Involvement of puromycin-sensitive aminopeptidase in proteolysis of tau protein in cultured cells, and attenuated proteolysis of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) mutant tau
Article first published online: 8 MAR 2010
© 2010 The Authors. Journal compilation © 2010 Japanese Psychogeriatric Society
Volume 9, Issue 4, pages 157–166, December 2009
How to Cite
YANAGI, K., TANAKA, T., KATO, K., SADIK, G., MORIHARA, T., KUDO, T. and TAKEDA, M. (2009), Involvement of puromycin-sensitive aminopeptidase in proteolysis of tau protein in cultured cells, and attenuated proteolysis of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) mutant tau. Psychogeriatrics, 9: 157–166. doi: 10.1111/j.1479-8301.2010.00307.x
- Issue published online: 8 MAR 2010
- Article first published online: 8 MAR 2010
- Received 30 January 2010; accepted 2 February 2010.
- Tau protein;
- puromycin-sensitive aminopeptidase;
In tauopathies, tau protein is hyperphosphorylated, ubiquitinated, and accumulated in the brain; however, the mechanisms underlying this accumulation remain unclear. To gain an understanding of the role of proteases in the metabolism of tau protein, in the present study we evaluated the effects of protease inhibitors in SH-SY5Y human neuroblastoma cells and COS-7 cells transfected with the tau gene. When cells were treated with 0.1–10 µmol/L of lactacystin and 1.0–20 µmol/L of MG-132 (inhibitors of proteasome), 0.1–10 µmol/L of CA-074Me (a cathepsin inhibitor), and 0.1–2 µmol/L of puromycin (a puromycin-sensitive aminopeptidase (PSA) inhibitor) for up to 24 h, there were no significant changes in tau protein levels. However, pulse-chase experiments demonstrated that the proteolysis of tau protein in SH-SY5Y cells was attenuated following treatment of cells with 200 nmol/L puromycin. Increased tau protein levels were also observed in SH-SY5Y cells treated with short interference (si) RNA to PSA to inhibit the expression of PSA. These data suggest that PSA is a protease that catalyses tau protein predominantly in SH-SY5Y cells. The protein metabolism of tau-containing mutations of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) was also investigated using pulse-chase experiments. The results indicate attenuated proteolysis of tau in cells transfected with mutant tau genes after 48 h. Further immunocytochemical analysis and subcellular fractionation experiments revealed that the mutations did not alter the intracellular distribution of tau and suggested that impaired accessibility of tau to PSA is unlikely to account for the attenuated proteolysis of tau protein. Western blotting with phosphorylation-dependent antibodies revealed that phosphorylation levels of tau at Thr231, Ser396, and Ser409 were increased in cells transfected with V337M, R406W, and R406W mutant tau genes, respectively. Together, the data suggest that attenuated proteolysis of FTDP-17 mutant tau may be explained by increased phosphorylation levels, resulting in resistance to proteolysis.