Background: Aspartate β-hydroxylase (ASPH) is silent in normal adult tissues only to re-emerge during oncogenesis where its function is required for generation and maintenance of malignant phenotypes. Exosomes enable prooncogenic secretome delivering and trafficking for long-distance cell-to-cell communication. This study aims to explore molecular mechanisms underlying how ASPH network regulates designated exosomes to program development and progression of breast cancer.
Methods: Stable cell lines overexpressing or knocking-out of ASPH were established using lentivirus transfection or CRISPR-CAS9 systems. Western blot, MTT, immunofluorescence, luciferase reporter, co-immunoprecipitation, 2D/3-D invasion, tube formation, mammosphere formation, immunohistochemistry and newly developed in vitro metastasis were applied.
Results: Through physical interactions with Notch receptors, ligands (JAGs) and regulators (ADAM10/17), ASPH activates Notch cascade to provide raw materials (especially MMPs/ADAMs) for synthesis/release of pro-metastatic exosomes. Exosomes orchestrate EMT, 2-D/3-D invasion, stemness, angiogenesis, and premetastatic niche formation. Small molecule inhibitors (SMIs) of ASPH's β-hydroxylase specifically/efficiently abrogated in vitro metastasis, which mimics basement membrane invasion at primary site, intravasation/extravasation (transendothelial migration), and colonization/outgrowth at distant sites. Multiple organ-metastases in orthotopic and tail vein injection murine models were substantially blocked by a specific SMI. ASPH is silenced in normal adult breast, upregulated from in situ malignancies to highly expressed in invasive/advanced ductal carcinoma. Moderate-high expression of ASPH confers more aggressive molecular subtypes (TNBC or Her2 amplified), early recurrence/progression and devastating outcome (reduced overall/disease-free survival) of breast cancer. Expression profiling of Notch signaling components positively correlates with ASPH expression in breast cancer patients, confirming that ASPH-Notch axis acts functionally in breast tumorigenesis.
Conclusions: ASPH-Notch axis guides particularly selective exosomes to potentiate multifaceted metastasis. ASPH's pro-oncogenic/pro-metastatic properties are essential for breast cancer development/progression, revealing a potential target for therapy.
Keywords: Aspartate β-hydroxylase (ASPH); Breast cancer; Exosome; Metastasis; Notch.