Anterior gradient protein-2 is a regulator of cellular adhesion in prostate cancer.

Diptiman Chanda,William Grizzle,Jonathan A Hensel,Selvarangan Ponnazhagan,Joo Hyoung Lee,Stephanie D Reilly,Claire Smith,Tatyana Isayeva,Gene P Siegal,Anandi Sawant,Raj Singh,Lucia R Languino

doi:10.1371/journal.pone.0089940

Abstract

Anterior Gradient Protein (AGR-2) is reported to be over-expressed in many epithelial cancers and promotes metastasis. A clear-cut mechanism for its observed function(s) has not been previously identified. We found significant upregulation of AGR-2 expression in a bone metastatic prostate cancer cell line, PC3, following culturing in bone marrow-conditioned medium. Substantial AGR-2 expression was also confirmed in prostate cancer tissue specimens in patients with bone lesions. By developing stable clones of PC3 cells with varying levels of AGR-2 expression, we identified that abrogation of AGR-2 significantly reduced cellular attachment to fibronectin, collagen I, collagen IV, laminin I and fibrinogen. Loss of cellular adhesion was associated with sharp decrease in the expression of α4, α5, αV, β3 and β4 integrins. Failure to undergo apoptosis following detachment is a hallmark of epithelial cancer metastasis. The AGR-2-silenced PC3 cells showed higher resistance to Tumor necrosis factor-related apoptosis- inducing ligand (TRAIL) induced apoptosis in vitro. This observation was also supported by significantly reduced Caspase-3 expression in AGR-2-silenced PC3 cells, which is a key effector of both extrinsic and intrinsic death signaling pathways. These data suggest that AGR-2 influence prostate cancer metastasis by regulation of cellular adhesion and apoptosis.

Highlights

Prostate cancer has the highest incidence rate among all cancers in men in the developed world and is the third leading cause of death behind lung and colorectal cancers [1]
Bone metastasis is a hallmark of prostate cancer dissemination, which offers an ideal setting to study the metastasis of such cancer cells within the microenvironment and the molecular signals that promote their survival in the metastatic niche
To elucidate if responses to such signals in the microenvironment alters AGR-2 expression in prostate cancer cells, PC3 cells were grown in 3-dimensional spheroids and maintained for 3 days in bone marrow-conditioned medium

Summary

Introduction

Prostate cancer has the highest incidence rate among all cancers in men in the developed world and is the third leading cause of death behind lung and colorectal cancers [1]. Distinct gene signatures governing stages of cancer progression are reported in breast cancer, such information regarding prostate cancer is still lacking [5]. AGR-2 has drawn considerable attention in recent years for its putative role in neoplastic progression and metastasis [8,9,10,11,12,13,14,15]. Few recent reports have shed light on the regulatory elements of AGR-2 function, but its specific role(s) in tumorigenesis and progression to metastasis is still lacking [18,19,20]. AGR-2 is reported to be androgen inducible and only over-expressed during early stages of carcinogenesis [13,21]. A recent study observed reduced AGR-2 expression in high grade tumors, which coincided with metastatic disease [13]

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Conclusion