Abstract B26: Reelin signaling in tumor microenvironment is required for metastasis of mammary carcinoma cells.

Abstract

Abstract We have investigated the role of reelin signaling in the microenvironment of breast cancer and found that reelin is essential for progression of mammary tumors to metastasis. Reelin signaling serves to position neurons in the developing central nervous system, but functions of this signaling pathway in other tissues have not been studied until recently. Our laboratory discovered that the reelin pathway is an important regulator of mammary gland development. We showed that reelin and Dab1, the intracellular adaptor protein for reelin, are required for timely development and proper morphology of the mammary gland. We also found that normal mammary epithelial cells (MECs) can respond to exogenous reelin by slowing their migration rate, while mouse mammary carcinoma 4T1 cells lose this response, likely through downregulation of Dab1 mRNA. Orthotopic injections of 4T1 cells into wild type Balb/C mice resulted in aggressive tumors that produced numerous metastases in the lungs by 4 weeks post-injection. However, when these cells were injected into mice that lack reelin or Dab1 (reeler and Dab1 mutant mice), we saw a dramatic reduction in lung metastases despite the presence of primary tumors comparable in size to the tumors formed in wild type mice. We show that this phenotype is dependent upon loss of reelin in the host environment, since tumor cells isolated from reeler mutant mice produce primary tumors and lung metastases when injected into Balb/C mice. Using soft agar colony assays and Western blotting, we show that the inability of 4T1 cells to metastasize in mutant animals might be due to a reduced capacity of mammary carcinoma cells to undergo epithelial to mesenchymal transition (EMT) in an environment deficient for reelin signaling. In addition, tumors from reeler and Dab1 mutant mice appear to have more differentiated cells as shown by anti-α smooth muscle Actin and anti-K14 immunostaining. Ki-67 staining showed no differences in proliferation between tumors from wild type, reeler or Dab1 mutant mice. Finally, tail vein injections of 4T1 cells into reeler mutant mice also fail to produce metastases, indicating that reelin signaling in the host environment might have important functions at several steps of the metastatic process. Our results implicate reelin signaling as an essential component of transition from the primary tumor to a metastatic carcinoma. Citation Format: Elvira Khialeeva, Joan W. Chou, Ellen M. Carpenter. Reelin signaling in tumor microenvironment is required for metastasis of mammary carcinoma cells.. [abstract]. In: Abstracts: AACR Special Conference on Cellular Heterogeneity in the Tumor Microenvironment; 2014 Feb 26-Mar 1; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(1 Suppl):Abstract nr B26. doi:10.1158/1538-7445.CHTME14-B26