Identification of Molecular Determinants of Primary and Metastatic Tumor Re-Initiation in Breast Cancer

Through in vivo selection of multiple ER-negative human breast cancer populations for enhanced tumor-forming capacity, we have derived sub-populations that generate tumors more efficiently than their parental populations at low cell numbers. Tumorigenic-enriched (TE) sub-populations displayed increased expression of LAMA4, FOXQ1 and NAP1L3—genes that are also expressed at greater levels by independently derived metastatic sub-populations. These genes promote metastatic efficiency. FOXQ1 promotes LAMA4 expression, while LAMA4 enhances clonal expansion upon substratum-detachment in vitro, tumor re-initiation in multiple organs, and disseminated metastatic cell proliferation and colonization. LAMA4’s promotion of cancer cell proliferation and tumor re-initiation requires β1-integrin. Increased LAMA4 expression marks the transition of human pre-malignant breast lesions to malignant carcinomas, while tumoral LAMA4 over-expression predicts reduced relapse-free survival in ER-negative patients. Our findings reveal common features that govern primary and metastatic tumor re-initiation and identify a key molecular determinant of these processes.