TGF beta (transforming growth factor beta) is a superfamily of cytokines that participate in a variety of cellular processes including growth, proliferation, differentiation, and apoptosis. There are 3 classes of receptors for TGF beta cytokines and they are known as type I, II, and III. TGF beta receptor type III (TGF beta-RIII) is a high affinity receptor for TGF beta-I and TGF beta-II and binds other TGF beta ligands with lower affinities. It is a 250-300 kDa protein that can exist as a single pass transmembrane protein or in its soluble/secreted form. TGF beta-RIII does not have enzymatic activity within the TGF beta signaling pathway. Instead, it frequently coexists with TGF beta-R I and acts as a reservoir for its TGF beta ligands (1). TGF beta signaling has been implicated in many hereditary, developmental, and malignant conditions. There is little known about the exact role of TGF beta -RIII compared to its type I and type II counterparts.
Overexpression of TGF beta has been identified in numerous cancerous models. Bandyopadhyay et. al. hypothesized that ectopic expression of soluble TGF beta-RIII might slow the tumorigenesis caused by TGF beta overexpression (2). The group transfected human colon cancer cells (HCT116) and breast cancer cells (MDA-MB-435) with a TGF beta-RIII vector, and collected soluble TGF beta-RIII that was secreted into the media. To verify that this soluble receptor indeed bound TGF beta, the group used a receptor binding affinity assay and crosslinking then visualized the results on western blot with the TGF beta-RIII antibody. The western blot with the TGF beta-RIII antibody showed a significant molecular weight shift, suggesting the soluble receptor successfully bound TGF beta. The group injected the TGF beta -RIII expressing cell lines into nude mice, and found that they grew significantly slowed than their wild type counterparts, suggesting TGF beta-RIII as a potential therapeutic target.
Murphy et. al. used the TGF beta-RIII antibody in their investigation of the differential expression of growth factors and receptors in ischemic ulcerating wounds (3). The group compared healing versus non-healing ulcers in hopes of finding cytokine targets to use for therapeutic manipulation of non-healing wounds. The group used the PDGFR antibody (AF-307), EGF antibody (AF-236), TGF beta-RIII antibody (AF-242-PB), TGF beta-1 antibody (AF-101-NA), and TGF beta-3 antibody (AF-243-NA) to stain tissue samples from the healing and non-healing wounds. Revascularization was the hallmark of the healing wounds and correlated with increased staining with the TGF beta-RIII antibody, as well as TGF beta-3 and PDGFR. The group suggests that TGF beta III and PDGFR may be useful cytokines for therapeutic manipulation to promote healing in ischemic ulcers.
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