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 (PS) overexpression induces apoptosis, we studied the effects of these proteins on cell cycle progression. Transiently transfected HeLa cells were bromodeoxyuridine (BrdU) labeled to visualize DNA synthesis by immunofluorescence and stained with propidium 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), compared with mock and neurofilament-light (NF-L) transfected cells. Analysis of BrdU incorporation in mitotically synchronized HeLa cells suggested that cells were arresting in the G1 phase of the cell cycle, and this was confirmed by FACS analysis. Interestingly, cell cycle progression was more inhibited by the expression of PS2(N141I) compared with wild-type PS2. In addition, 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 from 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 presenilins mediate cell cycle arrest by mechanisms other than simple changes in the steady-state levels of these cell-cycle-related proteins.