MYC drives temporal evolution of small cell lung cancer subtypes by reprogramming neuroendocrine fate [Bulk RNA-seq of RPM time-series cells]

Distinct SCLC molecular subtypes have been defined based on expression of lineage-related transcription factors: ASCL1, NEUROD1, POU2F3 or YAP1, but their origins remain unknown. To study transcriptional dynamics of MYC-driven tumor evolution and compare transcriptional states to human SCLC tumors, we performed bulk RNA-sequencing on various timepoints of Rb1/Trp53/MycT58A (RPM) tumor cells (from Ad-Cgrp-Cre infected mice) as they progress in culture. These bulk RNA-seq data of the RPM time-series cells complement time-series analysis of single-cell transcriptome profiling of similar timepoints and ultimately reveal that MYC drives the dynamic evolution of SCLC subtypes. We find that MYC promotes a temporal shift from an ASCL1-to-NEUROD1-to-YAP1+ state from a neuroendocrine cell of origin. MYC activates Notch signaling to dedifferentiate tumor cells to non-neuroendocrine fates. These findings support our overall conclusions that genetics, cell of origin, and tumor cell plasticity determine SCLC subtype. Overall design: We performed bulk RNA-sequencing of eight time points, days 3, 5, 7, 10, 12, 14, 19, and 21 during the RPM transition spanning 21 days in tissue culture. Day 0 is the first day mouse lung is digested and cells are placed in tissue culture.