RESUMEN
Overexpression of S100A7 (psoriasin), a small calcium-binding protein, has been associated with the development of psoriasis and carcinomas in different types of epithelia, but its precise functions are still unknown. Using human tissue specimens, cultured cell lines, and a mouse model, we found that S100A7 is highly expressed in preinvasive, well-differentiated and early staged human squamous cell carcinoma of the oral cavity (SCCOC), but little or no expression was found in poorly differentiated, later-staged invasive tumors. Interestingly, our results showed that S100A7 inhibits both SCCOC cell proliferation in vitro and tumor growth/invasion in vivo. Furthermore, we demonstrated that S100A7 is associated with the beta-catenin complex, and inhibits beta-catenin signaling by targeting beta-catenin degradation via a noncanonical mechanism that is independent of GSK3beta-mediated phosphorylation. More importantly, our results also indicated that beta-catenin signaling negatively regulates S100A7 expression. Thus, this reciprocal negative regulation between S100A7 and beta-catenin signaling implies their important roles in tumor development and progression. Despite its high levels of expression in early stage SCCOC tumorigenesis, S100A7 actually inhibits SCCOC tumor growth/invasion as well as tumor progression. Downregulation of S100A7 in later stages of tumorigenesis increases beta-catenin signaling, leading to promotion of tumor growth and tumor progression.
Asunto(s)
Proteínas de Unión al Calcio/metabolismo , Carcinoma de Células Escamosas/metabolismo , Regulación Neoplásica de la Expresión Génica , Neoplasias de la Boca/metabolismo , beta Catenina/metabolismo , Animales , Carcinoma de Células Escamosas/patología , Línea Celular Tumoral , Proliferación Celular , Progresión de la Enfermedad , Humanos , Ratones , Modelos Biológicos , Neoplasias de la Boca/patología , Trasplante de Neoplasias , Proteína A7 de Unión a Calcio de la Familia S100 , Proteínas S100 , Transducción de SeñalRESUMEN
Destruction of beta-catenin is regulated through phosphorylation-dependent interactions with the F box protein beta-TrCP. A novel pathway for beta-catenin degradation was discovered involving mammalian homologs of Drosophila Sina (Siah), which bind ubiquitin-conjugating enzymes, and Ebi, an F box protein that binds beta-catenin independent of the phosphorylation sites recognized by beta-TrCP. A series of protein interactions were identified in which Siah is physically linked to Ebi by association with a novel Sgt1 homolog SIP that binds Skp1, a central component of Skp1-Cullin-F box complexes. Expression of Siah is induced by p53, revealing a way of linking genotoxic injury to destruction of beta-catenin, thus reducing activity of Tcf/LEF transcription factors and contributing to cell cycle arrest.
Asunto(s)
Proteínas de Unión al Calcio , Proteínas Portadoras/fisiología , Proteínas de Ciclo Celular , Proteínas del Citoesqueleto/metabolismo , Proteínas de Drosophila , Proteínas de Unión al GTP , Proteínas de Choque Térmico , Proteínas de Insectos/fisiología , Proteínas Nucleares/fisiología , Transactivadores , Proteína p53 Supresora de Tumor/farmacología , Secuencia de Aminoácidos , Ciclo Celular/efectos de los fármacos , Proteínas del Citoesqueleto/efectos de los fármacos , Daño del ADN/fisiología , Proteínas de Unión al ADN/efectos de los fármacos , Proteínas de Unión al ADN/metabolismo , Humanos , Proteínas de Insectos/metabolismo , Proteínas de Insectos/farmacología , Factor de Unión 1 al Potenciador Linfoide , Datos de Secuencia Molecular , Proteínas Nucleares/metabolismo , Proteínas Nucleares/farmacología , Unión Proteica , Alineación de Secuencia , Transducción de Señal/efectos de los fármacos , Factores de Transcripción/efectos de los fármacos , Factores de Transcripción/metabolismo , Células Tumorales Cultivadas , Proteína p53 Supresora de Tumor/fisiología , Técnicas del Sistema de Dos Híbridos , Ubiquitina-Proteína Ligasas , beta CateninaRESUMEN
Reportedly, antiapoptotic Bcl-2 family proteins suppress apoptosis by binding to and inhibiting members of the CED-4 family of caspase activators. To explore this question, we used embryonic stem (ES) cells in which one (-/+) or both (-/-) copies of the gene encoding apoptotic protease activating factor 1 (Apaf-1), a CED-4 homologue, were disrupted by homologous recombination. Stable clones of heterozygous (-/+) and homozygous (-/-) Apaf-1 knockout ES cells that overexpressed Bcl-2 were generated. Withdrawal of serum growth factors or stimulation of heterozygous ES cells with staurosporine (STS), ultraviolet (UV)B irradiation, etoposide (VP16), or cisplatin induced apoptosis followed by cell death (determined by failure to exclude propidium iodide dye). These cell death stimuli also induced activation of several types of caspases and loss of mitochondrial membrane potential (DeltaPsi) in heterozygous (+/-) Apaf-1 knockout ES cells. In addition, overexpression of Bcl-2 protected against these events in Apaf-1-expressing ES cells. In contrast, STS, UVB, and VP16 induced little or no caspase activation and apoptosis in homozygous (-/-) Apaf-1 knockout ES cells. Nevertheless, Apaf-1-deficient ES cells subjected to these cell death stimuli or deprived of growth factors did eventually die through a nonapoptotic mechanism associated with loss of DeltaPsi. Moreover, Bcl-2 overprotection preserved DeltaPsi, reduced the percentage of Apaf-1(-/)- ES cells undergoing cell death, and increased clonigenic survival. The extent of Bcl-2-mediated cytoprotection was not significantly different for heterozygous (-/+) versus homozygous (-/-) Apaf-1 knockout cells. Furthermore, although Bcl-2 could be readily coimmunoprecipitated with Bax, associations with Apaf-1 were undetectable under conditions where Apaf-1 interactions with procaspase-9 were observed. We conclude that Bcl-2 has cytoprotective functions independent of Apaf-1, preserving mitochondrial function through a caspase-independent mechanism.