Fibronectin cell-binding domain triggered transmembrane signal transduction in human monocytes

Abstract

Fibronectin (Fn) fragments have recently been shown to stimulate tumor necrosis factor (TNF) secretion by human monocytes. In this study, we investigated the signal transduction mechanisms involved in Fn-induced TNF secretion. Treatment of human monocytes with Fn120, a chymotryptic cell-binding fragment of plasma Fn, failed to cause a detectable rise in Ca2+ mobilization. Fn120-induced TNF secretion could be inhibited with Ca2+ channel blockers. The protein kinase C (PKC) inhibitors H-7 and sphingosine inhibited the TNF-inducing activity of Fn120. HA1004 was used as a control for the isoquinoline sulfonamide derivatives and did not change Fn120-induced TNF secretion by monocytes. H-8 inhibited TNF secretion at higher concentrations. A calmodulin-dependent kinase inhibitor, W-7, was found to be effective, with 50% inhibition of Fn120-induced TNF secretion at 5 microM. The activation and translocation of PKC were measured directly. In unstimulated monocytes, approximately 70% of PKC activity was found in the cytosol and 30% in the membrane. Following the stimulation of monocytes with phorbol myristate acetate (100 nM), rapid and sustained translocation of PKC from the cytosol to the membrane was observed. The stimulation of monocytes with Fn120 triggered a rapid translocation of PKC within 2 to 5 min, followed by a return to normal levels within 8 min. These findings support the conclusion that Fn120-induced TNF secretion requires the activation of PKC.

A Site on Laminin α5, AQARSAASKVKVSMKF, Induces Inflammatory Cell Production of Matrix Metalloproteinase-9 and Chemotaxis

“…For example, proteolytic fragments of ECM, such as fibronectin (50,51), entactin, elastin (52,53), and type I collagen (46), are chemotactic for inflammatory cells. In the present study, we investigated whether laminin molecules modulate inflammatory cell functions.…”

Monocyte Activation by Circulating Fibronectin Fragments in HIV-1-Infected Patients

“…FN fragments and native FN have different biological properties (15)(16)(17)(18)(19)(20). Some FN fragments that are chemotactic for monocytes (17,36) can stimulate phagocytosis (37) and production of proinflammatory cytokines (15,16,38).…”

“…Considering that brief exposure to FNf induces monocytes to release TNF-␣ (22), this cytokine may be an intermediary in the signaling used by FNf to mobilize cell surface display of this enzyme. Within 2 min following stimulation with as little as 10 g/ml FNf protein kinase C translocates from the cytosol to the monocyte cell membrane (16). Compared with the effect of phorbols, the activation of protein kinase C induced by FNf is short-lived, but it appears to be responsible for the subsequent release of TNF-␣ since production of this cytokine following FNf stimulation can be blocked or suppressed by the kinase inhibitors H-7 and sphingosine and by Ca 2ϩ channel blocking agents (16).…”

“…Activation appears to result, in part, from stimulation by circulating cell-binding 110 -120 kDa fibronectin fragments (FNf). We postulate that continued viral replication, even at the low levels (11), stimulates release of enzymes that degrade fibronectin (FN) and other proteins (12)(13)(14), producing fragments with novel biological properties (15)(16)(17)(18)(19), including some that modify monocyte/macrophage behavior (20).…”

The role of nicotine, a7 nicotinic acetylcholine receptors and extracellular matrix remodeling in pulmonary fibrosis.

“…In the injured lung, fibronectin is deposited over denuded basement membranes where it is thought to support the migration of alveolar epithelial cells during repair [61]. It promotes the proliferation of fibroblasts, aids in the deposition of collagen, stimulates the chemotaxis of monocytes and other immune cells and induces cytokine production in macrophages [63][64][65][66][67][68][69]. Excessive fibronectin deposition, however, has been hypothesized to promote disrepair [70].…”