binds to cAMP protein kinase (PKA) catalytic subunit C3 and acts similarly to the PKA R1 regulatory subunit to inhibit PKA-C3 (Bettencourt da Cruz et al, 2008). Furthermore, neurodegeneration in sws Drosophila mutants is exacerbated by increased PKA-C3 expression.…”

Regulation of cAMP-dependent Protein Kinases

“…To substantiate these results, interaction analyses with homologous R subunits have to be performed. Recently, the D. melanogaster protein Swiss cheese was identified as a non-canonical R subunit binding to DC2, inhibiting both DC2 and the esterase activity of Swiss cheese mainly in the brain (44). Whether this regulation is conserved in mammalian tissues, awaits experimental evaluation, but this also points to the functional separation of conventional PKA and PrKX-like kinases.…”

Neuropathy target esterase: An essential enzyme for neural development and axonal maintenance

“…Thus, NTE is required for axonal maintenance. In addition, SWS acts as a noncanonical regulatory subunit to regulate the localization and kinase activity of the C3 catalytic subunit of PKA (PKA-C3), and disruption of this regulation can induce neurodegeneration (Bettencourt da Cruz et al, 2008).…”