NKX2-8/PTHrP Axis-Mediated Osteoclastogenesis and Bone Metastasis in Breast Cancer

Abstract

Bone metastasis is one of the most common distant metastasis of breast cancer, which could cause serious skeletal disease and increased cancer-related death. Therefore, identification of novel target(s) to develop therapeutics would improve patient outcomes. The role of NKX2-8 in modulation of bone remodeling was determined using osteoclastogenesis and micro-CT assays. The expression of NKX2-8 was examined via immunohistochemistry analysis in 344 breast cancer tissues. The mechanism underlying NKX2-8-mediated PTHrP downregulation was investigated using biotinylated deactivated Cas9 capture analysis, chromatin immunoprecipitation, co-immunoprecipitation assays. A bone-metastatic mouse model was used to examine the effect of NKX2-8 dysregulation on breast cancer bone metastasis and the impact of three PTHrP inhibitor on prevention of breast cancer bone metastasis. The downregulated expression of NKX2-8 was significantly correlated with breast cancer bone metastasis. In vivo bone-metastatic mouse model indicated that silencing NKX2-8 promoted, but overexpressing NKX2-8 inhibited, breast cancer osteolytic bone metastasis and osteoclastogenesis. Mechanistically, NKX2-8 directly interacted with HDAC1 on the PTHrP promoter, which resulted in a reduction of histone H3K27 acetylation, consequently transcriptionally downregulated PTHrP expression in breast cancer cells. Furthermore, targeting PTHrP effectively inhibited NKX2-8-downregulation-mediated breast cancer bone metastasis. Taken together, our results uncover a novel mechanism underlying NKX2-8 downregulation-mediated breast cancer bone metastasis and represent that the targeting PTHrP might be a tailored treatment for NKX2-8 silencing-induced breast cancer bone metastasis.