DOK7 expression in colorectal cancer cells and association with clinical and prognostic outcome [Abstract]

Background: The downstream of tyrosine kinase (DOK) protein family is presently known to have seven members, so called DOK1–7. The precise role of the DOK proteins is not entirely clear; some authors have suggested a potential tumour suppressor role for these proteins whilst others have shown an association between expression of these proteins and cell migration. Our study aimed to determine the expression profile of DOK7 in human colorectal cancer cell lines and its association with clinical and prognostic outcome. Material and Methods: Three human colorectal cancer cell lines (HRT18, HT115 and RKO) were analysed using polymerase chain reaction (PCR) to determine DOK7 expression. Primary colorectal cancer tissue collected at operation from 94 patients was examined by a consultant pathologist. Anti-DOK7 transgenes and expression constructs for human DOK7 were prepared and used for transfection and creation of sublines with differential expression of DOK7. Frozen sections of each tissue sample were used to extract RNA and this was used to generate cDNA which was analysed using quantitative transcript analysis to determine DOK7 expression. Patients were routinely followed up clinically and radiologically after surgery and the median follow up period was 65 months. The expression profile was then analysed against the clinical, pathological and outcome data. Results: DOK7 transcript expression was highly positive in HRT18 cells. HT115 and RKO cells on the other hand were negative for DOK7 expression. Knockdown in HRT18 cells (HRT18ΔDOK7) resulted in reduced expression of DOK7. The reduction of DOK7 in the cells resulted in a reduced rate of growth compared to wild-type cells and those transfected with control vector. Analysis of clinical data revealed that DOK7 expression was significantly negatively correlated with grade of tumour differentiation, TNM stage and Dukes stage. Furthermore, DOK7 expression was inversely correlated with patient survival (p=0.011). Conclusions: DOK7 expression was higher in non-aggressive tumour cells (HRT18) compared with aggressive tumour cells (HT115). However, DOK7 expression was also found to be negatively associated with patient survival suggesting a diverse role for this protein in malignant tumours. Further work is necessary to further elucidate the effect of DOK7 expression on cell function and cell migration response to mitogens and motogens