Carcinoma cells induce lumen filling and EMT in epithelial cells through soluble E-cadherin-mediated activation of EGFR.

In epithelial cancers, carcinoma cells coexist with normal cells. Although it is known that the tumor microenvironment (TME) plays a pivotal role in cancer progression, it is not completely understood how the tumor influences adjacent normal epithelial cells. In this study, a three-dimensional co-culture system comprising non-transformed epithelial cells (MDCK) and transformed carcinoma cells (MSV-MDCK) was used to demonstrate that carcinoma cells sequentially induce preneoplastic lumen filling and epithelial-mesenchymal transition (EMT) in epithelial cysts. MMP-9 secreted by carcinoma cells cleaves cellular E-cadherin (encoded by CDH1) from epithelial cells to generate soluble E-cadherin (sE-cad), a pro-oncogenic protein. We show that sE-cad induces EGFR activation, resulting in lumen filling in MDCK cysts. Long-term sE-cad treatment induced EMT. sE-cad caused lumen filling by induction of the ERK signaling pathway and triggered EMT through the sustained activation of the AKT pathway. Although it is known that sE-cad induces MMP-9 release and consequent EGFR activation in tumor cells, our results, for the first time, demonstrate that carcinoma cells can induce sE-cad shedding in adjacent epithelial cells, which leads to EGFR activation and the eventual transdifferentiation of the normal epithelial cells.

Soluble E-cadherin promotes cell survival by activating epidermal growth factor receptor.

High levels of the soluble form of E-cadherin can be found in the serum of cancer patients and are associated with poor prognosis. Despite the possible predictive value of soluble E-cadherin, little is understood concerning its patho-physiological consequences in tumor progression. In this study, we show that soluble E-cadherin facilitates cell survival via functional interaction with cellular E-cadherin. Exposure of cells to a recombinant form of soluble E-cadherin, at a concentration found in cancer patient's serum, prevents apoptosis due to serum/growth factor withdrawal, and inhibits epithelial lumen formation, a process that requires apoptosis. Further, soluble E-cadherin-mediated cell survival involves activation of the epidermal growth factor receptor (EGFR) and EGFR-mediated activation of both phosphoinositide-3 kinase (PI3K)/AKT and ERK1/2 signaling pathways. These results are evidence of a complex functional interplay between EGFR and E-cadherin and also suggest that the presence of soluble E-cadherin in cancer patients' sera might have relevance to cell survival and tumor progression.

Osteoblasts modulate Ca2+ signaling in bone-metastatic prostate and breast cancer cells.

Metastatic prostate and breast cancers display a predilection for the skeleton. The high incidence of skeletal metastasis may be a reflection of favorable reciprocal interactions between the bone microenvironment and disseminated cancer cells. Here we show that bone-metastatic PC3-ML prostate cancer cells and MDA-231 breast cancer cells-when co-cultured with human osteoblasts-down-regulate the increase in cytosolic free calcium (Ca(2+)) induced by agonist stimulation. This osteoblast promoted alteration of Ca(2+) signaling develops and reverts in a time-dependent manner. Most importantly, the Ca(2+) responses of cancer cells lacking bone metastatic potential are not affected by osteoblasts. The limited increase in cytosolic Ca(2+) observed in bone-metastatic cells does not result from depleted intracellular Ca(2+) stores but rather a decreased entry of Ca(2+) from the extracellular space. Interestingly, the inhibition of histone deacetylase in cancer cells replicates the changes in Ca(2+) signaling induced by osteoblasts, suggesting the participation of epigenetic mechanisms. Finally, cancer cells harvested from skeletal metastases induced in mice showed Ca(2+) responses identical to cells co-cultured with osteoblasts. However, Ca(2+) signaling in cancer cells recovered from metastases to soft-tissues was not affected, emphasizing the role of the bone microenvironment in regulating the functional behavior of bone-metastatic cells. We propose that osteoblasts protect selected malignant phenotypes from cell death caused by an excessive increase in cytosolic Ca(2+), thereby facilitating their progression into macroscopic skeletal metastases.

CX3CR1 is expressed by prostate epithelial cells and androgens regulate the levels of CX3CL1/fractalkine in the bone marrow: potential role in prostate cancer bone tropism.

We have previously shown that the chemokine fractalkine promotes the adhesion of human prostate cancer cells to bone marrow endothelial cells as well as their migration toward human osteoblasts in vitro. Thus, the interaction of fractalkine with its receptor CX3CR1 could play a crucial role in vivo by directing circulating prostate cancer cells to the bone. We found that although CX3CR1 is minimally detectable in epithelial cells of normal prostate glands, it is overexpressed upon malignant transformation. Interestingly, osteoblasts, stromal and mesenchymal cells derived from human bone marrow aspirates express the cell-bound form of fractalkine, whereas the soluble form of the chemokine is detected in bone marrow supernatants. To investigate the mechanisms regulating the levels of soluble fractalkine in the bone marrow, we focused on androgens, which play a critical role in both prostate cancer progression and skeletal metastasis. Here, we show that dihydrotestosterone dramatically increases the cleavage of fractalkine from the plasma membrane of bone cells and its action is reversed by nilutamide--an antagonist of the androgen receptor--as well as the wide-spectrum inhibitor of matrix metalloproteases, GM6001. However, dihydrotestosterone was unable to induce fractalkine-cleavage from human bone marrow endothelial cells. Thus, androgens could promote the extravasation of CX3CR1-bearing cancer cells on a fractalkine concentration gradient, while leaving unaltered their ability to adhere to the bone marrow endothelium. In conclusion, our results indicate that CX3CR1, fractalkine, and the enzymes responsible for its cleavage might represent suitable targets for therapies aiming to counteract skeletal secondary tumors from prostate adenocarcinoma.