ABSTRACT
The present analyses were undertaken to define the mechanisms by which fetuin-A modulates cellular adhesion. FLAG-tagged fetuin-A was expressed in breast carcinoma and HEK-293T cells. We demonstrated by confocal microscopy that fetuin-A co-localizes with histone H2A in the cell nucleus, forms stable complexes with histones such as H2A and H3 in solution, and shuttles histones to exosomes. The rate of cellular adhesion and spreading to either fibronectin or laminin coated wells was accelerated significantly in the presence of either endogenous fetuin-A or serum derived protein. More importantly, the formation of focal adhesion complexes on surfaces coated by laminin or fibronectin was accelerated in the presence of fetuin-A or histone coated exosomes. Cellular adhesion mediated by histone coated exosomes was abrogated by heparin and heparinase III. Heparinase III cleaves heparan sulfate from cell surface heparan sulfate proteoglycans. Lastly, the uptake of histone coated exosomes and subsequent cellular adhesion, was abrogated by heparin. Taken together, the data suggest a mechanism where fetuin-A, either endogenously synthesized or supplied extracellularly can extract histones from the nucleus or elsewhere in the cytosol/membrane and load them on cellular exosomes which then mediate adhesion by interacting with cell surface heparan sulfate proteoglycans via bound histones.
Subject(s)
Breast Neoplasms/metabolism , Cell Adhesion/physiology , Exosomes/metabolism , Focal Adhesions/metabolism , Histones/metabolism , alpha-2-HS-Glycoprotein/metabolism , Cell Line , Cell Line, Tumor , Cell Membrane/metabolism , Cell Nucleus/metabolism , Cytoplasm/metabolism , Female , Fibronectins/metabolism , HEK293 Cells , Heparin/metabolism , Heparitin Sulfate/metabolism , Humans , Laminin/metabolism , Polysaccharide-Lyases/metabolism , Proteoglycans/metabolismABSTRACT
Parkinson's Disease (PD) is marked by prominent motor symptoms that reflect striatal dopamine insufficiency. However, non-motor symptoms, including depression, are common in PD. It has been suggested that these changes reflect pathological involvement of non-dopaminergic systems. We examined regional changes in serotonin (5-HT) and norepinephrine (NE) systems in mice treated with two different 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment paradigms, at survival times of 3 or 16 weeks after the last MPTP injection. MPTP caused a decrease in striatal dopamine concentration, the magnitude of which depended on the treatment regimen and survival interval after MPTP treatment. There was significant involvement of other subcortical areas receiving a dopamine innervation, but no consistent changes in 5-HT or NE levels in subcortical sites. In contrast, we observed an enduring decrease in 5-HT and NE concentrations in both the somatosensory cortex and medial prefrontal cortex (PFC). Immunohistochemical studies also revealed a decrease in the density of PFC NE and 5-HT axons. The decrease in the cortical serotonergic innervation preferentially involved the thick beaded but not smooth fine 5-HT axons. Similar changes in the 5-HT innervation of post-mortem samples of the PFC from idiopathic PD cases were seen. Our findings point to a major loss of the 5-HT and NE innervations of the cortex in MPTP-induced parkinsonism, and suggest that loss of the beaded cortical 5-HT innervation is associated with a predisposition to the development of depression in PD.