Role for CD44 in Enhancing Invasion, Migration, and Growth of Triple Negative (TN) Breast Cancer Cells.

Abstract

Abstract Triple negative (TN) breast cancers are defined by a lack of expression of estrogen, progesterone, and her-2/neu receptors. It is widely recognized that TN breast cancers have a poorer prognosis than any other subtypes of breast caner. Given the lack of effective targeted therapies for TN breast cancer patients, understanding of the mechanisms of growth and invasion in the tissues provides insight into developing novel approaches to lower the mortality from TN breast cancer.Neoplastic epithelial cells in breast carcinomas interact with various components in the tissue microenvironment including extracellular matrix (ECM) and mesenchymal cells. Recent studies identified CD44 as a metastasis-related molecule with multiple functions by promoting cell-cell and cell-ECM interactions. CD44 is an integral transmembrane protein encoded by a single 20-exon gene. In the standard form (CD44s), 10 of the 20 exons are translated. Multiple variant isoforms exist (CD44v1-10) which arises from alternate mRNA splicing of the remaining 10 exons. In contrast to the ubiquitous expression of the standard form of CD44, splice variants are highly restricted in their expression in normal or malignant tissues. Indeed, CD44 variants containing v3, v5, v6, v7-8, v10 exons are expressed in malignant breast cancer tissues. However, there is limited information regarding the biological functions of these exons to promote tumor invasion and metastasis. The goal of this study is to evaluate specific exon(s) of CD44 expressed on TN breast cancer cells for promoting tumor progression and metastasis.In order to approach this goal, we utilized three TN cell lines (HCC38, HCC1937, and HCC1806) as model systems to evaluate CD44 in regulating invasion, migration, and growth in extracellular matrix (ECM) environments. Reverse transcriptase (RT)-PCR analysis using exon specific primers indicate that these cells expressed CD44v8-v10 and CD44s. We demonstrated that an inhibitory antibody against exon v10 of CD44 significantly inhibited b1 integrin-mediated migration and invasion into Matrigel and type I collagen gel. Importantly, this antibody also inhibited three dimensional (3D) growth which is a b1 integrin-independent process. The significant inhibition of these processes was also achieved when a FLAG-fusion exon v10 peptide (FLAG-v10, in which FLAG is tagged at the N-terminal of the peptide) was used as an inhibitor, implying that this exon would function to assemble molecular complexes on TN breast cancer cells that facilitate invasion, migration, and growth. Thus, these results suggest that generation of small synthetic molecules that block the functions of exon v10 of CD44 is promising approaches to inhibit invasion and metastasis of TN breast cancer cells. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6161.