Presenilin (PS1 and PS2) mutations cause early-onset familial Alzheimer's disease (AD). In addition to affecting beta-amyloid precursor protein (APP) processing and Abeta generation, PSs regulate a number of signaling pathways. We previously showed that PSs regulate both phospholipase C (PLC) and protein kinase C (PKC) alpha and gamma activities. We also reported that PS double knockout mouse embryonic fibroblasts (MEFs) have reduced levels of PKCalpha and enhanced levels of PKCdelta. Here, we determined whether the PS modulation of PLC/PKC has consequences for extracellular regulated kinase (Erk) signaling. Erk has been suggested to be important in AD pathology by modulating APP processing and tau phosphorylation. We found that knocking out PS1 or PS2 alone resulted in increased Erk activity and that this effect could be reversed by the PKCalpha inhibitor Gö6976. We also found that Erk activity following either PLC or PKC stimulation was significantly lower in PS double knockout cells and that treatment with the PKC activator phorbol 12,13-dibutyrate (PdBu) down-regulated total-Erk levels in all cells except PS double knockouts. These results demonstrate that PSs regulate Erk activity through a PKCalpha dependent pathway and that disruption of PLC/PKC signaling in the absence of both PS1 and PS2 results in lower downstream activation of Erk.