Cell-substratum interactions: serum spreading factor

Mechanism of initial attachment of corneal epithelial cells to polymeric surfaces

The initial attachment of cultured bovine corneal epithelial cells and stromal fibroblasts to two oxygen-containing synthetic polymers was studied. Cultured epithelial cells and stromal fibroblasts were seeded onto two oxygen-containing surfaces: 'tissue culture' polystyrene (TCPS) and a polymer film deposited by RF plasma deposition using a methylmethacrylate monomer (MMA/FEP). To establish the mechanism of cell attachment, the effect of the selective removal of the vitronectin and fibronectin from the serum used in the culture medium was tested. The attachment of cultured epithelial cells during the first 90 min of culture was reduced by 40% (TCPS)-80% (MMA/FEP) as a result of removing vitronectin from the medium. Attachment of these cells to TCPS was reduced by 85-95% when the serum was depleted of both fibronectin and vitronectin. However, depletion of fibronectin reduced cell attachment to TCPS by 20%, whilst on MMA/FEP cell attachment was equivalent, or higher, than that for intact serum. The attachment of cultured corneal stromal fibroblasts was similarly dependent on vitronectin but less dependent on fibronectin. Therefore, for the attachment of both cultured epithelial cells and fibroblasts to oxygen-containing surfaces in the presence of serum, there is a high requirement for serum vitronectin but a lesser requirement for fibronectin. The effects of the establishment of corneal epithelial cells in culture and the site of origin of the cells, were determined. Primary isolates of epithelial cells isolated from the limbal, central or peripheral regions of the cornea were less dependent on vitronectin for initial attachment to TCPS than were these cells after several passages in culture. Furthermore, the primary isolates were dramatically less responsive to vitronectin than the cultured cells. These results indicate that the mechanism of attachment of corneal epithelial cells to TCPS varies with the culture experience of the cells. Cells that are culture neophytes can employe endogenous mechanisms for the initial attachment to TCPS, whereas cells established in culture are dependent on exogenous vitronectin in order to attach.

Binding of vitronectin to opa-expressing Neisseria gonorrhoeae mediates invasion of HeLa cells

Neisseria gonorrhoeae induces local infections in the human genitourinary tract and can disseminate to other organs to cause severe disease. Blood-derived factors present in the genital mucosa have been suggested to facilitate the spread of N. gonorrhoeae in disseminated gonococcal infections. Using gentamicin invasion assays and confocal microscopy, we observed a strong stimulatory effect of fetal calf serum (FCS) on the gonococcal invasion of HeLa cells. FCS-mediated invasion was dependent on the expression of the epithelial cell invasion-associated Opa protein (plasmid-encoded Opa50 or its chromosomal homolog Opa30), while N. gonorrhoeae expressing noninvasive Opa proteins (Opa(51-60)) or no Opa protein (Opa-) was not invasive even in the presence of FCS. Incubation of N. gonorrhoeae MS11 with biotinylated FCS revealed a 78-kDa protein as the prominent protein binding to Opa50- or Opa30-expressing gonococci. This protein was recognized by antibodies against vitronectin (VN) in Western blots. Purified human or bovine VN efficiently bound to Opa50-expressing gonococci, while binding to noninvasive Opa- or Opa52-expressing gonococci was significantly lower. Binding of VN was inhibited by heparin in a concentration-dependent manner, indicating that the heparin binding sites present in VN or Opa50 may play an essential role in this interaction. Based on gentamicin invasion assays and confocal microscopy studies, VN binding was associated with an increased invasion of Opa50- and Opa30-expressing gonococci into HeLa cells. The ability of VN to mediate entry into epithelial cells may constitute an important event in the pathogenesis of local as well as disseminated gonococcal infections.

Adsorption of fibronectin and vitronectin onto Primaria and tissue culture polystyrene and relationship to the mechanism of initial attachment of human vein endothelial cells and BHK-21 fibroblasts

The two cell culture substrata, tissue culture polystyrene (TCPS) and Primaria, were compared in order to determine whether a nitrogen-containing surface such as Primaria attracts cells by a different mechanism to an oxygen-containing surface (TCPS). The amounts of vitronectin (Vn) and fibronectin (Fn) which adsorb from the fetal bovine serum (FBS) component of the culture medium onto Primaria and TCPS were determined. Primaria adsorbed two- to threefold more Fn than TCPS, but adsorbed similar amounts of Vn from medium containing FBS. The Fn and Vn binding sites on Primaria were distinct, as adsorption was non-competitive between these two proteins. The amounts of Fn and Vn that adsorbed onto the two surfaces were compared to the concentration dependence of the cell attachment activities of Fn and Vn. Whereas the amounts of Fn which adsorbed onto TCPS were suboptimal for cell attachment, Primaria adsorbed an Fn surface density that was supraoptimal for attachment of human vein endothelial cells and BHK-21 fibroblasts. We conclude that Primaria differs from TCPS in that both Fn and Vn mediate initial cell attachment to Primaria when the culture medium contains FBS, whereas cell attachment to TCPS is dependent upon Vn.

Roles of serum vitronectin and fibronectin in initial attachment of human vein endothelial cells and dermal fibroblasts on oxygen- and nitrogen-containing surfaces made by radiofrequency plasmas

Fluoropolymers modified by plasma modification were studied for their suitability as surfaces for the adhesion of cells. We compared films made by plasma modification of fluoroethylenepropylene (FEP) using nitrogen-containing gases (ammonia or dimethyl acetamide) with films deposited using oxygen-containing monomers (methanol, methyl methacrylate or sequential treatment with toluene then water). The surfaces were compared for the attachment and spreading of human vein endothelial cells and human dermal fibroblasts. The initial attachment and spreading of cultured fibroblasts and endothelial cells onto films deposited using nitrogen-containing gases were equivalent to that onto films deposited using oxygen-containing monomers, but there were some differences in the mechanism of attachment. With films deposited using oxygen-containing monomers, the initial attachment and spreading of endothelial cells failed when the medium contained 15% (v/v) serum from which both fibronectin (Fn) and vitronectin (Vn) had been removed. Similarly, initial attachment and spreading of endothelial cells onto films deposited using oxygen-containing monomers were reduced by 62-86% when the cells were seeded in medium containing Vn-depleted serum (which contained Fn). Endothelial cells attached and spread onto films made using oxygen-containing monomers, when seeded in medium containing Fn-depleted serum (which contained Vn). On films deposited using nitrogen-containing gases, the adhesion of endothelial cells was only slightly reduced in Vn-depleted medium (as compared to attachment in medium containing unmodified serum). Furthermore, surfaces which had incorporated nitrogen were more effective than were oxygen-containing films in adsorbing sufficient serum Fn as to promote endothelial cell attachment. Similar results were seen for the attachment and spreading of fibroblasts as for the endothelial cells. For fibroblasts, attachment and spreading onto oxygen-containing films and onto nitrogen-containing films were not simply dependent upon either the Vn content or the Fn content of the medium. Maximal attachment and spreading of fibroblasts were, however, dependent upon adsorption of both serum Vn and Fn.

Polystyrene chemistry affects vitronectin activity: an explanation for cell attachment to tissue culture polystyrene but not to unmodified polystyrene

Tissue culture polystyrene (TCPS) supports good attachment of adherent cells whereas unmodified polystyrene (PS) does not, but the mechanism of this difference is not well characterized. We have compared TCPS and PS for the amounts of vitronectin (Vn) and fibronectin (Fn) which adsorb from the fetal bovine serum (FBS) component of the culture medium. The significance of the amounts of Vn and Fn which adsorbed onto TCPS and PS was determined by reference to the concentration dependence of the cell attachment activity of Vn and Fn when adsorbed onto TCPS and PS, assayed using human vein endothelial cells and BHK-21 fibroblasts. The amount of Vn which adsorbed onto TCPS from medium containing 3-30% (v/v) FBS was supraoptimal for the attachment of endothelial cells and fibroblasts. On PS, the amount of Vn which adsorbed from this medium was less than for TCPS and was suboptimal for cell attachment. Higher levels of Fn adsorbed onto TCPS than to PS, but even the amounts of Fn which adsorbed onto TCPS were suboptimal for cell attachment. We propose that the principal mechanistic difference between TCPS and PS for the initial attachment and spreading of cells is that more Vn adsorbs onto TCPS from the serum component of the culture medium.

Role of serum vitronectin and fibronectin in adhesion of fibroblasts following seeding onto tissue culture polystyrene

The suitability of polymeric biomaterials as surfaces for the attachment and growth of cells has often been investigated in tissue culture. In this study the contribution that adsorption of serum fibronectin (Fn) or vitronectin (Vn) make to the attachment and spreading of fibroblast cells during the first 90 min following seeding was determined for two modified tissue culture polystyrenes, as model biomaterial surfaces. The amount of serum Vn and Fn which adsorbed onto tissue culture grade polystyrene (TCP) from different serum concentrations over the range of 0.1-30% (v/v) were determined and compared to attachment of cells of the BHK-21 and HT1080 fibroblast lines. There was no simple correlation between the amount of Fn or the amount of Vn adsorbed and cell attachment and spreading. The requirement for Fn or Vn for attachment and spreading of BHK-21 or HT1080 cells onto modified polystyrene (either TCP or to Primaria) during the first 90 min of cell culture was directly tested by selective removal of Fn or Vn from the serum prior to addition to the culture medium. Attachment and spreading of BHK-21 or HT1080 cells onto TCP or Primaria surfaces were reduced in a concentration-dependent manner when the cells were seeded in medium containing 2% (v/v) or higher concentrations of Vn-depleted serum. BHK-21 cells or HT1080 cells seeded in medium containing Fn-depleted serum (which contained Vn) attached and spread onto TCP or Primaria. Both BHK-21 cells and HT1080 cells failed to attach to TCP or Primaria when seeded in medium containing serum depleted of both Vn and Fn. The requirement for serum Vn or Fn for fibroblast attachment to TCP was also tested using cells of a human dermal fibroblast strain. The attachment of the dermal fibroblasts to TCP during the first 90 min of culture was not decreased by depletion of Vn from the 15% (v/v) serum, but there was a reduction in the proportion of the attached cells which had spread. Selective depletion of serum Fn did not have any effect on either cell attachment or spreading. Our results show that for fibroblast cells, particularly with cell lines such as BHK-21 or HT1080 but also with cell strains, the first binding of cells onto tissue culture polystyrene when plated in medium containing serum is a result of adsorption onto the surface of serum Vn. The adsorption of serum Vn onto the surface overcomes the effect of serum components which tend to decrease cell attachment.