Thrombospondin-1 acts as a ligand for CD148 tyrosine phosphatase

Abstract

CD148 is a receptor-type protein tyrosine phosphatase that is expressed in several cell types, including vascular endothelial cells and duct epithelial cells. Growing evidence demonstrates a prominent role for CD148 in negative regulation of growth factor signals, suppressing cell proliferation and transformation. However, its extracellular ligand(s) remain unknown. To identify the ligand(s) of CD148, we introduced HA-tagged CD148 into cultured endothelial cells and then isolated its interacting extracellular protein(s) by biotin surface labeling and subsequent affinity purifications. The binding proteins were identified by mass spectrometry. Here we report that soluble thrombospondin-1 (TSP1) binds to the extracellular part of CD148 with high affinity and specificity, and its binding increases CD148 catalytic activity, leading to dephosphorylation of the substrate proteins. Consistent with these findings, introduction of CD148 conferred TSP1-mediated inhibition of cell growth to cells which lack CD148 and TSP1 inhibition of growth. Further, we demonstrate that TSP1-mediated inhibition of endothelial cell growth is antagonized by soluble CD148 ectodomain as well as by CD148 gene silencing. These findings provide evidence that CD148 functions as a receptor for TSP1 and mediates its inhibition of cell growth.growth factor signaling | EGF receptor | VEGF receptor | ERK

Shed syndecan-2 inhibits angiogenesis

“…CD148 is known to be involved in the inhibition of cell migration in leukocytes, notably neutrophils and macrophages (de la Fuente-García et al, 1998;Zhu et al, 2008;Zhu et al, 2011), and, here for the first time we show it also has a role in regulating endothelial cell migration. Another ECM component, thrombospondin, has also been identified as a ligand for CD148, and this molecule is also known to bind HS, and is an inhibitor of angiogenesis (Takahashi et al, 2012). It is tempting to speculate that these three molecules are involved in some form of cell migration regulatory complex within the ECM, particularly as endothelial cell responses to thrombospondin-1 have been shown to involve b1 integrin.…”

The phosphatase CD148 promotes airway hyperresponsiveness through SRC family kinases

“…Future studies will more closely examine the role of CD148 in ASM integrin function and activation of focal adhesion complexes, other mechanisms by which CD148 could impact ASM contractility. CD148 function in ASM contractility could potentially be regulated by binding its recently identified ligands, thrombospondin-1 (TSP1) and syndecan-2, proteins that modulate interactions with extracellular matrix components (14,15). For example, TSP1 stimulates vascular smooth muscle cell migration through FAK, so it is plausible that TSP1 interactions with CD148 could regulate ASM contractility (68).…”

“…The physiologic function of CD148 outside of the hematopoietic system remains obscure, although it has been shown to be upregulated in epithelial cells grown at high density and has been implicated in regulating contact inhibition of cell growth. Recently, thrombospondin-1 (14) and syndecan-2 (15) were reported to specifically interact with the extra cellular domain of CD148; however, the functional consequences of these interactions are unclear.…”

Csk/CD148 and platelet SFK activation: a balancing act!

“…GPVI is a 60-kDa member of the immunoglobulinlike superfamily of receptors and has 2 immunoglobulin-like domains connected to an O-glycosylated region, a transmembrane domain, and a cytoplasmic tail. Although the GPVI monomer is functional, at least a portion of GPVI is present in a dimeric form 8 that binds collagen with high affinity. Like CLEC-2, ligand-induced signaling by GPVI is strongest when the receptor dimerizes, however, unlike CLEC-2, which has ITAM sequences within its cytoplasmic tail, GPVI uses ITAM sequences with the Fc receptor g (FcRg) chain by forming a salt bridge with FcRg.…”

“…Nor is it known whether the activity of CD148 in platelets can be regulated by binding of recently identified extracellular ligands for CD148 such as thrombospondin-1. 8 Answering these questions is critical to fully understanding the regulatory function of CD148 in platelets and for the development of novel antagonists as antithrombotic reagents that target the extracellular or phosphatase domain of CD148.…”