Claudin-2 Promotes Breast Cancer Liver Metastasis by Facilitating Tumor Cell Interactions with Hepatocytes

Abstract

hWe previously identified claudin-2 as a functional mediator of breast cancer liver metastasis. We now confirm that claudin-2 levels are elevated in liver metastases, but not in skin metastases, compared to levels in their matched primary tumors in patients with breast cancer. Moreover, claudin-2 is specifically expressed in liver-metastatic breast cancer cells compared to populations derived from bone or lung metastases. The increased liver tropism exhibited by claudin-2-expressing breast cancer cells requires claudin-2-mediated interactions between breast cancer cells and primary hepatocytes. Furthermore, the reduction of the claudin-2 expression level, either in cancer cells or in primary hepatocytes, diminishes these heterotypic cell-cell interactions. Finally, we demonstrate that the first claudin-2 extracellular loop is essential for mediating tumor cell-hepatocyte interactions and the ability of breast cancer cells to form liver metastases in vivo. Thus, during breast cancer liver metastasis, claudin-2 shifts from acting within tight-junctional complexes to functioning as an adhesion molecule between breast cancer cells and hepatocytes. Metastatic tumor cells must overcome numerous barriers in order to successfully disseminate to distant organs. The metastatic cascade consists of multiple steps, including local tumor cell migration, invasion and intravasation into the lymphatic system or bloodstream, survival in the circulation, adhesion/extravasation at the metastatic site, evasion of immunosurveillance, and eventual growth in a foreign microenvironment (29,30). Of these numerous steps, interactions between tumor cells and resident cells within the metastatic microenvironment represent the most important determinants contributing to the ability of cancer cells to metastasize to specific organs (14,24).The liver represents a common site of metastasis for solid cancers and represents the third most common site for breast cancer metastasis (12). Unique structural features of the liver, including the open fenestrae that characterize the sinusoidal endothelium coupled with the lack of an organized subendothelial basement membrane, have a great impact on tumor interactions within the hepatic microenvironment. Early in vivo electron microscopy studies revealed that breast cancer cells, upon seeding the liver, can extend cellular projections through the fenestrated endothelium into the space of Disse, making direct contact with hepatocytes (36). Subsequent in vitro studies revealed that breast cancer cells form electron-dense structures at points of contact between hepatocytes, which are reminiscent of tight-junctional complexes (37). The importance of cancer cell-hepatocyte interactions has been reinforced by the observation that colorectal cancer cells also interact directly with hepatocytes during liver metastasis (31, 32). However, the mechanisms underlying these heterotypic cell-cell interactions are largely unexplored.Claudins are key components within tight junctions, and they participate in homo-and hete...

Claudins and cancer: Fall of the soldiers entrusted to protect the gate and keep the barrier intact

“…Structurally, the first extracellular loop, among two extracellular loops in a claudin protein, contains charged amino acids to regulate paracellular ion selectivity of anions and cations [15]. However, first extracellular loop of claudin-2 protein is also essential for mediating breast tumor cell-hepatocyte interaction and the ability of breast cancer cells to form liver metastases in vivo [16]. The carboxy-terminal tail of claudins, which mostly differ in size and sequence between different claudin proteins, contain a PDZ-domain-binding motif that allows claudins to interact directly with cytoplasmic TJ-associated proteins including ZO-proteins.…”

Transcriptional Profiling of Breast Cancer Metastases Identifies Liver Metastasis–Selective Genes Associated with Adverse Outcome in Luminal A Primary Breast Cancer

“…By using experimental mouse models and a limited series of clinical metastatic biopsies, genes associated with the propensity of breast cancer relapse to the bone (16), lung (17,18), and brain (19) have been published. Furthermore, we (7) and others (20,21) have shown an association between claudin-2 expression and liver recurrence. However, because experimental mouse models incompletely capture the relevant genetic complexity of tumor progression within the human host, studies using patientderived biopsies from metastases may reveal additional clinically relevant site-specific attributes to complement and/or validate these preliminary reports.…”

Chordin-Like 1 Suppresses Bone Morphogenetic Protein 4-Induced Breast Cancer Cell Migration and Invasion

“…Retroviruses were generated in 293VSV packaging cells according to the manufacturer's instructions (Clontech). NMuMG-ErbB2 (8), NIC (22), and human breast cancer (MDA-MB-231, BT549, and HCC1954) cell lines were cultured as previously described (23)(24)(25).…”