EXPLORING THE ROLES OF TRPML3 IN TNBC PROLIFERATION, MIGRATION, AND BIOENERGETICS

Abstract

Despite advances in diagnosis and cancer therapy, triple-negative breast cancer (TNBC) remains the deadliest subtype of breast cancer. This high mortality rate is largely attributed to a lack of comprehensive understanding of its molecular basis and the absence of effective therapeutic targets for TNBC. Recent studies have demonstrated the significance of lysosomes in TNBC progression. However, the specific lysosomal proteins crucial for cell proliferation and tumor growth in TNBC remain unclear. In this study, we focus on the lysosomal transient receptor potential mucolipin-3 (TRPML3, or ML3) channel. TRPML3 is known for mediating the release of Ca2+ from lysosomes and endosomes into the cytosol. We demonstrate that loss of TRPML3 induced by shRNA in the TNBC cell line MDA-MB-231 leads to a reduction in TNBC proliferation. This reduction is accompanied by G2/M cell cycle arrest and an increase in apoptosis. Additionally, shTRPML3 inhibits the migration and invasion abilities of MDA-MB-231 cells, potentially by interfering with lysosomal function. Notably, shTRPML3 results in a significant decrease in the lysosomal numbers and lysosomal pH, along with an increase in lysosomal ATP. These effects correlate with a decreased mitochondrial oxygen consumption rate (OCR), decreased proton leak, and decreased OCR-ATP production. Not only does TRPML3 downregulation change how mitochondria work, but it also changes their structure, leading to a smaller and rounder mitochondrion. Additionally, loss of ML3 increases levels of total and mitochondrial ROS. Importantly, ML3 downregulation increases the efficacy of doxorubicin and paclitaxel, two important chemotherapeutic drugs. Collectively, our findings suggest that ML3 plays a multifaceted role in TNBC, influencing cell proliferation, cell motility, and cell death, as well as the anticancer drug response. Consequently, ML3 emerges as a potential therapeutic target for improving the treatment of TNBC.