TGF-β isoforms in cancer: Immunohistochemical expression and Smad-pathway-activity-analysis in thirteen major tumor types with a critical appraisal of antibody specificity and immunohistochemistry assay validity

Abstract

The literature on TGF-ß in cancer including data on the expression or activation of TGF-ß pathway components in specific tumors types is steadily growing. However, no systematic and uniform analysis exists reporting expression levels of the main TGF-ß pathway components across the most frequent tumor types. We used a standardized immunohistochemical assay investigating TGF-ß isoform expression and pathway activation across 13 different tumor types and corresponding non-neoplastic tissues. The study was performed on tissue microarrays allowing for the parallel analysis of a total of 1638 human tumor samples. TGF-ß1, TGF-ß2 and p-Smad2/3 were substantially expressed in multiple cancers widening the options for TGF-ß isoform directed therapies. Of note, TGF-ß antigens appear to be expressed in an individual manner pointing towards a need for patient preselection for TGF-β isoform specific treatment. Yet, a thorough investigation of antibody specificity and assay validity revealed that immunohistochemistry did not correlate with other detection methods on mRNA or protein level in all instances. As such, with the currently available means (i.e. antibodies tested) a stratification of patients within clinical trials for TGF-ß directed antisense therapies based upon TGF-β immunohistochemistry alone has to be interpreted with caution and should be carefully evaluated in combination with other parameters.

Integrin αvβ8–expressing tumor cells evade host immunity by regulating TGF-β activation in immune cells

“…L-TGF-β is secreted mainly as a protein complex bound to immune, fibroblast, or endothelial cell surfaces or incorporated into the extracellular matrix by TGF-β binding proteins (e.g., LTBP1-4, GARP) or other proteins (8,23,43,44). Attempts to immunohistochemically localize TGF-β isoforms to specific cellular compartments within tumors have been largely inconclusive due to antibody specificity (45). Therefore, staining of cells isolated from disaggregated tumors is more reliable as a method to understand what cells present cell-surface L-TGF-β.…”

Quantitation of TGF-β proteins in mouse tissues shows reciprocal changes in TGF-β1 and TGF-β3 in normal vs neoplastic mammary epithelium

“…As TGF-β pathway antagonists are moving into clinical trials, this study provides baseline information to help in addressing the potential desirability and consequences of isoform-specific therapeutic neutralization of TGF-β. The need for improved methods to quantitate TGF-β proteins was highlighted recently by a large cancer tissue microarray study showing that TGF-β immunohistochemistry results did not correlate well with TGF-β levels assessed by mRNA quantitation or Western blotting [26], thereby posing challenges for how best to stratify patients for clinical trials with anti-TGF-β therapies. We have refined the existing methodology for TGF-β protein quantitation and made a number of important findings as discussed below.…”

Metformin inhibits proliferation and migration of glioblastoma cells independently of TGF-β2

“…6 Transforming growth factor beta (TGF-b) is a pivotal immunosuppressive factor in GBM. 7 Although both isoforms, TGF-b 1 and TGF-b 2 , are expressed in GBM tissue, 8 TGF-b 2 seems to be more important for pathogenesis. 9 TGF-b 2 can both inhibit or activate proliferation and migration of BTICs, with more predominant effects on mesenchymal BTICs.…”