SHARP1 Suppresses Angiogenesis of Endometrial Cancer by Decreasing Hypoxia-Inducible Factor-1α Level

Recent data support a role for SHARP1, a basic helix-loop-helix transcription repressor, in the regulation of malignant cell behavior in several human cancers. However, the expression and role of SHARP1 during the development of endometrial cancer (EC) remain unclear. Here we show that upregulation of SHARP1 suppressed tumor angiogenesis by decreasing hypoxia-inducible factor-1 alpha (HIF-1 alpha), inhibited cell viability and tumor growth in EC. Immunohistochemical staining showed that the expression of SHARP1 was negatively correlated with tumor stage, histological grade, myometrial invasion, lymph node metastasis, blood vessel permeation in the myometrium and HIF-1 alpha expression. Mechanistic studies showed that SHARP1 interacted with HIF-1 alpha physically, and the protein level of HIF-1 alpha and the mRNA level of its target genes (VEGFA, ANGPTL4 and CA9) were decreased by SHARP1 under hypoxia. Upregulation of SHARP1 in EC impeded hypoxia-induced angiogenesis by reducing VEGF secretion. Immunohistochemical analysis verified a correlation between decreased SHARP1 expression and increased microvessel density in EC tissues. Additionally, SHARP1 inhibited cell viability in EC cell lines. Overexpression of SHARP1 in vivo inhibited tumor growth and angiogenesis, and decreased HIF-1 alpha expression. In this study, we established SHARP1 as a novel tumor suppressor of EC and shed light on the mechanisms by how SHARP1 inhibited EC progression. Therefore, SHARP1 may be a valuable prognostic biomarker for EC progression and shows promise as a new potential target for antiangiogenic therapeutics in human EC.