Knockdown of P4HA1 or P4HA2 expression in MDA-MB-231 cells inhibits tumor growth and metastasis. A, immunoblot assays were performed using lysates prepared from MDA-MB-231 subclones exposed to 20% or 1% O2 for 48 hours. B, tumor volume measured versus time (mean ± SEM, n = 5, ANOVA) C, final tumor weight (in grams, mean ± SEM, n = 5, ANOVA) D, lung sections (5 × 5 mm (left) or .2 × .2 mm (right)) were stained with hematoxylin and eosin. E, human genomic DNA content in mouse lungs was quantified using qPCR (mean ± SEM, n = 5, ANOVA). F, tumor volume versus time G, human DNA content in mouse lungs determined by qPCR (mean ± SEM, n = 5, ANOVA). H, immunohistochemical staining of axillary lymph node sections for human vimentin. I, vimentin staining quantified by image analysis (mean ± SEM, n = 5, ANOVA). J, immunohistochemical staining of primary tumor sections for P4HA1 or P4HA2. Scale bar = 200 μm. **P < 0.01, ***P < 0.001 vs. shLKO.1.