Differential Binding of Transforming Growth Factor-β1, -β2, and -β3 by Fibroblasts and Epithelial Cells Measured by Affinity Cross-Linking of Cell Surface Receptors

Abstract

A murine fibroblast cell line (AKR-2B clone 84A) and an epithelial cell line (BALB/MK) were compared for their ability to bind different transforming growth factor-beta (TGF beta) species. The results of competitive binding assays indicated that the epithelial cells had a higher affinity for TGF beta than the fibroblasts. This difference may be the basis for the sensitivity of epithelial cells to much lower concentrations of TGF beta than fibroblasts. Affinity cross-linking studies showed that both cell types express the three cell surface TGF beta-binding molecules that have been previously described for a variety of cell types. The complexity of these cell surface binding proteins was further evaluated using all possible combinations of radiolabeled ligands in competition with each of the three unlabeled TGF beta species. Differences in the ability of specific TGF beta types to compete with radiolabeled TGF beta 2 for binding to the type I and II receptors were observed, with TGF beta 1 being more potent for epithelial cells, and TGF beta 2 being more potent for fibroblasts. In addition, a difference in the ability of different TGF beta species to compete the [125I]TGF beta 3 from epithelial cell surface receptors was apparent. TGF beta 2 was not able to compete with [125I]TGF beta 3 for binding to the type II receptor at any concentration tested, while TGF beta 1 and TGF beta 3 were about equally potent in competition for this receptor type. These differences in cell surface receptor binding of structurally and biologically similar molecules may reflect different functions for these molecules.

Transforming Growth Factor β Signaling via Ras in Mesenchymal Cells Requires p21-Activated Kinase 2 for Extracellular Signal-Regulated Kinase-Dependent Transcriptional Responses

“…Specifically, TGF-h-activated PI3K/PAK2/c-Abl was required for the induction of morphologic transformation, proliferation, and anchorage-independent growth of fibroblasts in a Smad-independent manner. Identification of these cell typespecific pathways extends earlier studies documenting differential binding of TGF-h to its receptors (12,13) and the induction of distinct transcription factors of the Jun/activator protein 1 family in fibroblasts and keratinocytes, leading to distinct, even opposite, transcriptional outcomes (13,14). Other Smad-independent signaling molecules include (but are not limited to) TGF-hactivated kinase-1/p38, c-jun-NH 2 -kinase, Rho family proteins (Rac, cdc42, and RhoA), and Ras (15)(16)(17)(18)(19).…”

Blockade of Transforming Growth Factor-β Signaling Does Not Abrogate Antiestrogen-induced Growth Inhibition of Human Breast Carcinoma Cells

“…Human recombinant TGF-␤1 (Genentech) was used to generate a standard curve from which the receptor binding activity in CM was calculated. In this assay, TGF-␤1 and TGF-␤2 are equipotent in displacing 125 I-TGF-␤1 binding (35). Addition of 1 M tamoxifen directly to the radioreceptor assay has no effect on TGF-␤1 binding by AKR-2B cells.…”

Inappropriate expression of human transforming growth factor (TGF)-α in the uterus of transgenic mouse causes downregulation of TGF-β receptors and delays the blastocyst-attachment reaction

“…TGF-ßs exert their effects via interactions with three well-defined cell surface receptors: type I (TßRI), type II (TßRII) and type III (TßRIII). These receptor subtypes are expressed in a variety of cell types (Massagué & Like 1985, Wakefield et al 1987, Cheifetz et al 1988, Roberts & Sporn 1990, Lyons et al 1991, Mitchell & O'Connor-McCourt 1991. TßRI and TßRII are serine/threonine kinases (Lin et al 1992, Ebner et al 1993, Bassing et al 1994, while TßRIII is a membrane proteoglycan with a short cytoplasmic tail and devoid of any consensus signaling motif (Lopez-Casillas et al 1991, Wang et al 1991, Moren et al 1992).…”