Abstract LB-035: Caveolin-1 loss alters matrix protein deposition and duct formation in murine mammary glands

Abstract

Abstract Breast cancer is responsible for 28.5% of all newly diagnosed cancers in women, but has only a 20% 5-year survival rate. The microenvironment, which is comprised of fibroblasts, extracellular matrix (ECM), immune cells and endothelial cells, is abnormal in malignant mammary glands in comparison to healthy tissues. The complex and ill-understood changes which take place in the ECM, a supportive stromal tissue comprised of collagens glycoproteins and proteoglycans, and the subsequent changes in its physical composition have been reported to act as a contributing factor for the development of the disease. Of particular interest is the composition and density of the ECM and cross-linking of these proteins which contributes to the increased mechanical stiffness of the tumor. The aberrant ECM associated with breast tumors is in part mediated by reduced expression of caveolin-1 (cav-1), a scaffolding protein of caveolae, which participates in endocytosis and cellular signaling cascades, and has been reported to act as a tumor suppressor. Decreased expression of cav-1 has been observed in patients with breast cancer and has been linked to metastasis and decreased patient survival. In particular, decreased expression of cav-1 has been reported in fibroblasts, mesenchymal cells which synthesize ECM, in patients with breast cancer. To determine whether the absence of cav-1 results in an abnormal mammary gland architecture, the expression of several ECM proteins in addition to changes in duct structure were assessed in the mammary glands of cav-1 deficient (cav-1 -/-) and wild type (cav-1 +/+) mice. The ECM proteins fibronectin, tenascin-c and collagen-I were analyzed given their atypical expression in breast cancers. Overall, expression of fibronectin and collagen-1 were elevated in the mammary glands of cav-1 -/- mice in comparison to mammary glands of cav-1 +/+ mice. Conversely, tenascin-c appeared to be downregulated in the mammary glands of cav-1 -/- mice when compared to the mammary glands of cav-1 +/+ mice. Utilizing α smooth muscle actin as a marker of the myoepithelial cells surrounding the ducts, the number of mammary lactiferous ducts in histological sections was counted. Results demonstrated a significant increase in the number of ducts in cav-1 -/- mice compared to cav-1 +/+ mice, averaging 7.8 and 4.6 ducts per 9.4 x105 μm2 of tissue respectively (p<0.0001). In addition, significant increases were observed in average duct circumference, 280.8μm and 203.8μm (p = 0.0273), and stromal area, 11,166μm2 and 5,391μm2 (p = 0.0109), in cav-1 -/- and cav-1 +/+ mice, respectively. Patent ducts were compared to determine the total openness of duct lumens independent of total stromal tissue. This was calculated by dividing the luminal area by the stromal area and multiplying by 100 to yield a percentage of openness. Despite increases in stromal area and protein deposition, cav-1 -/- ducts had increased patency at 14.6% openness compared to 9.5% for cav-1 +/+ (p = 0.0307). These data demonstrate that cav-1 expression is directly linked to increased expression of ECM proteins and aberrant development of lactiferous ducts and suggest a potential role of the loss of cav-1 in prompting tumor initiation and progression. Citation Format: Christopher M. Thompson, Abigail Hielscher. Caveolin-1 loss alters matrix protein deposition and duct formation in murine mammary glands. [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 LB-035.