Abstract C07: Ciliogenesis and Hh signaling are suppressed downstream of KRas during ADM
Authors: Bangs Fiona , O'Neill Eric 
Published: March 2020

Abstract
Acinar-to-ductal metaplasia (ADM) is a homeostatic mechanism where in response to inflammation for example during pancreatitis, acini dedifferentiate, adopting a progenitor-like cell fate before proliferating and redifferentiating to regenerate the pancreas. In pancreatic ductal adenocarcinoma (PDAC) constitutive activation of KRas promotes ADM; however, redifferentiation is blocked and instead progenitor-like cells are locked in an irreversible duct-like state leading to neoplastic transformation and PanIN formation. Hedgehog (Hh) signaling drives regeneration of the pancreas following ADM. Hh signaling is transduced via the primary cilium, a non-motile microtubule-based organelle that projects from the cell surface. Most vertebrate cells have a single cilium; however, acini lack cilia. Upon ADM progenitor-like cells assemble a cilium, consistent with a requirement of Hh signaling for redifferentiation. Cilia are lost in many tumors, including PDAC, where cilia are absent from low-grade PanIN, but the consequence of this is not fully understood. It has recently been reported that cilia loss potentiates KRas signaling in PDAC. Here we have assessed the requirement for cilia during ADM. We show that upon ADM progenitor-like cells expressing activated KRas (from KC mice; LSL-KRasG12D/+;Pdx1Cre) assemble fewer cilia compared to WT cells (from control litter mates). The ciliary axoneme is assembled via intraflagellar transport (IFT). We demonstrate that components of the IFT machinery are present and that the basal body, a structure derived from the mother centriole that nucleates the axoneme, is competent to form cilia in KC cells. Indicating that KC cells are able to assemble cilia, however, we show that ciliogenesis is blocked due in part to ectopic activation of the cilium disassembly pathway. This pathway is mediated via AurkA, known to be upregulated in PDAC. We show that AurkA is also upregulated in KC ADM cells and that inhibition of AurkA restores cilia to WT levels. Cells that lack cilia are unable to respond to Hh signals. We show that decreased cilia in KC ADM cells diminishes their response to Hh signaling. Rescuing cilia through inhibition of AurkA reduces the capacity of KC cells to undergo ADM and restores their response to Hh signals. We conclude that fewer cilia in KC cells caused by upregulation of AurkA prevents a full response to Hh signaling and as such redifferentiation of progenitor-like cells formed during ADM fails to occur. Instead these cells are locked in a metaplastic state predisposed to neoplastic transformation, resulting in the formation of PanIN. This study suggests that restoration of cilia could be used as a mechanism to restore responsiveness to Hh signaling during early disease stages such as chronic pancreatitis, to prevent formation of precursor lesions.
Citation Format: Fiona Bangs, Eric O'Neill. Ciliogenesis and Hh signaling are suppressed downstream of KRas during ADM [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr C07.