RESUMEN
The cysteine-type peptidase cathepsin X is highly upregulated in several cancers and presumably promotes tumor invasion through bypassing cellular senescence. Here, we present first evidence that the underlying mechanism may involve the regulation of the insulin-like growth factor (IGF) system, a well-known activator of proliferating tumor cells. Cathepsin X deficiency leads to a reduced phosphorylation of the IGF-I receptor in response to IGF-I stimulation. In addition, downstream signaling through focal adhesion kinase was also affected. Taken together, our results indicate that cathepsin X is able to assist in IGF signaling, which may be an important progress toward understanding cathepsin X-dependent tumorigenesis.
Asunto(s)
Catepsina Z/genética , Catepsinas/genética , Próstata/metabolismo , Neoplasias de la Próstata/genética , Neoplasias de la Próstata/metabolismo , Precursores de Proteínas/genética , Receptor IGF Tipo 1/metabolismo , Catepsina Z/metabolismo , Catepsinas/metabolismo , Línea Celular Tumoral , Senescencia Celular , Proteína-Tirosina Quinasas de Adhesión Focal/metabolismo , Humanos , Masculino , Fosforilación , Próstata/citología , Próstata/patología , Neoplasias de la Próstata/patología , Precursores de Proteínas/metabolismo , Interferencia de ARN , Transducción de SeñalRESUMEN
Cellular senescence represents a powerful tumor suppressor mechanism to prevent proliferation and invasion of malignant cells. Since tumor cells as well as primary fibroblasts lacking the lysosomal cysteine-type carboxypeptidase cathepsin X exhibit a reduced invasive capacity, we hypothesized that the underlying reason may be the induction of cellular senescence. To investigate the cellular and molecular mechanisms leading to diminished migration/invasion of cathepsin X-deficient cells, we have analyzed murine embryonic fibroblasts (MEF) derived from cathepsin X-deficient mice and neonatal human dermal fibroblasts (NHDF) transfected with siRNAs targeting cathepsin X. Remarkably, both cell types exhibited a flattened and enlarged cell body, a characteristic phenotype of senescent cells. Additional evidence for accelerated senescence was obtained by detection of the common senescence marker ß-galactosidase. Further examination revealed increased expression levels of senescence-associated genes such as p16, p21, p53, and caveolin in these cells along with a reduced proliferation rate. The accelerated cellular senescence induced by cathepsin X deficiency was rescued by simultaneous expression of exogenous cathepsin X. Finally, cell cycle analysis confirmed a marked reduction of the synthesis rate and prolongation of the S-phase, while susceptibility to apoptosis of cathepsin X-deficient cells remained unchanged. In conclusion, cathepsin X deficiency leads to accelerated cellular senescence and consequently to diminished cellular proliferation and migration/invasion implying a potential role of cathepsin X in bypassing cellular senescence.
Asunto(s)
Catepsinas/biosíntesis , Senescencia Celular , Animales , Apoptosis/genética , Catepsinas/genética , Caveolinas/biosíntesis , Caveolinas/genética , Ciclo Celular , Proliferación Celular , Células Cultivadas , Inhibidor p16 de la Quinasa Dependiente de Ciclina/biosíntesis , Inhibidor p16 de la Quinasa Dependiente de Ciclina/genética , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/biosíntesis , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/genética , Regulación hacia Abajo , Ensayo de Inmunoadsorción Enzimática , Fibroblastos/citología , Fibroblastos/metabolismo , Humanos , Ratones , Ratones Noqueados , Reacción en Cadena de la Polimerasa , Interferencia de ARN , ARN Interferente Pequeño , Proteína p53 Supresora de Tumor/biosíntesis , Proteína p53 Supresora de Tumor/genética , beta-Galactosidasa/análisisRESUMEN
The kallikrein-kinin system and the renin-angiotensin system interact at different levels and are linked by various molecules such as angiotensin-converting enzyme which degrades bradykinin into inactive peptides. Here we report that a cysteine-type carboxypeptidase, cathepsin X, is able to modulate the kallikrein-kinin system through carboxyterminal processing of the small peptide hormones bradykinin and kallidin. Both peptides are thereby converted from bradykinin B(2) receptor ligands to bradykinin B(1) receptor specific ligands. Cathepsin X, which has previously been recognized as an inflammatory marker may therefore act as a type I kininase. In addition, we have identified cathepsin X as an alternative possible link between the kallikrein-kinin system and the renin-angiotensin system in that it not only cleaves kinins C-terminally, but also converts angiotensin I to angiotensin II.