Figueiredo KA, Rossi G, Cox ME 2009 Relaxin promotes clustering, migration, and activation states of mononuclear myelocytic cells. Ann N Y Acad Sci. 1160:353-60
Monocytes are leukocytic precursors of macrophages, dendritic cells, and osteoclasts, with critical roles in inflammation and tumor biology. Tumors can elicit signals that activate monocytes to extravasate, infiltrate tumors, and differentiate into tumor-associated macrophages (TAMs), which can modulate host immune surveillance. In order to assess whether relaxin can influence monocyte activation status, we assessed its ability to alter cell-cell clustering and cytokine expression of the monocytic cell line THP-1. Here we report that relaxin can induce time- and substrate-dependent homotypic cell-cell clustering of monocytes. In addition, we demonstrate that relaxin can suppress macrophage migration in an adenylate cyclase-independent, nitric oxide synthase-dependent fashion. We confirm relaxin-induced upregulation of vascular endothelial growth factor expression and regulation of M1/M2 cytokine profiles. By stimulating monocyte activation and modulating inflammatory cytokine expression and migratory activity of resulting macrophages in response to endotoxin exposure, relaxin may be a critical regulator of the macrophage activation state that regulates the TAM phenotype.
Figueiredo KA, Mui AL, Nelson CC, Cox ME 2006 Relaxin stimulates leukocyte adhesion and migration through a relaxin receptor LGR7-dependent mechanism. J Biol Chem 281:3030-9
Leukocytes are critical effectors of inflammation and tumor biology. Chemokine-like factors produced by such inflammatory sites are key mediators of tumor growth that activate leukocytic recruitment and tumor infiltration and suppress immune surveillance. Here we report that the endocrine peptide hormone, relaxin, is a regulator of leukocyte biology with properties important in recruitment to sites of inflammation. This study uses the human monocytic cell line THP-1 and normal human peripheral blood mononuclear cells to define a novel role for relaxin in regulation of leukocyte adhesion and migration. Our studies indicate that relaxin promotes adenylate cyclase activation, substrate adhesion, and migratory capacity of mononuclear leukocytes through a relaxin receptor LGR7-dependent mechanism. Relaxin-stimulated cAMP accumulation was observed to occur primarily in non-adherent cells. Relaxin stimulation results in increased substrate adhesion and increased migratory activity of leukocytes. In addition, relaxin-stimulated substrate adhesion resulted in enhanced chemotaxis to monocyte chemoattractant protein-1. These responses in THP-1 and peripheral blood mononuclear cells are relaxin dose-dependent and proportional to cAMP accumulation. We further demonstrate that LGR7 is critical for mediating these biological responses by use of RNA interference lentiviral short hairpin constructs. In summary, we provide evidence that relaxin is a novel leukocyte stimulatory agent with properties affecting adhesion and chemomigration.
Figueiredo KA, Palmer JB, Mui AL, Nelson CC, Cox ME 2005 Demonstration of upregulated H2 relaxin mRNA expression during neuroendocrine differentiation of LNCaP prostate cancer cells and production of biologically active mammalian recombinant six histidine tagged H2 relaxin. Ann N Y Acad Sci. 1041:320-7
Relaxin was recently implicated as a regulator of breast and prostate cancer progression. We characterized upregulated H2 relaxin gene expression during neuroendocrine differentiation of the human prostate cancer model, LNCaP. To examine the impact of relaxin on host cells associated with prostatic adenocarcinomas, we generated recombinant 6 His-tagged relaxin (RLXH) in a mammalian expression system. This immunoreactive and biologically active relaxin preparation was used to screen a variety of cell types for cAMP responsiveness. Of the cell types screened, none was more responsive to RLXH than the well-characterized monocyte/macrophage cell line THP-1.
Soanes KH, Figueiredo KA, Richards RC, Mattatall NR, Ewart KV 2004 Sequence and expression of C-type lectin receptors in Atlantic salmon (Salmo salar). Immunogenetics. 56(8): 572-584.
The diverse receptors of the C-type lectin superfamily play key roles in innate immunity. In mammals, cell surface receptors with C-type lectin domains are involved in pathogen recognition and in immune response, and in some cases are exploited by pathogens to gain entry into cells. This study reports on sequence and expression analysis of three paralogous group II C-type lectins from the teleost fish Atlantic salmon (Salmo salar). Each of the receptors showed similarity to immune-relevant mammalian receptors in terms of amino acid sequence and overall organization within the C-type lectin-like domain (CTLD). Two of the three have cytoplasmic motifs consistent with the immunoreceptor tyrosine-based activation motifs (ITAM), which are known to modulate downstream functions in leukocytes. All three C-type lectin receptors were expressed in multiple tissues of healthy fish, including peripheral blood leukocytes and salmon head kidney cells (SHK-1). Each receptor was up-regulated in salmon liver in response to infection by Aeromonas salmonicida and one receptor was substantially up-regulated in cultured SHK-1 cells in response to lipopolysaccharide (LPS). Putative binding sites for the CAAT-enhancer-binding protein (C/EBP) family of transcription factors in the regulatory regions of these C-type lectin genes may mediate their response to bacteria and LPS in salmon leukocytes. The identification of these types of receptors in distinct populations of cells within the immune system will provide important markers for identifying and categorizing the state of differentiation or activation of these cells and lead to further understanding of the interaction between the salmon host and multiple pathogens.