RESUMEN
CTEN/TNS4 is an oncogene in colorectal cancer (CRC), which can induce cell motility although its mechanistic basis of activity and the clinical implications of Cten expression are unknown. As Cten is in complex with integrins at focal adhesions, we hypothesised that it may interact with integrin-linked kinase (ILK). Through forced expression and knockdown of Cten in HCT116 and SW620 (respectively, showing low and high Cten expression), we showed that Cten could regulate ILK. However, inhibition of ILK after forced expression of Cten abrogated the motility-inducing effects of Cten, thereby demonstrating that the Cten-ILK interaction was functionally relevant. Combined knockdown of Cten and ILK had no additive effects on cell motility compared with knockdown of each individually. In order to investigate the clinical implications of Cten expression, a series of 462 CRCs were evaluated by immunohistochemistry. High expression of Cten was associated with advanced Dukes' stage (P<0.001), poor prognosis (P<0.001) and distant metastasis (P=0.008). The role of Cten in metastasis was tested by (a) intrasplenic injection of CRC cells stably transfected with a Cten expression vector into nude mice and (b) testing a series of primary human CRCs and their metastases by immunohistochemistry. Compared with controls, mice injected with cells expressing Cten developed larger tumours in the spleen (P<0.05) and liver (P<0.05). In the human cases, compared with primary tumours, the metastatic deposits had a significantly higher frequency of nuclear localisation of Cten (P=0.002). We conclude that Cten expression is of prognostic significance in CRC, and we delineate a Cten-ILK pathway controlling cell motility and possibly promoting metastasis.
Asunto(s)
Carcinoma/patología , Neoplasias Colorrectales/patología , Proteínas de Microfilamentos/fisiología , Proteínas Serina-Treonina Quinasas/fisiología , Adulto , Anciano , Anciano de 80 o más Años , Animales , Biomarcadores de Tumor/genética , Biomarcadores de Tumor/metabolismo , Biomarcadores de Tumor/fisiología , Carcinoma/diagnóstico , Carcinoma/genética , Carcinoma/metabolismo , Neoplasias Colorrectales/diagnóstico , Neoplasias Colorrectales/genética , Neoplasias Colorrectales/metabolismo , Femenino , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Técnicas de Silenciamiento del Gen , Células HCT116 , Humanos , Masculino , Ratones , Proteínas de Microfilamentos/antagonistas & inhibidores , Proteínas de Microfilamentos/genética , Proteínas de Microfilamentos/metabolismo , Persona de Mediana Edad , Metástasis de la Neoplasia , Proteínas Serina-Treonina Quinasas/metabolismo , ARN Interferente Pequeño/farmacología , Transducción de Señal/efectos de los fármacos , Transducción de Señal/fisiología , Tensinas , Células Tumorales Cultivadas , Regulación hacia Arriba/efectos de los fármacos , Regulación hacia Arriba/genética , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
BACKGROUND AND AIMS: KRAS and BRAF mutations occur in colorectal cancers (CRCs) and are considered mutually exclusive methods of activating the RAS/RAF/MEK/ERK pathway. This pathway is a therapeutic target and KRAS mutation may predict tumour responsiveness. The purpose of this study was to investigate the relationship between KRAS and BRAF mutations in 24 CRC cell lines and 29 advanced CRCs. METHODS: KRAS and BRAF mutations were detected using high resolution melting and sequencing. Expression of mutations was confirmed by reverse transcription- PCR (RT-PCR) and sequencing. CpG island methylator phenotype (CIMP) was tested by methylation-specific PCR. RESULTS: KRAS or BRAF mutation occurred in 79% of cell lines and 59% of CRCs. In the cell lines, KRAS mutations occurred in 54% of cases (with 62% in codons 12/13 and 38% in other codons). Four cell lines had a homozygous mutation. Only heterozygous BRAF mutations were detected in 29% cell lines. The V600E mutation occurred most commonly and was associated with CIMP+ status (p = 0.005). Mutations at codons 529 and 581 were also found and, in one case, BRAF and KRAS mutation co-occurred. Unexpectedly, BRAF splice variants (with a predicted kinase-dead protein) were found in 5/24 (21%) cell lines. In advanced CRCs, KRAS mutations occurred in 48% of cases (64% codons 12/13, 36% other codons) and BRAF mutations in 10% (66% V600E, 33% exon 11). A compound KRAS/BRAF mutation was not seen. CONCLUSIONS: Disrupted Ras/Raf signalling is common in CRC. Homozygous KRAS mutations and concomitant KRAS/BRAF mutations may be indicative of a gene dosage effect. The significance of BRAF splice variants is uncertain but may represent another layer of complexity. Finally, if KRAS mutation is to be used for predictive testing, then the whole gene may need to be screened as mutations occur outside codons 12/13.