Regulation of Transcription of the Human Presenilin-1 Gene by Ets Transcription Factors and the p53 Protooncogene

Abstract

The expression of the human presenilin-1 cellular gene is suppressed by the p53 protooncogene. The rapid kinetic of the down-regulation has suggested that it may result from a primary mechanism. We show here that p53 also suppresses the transcription of a presenilin-1 promoter-chloramphenicol acetyltransferase reporter synthetic gene in transient infection assays in neuroblastoma (SK-N-SH) and hepatoma (HepG2) cell lines. Only a minimum promoter including sequences from ؊35 to ؉ 6 from the transcription initiation is sufficient to confer down-regulation. We have previously defined a crucial DNA element controlling 90% of the expression of the gene within the same short area, and the identification of the transcription factors involved should also provide insights into the regulation of PS1 by p53. This region contains an Ets transcription factor binding motif, and a 2-base pair alteration within the core sequence (GGAA to TTAA) of the Ets consensus also reduced transcription by more than 90%. We now show that Ets1 and Ets2 indeed transactivate a PS1 promoter-chloramphenicol acetyltransferase reporter including the (؊35 to ؉6) fragment. Furthermore, in vitro translated Ets2 binds specifically to the ؊10 Ets motif in electrophoretic mobility shift assays. Therefore, Ets1/2 factors bind specifically to the ؊10 Ets element and activate PS1 transcription. We also show that the coactivator p300 enhances the activation by Ets1 and Ets2 as well as the repression by p53. p300 is known to interact with p53 as well as with Ets1 and Ets2. We show that p53 does not bind directly to the PS1 promoter. Hence the repression of PS1 transcription by p53 is likely to be mediated through protein-protein interactions.Presenilin genes (PS1 and PS2) encode highly homologous integral membrane proteins (1, 2). A majority of early onset or familial Alzheimer's disease (FAD) 1 cases results from mutations in PS1, PS2, or amyloid precursor protein (APP) with a majority of cases in PS1 (3, 4). The pathogenesis of FAD includes as an early invariant the development of amyloid plaques containing specifically A␤42/43 polypeptide (3, 5). A␤42 is produced by sequential proteolytic cleavage of ␤ APP (6). PS1 appears to play a crucial role in the normal metabolism of APP as well as in the pathological increase of A␤42 (7). The exact function of PS1 in the processing of APP is still unclear. PS1 appears to be tightly associated within a multiprotein complex with ␥ secretase, the second of two proteases that cleave APP and that has not yet been identified (8). Recent evidence has suggested that PS1 itself may contain ␥ secretase catalytic activity (9 -11). Furthermore, evidence that an endoprotease activity crucial for normal biological function is contained in PS1 or requires PS1 has also been derived from examining the function of PS1 in Notch receptor cleavage and activation. The PS1 homologue in Caenorhabditis elegans, SEL-12, is required for Notch receptor signaling and cell fate determination (12). Similar to APP, Notch undergoes intramembrane p...

Ablation of a peptidyl prolyl isomerase Pin1 from p53-null mice accelerated thymic hyperplasia by increasing the level of the intracellular form of Notch1

“…Moreover, Notch1 is cleaved by presenilin1, a component of g-secretase, and this generated NIC moves into the nucleus to form a transcriptional complex (Lai, 2002). p53 has been shown to downregulate presenilin-1 transcription and thereby inactivate thymic Notch1 signal (Roperch et al, 1998;Amson et al, 2000;Pastorcic and Das, 2000). The extreme elevation of NIC levels in the Pin1À/Àp53À/À thymocytes in the present study may have been caused in part by an increase in presenilin-1, as shown in Figure 4a.…”

“…p53 downregulates presenilin-1, a component of the g-secretase complex required to cleave and consequently activate Notch1. Thus, p53 may negatively regulate Notch1 activation (Roperch et al, 1998;Amson et al, 2000;Pastorcic and Das, 2000). Notch1 is expressed at varying levels in developing and mature T cells, from hematopoietic progenitors to peripheral lymphocytes .…”

Interactions of mutant p53 with DNA: guilt by association

“…The sequence-specific transactivators Ets-1 and NF-Y, implicated in the regulation of cancer-associated genes (reviewed by Pang et al, 1996;Gu et al, 1999;Gilliland, 2001;Oikawa, 2004), have emerged as important constituents of the mutp53 transcriptome. In contrast to wtp53 which by binding to Ets-1 inhibits its transcriptional activity (Pastorcic and Das, 2000;Gu et al, 2004), mutp53 proteins cooperate with Ets-1 and augment the transcription of cancerassociated genes by Ets-1 (Sampath et al, 2001; our own unpublished data). Similarly, the interaction of mutp53 proteins with the transcription factor NF-Y converts the 'normal' functional outcome of the NF-Y interaction with wtp53.…”

Transcription regulation by mutant p53

“…Although wtp53 inhibits Sp1-dependent activation, presumably by interfering with DNA binding by Sp1 (Bargonetti et al, 1997), mutp53 proteins cooperate with Sp1 and amplify its activating effects on transcription. Similarly, the physical association between wtp53 and Ets-1 is inhibitory to Ets-1 activity (Pastorcic and Das, 2000) whereas the mutp53/Ets-1 interaction potentiates Ets-1-mediated transcription (Sampath et al, 2001). A similar picture emerges with regard to NF-Y.…”

“…It appears most likely that functional interactions of the wtp53 N-terminal domain with the basal transcriptional machinery are also retained in mutp53 and are required for full transcriptional potency. Indeed, several of the proteins reported to interact with mutp53 and to affect its function are known to interact also with wtp53; these include Sp1 (Bargonetti et al, 1997;Pastorcic and Das, 2000;Kim and Deppert, 2003), Ets-1 (Sampath et al, 2001), and NF-Y (Di Agostino et al, 2006). Interestingly, the interactions of these proteins with wtp53 often result in opposite transcriptional outcomes than those observed with mutp53.…”