The fibroblast surface markers FAP, anti‐fibroblast, and FSP are expressed by cells of epithelial origin and may be altered during epithelial‐to‐mesenchymal transition

Abstract

The identification of fibroblasts and cancer-associated fibroblasts from human cancer tissue using surface markers is difficult, especially because the markers used currently are usually not expressed solely by fibroblasts, and the identification of fibroblast-specific surface molecules is still under investigation. It was aimed to compare three commercially available antibodies in the detection of different surface epitopes of fibroblasts (anti-fibroblast, fibroblast activation protein α, and fibroblast surface protein). The specificity of their expression, employing fibroblast cell lines and tumor-derived fibroblasts from breast and prostate tissues was investigated. Both the established fibroblast cell line HFF-1 and ex vivo primary fibroblasts isolated from breast and prostate cancer tissues expressed the tested surface markers to different degrees. Surprisingly, those markers were expressed also by permanent cell lines of epithelial origin, both benign and cancer-derived (breast-cell lines MCF 10A, HMLE and prostate-cell lines BPH-1, DU 145, and PC-3). The expression of fibroblast activation protein α increased on the surface of previously described models of epithelial cells undergoing epithelial-to-mesenchymal transition in response to treatment with TGF-β1. To prove the co-expression of the fibroblast markers on cells of epithelial origin, we used freshly dissociated human prostate and breast cancer tissues. The results confirmed the co-expression of anti-fibroblast and fibroblast surface protein on CD31/CD45-negative/EpCAM-positive epithelial cells. In summary, our data support the findings that the tested fibroblast markers are not fibroblast specific and may be expressed also by cells of epithelial origin (e.g., cells undergoing EMT). Therefore, the expression of these markers should be interpreted with caution, and the combination of several epitopes for both positive (anti-fibroblast or fibroblast activation protein α) and negative (EpCAM) identification of fibroblasts from breast and prostate tumor tissues is advised. © 2017 International Society for Advancement of Cytometry.

In search of definitions: Cancer‐associated fibroblasts and their markers

“…Other available surface markers such as PDGFRα/β work well here, as do more general fibroblast surface markers like Thy‐1 cell surface antigen (CD90), provided that the cell population is also subjected to selection with negative markers . This is especially important, as a significant number of commonly used fibroblast markers display expression over a number of different cell types, running the risk of inadvertent sample contamination if a proper negative selection is not carried out. Further stratification of the isolated general population could then be carried out using various more subtype‐specific markers such as FAP, PDGFRβ and GPR77/CD19 …”

“…S100 calcium binding protein A4 (S100A4), also known as fibroblast‐specific protein 1 (FSP1), for example, is a marker that has been used in a number of publications in order to confirm the CAF phenotype of examined cells . However, recent studies have raised some suspicion on the specificity of FSP1, as it has been observed to be less reliable for fibroblast identification from primary tumor samples than FAP . It has also been confirmed to be expressed by metastatic prostate cancer‐derived epithelial cell lines and tissues .…”

“…However, recent studies have raised some suspicion on the specificity of FSP1, as it has been observed to be less reliable for fibroblast identification from primary tumor samples than FAP . It has also been confirmed to be expressed by metastatic prostate cancer‐derived epithelial cell lines and tissues . Furthermore, FSP1 expression in fibroblasts is also strongly variable between different CAF sub‐populations …”

“…Considered to be a marker for quiescent fibroblasts, rather than CAFs. 6,25,75 No POSTN Not specific for cancer-associated fibroblasts and is expressed in normal fibroblasts. 41,54 No COL1 A histochemical marker commonly used in older lo identify fibroblast populations.…”

Step-Wise Chondrogenesis of Human Induced Pluripotent Stem Cells and Purification Via a Reporter Allele Generated by CRISPR-Cas9 Genome Editing

“…However, the results of surface marker analyses should be interpreted with caution, as surface markers do not necessarily reflect cell function and as stem and/or progenitor cells can be highly plastic, and lineage-origin dependent. [30,31]…”