Studies of microtubule acetylation and EDA-fibronectin as potential therapeutic targets in breast cancer progression

Abstract

Heterogeneous populations of cancer cells as well as stromal cells, which produce extracellular matrix (ECM) proteins, characterize the tumor microenvironment. In the present report, I studied microtubule acetylation in triple negative breast cancer (TNBC) and extra domain A (EDA)-containing fibronectin (FN), FN(+)EDA, in the tumor microenvironment as probable targets in breast cancer therapy. Generally, microtubules are used as targets for anticancer drugs in breast cancer. However, such therapies often exhibit severe side effects. Therefore, there is a need to develop novel anticancer agents that regulate microtubules in certain cancer cells. In part 1, I identify and report chemical compounds that specifically bind to acetylated microtubules in TNBC. These compounds interfered in the interaction of alpha-tubulin acetyltransferase 1, a major acetyltransferase, with the microtubules. Subsequently, this interference led to a higher rate of apoptosis in MDA-MB-231 cells (a TNBC cell line) than that in MCF-10A and MCF-7 cells. Furthermore, treating mouse xenografts with these chemical compounds noticeably diminished TNBC progression in them. Based on these results, it is suggested that the newly identified chemical compounds can act as therapeutic agents by regulating microtubule acetylation enrichment in TNBC. Cancer associated fibroblasts (CAFs) in the tumor microenvironment play important roles in cancer development. Previous reports have suggested that the expression of SPIN90 in fibroblasts is closely related to CAF differentiation, and that SPIN90-deficient CAFs accelerate tumor formation in breast cancer. However, the exact mechanism that mediates these tumor-stroma interactions remains unclear. In part 2, FN(+)EDA, which is produced by Spin90-knockout (KO) mouse embryonic fibroblasts (MEFs), is shown to increase their own CAF differentiation. Increased FN(+)EDA in Spin90-KO MEFs improved fibril formation in the ECM and bound to integrin α4β1 as the mediating receptor. Additionally, secretion of FN(+)EDA from Spin90-KO MEFs affected the proliferation and invasion of breast cancer cells. Irigenin, which can inhibit the interaction between integrin α4β1 and FN(+)EDA, efficiently blocked the effects of FN(+)EDA, including fibril formation by Spin90-KO MEFs, and breast cancer progression. In an orthotopic breast cancer mouse experiment, inoculation of irigenin significantly diminished tumor growth and metastases. Moreover, expression of stromal FN(+)EDA was high around the tumor in human breast cancer patient tissues. These data indicate that SPIN90 downregulation promotes FN(+)EDA production, which can support ECM stiffening in breast cancer stroma. In summary, this suggests that irigenin is a potential therapeutic agent against breast cancer progression.