Tissue Transglutaminase Mediated Tumor–Stroma Interaction Promotes Pancreatic Cancer Progression

Abstract

Purpose Aggressive pancreatic cancer is commonly associated with a dense desmoplastic stroma, which forms a protective niche for cancer cells. The objective of the study was to determine the functions of tissue transglutaminase (TG2), a Ca2+-dependent enzyme which crosslinks proteins through transamidation and is abundantly expressed by pancreatic cancer cells in the pancreatic stroma. Experimental Design Orthotopic pancreatic xenografts and co-culture systems tested the mechanisms by which the enzyme modulates tumor-stroma interactions. Results We show that TG2 secreted by cancer cells effectively molds the stroma by crosslinking collagen, which in turn activates fibroblasts and stimulates their proliferation. The stiff fibrotic stromal reaction conveys mechanical cues to cancer cells leading to activation of the YAP/TAZ transcription factors, promoting cell proliferation and tumor growth. Stable knockdown of TG2 in pancreatic cancer cells led to decreased size of pancreatic xenografts. Conclusions Taken together, our results demonstrate that TG2 secreted in the tumor microenvironment orchestrates the crosstalk between cancer cells and stroma fundamentally impacting tumor growth. Our study supports TG2 inhibition in the pancreatic stroma as a novel strategy to block pancreatic cancer progression.

Tissue Transglutaminase Activates Cancer-Associated Fibroblasts and Contributes to Gemcitabine Resistance in Pancreatic Cancer

“…After cell implantation, mice were treated with gemcitabine twice a week for 4 weeks at a dose of 25 mg/kg via intraperitoneal injection ( n  = 7 per PBS group and n  = 8 per gemcitabine group). In concordance with our previous data [7], average tumor volumes and weights were significantly decreased in xenografts derived from AsPC1 + shTG2 cells compared with controls (Figure 2 A , left and middle , P  = .002 and P  = .001, respectively), whereas there was no significant difference in the number of macrometastases between the two groups (Figure 2 A , right , P  = .55). Gemcitabine treatment decreased the average tumor volume and weight in both AsPC1 + shCtrl–and AsPC1 + shTG2–derived xenografts compared with PBS (Figure 2 A , left and middle, P  < .002).…”

“…Among PDA cells, AsPC1 and BxPC3 cells expressed relatively abundant TG2, whereas Panc1 and Paca2 cells expressed relatively low TG2 levels. Fibroblasts also expressed endogenous TG2, consistent with our previous observations demonstrating TG2 expression in PDA-associated stroma [7]. TG2 was knocked down in AsPC1 and BxPC3 cells by stably transducing shRNA targeting TG2 (shTG2).…”

“…TG2 was stably knocked down in AsPC1 and BxPC3 cells by transducing MISSION shRNA Lentiviral Transduction Particles (Sigma-Aldrich) as previously described [7]. Briefly, the PDA cells were transduced with scrambled shRNA (shCtrl) or shTG2, followed by polyclonal selection with puromycin (1 μg/ml).…”

“…Briefly, 1.5 × 10 5 AsPC1 cells, stably transduced with shRNA targeting TG2 or scrambled shRNA (shCtrl; control), diluted in 50 μl of medium were injected into the tail of pancreas of 7- to 8-week-old female nude mice (nu/nu Balbc) from Harlan (Indianapolis, IN) using a 27.5-gauge needle under isoflurane anesthesia, as previously described [7]. Gemcitabine at a concentration of 25 mg/kg or PBS (control) was administered to tumor-bearing mice ( n  = 7 per PBS group and n  = 8 per gemcitabine group) twice a week for 4 weeks via intraperitoneal injection.…”

“…Tissue transglutaminase (TG2), a calcium (Ca 2+ )-dependent enzyme that catalyzes protein transamidation through acyl-transfer between glutamine and lysine residues, is abundantly expressed in pancreatic cancer cells and secreted in the pancreatic stroma. We recently showed that TG2 contributes to pancreatic cancer progression by modulating the tumor microenvironment (TME) through collagen cross-linking, which in turn stimulates proliferation and activation of fibroblasts [7]. This fibroblast and TG2-mediated cross-linked collagen- rich stroma in turn stimulates tumor growth by activating the Yes-associated protein and transcriptional co-activator with PDZ-binding motif oncogenic signaling.…”