Abstract PS4-44: Expression of the claudin transmembrane tight junction protein family (CLDN) and the prediction value of a claudin subset to the clinical outcome of patients with breast cancer

Abstract

Abstract Background: Tight Junction (TJ) proteins are directly or indirectly involved in breast cancer progression and metastasis where the mutual adhesiveness of cancer cells is significantly weaker than normal cells and so reduced cell-cell interaction results in a loss of normal tissue architecture (1). This adhesiveness is in addition to the role of the proteins in the control of the barrier functions of epithelial and endothelial cells. The claudin family (CLDN) of transmembrane proteins, the largest protein family of the tight junctions, are located in the TJ of cells of epithelial and endothelial origin where they are key in the maintenance of TJ function and have been increasingly shown to have important roles during key steps in the progression of cancer. We have previously demonstrated that the expression of some TJ molecules (occludin, claudins -5, -16, -20) are associated with disease progression in breast cancer (2-5). This study sought to evaluate the possible clinical and prognostic value of the entire CLDN family, in patients with breast cancer. Methods: Members of the claudin family of transmembrane TJ proteins were assessed and correlated with clinical and pathological parameters at the messenger level in a Cardiff breast cancer cohort. Breast cancer primary tumours (n=114) and matched background tissue (n=30) were processed for RNA extraction. RNA was reverse transcribed and quantified before analysis by Q-PCR CLDN-1 to -24. The expression profile was analysed against the clinical and pathological information and most importantly the clinical outcome of the patients. Results. Mammary tissues expressed varying levels of CLDNs. However, the levels of CLDN1, CLDN3, CLDN4, CLDN11, CLDN19, and CLDN22 were found to be significantly aberrant in breast cancer tissues compared with normal tissues. Members of the family, namely CLDN10, CLDN11, and CLDN18 were found to have a significant predictive value to the prognosis when using the Nottingham Prognostic Index. Of the claudin family, we identified eight members whose expression was negatively correlated with long term survival, and three members positively correlated with the survival. A comprehensive bioinformatic analyses of these CLDN members revealed a highly significant signature in predicting the clinical outcome. A favourable CLDN signature predicted a subset of the patients who all survived the ten-year followup, compared with those with unfavourable signature (69.1%), p<0.0001 (Log ranked). Likewise, the CLDN signature also successfully predicted the occurrence of breast cancer related incidence (97.6% vs 61.8%, p<0.0001). Multivariate analyses confirmed that the CLDN signature has a highly significant value as an independent predictor for both overall survival (p=0.001) and disease-free survival (p=0.001). Moreover, the predictive power was more profound for patients with ER negative and Her2 negative tumours. Discussion: Claudins, key tight junctional transmembrane proteins, have important prognostic value in human breast cancer. Together with their pivotal roles in controlling the adhesiveness and permeability of the cell layers, this family is a key player in the development and progression of breast cancer.