Stress-induced Cdk5 activity enhances cytoprotective basal autophagy in Drosophila melanogaster by phosphorylating acinus at serine437

Abstract

Cdk5 is a post-mitotic kinase with complex roles in maintaining neuronal health. The various mechanisms by which Cdk5 inhibits and promotes neurodegeneration are still poorly understood. Here, we show that in Drosophila melanogaster Cdk5 regulates basal autophagy, a key mechanism suppressing neurodegeneration. In a targeted screen, Cdk5 genetically interacted with Acinus (Acn), a primarily nuclear protein, which promotes starvation-independent, basal autophagy. Loss of Cdk5, or its required cofactor p35, reduces S437-Acn phosphorylation, whereas Cdk5 gain-of-function increases pS437-Acn levels. The phospho-mimetic S437D mutation stabilizes Acn and promotes basal autophagy. In p35 mutants, basal autophagy and lifespan are reduced, but restored to near wild-type levels in the presence of stabilized AcnS437D. Expression of aggregation-prone polyQ-containing proteins or the Amyloid-β42 peptide, but not alpha-Synuclein, enhances Cdk5-dependent phosphorylation of S437-Acn. Our data indicate that Cdk5 is required to maintain the protective role of basal autophagy in the initial responses to a subset of neurodegenerative challenges.

Hyperactive Innate Immunity Causes Degeneration of Dopamine Neurons upon Altering Activity of Cdk5

“…If altering Cdk5α does not intensify microbial challenge, why does it activate the innate immune response? Defective autophagy can stimulate innate immunity, including AMP expression ( Tusco et al, 2017 ; Wu et al, 2007 ), and data from us and others show that altering Cdk5α levels or inactivating Cdk5 kinase activity can disrupt autophagy ( Nandi et al, 2017 ; Spurrier et al, 2018 ; Trunova and Giniger, 2012 ). Thus, we hypothesized that reduced autophagy in flies having an altered level of Cdk5α may be responsible for overactivated innate immunity.…”

“…It is not clear what molecular events are responsible for the reduction of Mitf transcript and reduced expression of V-ATPase upon altering the Cdk5α level, but expression profiling of wild-type Drosophila shows that most of the V-ATPase family genes are downregulated with age ( Spurrier et al, 2018 ) and that Cdk5α -altered Drosophila have an accelerated aging rate ( Spurrier et al, 2018 ). Thus, we hypothesize that the enhanced rate of aging from altered Cdk5α contributes to the reduced expression of the V-ATPase family, leading to lysosomal abnormality and compromised autophagy, probably in combination with more direct effects of Cdk5 on components of the autophagy machinery, such as the RNA-splicing factor acinus ( Nandi et al, 2017 ).…”

Altered expression of the Cdk5 activator-like protein, Cdk5α, causes neurodegeneration in part by accelerating the rate of aging

“…Conversely, we do not detect binding of Drosophila Cdk5α protein to classical CDKs, such as Cdk1, 2, 4 or 6 ( Connell-Crowley et al, 2000 ). Moreover, for all phenotypes that have been tested, the effects of deleting Cdk5 are indistinguishable to those of deleting Cdk5α ( Connell-Crowley et al, 2007 ; Kang et al, 2012 ; Kissler et al, 2009 ; Nandi et al, 2017 ). Therefore, although we cannot formally rule out the possibility of non-Cdk5-associated effects of altered Cdk5α expression, the simplest hypothesis is that the Cdk5α phenotypes demonstrated here arise from altered activity of Cdk5/Cdk5α kinase.…”

“…In mammals, there are two major Cdk5 activators, p35 and p39, whereas Drosophila has only a single activator, encoded by the gene Cdk5α , that is closely related to mammalian p35 and p39, and is sometimes referred to as ‘D-p35’ ( Connell-Crowley et al, 2000 ; Tsai et al, 1994 ). In the absence of Cdk5α , Cdk5 kinase is expected to be functionally silent in Drosophila ( Connell-Crowley et al, 2000 ) and, in all cases tested to date, the mutant phenotypes of Drosophila Cdk5 and Cdk5α have been indistinguishable ( Connell-Crowley et al, 2007 ; Kang et al, 2012 ; Kissler et al, 2009 ; Nandi et al, 2017 ). Expression of p35 and p39 in mammals, and of Cdk5α in Drosophila , is largely restricted to neurons, localizing Cdk5 activity to the nervous system ( Connell-Crowley et al, 2000 ; Tang et al, 1995 ; Tsai et al, 1994 ).…”

Regulation of the Unfolded Protein Response by BiP AMPylation protects photoreceptors from light-dependent degeneration

“…TEMs of retina sections were performed as previously described (Jenny, Fluorescence images were quantified using ImageJ (NIH) adapting previous methods 460 (Nandi et al, 2017). For each antibody, a threshold was determined, removing the lowest 10% of 461 signal in LD control samples (to reduce variation from low level background signals).…”