Conservation of the notch1 signaling pathway in gastrointestinal (GI) neuroendocrine (NE) tumor cells

Abstract

Introduction: The Notch1 pathway regulates the endocrine phenotype in differentiating NE cells. During development, Notch1 silences NE markers by increasing the levels of HES1 and suppressing hASH1 (human achaete-scute homolog-1, a NE transcription factor). GI NE tumors cells express high levels of hASH1 but lack Notch1. We hypothesized that stable expression of Notch1 in NE tumor cells could lead to decrease in NE marker production and growth inhibition through suppression of hASH1. Methods: BON cells were stably transduced with an estrogen inducible Notch1 construct to create BON-NIER cells. BON and BON-NIER cells were treated with either control (C) or 1μM estradiol (E2) for 4 days and were analyzed using western blot for the expression of hASH1, HES1, and the NE marker, chromogranin A. Protein levels were standardized to GAPDH. Cellular growth was analyzed by standard cell counts in triplicate. Results: Notch1 activation by E2 treatment resulted in a 47% reduction in chromogranin A and 14% reduction in hASH1. Importantly, Notch1 activation also led to an increase in HES1 levels. Growth curves and showed a marginal reduction in cell number in the estradiol treated BON-NIER cells. Conclusions: The Notch1 signaling pathway, which regulates NE during development, can control hormone production and growth of GI NE tumor cells. This pathway could be exploited in the treatment of these tumors.TABLE—ABSTRACT 84Relative protein levels & cell numberBON CBON E2BON-NIER CBON-NIER E2Chromogranin A100%100%100%53%hASH1100%93%100%86%HES1100%72%100%530%Cell growth6.8 × 1056.6 × 1056.8 × 1055 × 105