NeuroD1 Promotes Proliferation Of Colorectal Carcinoma Cell Through Enhancing The Pentose Phosphate Pathway Via Glucose-6-phosphate Dehydrogenase

During the multi-step process of tumor cell development,it acquires a variety of biological abilities,one of which is the reprogramming of energy metabolism.As discovered by Warburg,tumor cells tend to obtain energy through glycolysis followed by fermentation even under sufficient oxygen supply(Warburg effect).Furthermore,other glucose metabolic processes,including pentose phosphate pathway which provides building materials for nucleic acids biosynthesis and NADPH for lipid biosynthesis,are also enhanced in tumor cells.Despite their importance in promoting tumor development,the molecular mechanism regulating tumor glucose metabolic reprogramming has not been totally elucidated.NeuroD1 is a type II basic helix-loop-helix(b HLH)transcription factor that binds to the b HLH consensus E-box site in the promoter of its target genes and activates their transcription.Previous reports have shown that NeuroD1 is expressed in pancreatic islet endocrine cells,the intestine,and a subset of neurons in the central and peripheral nervous system,and is crucial for regulating neuronal growth.However,the roles of NeuroD1 in promoting tumorigenesis have not totally elucidated,and whether it is involved in tumor glucose metabolic reprogramming remains unknown.In this study,we found that knocking down NeuroD1 expression in colon cancer cells HCT116 reduced glucose uptake and lactate production,suggesting that NeuroD1 might be involved in tumor cells glucose metabolic reprogramming.Through screening of a series of glucose metabolic regulatory factors using quantitative real-time PCR,we found that NeuroD1 enhances the expression level of G6 PD,the first rate-limiting enzyme in the pentose phosphate pathway.Concomitantly,NeuroD1 enhanced tumor cells proliferation,most plausibly by regulating nucleotides and DNA synthesis.Furthermore,NeuroD1 promoted the production of NADPH,a crucial intracellular reductant,and reduced intracellular ROS levels,thus promoting tumor cells antioxidant defense.Importantly,while previous study revealed that NeuroD1 suppresses the transcription of tumor suppressor gene p53,which also could act as a G6 PD negative regulator,we revealed that NeuroD1 could enhance G6 PD expression,and subsequently,pentose phosphate pathway even in p53 knocked out cells by regulating the transcriptional activity of G6 PD.These results indicate that NeuroD1 regulation on G6 PD could occur in a p53-independent pathway.Finally,we showed that the expression levels of NeuroD1 and G6 PD are positively correlated in clinical colon cancer tissues.Together,we revealed for the first time that NeuroD1 is crucial in enhancing tumor cells pentose phosphate pathway by regulating the transcriptional activity of G6 PD promoter;and that NeuroD1/G6 PD pathway is crucial for colon cancer cells proliferation and tumorigenesis.Our research linked-up NeuroD1 to tumor cells metabolic reprogramming,and provides new insight regarding NeuroD1 function and its molecular regulatory mechanism in tumorigenesis.At the same time,we reveal the potential of targeting NeuroD1 for therapeutic strategy for treating colon cancer cells.