Studies on the roles of miR-130b-3p/SPIN90 and microtubule acetylation/JNK signaling in breast cancer progression

Abstract

Breast cancer tissue consists of cancer cells and their microenvironment that interact closely to promote cancer progression, both of which serve as effective therapeutic targets for cancer treatment. Here, I studied the regulatory mechanism of cancer-associated fibroblasts (CAFs) by miR-130b-3p/SPIN90 and triple-negative breast cancer (TNBC) by microtubule acetylation/JNK signaling pathway. Activated fibroblasts in the tumor microenvironment (TME), termed CAFs, are the most abundant stromal cells in tumor tissues, and actively secrete growth factors and extracellular matrix components, contributing to cancer advancement. SPIN90 depletion in fibroblasts has been reported to induce CAF activation, however, the mechanism governing SPIN90 in CAFs has not been yet elucidated. In part I, I propose that miR-130b-3p directly downregulates SPIN90 by complement binding. Since a decrease in SPIN90 in CAFs was more pronounced in ER-positive breast cancer tissues than in negative tissues, miR-130b-3p was selected through bioinformatics analysis of data from patients with estrogen receptor (ER)-positive breast cancer. Ectopic expression of miR-130b-3p in fibroblasts, along with SPIN90 downregulation, caused differentiation into CAFs, thus supporting cancer cell migration and invasion. miR-130b-3p was mainly secreted from luminal A breast cancer cells and transferred to fibroblasts via exosomes. In addition, miR-130b-3p was increased in the tumor stroma in which SPIN90 was downregulated in tumor tissue of MCF-xenograft mice. Taken together, these results demonstrate that miR-130b-3p is a key modulator of SPIN90 downregulation in breast CAFs, activated fibroblasts by miR-130b-3p exhibit a myofibroblastic CAF phenotype. Furthermore, the inverse correlation between miR-130b-3p and SPIN90 in human CAFs suggests the clinical significance of the miR-130b-3p /SPIN90 axis for breast CAF activation. Microtubule acetylation has been suggested as a potential marker for TNBC, which is highly heterogeneous and aggressive. Specific novel inhibitors of microtubule acetylation, GM-90257 and GM-90631 (GM compounds), induce TNBC cancer death, but the underlying mechanisms are not fully understood. In part II, I demonstrate that GM compounds function as anticancer agents of TNBC by activating JNK/AP-1 pathway. JNK signaling was selected as a candidate target for GM compounds via RNA-seq analysis of MDA-MB-231 treated with GM-90257. Next, direct inhibition of JNK alleviated Bcl2 reduction and cell death induced by GM compounds, and JNK activation triggered intranuclear c-Jun phosphorylation and c-Fos increase, thereby activating the AP-1 transcription factor. GM compounds induced TNBC cell death and mitotic arrest through AP-1 activation in vitro, and these results were also reproduced in vivo, validating the significance of microtubule acetylation/JNK/AP-1 axis activation by GM compounds. Moreover, GM compounds demonstrated strong potential to treat TNBC by significantly attenuating the tumor growth, metastasis and death due to cancer in mice.