PS dependent cleavage of SorLA CTF. Mouse embryonic fibroblasts that are PS-/- were transiently transfected with SorLA in the same fashion as figure 3a. Cells transiently transfected with SorLA produce a ~250 kDa holoprotein labeled by anti-V5. In the absence of PS1 or the presence of a dominant negative PS1 mutant (D385E) the levels 15 kDa anti-SorLAct positive SorLA CTF markedly increased. Cotransfection of PS1 wt or PS1 familial Alzheimer's disease linked mutant (M139V) and SorLA wt lead to a reduction in the levels of 15 kDa anti-SorLA positive SorLA 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.