Conserved Stress-protective Activity between Prion Protein and Shadoo

Abstract

Shadoo (Sho) is a neuronally expressed glycoprotein of unknown function. Although there is no overall sequence homology to the cellular prion protein (PrP C ), both proteins contain a highly conserved internal hydrophobic domain (HD) and are tethered to the outer leaflet of the plasma membrane via a C-terminal glycosylphosphatidylinositol anchor. A previous study revealed that Sho can reduce toxicity of a PrP mutant devoid of the HD (PrP⌬HD). We have now studied the stress-protective activity of Sho in detail and identified domains involved in this activity. Like PrP C , Sho protects cells against physiological stressors such as the excitotoxin glutamate. Moreover, both PrP C and Sho required the N-terminal domain for this activity; the stress-protective capacity of PrP⌬N as well as Sho⌬N was significantly impaired. In both proteins, the HD promoted homodimer formation; however, deletion of the HD had different effects. Although Sho⌬HD lost its stress-protective activity, PrP⌬HD acquired a neurotoxic potential. Finally, we could show that the N-terminal domain of PrP C could be functionally replaced by that of Sho, suggesting a similar function of the N termini of Sho and PrP C . Our study reveals a conserved physiological activity between PrP C and Sho to protect cells from stress-induced toxicity and suggests that Sho and PrP C might act on similar signaling pathways.

Cytoprotective and toxic functions of the prion protein family

“…showing similar cytoprotective features (43,64) in models for exploration of the toxic and protective functions of the PrP.…”

“…PrPCR, expressed in CGN or neural stem cell (NSC) cultures, increase the sensitivity of the cells to glutamate (42), contrarily PrP113-133, which has no such sensitizing effect when expressed in the human neuroblastoma SH-SY5Y cells (43). It must be noted that these effects were observed in different cell types.…”

“…In previous studies it was demonstrated that the presence of the HD is required for various protective effects of the Shadoo, such as protection against toxicity of PrP32-121, or Doppel in CGN cultures (64) or against glutamate toxicity (43). This domain also acts as an interface of PrP binding (43,100), and shows the highest sequential similarity to the analogous region of PrP.…”

“…Even though the expression of these mutants causes severe toxicity in PrP null transgenic mice (33)(34)(35) and in CGN cultures (64,97), they show reduced effect (43,98), or no effect (42,96) when expressed in immortalized cell lines. The most obvious phenotype associated with the Shmerling or CR mutations in PrP-s in cell models is the drug hypersensitivity and the occurrence of spontaneous inward cationic currents (37,39).…”

“…Using SB system, we established stable expressions of PrPCR, PrP-WT and EGFP in Zpl2-1 immortalized hippocampal Prnp-knockout cells (79), and in SH-SY5Y human neuroblastoma cells of very low endogenous PrP level (43,86).…”