Interaction of stellate cells with pancreatic carcinoma cells

Abstract

Pancreatic cancer is characterized by its late detection, aggressive growth, intense infiltration into adjacent tissue, early metastasis, resistance to chemo- and radiotherapy and a strong "desmoplastic reaction". The dense stroma surrounding carcinoma cells is composed of fibroblasts, activated stellate cells (myofibroblast-like cells), various inflammatory cells, proliferating vascular structures, collagens and fibronectin. In particular the cellular components of the stroma produce the tumor microenvironment, which plays a critical role in tumor growth, invasion, spreading, metastasis, angiogenesis, inhibition of anoikis, and chemoresistance. Fibroblasts, myofibroblasts and activated stellate cells produce the extracellular matrix components and are thought to interact actively with tumor cells, thereby promoting cancer progression. In this review, we discuss our current understanding of the role of pancreatic stellate cells (PSC) in the desmoplastic response of pancreas cancer and the effects of PSC on tumor progression, metastasis and drug resistance. Finally we present some novel ideas for tumor therapy by interfering with the cancer cell-host interaction.

Figure 1

Characteristics of quiescent (fat-storing phenotype) and activated PSC (myofibroblast-like phenotype). In acute and chronic pancreatitis, but also in pancreas carcinomas, PSC change their phenotype from a quiescent fat-storing phenotype to a highly active myofibroblast-like phenotype. Hereby the cells lose their Vitamin A containing fat droplets, express other cytofilaments, increase their proliferation rate and produce growth factors, cytokines, connective tissue, MMPs and TIMPs. In addition, as we have learned recently from animal models, part of the activated PSC originate from stem/progenitor cells of bone marrow.

Figure 2

Immunofluorescence microscopy of cultured PSC, which have been isolated from pancreatic ductal adenocarcinoma. (a) vimentin immunofluorescence (red); (b) alpha‑smooth muscle actin immunofluorescence (red). Cell nuclei are stained blue (Hoechst 33258). FB, alpha-smooth muscle actin negative fibroblast.

Figure 3

Paracrine and autocrine stimulation of activated pancreatic stellate cells in culture. Injured acinar cells, activated inflammatory cells, aggregating platelets, ethanol and acetaldehyde stimulate PSC proliferation, matrix- and MMP-synthesis and PSC motility. Via autocrine stimulatory loops PSC proliferation and ECM-synthesis are also stimulated. AM, adrenomedullin; SDF-1, stromal cell-derived factor-1; ET-1, endothelin-1.

Figure 4

Interaction of PSC with pancreas carcinoma cells. Pancreas carcinoma cells (CC) accelerate transformation of quiescent PSC to the myofibroblast-like phenotype. This cell type is attracted by CC and stimulated to proliferate, produce ECM and growth factors. PSC stimulate angiogenesis, CC proliferation, chemoresistance, invasion, and motility. In addition, PSC reduce anoikis/apoptosis of CC. AM, adrenomedullin; SDF-1, stromal cell‑derived factor-1.

Figure 5

Microphotographs of PSC (isolated from PDA) in co-culture with primary pancreas carcinoma cells (ULA-PaCa). (a) phase contrast; (b) alpha-smooth muscle actin immunofluorescence (red); (c) vinculin, red-yellow, f-actin, green; (d) paxillin, red-yellow; f-actin, green. Cell nuclei are stained blue (Hoechst 33258). CC, panceas carcinoma cells (ULA-PaCa); PSC, pancreatic stellate cells.

Figure 6

Effect of PSC supernatants (PSC-SN) and degraded extracellular matrix on proliferation (BrdU-incorporation) of cultured Panc1 cells. (a) Activated PSC were cultured in 6-well plates until confluency. Then, medium was changed and in the absence of fetal calf serum new medium was conditioned for 3 days. The PSC supernatant was used to stimulate Panc1 cells (see b). The cultured PSC were washed and then lysed using distilled water. After another 3 washing steps the remaining ECM was degraded at 37 °C by addition of 2ml CC supernatant (containing proteases and MMPs). Degraded matrix was preincubated with neutralizing antibodies or directly added to cultured Panc1 cells (see c). (b), PSC supernatant was added to cultured Panc1 and proliferation was quantified by BrdU-incorporation. (c) Degraded matrix (with and w/o preincubation with neutralizing antibodies) was added to cultured Panc1 and proliferation was quantified by BrdU-incorporation. * p < 0.05.