Högskolan i Skövde

RAD50/MRE11/NBS1 complex is essential for DNA double-strand break repair and for maintaining genomic integrity. In this study, we immunohistochemically examined MRE11, NBS1 and RAD50 expression in primary CRCs (n = 208), the corresponding distant (n= 41) and adjacent normal mucosa ( n= 130), and lymph node metastases ( n= 26), and investigated their clinicopathological significance in colorectal cancers ( CRCs). We found that the intensity and percentage of MRE11 and NBS1 in primary CRCs were positively correlated with each other and with RAD50 (P < 0.0001). Strong expression of MRE11, NBS1 or combined RAD50/MRE11/NBS1 was related to MSS, positive hMLH1 expression, earlier tumour stage (TNM stage I and II) and favourable survival (P < 0.05). A high percentage of MRE11 expression was associated with less local recurrence and high apoptotic activity (P < 0.05). In MSS CRCs, the expression of MRE11 and NBS1 was stronger than that in normal mucosa (P < 0.05), and strong expression of NBS1 in primary tumour was related to favourable survival of patients in TNM stage I and II (univariate analysis: P = 0.03; multivariate analysis: P = 0.07). In MSI CRCs, neither MRE11 nor NBS1 expression showed differences among normal mucosa, primary tumour and metastasis, or among clinicopathological variables. In conclusion, RAD50/MRE11/NBS1 proteins interacted with each other, which had different clinicopathological significance in MSS and MSI CRCs, and further, each component of the complex might have additional roles. NBS1 might be a prognostic factor for patients with MSS tumour in TNM stage I and II.