RESUMEN
POT1 is a 3' telomeric single-stranded overhang binding protein that has been implicated in chromosome end protection, the regulation of telomerase function, and defining the 5' chromosome terminus. In human cancer cells that exhibit constitutive hTERT activity, hPOT1 exerts control over telomere length. Primary human fibroblasts express low levels of catalytically active hTERT in an S-phase-restricted manner that fails to counteract telomere attrition with cell division. Here, we show that diploid human fibroblasts in which hPOT1 expression has been suppressed harbor telomeres that are longer than control cells. This difference in telomere length delays the onset of replicative senescence and is dependent on S-phase-restricted hTERT expression. These findings are consistent with the view that hPOT1 promotes a nonextendable telomere state resistant to extension by S-phase-restricted telomerase. Manipulating this function of hPOT1 may thus hasten the cytotoxic effects of telomerase inhibition.
Asunto(s)
Diploidia , Fibroblastos/enzimología , Supresión Genética , Telomerasa/metabolismo , Proteínas de Unión a Telómeros/metabolismo , Telómero/metabolismo , Proliferación Celular , Células Cultivadas , Senescencia Celular , Fibroblastos/citología , Regulación de la Expresión Génica , Humanos , Masculino , ARN Mensajero/genética , ARN Mensajero/metabolismo , Fase S , Complejo Shelterina , Telomerasa/antagonistas & inhibidores , Proteínas de Unión a Telómeros/genética , Factores de TiempoRESUMEN
The introduction of SV40 small t antigen or the suppression of PP2A B56gamma subunit expression contributes to the experimental transformation of human cells. To investigate the role of cancer-associated PP2A Aalpha subunit mutants in transformation, we introduced several PP2A Aalpha mutants into immortalized but nontumorigenic human cells. These PP2A Aalpha mutants exhibited defects in binding to other PP2A subunits and impaired phosphatase activity. Although overexpression of these mutants failed to render immortalized cells tumorigenic, partial suppression of endogenous PP2A Aalpha expression activated the AKT pathway and permitted cells to form tumors in immunodeficient mice. These findings suggest that cancer-associated Aalpha mutations contribute to cancer development by inducing functional haploinsufficiency, disturbing PP2A holoenzyme composition, and altering the enzymatic activity of PP2A.
