Proton-linked monocarboxylate transporters (MCTs) must transport monocarboxylate efficiently to facilitate monocarboxylate efflux in glycolytically active cells, and transport monocarboxylate slowly or even shut down to maintain a physiological monocarboxylate concentration in glycolytically inactive cells. To discover how MCTs solve this fundamental aspect of intracellular monocarboxylate homeostasis in the context of multicellular organisms, we analyzed pyruvate transport activity of human monocarboxylate transporter 2 (MCT2). Here we show that MCT2 transport activity exhibits steep dependence on substrate concentration. This property allows MCTs to turn on almost like a switch, which is physiologically crucial to the operation of MCTs in the cellular context. We further determined the cryo-electron microscopy structure of the human MCT2, demonstrating that the concentration sensitivity of MCT2 arises from the strong inter-subunit cooperativity of the MCT2 dimer during transport. These data establish definitively a clear example of evolutionary optimization of protein function.

N-myc downstream-regulated gene 1 (NDRG1) is known as tumor/metastasis suppressor in a variety of cancers including pancreas, being involved in angiogenesis, cancer growth and metastasis. However, the precise molecular mechanism how NDRG1 exerts its inhibitory function in pancreatic cancer remains unclear. In this investigation, we demonstrated that K-Ras plays a vital role in modulating NDRG1 protein level in PDAC cancer cells in vitro, which is mediated through ERK signaling. Noteworthy, K-Ras downstream Akt/mTOR signaling is inhibited upon NDRG1 overexpression, resulting in decease of HIF1α level. Moreover, NDRG1 has a unique role in modulating cancer metabolism of pancreatic ductal adenocarcinoma (PDAC). The mechanism accounting for NDRG1 in modulating aerobic glycolysis, at least partly, relied on its regulation of glycolysis genes including GLUT1, HK2, LDHA and PDK1. Additionally, NDRG1 is shown to suppress the activity of HIF1α, which is responsible for regulation of glycolysis enzymes. The current study is the first to elucidate a unique facet of the potent tumor/metastasis suppressor NDRG1 in the regulation of PDAC glycolysis, leading to important insights into the mechanism by which NDRG1 exert inhibitory function in PDAC.