Identification of an Endogenously Generated Cryptic Collagen Epitope (XL313) That May Selectively Regulate Angiogenesis by an Integrin Yes-associated Protein (YAP) Mechano-transduction Pathway

Abstract

Extracellular matrix (ECM) remodeling regulates angiogenesis. However, the precise mechanisms by which structural changes in ECM proteins contribute to angiogenesis are not fully understood. Integrins are molecules with the ability to detect compositional and structural changes within the ECM and integrate this information into a network of signaling circuits that coordinate context-dependent cell behavior. The role of integrin ␣v␤3 in angiogenesis is complex, as evidence exists for both positive and negative functions. The precise downstream signaling events initiated by ␣v␤3 may depend on the molecular characteristics of its ligands. Here, we identified an RGD-containing cryptic collagen epitope that is generated in vivo. Surprisingly, rather than inhibiting ␣v␤3 signaling, this collagen epitope promoted ␣v␤3 activation and stimulated angiogenesis and inflammation. An antibody directed to this RGDKGE epitope but not other RGD collagen epitopes inhibited angiogenesis and inflammation in vivo. The selective ability of this RGD epitope to promote angiogenesis and inflammation depends in part on its flanking KGE motif. Interestingly, a subset of macrophages may represent a physiologically relevant source of this collagen epitope. Here, we define an endothelial cell mechano-signaling pathway in which a cryptic collagen epitope activates ␣v␤3 leading to an Src and p38 MAPK-dependent cascade that leads to nuclear accumulation of Yes-associated protein (YAP) and stimulation of endothelial cell growth. Collectively, our findings not only provide evidence for a novel mechano-signaling pathway, but also define a possible therapeutic strategy to control ␣v␤3 signaling by targeting a proangiogenic and inflammatory ligand of ␣v␤3 rather than the receptor itself.

YAP Overexpression in Breast Cancer Cells Promotes Angiogenesis Through Activating Yap Signaling in Vascular Endothelial Cells

“…Finally, this hypothesis was verified in present study. YAP activation in ECs was regulated by mechanical stress and/or G-protein-coupled receptor signaling [10,14,23]. Our results revealed that both mechanical stress and G-protein-coupled receptor signaling were involved in YAP activation in ECs when treated with conditioned media from BCs that over-expression of YAP.…”

“…Hippo-YAP signaling has emerged as a key pathway that regulates endothelial cells activation were considered as important contributions to tumor-associated angiogenesis [7,10,13,14]. Therefore, we tested whether YAP in HUVECs mediated CM-YAP+ induced angiogenesis.YAP expression level in HUVECs was effectively downregulated using shRNA (Figure 2A).…”

Cryptic epitopes and functional diversity in extracellular proteins

“…Unfolding has also been shown to transform collagen type I from a β1 integrinassociated ligand to an αvβ3-dependent ligand due to exposure of an RGD epitope (Davis, 1992;Montgomery et al, 1994). A similar pathway has been identified for collagen-stimulated endothelial cell proliferation in angiogenesis (Ames et al, 2015).…”

Cryptic collagen elements as signaling hubs in the regulation of tumor growth and metastasis

“…(c) Example of the generation of cryptic collagen epitopes generated by applying cell-mediated mechanical tension or contraction thereby unwinding or altering the triple-helical collagen structure The terms matrikine and matricryptin have been coined to describe small bioactive peptides or fragments of ECM molecules that exhibit distinct functions as compared to their intact parent protein (Ricard-Blum & Salza, 2014;Ricard-Blum & Vallet, 2016). A rapidly growing subgroup of these matrikine-like molecules (Ames et al, 2016;Colorado et al, 2000;Cretu et al, 2007;Gunda, Boosani, Verma, Guda, & Sudhakar, 2012;Kamphaus et al, 2000;Karagiannis & Popel, 2007;Koskimaki et al, 2010;Lambert et al, 2018;Lindsey et al, 2015;Maeshima et al, 2001;O'Reilly et al, 1997;Ortiz-Urda et al, 2005;Park & Scherer, 2012;Patel & Snelgrove, 2018;Ramchandran et al, 1999;Ricard-Blum & Salza, 2014;Ricard-Blum & Vallet, 2016;Weckmann et al, 2012;J. Xu et al, 2001;R.…”