Promyelocytic Leukemia Protein regulates Angiogenesis and Epithelial-Mesenchymal Transition to limit metastasis in MDA-MB-231 breast cancer cells.

Promyelocytic Leukemia Protein (PML) is the core protein of nuclear bodies (NBs) that regulate a large number of cellular processes, including, context dependent, tumor -suppressor and pro-oncogenic effects. PML knockdown (KD) in breast cancer lines MDA-MB-231, but not MCF7, cells showed higher cell proliferation, increased migration properties and prolonged stem cell -like survival in line with gene enrichment results from RNA sequencing analysis. MDA-MB-231 PML KD cells showed an increase of hypoxic and mesenchymal characteristics manifested by higher HIF1a and the EMT-TWIST2 protein levels respectively. Mechanistically, PML loss caused an increase of HIF1a and TWIST2 RNA levels. Interestingly, TWIST2 binds to PML. Moreover, PML directly opposed the action of HIF1a and TWIST2 on VEGFa and CD24 reporters, respectively. Tumor xenografts of MDA-MB-231 PML KD cells showed a higher micro vessel content, grew faster and had higher metastatic ability with a preference for lung. Thus, PML opposes the aggressive cancer phenotype by multiple mechanisms that antagonize the HIF-hypoxia-angiogenic and EMT axis.