Abstract 2703: Proteomic identification of Galectin-1 in murine primary and metastatic triple-negative breast tumors
Authors: Balestrieri Kassondra , Kew Kim , Ramez Mohamed , Pittman Keith , Vohra Nasreen , Verbanac Kathryn 
Published: August 2018

Abstract
The purpose of this study was to identify proteins associated with Triple Negative Breast Cancer (TNBC) metastases using a proteomics approach, in order to gain insight into pathways and mechanisms that could help identify biomarkers or targets for intervention. For our investigations, we used a murine claudin-low tumor model that mirrors human claudin-low TNBC molecular profiles, T11. Cultured T11 cells were lysed, trypsin-digested, and analyzed by liquid chromatography mass spectrometry (LC/MS). A total of 104 proteins were identified with &gt;95% confidence using Protein Pilot software. Among these proteins was Galectin-1 (Gal-1); seven distinct Gal-1 peptides were identified with protein coverage of 58%. Galectins are a family of ß-galactoside-binding proteins that share homology in the carbohydrate binding domain. Gal-1 was selected for further investigation due to its reported roles in cancer progression and immune evasion. Gal-1 expression was next examined in naïve murine lung tissue and in lung metastases from mice orthotopically implanted with T11. Lung tissue was homogenized, trypsin-digested and analyzed by LC/MS. Although Gal-1 was not identified in naïve lungs, three Gal-1 peptides (28% protein coverage) were identified with &gt;95% confidence in lungs with macrometastases. LC/MS analysis did not identify any other galectin family members in primary tumor or lung metastases. Matrix-assisted laser desorption ionization (MALDI) imaging of trypsin-digested tissue sections revealed two distinct Gal-1 peptides localized to tumor regions within metastatic lung tissue. Immunohistochemistry (IHC) analysis showed higher Gal-1 expression in orthotopic T11 primary tumors compared to naïve mammary fat pad, and also higher Gal-1 expression in T11 lung metastases compared to naïve lung. Within tumors, Gal-1 was detected in extracellular matrix, in the cytoplasm of tumor cells and associated with tumor cell membranes. These findings are supported by our analysis of both murine and human genomic data sets, which showed Gal-1 overexpression in claudin-low TNBC compared to other breast cancer subtypes and normal breast tissue. There are several reports that exogenous Gal-1 induces an M2-like phenotype in myeloid cells, consistent with our prior findings that primary tumors, pre-metastatic and metastatic lungs exhibit significant M2-like myeloid cell infiltrates. Future investigations in our lab will focus on determining the role of tumor-produced Gal-1 in the regulation of myeloid cell function to promote cancer progression.
Citation Format: Kassondra Balestrieri, Kim Kew, Mohamed Ramez, Keith Pittman, Nasreen Vohra, Kathryn Verbanac. Proteomic identification of Galectin-1 in murine primary and metastatic triple-negative breast tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2703.