MiR-199b-5p was downregulated during the angiogenesis process of HUVECs. (A) Real-time PCR analysis of the knockdown efficiency of ALK1 using siALK1-1, siALK1-2, siALK1-3 and their combination (siALK1-pool) (N = 3). (B) The sequences of siALK1-1, siALK1-2, and siALK1-3. (C) HUVECs transfected with siALK1-2 were subjected to the tube formation assay in matrigel and culture plate, respectively (N = 3). Representative images of tube formation are presented. Scale bars = 500 μm. (D) Real-time PCR analysis of candidate miRNAs possibly targeting ALK1 including miR-7, miR-96, miR-145, miR-181a-5p, miR-181b-5p, miR-181c-5p, miR-181d-5p, miR-199b-5p, miR-324-5p, miR-399-5p, miR-874-3p and miR-4262 in breast cancer cell lines (T47D, MDA-MB-231, MCF-7, and BT474) and a normal breast cell line (HBL-100) (N = 3). (E) Enlarged figure of Real-time PCR analysis of miR-199b-5p in breast cancer cell lines (T47D, MDA-MB-231, MCF-7, and BT474) and a normal breast cell line (HBL-100) (N = 3). (F) The Kaplan–Meier plot of overall survival and disease-free survival in TCGA database was analyzed according to miR-199b-5p expression. (G) Real-time PCR analysis of the expression of miR-199b-5p in HUVECs induced with VEGF (0, 1, and 2.5 ng/ml) for 24 h (N = 3). The data are presented as the means ± SD; *P < 0.05 and **P < 0.01 versus the control group. HUVECs, human umbilical vein endothelial cells; ALK1, Activin receptor-like kinase 1.