Insights into intestinal neuroendocrine tumors in relation to normal human EEC differentiation [RNAseq]

Underlying this aberrant expression pattern we found diverse SI-NET enhancers. EECs normally differentiate through an intermediate HES6hi/ASCL1+ oscillatory state before NEUROD1+ pre-terminal cells emerge; ASCL1 expression then persists only in mature EC cells. In contrast, although SI-NETs express NEUROD1, they strictly lack ASCL1 and other genes normally co-expressed with ASCL1.

Notably, ASCL1 and loci encoding transcription factors that define non-EC cell types (ISL1, ARX, PAX6, PDX1) are marked with H3K27me3, signifying epigenetic silencing. SI-NETs express CDKN1B but other CDK inhibitors, e.g., CDKN2A and CDKN1C, are epigenetically silenced, suggesting that tumor cells may especially depend on wild-type CDKN1B function. Chromatin and transcriptional features of SI-NETs, revealed for the first time with respect to normal EEC differentiation, will help identify tumorigenic pathways and candidate therapeutic targets.