Sortilin is processed into a CTF that is increased by γ-secretase inhibition or knockout. a) HEK 293T cells transiently transfected with sorV5 produce a ~95 kDa holoprotein labeled by anti-V5 and anti-Sor NT antibody (not shown). A ~16 kDa CTF of SorV5 is detected by an anti-V5 antibody is present in the cell lysate, and anti-SorNT detects a secreted fragment of ~95 kDa (sSor) that does not label with anti-V5. The anti-V5 positive SorV5 CTF increased with γ-secretase inhibitor treatment (LY411,575 and compound E) and decreased with either PMA or a metalloprotease inhibitor, GM6001. sSor increased upon PMA treatment and decreased upon treatment with a metalloprotease inhibitor, GM6001. b) Mouse embryonic fibroblasts that are PS-/- were transiently transfected with SorV5 plus empty vector, PS1, PS1 M139V, or PS1 D385E. In the absence of PS1 or the presence of a dominant negative PS1 mutant (D385E) the levels 16 kDa SorV5 CTF are markedly increased. However, cotransfection of PS1 wt or PS1 familial Alzheimer's disease linked mutant (M139V) and SorV5 lead to an almost complete reduction in the levels of 16 kDa anti-V5 positive SorV5 CTF. Anti-β-actin was included as a loading control and anti-PS1ct antibody demonstrated that PS1 wt and M139V underwent endoproteolysis whereas D385E did not.