Presenilin overexpression arrests cells in the G1 phase of the cell cycle - Arrest potentiated by the Alzheimer's disease PS2(N141I) mutant

To investigate the mechanism by which presenilin CPS) overexpression induce s apoptosis, we studied the effects of these proteins on cell cycle progres sion, Transiently transfected HeLa cells were bromodeoxyuridine (BrdU) labe led to visualize DNA synthesis by immunofluorescence and stained with propi dium iodide to measure DNA content by fluorescence-activated cell sorting ( FACS), BrdU labeling was decreased in cells expressing presenilin-1 (PS1), presenilin-2 (PS2), an Alzheimer's disease-associated missense mutation PS2 (N141I), and the carboxyl-terminally deleted PS2 construct PS2(166aa), comp ared with mock and neurofilament-light (NF-L) transfected cells. Analysis o f BrdU incorporation in mitotically synchronized HeLa cells suggested that cells were arresting in the G1 phase of the cell cycle, and this was confir med by FAGS analysis. Interestingly, cell cycle progression was more inhibi ted by the expression of PS2(N141I) compared with wild-type PS2, In additio n, ATM, the gene product mutated in ataxia-telangiectasia, does not appear to be a downstream effector of PS-induced cell cycle arrest as transfection of PS constructs into an ataxia-telangiectasia cell line also resulted in cell cycle inhibition. Quantitative immunoblotting of whole-cell lysates fr om PS-transfected cells did not reveal increases or decreases in the steady -state levels of p21, p27, p53, pRb, or c-myc, suggesting that the presenil ins mediate cell cycle arrest by mechanisms other than simple changes in th e steady-state levels of these cell-cycle-related proteins.