Abstract
Cyclooxygenase-2 (COX-2) is a critically important mediator of inflammation that significantly influences tumor angiogenesis, invasion, and metastasis. We investigated the role of COX-2 expressed by triple negative breast cancer cells in altering the structure and function of the extracellular matrix (ECM). COX-2 downregulation effects on ECM structure and function were investigated using magnetic resonance imaging (MRI) and second harmonic generation (SHG) microscopy of tumors derived from triple negative MDA-MB-231 breast cancer cells, and a derived clone stably expressing a short hairpin (shRNA) molecule downregulating COX-2. MRI of albumin-GdDTPA was used to characterize macromolecular fluid transport in vivo and SHG microscopy was used to quantify collagen 1 (Col1) fiber morphology. COX-2 downregulation decreased Col1 fiber density and altered macromolecular fluid transport. Immunohistochemistry identified significantly fewer activated cancer associated fibroblasts (CAFs) in low COX-2 expressing tumors. Metastatic lung nodules established by COX-2 downregulated cells were infrequent, smaller, and contained fewer Col1 fibers.COX-2 overexpression studies were performed with tumors derived from triple negative SUM-149 breast cancer cells lentivirally transduced to overexpress COX-2. SHG microscopy identified significantly higher Col1 fiber density in COX-2 overexpressing tumors with an increase of CAFs. These data expand upon the roles of COX-2 in shaping the structure and function of the ECM in primary and metastatic tumors, and identify the potential role of COX-2 in modifying the number of CAFs in tumors that may have contributed to the altered ECM.
Highlights
Cyclooxygenase-2 (COX-2) is an active mediator of the inflammatory response of cells [1]
We have shown that downregulating COX2 expression significantly impacted extracellular matrix (ECM) structure, by reducing collagen 1 (Col1) fiber volume, and ECM function, by altering permeability and macromolecular transport, in MDA-MB-231 tumors
COX-2 downregulation reduced the ability of these triple negative breast cancer (TNBC) cells to form metastatic lung nodules and to metastasize to lymph nodes
Summary
Cyclooxygenase-2 (COX-2) is an active mediator of the inflammatory response of cells [1]. Silencing COX-2 in MDA-MB-231 metastatic TNBC cells inhibited tumor onset and growth in an orthotopic xenograft model, and inhibited pulmonary colonization in an experimental model of metastasis [17] These changes were attributed to reduced invasiveness, reduced angiogenic capabilities, and reduced expression of pro-metastatic components of the extracellular matrix (ECM) [19]. Studies were performed in triple negative MDA-MB-231 tumors derived from cells with COX2 downregulated by stable expression of COX-2 short hairpin RNA (shRNA) and in triple negative SUM-149 tumors derived from cells with COX-2 overexpressed following lentiviral transduction These tumors were used to investigate the relationship between COX-2 expression, vascular parameters, and macromolecular transport, using MRI, and Col fiber distribution, using second harmonic generation (SHG) confocal microscopy. These data expand upon the role of COX-2 in modifying the structure and function of the ECM, and identify the potential role of COX-2 in activating fibroblasts in the tumor
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