Loss of claudins-1 and -7 and expression of claudins-3 and -4 correlate with prognostic variables in prostatic adenocarcinomas

Summary

Claudins, members of a large family of adherent junction proteins, regulate the integrity and function of tight junctions and influence tumorigenesis. Recent studies have shown that altered levels of the different claudins may be related to invasion and progression of carcinoma cells in several primary neoplasms. However, there is no reported study documenting the pattern of claudin expression in prostatic adenocarcinomas (PACs). Formalin-fixed paraffin-embedded sections from 141 PACs were immunostained by manual and automated methods on the Xmatrx (BioGenex, San Ramon, CA) using antihuman claudin-1, -3, -4, -5, and -7 antibodies (Zymed, San Francisco, CA). Membranous immunoreactivity for each protein was semiquantitatively scored in both the tumor and adjacent benign epithelium in each case. Results were correlated with clinicopathologic variables. Variable membranous positivity was noted in the adjacent benign glands for all 5 proteins in all cases. PACs showed variable membranous positivity ranging from decreased, similar to, and increased in relation to the adjacent benign epithelium for all claudins. Decreased expression of claudin-1 correlated with high tumor grade (P = .001) and biochemical disease recurrence (P = .01), whereas decreased claudin-7 correlated with high tumor grade (P < .0001). In contrast, expression of claudin-3 correlated with advanced stage tumors (P = .03) and recurrence (P = .02), and expression of claudin-4 correlated with advanced stage (P = .02). On multivariate analysis, advanced stage (P = .026) and decreased claudin-1 protein expression (P = .005) independently predicted disease recurrence. Immunohistochemical expression and prognostic significance of claudins are variable in PACs, with decreased expression of claudin-1 emerging as an independent prognostic variable warranting further study.

Introduction

The interrelationship of adjacent epithelial cells underlies overall tissue structure and polarized barrier formation [1]. Tight junctions (TJs) are one form of epithelial cell-cell adhesion, sealing the intercellular space between adjacent cells just below the apical surface [2]. TJs are composed of integral membrane proteins, including claudins, occludins, and junctional adhesion molecule and peripheral membrane proteins, including zonulae occludens, MAGI-1, Pilt, and others [3]. The resultant complexes have long been associated with segregation of the apical and basolateral compartments and paracellular permeability [4]. More recently, the TJ is better known as a sophisticated apparatus capable of recruiting signaling proteins, thereby regulating various cellular processes including cell growth and differentiation and tumorigenesis [5], [6]. Abnormal function of TJs and subsequent exchange of luminal and serosal fluid compartments may promote carcinogenesis by facilitating protein interactions [7].

Claudins, a complex network of TJ proteins working in collaboration with other TJ partners, have been the focus of a multitude of studies since the turn of the century. Since the identification and cloning of the claudin-1 gene, more than 20 claudin genes encoding a series of approximately 20 to 27 kDa integral membrane proteins have been identified [5], [8], [9]. Most tissues express multiple claudins, which can interact with one another with a given cell and with the claudins of adjacent cells [10].

The abnormal regulation of the claudin TJ proteins has been reported in various human epithelial cancers including both increased and decreased expression levels of specific claudins [10]. Differential expression of multiple claudins has been reported in several cancers including colorectal [11], [12], pancreatic [13], [14], breast [15], [16], [17], [18], [19], and ovarian [20], [21]. In prostate cancer, claudin-3 and claudin-4 expression were studied as potential targets for Clostridium perfringens enteroxin toxin-mediated therapy [22] and claudin-7 as a regulator of prostate specific antigen [23]. One additional study documented the expression of claudins-1, -2, -3, -4, -5, and -7 as potential markers of epithelial differentiation in several malignancies including 10 prostate carcinomas [24] and reports that the claudins evaluated in the current study are present in prostate cancer. However, the pattern of claudin protein expression and their correlation with prognostic variables have not yet been characterized in prostate cancer.

Abnormal claudin protein regulation as a critical step in cancer progression and as novel therapeutic targets [6], [10], [25], [26], [27] continues to gain interest. In the current study, we investigated the expression of claudins-1, -3, -4, -5, and -7 in both the benign and tumor components in prostatic adenocarcinomas (PACs) and correlated the results with clinicopathologic variables and disease outcome.