The role of circadian gene regulation in pancreatic cancer progression and immune evasion

Abstract public domain (NIH RePORTER)

Summary Abstract: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal human cancers due to a proclivity for metastatic spread coupled by its ability to avoid immune recognition due to a highly immunologically “cold” tumor microenvironment (TME). Understanding how PDAC evades anti-tumor immunity to facilitate metastasis remains of utmost priority. Circadian rhythms arise from an internal ‘molecular clock’ that produces 24-hour cycles to coordinate biological processes and is controlled by the transcription factor complex Clock-Bmal1 which positively regulates gene expression. Dec2 is a transcriptional repressor and functions to inhibit Bmal1 by displacing Bmal1 from gene promoters. We found that deletion of either Dec2 or Bmal1 in murine pancreatic models inhibits tumor progression and metastasis by reversing the “cold” TME to “hot” restoring anti-tumor immunity. We hypothesize that Dec2 and Bmal1 are critical drivers of PDAC tumor progression and metastasis by promoting immune evasion in a cell-intrinsic circadian fashion. We will investigate this hypothesis through the following specific aims: Aim1: Elucidate the role of the molecular clock in promoting PDAC metastasis. Metastasis is a multistep process that involves tumor cell intravasation within the primary tumor, extravasation from the vasculature of the target organ to metastatic outgrowth within the target organ. Our data indicate that Dec2 and Bmal1 can potentially regulate all of these steps. In this aim we will dissect the metastatic cascade to determine which components are under circadian regulation. We hypothesize that metastasis is regulated in a circadian fashion through tumor cell intrinsic rhythms (i.e. Dec2, Bmal1) as well host immune circadian rhythms in the liver. Aim2: Determine the transcriptional mechanism(s) of PDAC immunosuppression by Dec2 and Bmal1. Our gene expression studies indicate that Dec2 and Bmal1 inversely regulate a subset of genes that correspond to inflammatory / interferon response pathways, suggesting that these genes may be under circadian control. We hypothesize that disruption of intrinsic circadian gene regulation promotes inflammatory pathway activation through the activation of a ‘viral mimicry’ response to facilitate tumor immune recognition. To test this, we will perform next generation sequencing studies including time-series RNAseq and CUT&RUN analyses to define the impact of Dec2 or Bmal1 knockout on circadian gene regulation particularly at interferon response genes and the extent to which this is driven by the intrinsic ‘viral mimicry‘response. Mouse models are required for these studies due to genetic manipulation and mechanistic interrogation inimmunocompetent whole organisms.

Public health relevance public domain (NIH RePORTER)

PROJECT NARRATIVE Pancreatic Ductal Adenocarcinoma (PDAC) is one of the deadliest cancers due to its proclivity for metastatic spread. We have found that circadian rhythm genes Dec2 and Bmal1 serve to promote PDAC metastasis through evading recognition by the immune system. This proposal will investigate the mechanisms of this and will reveal a new understanding how circadian biology regulates cancer metastasis