Nuclear Protein Tyrosine Phosphatase Shp-2 Is One Important Negative Regulator of Nuclear Export of Telomerase Reverse Transcriptase

Abstract

Aging is one major risk factor for numerous diseases. The enzyme telomerase reverse transcriptase (TERT) plays an important role for aging and apoptosis. Previously, we demonstrated that inhibition of oxidative stress-induced Src kinase family-dependent nuclear export of TERT results in delayed replicative senescence and reduced apoptosis sensitivity. Therefore, the aim of this study was to investigate mechanisms inhibiting nuclear export of TERT. First, we demonstrated that H 2 O 2 -induced nuclear export of TERT was abolished in Src, Fyn, and Yes-deficient embryonic fibroblasts. Next, we wanted to identify one potential negative regulator of this export process. One candidate is the protein tyrosine phosphatase Shp-2 (Shp-2), which can counteract activities of the Src kinase family. Indeed, Shp-2 was evenly distributed between the nucleus and cytosol. Nuclear Shp-2 associates with TERT in endothelial cells and dissociates from TERT prior to its nuclear export. Overexpression of Shp-2 wt inhibited H 2 O 2 -induced export of TERT. Overexpression of the catalytically inactive, dominant negative Shp-2 mutant (Shp-2(C459S)) reduced endogenous as well as overexpressed nuclear TERT protein and telomerase activity, whereas it had no influence on TERT(Y707F). Binding of TERT(Y707F) to Shp-2 is reduced compared with TERTwt. Ablation of Shp-2 expression led only to an increased tyrosine phosphorylation of TERTwt, but not of TERT(Y707F). Moreover, reduced Shp-2 expression decreased nuclear telomerase activity, whereas nuclear telomerase activity was increased in Shp-2-overexpressing endothelial cells. In conclusion, Shp-2 retains TERT in the nucleus by regulating tyrosine 707 phosphorylation.Telomeres are the physical ends of the chromosomes. They maintain chromosome stability, genetic integrity and cell viability in a variety of different species (1, 2). Telomeres can also function as a mitotic clock, because telomeres are progressively shortened during each cell division. The enzyme telomerase, with its catalytic subunit telomerase reverse transcriptase (TERT), 5 counteracts the shortening of telomeres. Introduction of TERT into human cells extended both their life-span and their telomeres to lengths typical of young cells (3-5). In addition to this well known function of TERT, functions independent of telomere shortening have been described. TERT has been shown to inhibit apoptosis (6, 7). Recently, it has been demonstrated that TERT is also localized in the mitochondria, but its function there is discussed controversially (8 -10). TERT is regulated by transcriptional and post-translational mechanisms. Phosphorylation, binding proteins, and cellular localization have been described for post-translational modifications of TERT (11-15). TERT can be phosphorylated and its activity is regulated by kinases like c-Abl, PKC, ERK1/2, and Akt (16 -20). We demonstrated that TERT is tyrosine-phosphorylated by the Src kinase family under conditions of oxidative stress (21, 22). Functionally, this results in nuclear export of TERT ...

New Approaches to Prevent LEOPARD Syndrome-associated Cardiac Hypertrophy by Specifically Targeting Shp2-dependent Signaling

“…However, studies in other tissues, such as endothelial cell cultures or 293T cells, have found that C459S does indeed exert dominant-negative effects in those systems (13,38,39). Therefore, loss of dominance in the C459S-Q510E double mutant is, in our opinion, an unlikely explanation.…”

Low expression of SHP-2 is associated with less favorable prostate cancer outcomes

“…The function of nuclear SHP-2 in prostate cancer could be involved in migration and invasion since nuclear expression correlated with extracapsular extension of the cancer. Prior studies have also reported SHP-2 in the nucleus [16][17][18][19]. Since SHP-2 lacks a typical nuclear localization signal sequence, it could be transported to the nucleus in association with proteins such as Gab1 [19].…”

“…Prior studies have also reported SHP-2 in the nucleus [16][17][18][19]. Since SHP-2 lacks a typical nuclear localization signal sequence, it could be transported to the nucleus in association with proteins such as Gab1 [19]. Although it remains unclear, differential compartmentalization may alter SHP-2 function.…”

“…Although it remains unclear, differential compartmentalization may alter SHP-2 function. For example, SHP-2 has been associated with the regulation of STAT5a as well as telomerase reverse transcriptase in the nucleus [17,19]. However, further studies are required to determine whether this PTP functions similarly in prostate cancer.…”

S-nitrosylated SHP-2 contributes to NMDA receptor-mediated excitotoxicity in acute ischemic stroke

“…Thirty minutes later, SNO-SHP-2 formation was detected by the biotin-switch assay. Old SNOC and GSH were controls in the absence of an NO donor; without methyl methanethiosulfonate (MMTS; without the free thiol blocker) and without N- [6- negative (34), failed to protect neurons from NMDA toxicity. These data suggest that rescue of cortical neurons by SHP-2 expression requires its catalytic activity and that S-nitrosylation of SHP-2 might inhibit the neuroprotective pathway.…”