Effect of three-dimensional collagen I and global histone acetylation on gemcitabine resistance in pancreatic cancer cells.

Abstract

e14515 Background: Pancreatic ductal adenocarcinoma (PDAC) is associated with a pronounced collagen-rich stromal reaction that has been shown to contribute to chemo-resistance. PDAC is also associated with epigenetic changes. We have previously shown that PDAC cells are resistant to gemcitabine in the collagen microenvironment because of increased expression of the chromatin remodeling protein high mobility group A2 (HMGA2) and increased ERK1/2 signaling. Methods: Pancreatic tissue microarrays were stained with trichrome and for histone H3K9, H3K27 acetylation (Ac), and histone acetyltransferase (HATs) expression. PDAC cells were plated onto tissue culture plastic or in 3D collagen gels and protein expression was assessed by Western blotting. DNA damage response was assessed by comet and clonogenic assays. Results: Human PDAC tumors display in areas of fibrosis higher histone H3K9Ac and H3K27Ac. Moreover, PDAC cells upregulate H3K9Ac and H3K27Ac along with GCN5, PCAF and p300 HATs when grown in 3D collagen. Inhibiting ERK1/2 activity and/or decreasing HMGA2 expression attenuates the effect of collagen on H3Ac and HAT expression. Human PDAC tumors with HMGA2 also demonstrate H3Ac and HAT expression. Additionally, cells in 3D collagen demonstrate reduced tailing with the comet assay, increased clonogenic potential and increased γH2AX following gemcitabine treatment, suggesting an increased repair response to damaged DNA in the collagen microenvironment. Significantly, downregulation of HATs along with inhibition of ERK1/2 activity attenuates gemcitabine-induced γH2AX detected in 3D collagen. Conclusions: Collagen microenvironment limits the effectiveness of gemcitabine through ERK1/2 and HMGA2-dependent HAT expression. HMGA2 expression is associated with histone acetylation and HAT expression in human PDAC tumors, particularly in area of fibrosis, suggesting that fibrosis may contribute to chemo-resistance through increased HMGA2-HAT signaling. Given that very little progress has been made in the treatment of pancreatic cancer, targeting HATs could be a novel approach to sensitize pancreatic tumors to chemotherapy.