Inactivation of the Transcription Factor GLI1 Accelerates Pancreatic Cancer Progression

Lisa D Mills,Lizhi Zhang,Ronald Marler,Phyllis Svingen,Maite G Fernandez-Barrena,Maneesh Dave,William Bamlet,Robert R Mcwilliams,Gloria M Petersen,William Faubion,Martin E Fernandez-Zapico

doi:10.1074/jbc.m113.539031

Abstract

The role of GLI1 in pancreatic tumor initiation promoting the progression of preneoplastic lesions into tumors is well established. However, its function at later stages of pancreatic carcinogenesis remains poorly understood. To address this issue, we crossed the gli1 knock-out (GKO) animal with cre-dependent pancreatic activation of oncogenic kras concomitant with loss of the tumor suppressor tp53 (KPC). Interestingly, in this model, GLI1 played a tumor-protective function, where survival of GKO/KPC mice was reduced compared with KPC littermates. Both cohorts developed pancreatic cancer without significant histopathological differences in survival studies. However, analysis of mice using ultrasound-based imaging at earlier time points showed increased tumor burden in GKO/KPC mice. These animals have larger tumors, decreased body weight, increased lactate dehydrogenase production, and severe leukopenia. In vivo and in vitro expression studies identified FAS and FAS ligand (FASL) as potential mediators of this phenomenon. The FAS/FASL axis, an apoptotic inducer, plays a role in the progression of pancreatic cancer, where its expression is usually lost or significantly reduced in advanced stages of the disease. Chromatin immunoprecipitation and reporter assays identified FAS and FASL as direct targets of GLI1, whereas GKO/KPC mice showed lower levels of this ligand compared with KPC animals. Finally, decreased levels of apoptosis were detected in tumor tissue in the absence of GLI1 by TUNEL staining. Together, these findings define a novel pathway regulated by GLI1 controlling pancreatic tumor progression and provide a new theoretical framework to help with the design and analysis of trials targeting GLI1-related pathways.

Highlights

GLI1 is required for pancreatic tumor initiation; its role at later stages of carcinogenesis remains elusive
Gli1 heterozygous mouse (GHet)/KPC survival was similar to KPC (p ϭ 0.2210) mice suggesting that one wild-type gli1 allele is sufficient to maintain functional GLI1 activity (Fig. 1B)
All three cohorts (KPC, gli1 knock-out (GKO)/KPC, and gli1 heterozygous mouse (GHet)/KPC) developed fibrotic pancreas tumors that were similar in size (Fig. 1C) and showed similar oncogenic KRAS activity, as determined by the activation of the downstream effectors ERK (Fig. 1D and data not shown for GHet/KPC)

Summary

Background

GLI1 is required for pancreatic tumor initiation; its role at later stages of carcinogenesis remains elusive. Role of GLI1 in Pancreatic Cancer Progression bling these late stages of the disease This mouse model contained p48 cre-dependent activation of oncogenic Kras and loss of tumor suppressor tp (KPC) and gli resulting in the GKO/ KPC mouse. We hypothesized that the loss of Gli in this model would result in prolonged survival and lower frequency of pancreas tumors Both cohorts retained the common biological and molecular features of advanced pancreatic cancer, but GKO/KPC mice developed early signs of tumor burden and perished within the 1st month of life. TUNEL staining of pancreas sections resulted in decreased levels of apoptosis in the GLI1-null group demonstrating the existence of a novel GLI1-FASL/FAS axis in pancreatic cancer We hope this knowledge will provide a new theoretical framework to help with the analysis of existing studies targeting GLI1-related pathways as well as the design of future clinical trials

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION