Functional characterization of haptoglobin (Hp) in breast cancer

Abstract

Background: Altered energy metabolism is one of the hallmarks in cancer which is characterized by preferential dependence on glycolysis. HP is a secreted glycoprotein which binds to free hemoglobin and prevent the loss of iron. Elevated HP was detected in patients with inflammatory diseases and a variety of cancers. In this study, we aim to investigate the functional roles of HP in breast cancer especially the relationship with glycolysis pathway. Methods: MTT, cell cycle, apoptosis, aldehyde dehydrogenase (ALDH) activity and glucose uptake assay were performed in triple negative breast cancer cells (MDA-MB-231 and MDAMB-468). Gene expression was analyzed by qRT-PCR and serum HP concentration was evaluated by enzyme-linked immunosorbent assay (ELISA). Lactate dehydrogenase (LDH) activity kit was used for enzyme activity quantification. Result: HP was overexpressed in cancer tissues and serum of breast cancer patients. Knockdown by siRNA led to decreased cell proliferation which was associated with G1 phase cell cycle arrest and increased early apoptotic cells. ALDH activity was inhibited upon HP knockdown. Glucose uptake and LDH activity was significantly impeded in breast cancer cells and cell culture supernatant, respectively. Also, qRT-PCR analysis revealed that glycolysis-related genes were altered upon HP silencing. Conclusions: Our data suggested that HP is overexpressed in breast cancer with oncogenic role and it is involved in glycolysis. These findings may provide novel diagnostic and therapeutic strategies towards this malignant disease.