Sex-specific disruptions in PKCγ signaling in a mouse model of spinocerebellar ataxia type 14
Sarah A. Wolfe, Yuliang Ma, Tomer M. Yaron-Barir, Carly Chang, Caila A. Pilo, Majid Ghassemian, Amanda J. Roberts, Sang Ryeul Lee, Benjamin A. Henson, Kristen Jepsen, Jared L. Johnson, Lewis C. Cantley, Susan S. Taylor, George Gorrie, Alexandra C. Newton
Sarah A. Wolfe, Yuliang Ma, Tomer M. Yaron-Barir, Carly Chang, Caila A. Pilo, Majid Ghassemian, Amanda J. Roberts, Sang Ryeul Lee, Benjamin A. Henson, Kristen Jepsen, Jared L. Johnson, Lewis C. Cantley, Susan S. Taylor, George Gorrie, Alexandra C. Newton
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Research Article Cell biology Neuroscience

Sex-specific disruptions in PKCγ signaling in a mouse model of spinocerebellar ataxia type 14

Abstract

Spinocerebellar ataxia type 14 (SCA14) is an autosomal dominant neurodegenerative disease caused by mutations in the gene encoding protein kinase C γ (PKCγ), a Ca2+- and diacylglycerol-dependent Ser/Thr kinase dominantly expressed in cerebellar Purkinje cells. These mutations impair autoinhibitory constraints to increase the basal activity of the kinase, resulting in deficits in the cerebellum that are not observed upon simple deletion of the gene, and severe ataxia. To better understand the impact of aberrant PKCγ signaling in disease pathology, we developed a knockin murine model of the SCA14 mutation ΔF48 in PKCγ. This fully penetrant mutation is severe in humans and is mechanistically informative, as it has high basal activity but is unresponsive to agonist stimulation. Genetic, behavioral, and molecular testing revealed that ΔF48 PKCγ mice have ataxia-related phenotypes and an altered cerebellar phosphoproteome driven primarily by enhanced Ca2+/calmodulin-dependent kinase 2 signaling, effects that were more severe in male mice. Analysis of existing human data revealed that SCA14 has a significantly earlier age of onset for males compared with females. Data from this clinically relevant mutation suggested that enhanced basal activity of PKCγ is sufficient to cause ataxia and that treatment strategies to modulate aberrant PKCγ may be particularly beneficial in males.

Authors

Sarah A. Wolfe, Yuliang Ma, Tomer M. Yaron-Barir, Carly Chang, Caila A. Pilo, Majid Ghassemian, Amanda J. Roberts, Sang Ryeul Lee, Benjamin A. Henson, Kristen Jepsen, Jared L. Johnson, Lewis C. Cantley, Susan S. Taylor, George Gorrie, Alexandra C. Newton

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Figure 1

Cartoon summarizing biochemical properties of WT and ΔF48 PKCγ.

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Cartoon summarizing biochemical properties of WT and ΔF48 PKCγ. Left: In...
Left: In the absence of the second messengers diacylglycerol (DG) and Ca2+, WT PKC is maintained in an autoinhibited conformation driven by phosphorylation of the hydrophobic motif (green circle) and binding of the pseudosubstrate (red rectangle) to the substrate-binding cavity (20). This species of PKC is phosphatase resistant and stable, with a half-life in cells of over 48 hours. Agonist-evoked generation of second messengers results in reversible Ca2+-dependent recruitment to membranes via the C2 domain (yellow oval), followed by binding of DG to the C1B domain (orange oval), events that promote the release of the pseudosubstrate from the substrate-binding cavity to allow substrate binding and downstream signaling. Right: ΔF48 PKCγ is in a “frozen” and partially open conformation with basal activity (approximately 1/3 the kcat of Ca2+/lipid–stimulated WT enzyme) (31). Although ΔF48 PKCγ can bind second messengers and translocate to membranes, communication of the C1B domain with the pseudosubstrate is lost and thus activity is unresponsive to second messenger binding. This partially open conformation is phosphatase labile and relatively unstable (half-life in cells ~10 hours).