Phosphorylation-regulated cleavage of the reticulon protein Nogo-B by caspase-7 at a noncanonical recognition site.
Reticulons (RTNs) are a large family of transmembrane proteins present throughout the eukaryotic domain in virtually every cell type. Despite their wide distribution, their function is still mostly unknown. RTN4, also termed Nogo, comes in three isoforms, Nogo-A, -B, and -C. While Nogo-A has been described as potent inhibitor of nerve growth, Nogo-B has been implicated in vascular remodeling and regulation of apoptosis. We show here that Nogo-B gets cleaved by caspase-7, but not caspase-3, during apoptosis at a caspase nonconsensus site. By a combination of MS and site-directed mutagenesis we demonstrate that proteolytic processing of Nogo-B is regulated by phosphorylation of Ser(16) within the cleavage site. We present cyclin-dependent kinase (Cdk)1 and Cdk2 as kinases that phosphorylate Nogo-B at Ser(16) in vitro. In vivo, cleavage of Nogo-B is markedly increased in Schwann cells in a lesion model of the rat sciatic nerve. Taken together, we identified an RTN protein as one out of a selected number of caspase targets during apoptosis and as a novel substrate for Cdk1 and 2. Furthermore, our data support a functionality of caspase-7 that is distinct from closely related caspase-3.
Schweigreiter
Rüdiger
R
Division of Neurobiochemistry, Biocenter, Innsbruck Medical University, Innsbruck, Austria.
Stasyk
Taras
T
Contarini
Igea
I
Frauscher
Silke
S
Oertle
Thomas
T
Klimaschewski
Lars
L
Huber
Lukas A
LA
Bandtlow
Christine E
CE
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D016203:CDC2 Protein Kinase / Q000378:metabolism; D016466:CHO Cells; D053179:Caspase 7 / Q000378:metabolism*; D061945:Caspase Inhibitors; D006224:Cricetinae; D003412:Cricetulus; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D008969:Molecular Sequence Data; D009185:Myelin Proteins / Q000737:chemistry / Q000378:metabolism*; D000070798:Nogo Proteins; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D051381:Rats; D012584:Sciatic Nerve / Q000187:drug effects / Q000473:pathology; D013379:Substrate Specificity / Q000187:drug effects
D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D009185:Myelin Proteins; D000070798:Nogo Proteins; C000603199:RTN4 protein, human; C000603197:Rtn4 protein, rat; D010768:Phosphoserine; D016203:CDC2 Protein Kinase; D051357:Cyclin-Dependent Kinase 2; D053179:Caspase 7