LOXL4 knockdown enhances tumor growth and lung metastasis through collagen-dependent extracellular matrix changes in triple-negative breast cancer

// Sul Ki Choi 1, 2, * , Hoe Suk Kim 1, * , Tiefeng Jin 1, 3 , Woo Kyung Moon 1, 2 1 Department of Radiology, Seoul National University Hospital, Jongno-gu, Seoul 03080, Korea 2 Department of Biomedical Sciences, Seoul National University College of Medicine, Jongno-gu, Seoul 03080, Korea 3 Department of Pathology and Cancer Research Center, Yanbian University Medical College, Yanji 133002, China * These authors have contributed equally to this work Correspondence to: Woo Kyung Moon, email: moonwk@snu.ac.kr Keywords: triple-negative breast cancer (TNBC), lysyl oxidase-like 4 (LOXL4), collagen, tumor progression, overall survival Received: September 24, 2016      Accepted: December 20, 2016      Published: January 02, 2017 ABSTRACT Lysyl oxidase (LOX) family genes catalyze collagen cross-link formation. To determine the effects of lysyl oxidase-like 4 (LOXL4) expression on breast tumor formation and metastasis, we evaluated primary tumor growth and lung metastasis in mice injected with LOXL4-knockdown MDA-MB-231 triple-negative human breast cancer cells. In addition, we analyzed overall survival in breast cancer patients based on LOXL4 expression using a public online database. In the mouse xenograft model, LOXL4 knockdown increased primary tumor growth and lung colonization as well as collagen I and IV, lysine hydroxylase 1 and 2, and prolyl 4-hydroxylase subunit alpha 1 and 2 levels. Second harmonic generation imaging revealed that LOXL4 knockdown resulted in the thickening of collagen bundles within tumors. In addition, weak LOXL4 expression was associated with poor overall survival in breast cancer patients from the BreastMark dataset, and this association was strongest in triple-negative breast cancer patients. These results demonstrate that weak LOXL4 expression leads to remodeling of the extracellular matrix through induction of collagen synthesis, deposition, and structural changes. These alterations in turn promote tumor growth and metastasis and are associated with poor clinical outcomes in triple-negative breast cancer.