Activating mutations in the KRAS oncogene are prevalent in pancreatic ductal adenocarcinoma (PDAC). We previously demonstrated that pancreatic intraepithelial neoplasia (PanIN) formation, which precedes malignant transformation, associates with the expression of immediate early response 3 (Ier3) as part of a prooncogenic transcriptional pathway. Here, we evaluated the role of IER3 in PanIN formation and PDAC development. In human pancreatic cancer cells, IER3 expression efficiently sustained ERK1/2 phosphorylation by inhibiting phosphatase PP2A activity. Moreover, IER3 enhanced KrasG12D-dependent oncogenesis in the pancreas, as both PanIN and PDAC development were delayed in IER3-deficient KrasG12D mice. IER3 expression was discrete in healthy acinar cells, becoming highly prominent in peritumoral acini, and particularly high in acinar ductal metaplasia (ADM) and PanIN lesions, where IER3 colocalized with phosphorylated ERK1/2. However, IER3 was absent in undifferentiated PDAC, which suggests that the IER3-dependent pathway is an early event in pancreatic tumorigenesis. IER3 expression was induced by both mild and severe pancreatitis, which promoted PanIN formation and progression to PDAC in KrasG12D mice. In IER3-deficient mice, pancreatitis abolished KrasG12D-induced proliferation, which suggests that pancreatitis enhances the oncogenic effect of KRAS through induction of IER3 expression. Together, our data indicate that IER3 supports KRASG12D-associated oncogenesis in the pancreas by sustaining ERK1/2 phosphorylation via phosphatase PP2A inhibition.
Maria Noé Garcia, Daniel Grasso, Maria Belen Lopez-Millan, Tewfik Hamidi, Celine Loncle, Richard Tomasini, Gwen Lomberk, Françoise Porteu, Raul Urrutia, Juan L. Iovanna
(A) IHC for p-MEK1/2 and p-ERK1/2 at 14 weeks of age and Western blot of p-MEK1/2 and p-ERK1/2 at 14 and 40 weeks from KrasG12D;Ier3+/+ and KrasG12D;Ier3–/– mice in pancreatic lysates. (B) IHC for p-MEK1/2 and p-ERK1/2 at 5 and 8 weeks of age and Western blot for p-MEK1/2 and p-ERK1/2 at 8 weeks from KrasG12D;Ink4afl/fl;Ier3+/+ and KrasG12D;Ink4afl/fl;Ier3–/– mice in pancreatic lysates. In A and B, relative band quantification is shown below blots. (C) IF for IER3 (green) and p-ERK1/2 (red) in paraffin sections from a KrasG12D;Ink4afl/fl;Ier3+/+ mouse. Original magnification, ×10, ×20, and ×40 (A and B, as indicated); ×40 (C).