Loss of WISP-2/CCN5 signaling in human pancreatic cancer: A potential mechanism for epithelial-mesenchymal-transition

Abstract

The objective of this study was to explore the pathophysiological relevance of WISP-2/CCN5 in progression of human pancreatic adenocarcinoma (PAC). We found WISP-2/CCN5 mRNA and protein expression was faint and sporadic in PAC and detected in only 8.7–20% of the samples with varying grades as compared to adjacent normal and chronic pancreatitis samples where expression was very high in the ducts and acini. Colocalization studies in tissue-microarray slides revealed WISP-2/CCN5 mRNA loss was associated with p53 overexpression in PAC. Like tissue samples, p53 mutant-PAC cell lines show loss of WISP-2/CCN5. Moreover, functional analysis studies demonstrate exposure of pancreatic cancer cells to WISP-2/CCN5 recombinant protein enhances mesenchymal–epithelial-transition (MET). Collectively, we suggest WISP-2/CCN5 silencing may be a critical event during differentiation and progression of PAC and mutant p53 is possibly an important player in pursuing this episode.

Introduction

Pancreatic adenocarcinoma is second only to colorectal carcinoma as the most frequent cause of digestive tract cancer death. In the United States it is the fourth most common cause of cancer death in men and fifth most common in women [1], [2], [3]. Effective diagnostic and therapeutic strategies are deficient [3]. Therefore, pancreatic cancer is an exigent disease for clinicians and researchers who for decades have been struggling to find a promising treatment for this fatal disease. Histopathological and immunohistochemical studies suggest this malignancy arises from pancreatic ducts through sequential atypical histological preneoplastic changes (also known as pancreatic intraepithelial neoplasms; PanINs) along with the accumulation of multiple genetic and epigenetic lesions [4], [5], [6], [7], [8]. However, considering the complexity of the disease, the molecular mechanisms for the development of pancreatic adenocarcinoma has remained elusive. Therefore, multiple studies in different disciplines are warranted to dissect the molecular events leading to the development of this lethal disease.

After the discovery of three structurally allied genes, which are Cyr61 (cysteine rich protein), CTGF (connective tissue growth factor), and Nov (nephroblastoma over-expressed gene), the CCN family of growth factors has emerged [9]. Subsequently, multiple genes have been included in this family, WISP-2 (Wnt-1-induced signaling protein-2)/CCN5 is one of these genes [10], [11]. WISP-2/CCN5 is a secreted protein of 29 kDa [10] and is known to play positive or negative roles in cancer cell proliferation regulated by serum, growth factors, carcinogen and other disease-related events [12], [13], [14], [15], [16], [17]. In human breast biopsy samples, WISP-2/CCN5 is overexpressed in hyperplastic and pre-neoplastic ductal carcinoma in situ tissues while expression was undetectable or minimally detected in areas of invasive carcinoma and completely absent in normal breast tissues [12]. Multiple functional analyses suggest that WISP-2/CCN5 could be a biphasic player in the genesis of breast cancer. Its presence is required for non-invasive estrogen receptor positive breast tumor cell proliferation and at the same time it protects the preneoplastic cells from progressing to invasive disease.

These achievements attracted us to explore the expression status at mRNA and protein levels of WISP-2/CCN5 gene in PAC samples, their adjacent normal and benign lesions areas and different PAC cell lines. We also determined the pathobiological significance of this signaling molecule. The evidence is provided from these studies that WISP-2/CCN5 signaling is silenced in PAC during differentiation and progression of this disease, and suggest mutational changes of p53 may be associated with the loss of WISP-2/CCN5 signaling. Moreover, in vitro studies suggest loss of WISP-2/CCN5 signaling may be a crucial event for epithelial-mesenchymal-transition (EMT).