C1q‐tumour necrosis factor‐related protein 8 (CTRP8) is a novel interaction partner of relaxin receptor RXFP1 in human brain cancer cells

Abstract

We report a novel ligand-receptor system composed of the leucine-rich G-protein-coupled relaxin receptor, RXFP1, and the C1q-tumour necrosis factor-related protein 8 (CTRP8) in human primary brain cancer, a tumour entity devoid of the classical RXFP1 ligands, RLN1-3. In structural homology studies and computational docking experiments we delineated the N-terminal region of the globular C1q region of CTRP8 and the leucine-rich repeat units 7 and 8 of RXFP1 to mediate this new ligand-receptor interaction. CTRP8 secreted from HEK293T cells, recombinant human (rh) CTRP8, and short synthetic peptides derived from the C1q globular domain of human CTRP8 caused the activation of RXFP1 as determined by elevated intracellular cAMP levels and the induction of a marked pro-migratory phenotype in established glioblastoma (GB) cell lines and primary cells from GB patients. Employing a small competitor peptide, we were able to disrupt the CTRP8-RXFP1-induced increased GB motility. The CTRP8-RXFP1-mediated migration in GB cells involves the activation of PI3K and specific protein kinase C pathways and the increased production/secretion of the potent lysosomal protease cathepsin B (cathB), a known prognostic marker of GB. Specific inhibition of CTRP8-induced cathB activity effectively blocked the ability of primary GB to invade laminin matrices. Finally, co-immunoprecipitation studies revealed the direct interaction of human CTRP8 with RXFP1. Our results support a therapeutic approach in GB aimed at targeting multiple steps of the CTRP8-RXFP1 signalling pathway by a combined inhibitor and peptide-based strategy to block GB dissemination within the brain.

C1q/TNF‐related peptide 8 (CTRP8) promotes temozolomide resistance in human glioblastoma

“…Here, we show that RXFP1 agonist CTRP8 (Glogowska et al ., 2013) mitigated the ability of first‐line GBM drug TMZ to induce DNA damage. Patient GBM‐1/2 cells (Fig.…”

“…Here, we demonstrate a novel mechanism which links our recently discovered autocrine/paracrine CTRP8 activation of the G protein‐coupled receptor RXFP1 with the oncogenic STAT3 signaling pathway predictive of poor clinical outcome in human GBM patients (Birner et al ., 2010; Glogowska et al ., 2013). Our data provide first evidence that an activated CTRP8‐RXFP1‐STAT3 axis promotes BER and increases resistance to the first‐line chemotherapeutic drug TMZ in human GBM cells.…”

“…In various tumors, the RLN2‐RXFP1 has emerged as an important ligand–receptor system involved in controlling growth, migration/tissue invasion, angiogenesis, and metastasis (Klonisch et al ., 2007). Contrary to other tumors, malignant brain tumors such as Grade III anaplastic astrocytoma and Grade IV glioblastoma (GBM) express RXFP1 but fail to express RLN2 (Glogowska et al ., 2013). Instead, we recently identified secreted adiponectin paralog C1q/tumor necrosis factor‐related peptide 8 (CTRP8) as a novel RXFP1 agonist in human GBM (Glogowska et al ., 2013; Peterson et al ., 2009).…”

“…Contrary to other tumors, malignant brain tumors such as Grade III anaplastic astrocytoma and Grade IV glioblastoma (GBM) express RXFP1 but fail to express RLN2 (Glogowska et al ., 2013). Instead, we recently identified secreted adiponectin paralog C1q/tumor necrosis factor‐related peptide 8 (CTRP8) as a novel RXFP1 agonist in human GBM (Glogowska et al ., 2013; Peterson et al ., 2009). Of all 16 currently known CTRP members, CTRP8 is the least studied, in part, due to the fact that CTRP8 is a pseudogene in mice (Peterson et al ., 2009).…”

“…Located at the N terminus of the C1q/TNF globular domain of CTRP8 is the putative RXFP1 interacting site ‘AYAAFSV’ (Shemesh et al ., 2008). In human GBM cells, the CTRP8‐mediated autocrine/paracrine RXFP1 activation resulted in elevated intracellular cAMP levels, PI3 kinase pathway activation, and the phosphorylation of PKC isoforms (Glogowska et al ., 2013). Like RLN2 in other neoplastic models, the interaction of CTRP8 with RXFP1 promoted GBM matrix invasion and coincided with increased production and secretion of lysosomal protease cathepsin‐B, a known prognostic marker of GBM (Glogowska et al ., 2013).…”