Abstract
Angiogenesis plays a key role in various physiological and pathological conditions, including inflammation and tumor growth. The bone morphogenetic protein (BMP) antagonist gremlin has been identified as a novel pro-angiogenic factor. Gremlin promotes neovascular responses via a BMP-independent activation of the vascular endothelial growth factor (VEGF) receptor-2 (VEGFR2). BMP antagonists may act as covalent or non-covalent homodimers or in a monomeric form, while VEGFRs ligands are usually dimeric. However, the oligomeric state of gremlin and its role in modulating the biological activity of the protein remain to be elucidated.Here we show that gremlin is expressed in vitro and in vivo both as a monomer and as a covalently linked homodimer. Mutagenesis of amino acid residue Cys141 prevents gremlin dimerization leading to the formation of gremlinC141A monomers. GremlinC141A monomer retains a BMP antagonist activity similar to the wild-type dimer, but is devoid of a significant angiogenic capacity. Notably, we found that gremlinC141A mutant engages VEGFR2 in a non-productive manner, thus acting as receptor antagonist. Accordingly, both gremlinC141A and wild-type monomers inhibit angiogenesis driven by dimeric gremlin or VEGF-A165. Moreover, by acting as a VEGFR2 antagonist, gremlinC141A inhibits the angiogenic and tumorigenic potential of murine breast and prostate cancer cells in vivo.In conclusion, our data show that gremlin exists in multiple forms endowed with specific bioactivities and provide new insights into the molecular bases of gremlin dimerization. Furthermore, we propose gremlin monomer as a new inhibitor of VEGFR2 signalling during tumor growth.
Highlights
The transforming growth factor-β (TGF-β) superfamily comprises over thirty cystine-knot secreted proteins, including the members of the bone morphogenetic protein (BMP) family
Gremlin immunoprecipitated from the lysates of murine organs and analysed by SDS-PAGE under reducing conditions migrates as immunoreactive 20-24 kDa bands, as anticipated for the nonglycosylated and N-glycosylated forms of the protein monomer, respectively [24]
To assess whether gremlinC141A may act as a VEGFR2 antagonist, we evaluated the capacity of gremlinC141A to affect the pro-angiogenic of activity of vascular endothelial growth factor (VEGF)-A165
Summary
The transforming growth factor-β (TGF-β) superfamily comprises over thirty cystine-knot secreted proteins, including the members of the bone morphogenetic protein (BMP) family. They transduce a variety of cellular responses through the assembly of heterodimeric serine/threonine kinase receptors, leading to the activation of smad transcription factors [1]. Gremlin is a multifunctional protein belonging to the DAN family of BMP antagonists It plays essential roles during embryonic development [7,8,9] and in the pathogenesis of several human diseases, such as fibrosis [10] and cancer [11, 12], where it can promote epithelialto-mesenchymal transition (EMT) [13] by inhibiting BMP2, BMP-4 and BMP-7. Gremlin is overexpressed in several human cancers [12], where it may neutralize the negative regulatory role of BMPs on cell proliferation, modulate EMT [13], and enhance tumor growth by stimulating tumor angiogenesis [14, 15] and inflammation [16]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
