Oncogenic KRAS/ERK/JUNB signaling suppresses differentiation regulator GATA6 in pancreatic cancer
Zheng Zhong, Xinang Cao, Pei-Ju Liao, Raman Sethi, Jeffrey A. Klomp, Clint A. Stalnecker, Jinmiao Chen, Yue Wan, Channing J. Der, David M. Virshup
Zheng Zhong, Xinang Cao, Pei-Ju Liao, Raman Sethi, Jeffrey A. Klomp, Clint A. Stalnecker, Jinmiao Chen, Yue Wan, Channing J. Der, David M. Virshup
View: Text | PDF
Research Article Cell biology Oncology

Oncogenic KRAS/ERK/JUNB signaling suppresses differentiation regulator GATA6 in pancreatic cancer

Abstract

GATA6 is a master regulator of differentiation in the pancreas, and its expression levels determine the 2 main molecular subtypes of pancreatic cancer. High GATA6 levels contribute to the classical pancreatic cancer subtype, which is associated with a higher degree of tumor differentiation and better disease prognosis. However, why GATA6 expression varies across pancreatic cancers and what regulates GATA6 expression remain elusive. Here, we report that oncogenic KRAS-activated ERK signaling suppresses GATA6 transcription in pancreatic cancers. GATA6 mRNA levels inversely correlated with KRAS/ERK activity in pancreatic tumors. A genome-wide CRISPR screen in a GATA6-EGFP reporter knockin cell line identified JUNB as the ERK-regulated transcriptional repressor for GATA6. Active ERK stabilized JUNB protein, while KRAS/ERK inhibition led to ubiquitin-independent proteasomal degradation of JUNB and increased transcription of GATA6. Upregulation of GATA6 enhanced chemosensitivity of pancreatic cancer cells, and KRAS/ERK inhibitors synergized with chemotherapy in a GATA6-dependent manner. Our study identifies how oncogenic KRAS/ERK signaling suppresses GATA6 to cause dedifferentiation in pancreatic cancer. Combining KRAS/ERK inhibitors with standard-of-care chemotherapies could be a promising therapeutic strategy for treating pancreatic cancers.

Authors

Zheng Zhong, Xinang Cao, Pei-Ju Liao, Raman Sethi, Jeffrey A. Klomp, Clint A. Stalnecker, Jinmiao Chen, Yue Wan, Channing J. Der, David M. Virshup

×

Figure 7

ERK stabilizes JUNB in a GSK3/FBXW7-independent manner.

Options: View larger image (or click on image) Download as PowerPoint
ERK stabilizes JUNB in a GSK3/FBXW7-independent manner. (A) Illustration...
(A) Illustration of the knockin of an EGFP-IRES-mCherry cassette into the JUNB locus. (B) Targeting the KRASG12D-activated MEK/ERK axis decreased JUNB-EGFP fusion protein abundance. HPAF-II JUNB-EGFP-IRES-mCherry cells were treated with small-molecule inhibitors (targets of the inhibitors shown on the left) at the indicated concentrations for 24 h, followed by flow cytometry analysis. (C) JUNB protein abundance decreased over time upon MEK/ERK inhibition. HPAF-II cells were treated with 100 nM trametinib for the indicated time. n = 2 biological replicates/condition. (D) JUNB mRNA was not affected by MEK inhibition. HPAF-II cells were treated with DMSO or 100 nM trametinib for 24 h. n = 2 technical replicates/condition. (E) MEK/ERK inhibition decreased JUNB abundance in Panc03.27 and Panc08.13 cells. Cells were treated with DMSO or 100 nM trametinib for 24 h. n = 2 biological replicates/condition. (F and G) MEK/ERK inhibition promoted JUNB degradation. (F) HPAF-II cells were treated with 40 μg/mL CHX with or without 100 nM trametinib for the indicated time. MYC, a short half-life protein, was used as a control for CHX. (G) Quantification (mean ± SD) of JUNB bands. n = 2 biological replicates/condition. (H) MEK/ERK inhibition decreased JUNB abundance in vivo. HPAF-II tumors from the study shown in Figure 2D were stained for JUNB. Scale bar: 100 μm. (I) MEK/ERK inhibition–caused JUNB degradation was independent of GSK3 activity. HPAF-II cells were treated with DMSO or a GSK3 inhibitor (5 μM BIO or 5 μM CHIR99021) with or without 100 nM trametinib for 24 h. n = 2 biological replicates/condition. (J) MEK/ERK inhibition–caused JUNB degradation was independent of FBXW7. HPAF-II cells with WT or homozygous knockout of FBXW7 were treated with 40 μg/mL CHX and 100 nM trametinib for the indicated time. n = 2 biological replicates/condition.