Fibroconectin(Fn) is a large, multidomain glycoprotein, which exists in a soluble form in plasma and an insoluble fibrillar form in extracellular matrices. Fn affects many aspects of cellular responses. However, it it not known whether Fn could
activate
macrophages for the tumor cell killing. We report that Fn induces the tumoricidal activity of macrophages for murine bladder tumor(MBT-2) cell. tumoricidal activity was determined by 3[H]-thymidine uptake of MBT-2 cell. Fn alone had no effect,
wheras
recombinant interferon-γ9IFN-γ) weakly induced the tumoricidal activiy of macrophages for MBT-2 cells. However combination of Fn with recombinant IFN-γ synergized to activate macrophages to kill MBT-2 cells in a dose dependent manner. At this
point
nitric oxide(NO) was secreted by activated macrophages, and the secretion of NO and tumoricidal activity of macrophage were inhibited in the presence of NG-monomethyl-L-arginine(NGMMA), a competitive inhibitor of NO synthase(NOS).
Fn has various cell binding sites. The Arg0Glv-Asp(RGD) sequence present in the central cell binding domain of Fn is the prototype of these sites. Engineered fibronection(eFn) is formed by RGD-rich sequence. Combination of eFn, instead of Fn,
with
recombginant IFN-γ resulted in more powerful activatin of macrophage in tumor cell tumor cell killing than Fn.
In conclusion our results demonstrate that by IFN-γ via a process involving L-arginine dependent NO production. Especially, RGD sequence of Fn has important role for tumoricidal activity of macrophage. Although the precise mechanism of Fn to
promote NO
synthesis induced by IFN-γremains to be further elucidated, Fn-meddiated macrophage adheion by specialized cell surface receptors and activation of intracellular signals might be important in the development of macrophage activation.
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