Abstract 4397: Mesenchymal stem cell-derived collagen I plays a role in organizing breast cancer cell migration and metastasis

Background: Accumulating evidence suggests that mesenchymal stem cells (MSCs) are recruited to the tumor microenvironment and play roles in tumor progression; however the underlying mechanisms by which MSCs promote breast cancer migration and invasion need further investigation. Studies have demonstrated that collagen plays an important role in breast tumorigenesis by activating signaling pathways. We hypothesize that MSCs may promote breast cancer progression through regulating collagen-induced signaling in breast cancer cells. Methods: We isolated carcinoma-associated MSCs (CA-MSCs) from human breast cancer metastasis to lymph node (LNM) and liver (LM). CA-MSCs were subjected to multilineage differentiation assays and labeled with Ds-Red. COAL I expression and its receptor discoidin domain receptor 2 (DDR2) were downregulated in the CA-MSCs-DsRED using specific shRNA. We established single culture and co-cultures of CA-MSCs with GFP labeled breast cancer cells (BCCs) MDA-MB-231 and MCF10ACA1a which were used for Live Imaging Microscopy, IHC, RT-PCR, WB, immunofluorescence, 3D proliferation and invasion assays, and in vivo xenograft experiments. Results: CA-MSCs had spindle morphology, normal karyotype, were nontumorigenic in vivo, and possessed tri-lineage differentiation ability (osteoblast, adipocyte, and chondrocyte). CA-MSCs exhibited high mRNA and protein levels of collagen I (COAL I) and its receptor DDR2. ShRNA-mediated knockdown of COAL I or DDR2 in CA-MSCs induced a change in morphology towards epithelial, decreased expression of epithelial to mesenchymal transition (EMT) markers, and impaired migration. Co-culture of CA-MSCs with BCCs led to increased BCC proliferation, EMT, invasion, and increased DDR2 expression in BCCs compared to single cultures of BCCs, which was blocked by COAL1 and DDR2 shRNA in CA-MSCs. Live imaging studies revealed that shCOAL1 and shDDR2 was sufficient to completely disrupt the organized migration pattern of BCCs aligned with CA-MSCs. In vivo, xenografts derived from MDA-MB-231 cells co-cultured with shControl CA-MSCs exhibited increased collagen I deposition in the tumor microenvironment, increased tumor growth, and metastasis compared to the single cultures of MDA-MB-231 cells. Remarkably, shDDR2 in CA-MSCs reduced tumorigenesis and metastasis. Conclusion: We successfully isolated and characterized CA-MSCs, confirming their presence in human breast cancer metastasis. Our findings suggest that collagen I and its receptor DDR2 play a role in directional migration of breast cancer cells in alignment with CA-MSCs, a function that may be implicated in breast cancer invasion and metastasis. Downregulation of collagen I expression and signaling reduces tumor growth and metastasis in vivo. Modifying tumor microenvironment by manipulating collagen I and/or DDR2 levels in MSCs might be therapeutically useful in preventing metastasis. Citation Format: Maria E. Gonzalez, Emily Martin, Caroline Arellano-Gracia, Arjun Lama, Celina G. Kleer. Mesenchymal stem cell-derived collagen I plays a role in organizing breast cancer cell migration and metastasis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4397.