ABSTRACT
Human invasive amoebiasis is highly destructive, causing rapid necrosis and liquefaction of all tissues reached by the trophozoites. Degradation of extracellular matrix components (EMC) has been demonstrated during invasion of the basal lamina. Pursuing the idea that trophozoites might behave similarly to other invasive cells with respect to their interaction with EMC, plasma membrane proteins biochemically or functionally related to integrins were looked for. A 140 kDa molecular mass membrane protein from Entamoeba histolytica trophozoites with the characteristics of a beta 1 integrin-like fibronectin receptor was identified.
Subject(s)
Entamoeba histolytica/chemistry , Integrins/analysis , Animals , Cell Adhesion , Fluorescent Antibody Technique , Molecular Weight , Receptors, Fibronectin/analysisABSTRACT
A 37 kDa protein has been described as a putative receptor for fibronectin (Fn) on E. histolytica trophozoites (1). We have now identified a membrane protein that binds biotinylated fibronectin (BFn) with an apparent molecular weight of 140 kDa. Using BFn we were able to follow this protein during partial purification through DEAE-cellulose and Fn-Sepharose chromatography. Antisera prepared against a peptide corresponding to the deduced amino acid sequence for the putative receptor binding site for human Fn (2) recognized a protein with the same molecular weight. The purified protein was also recognized by this sera. We propose that this protein may function as a Fn receptor and will explore the possibility for it being an integrin.
Subject(s)
Carrier Proteins/isolation & purification , Entamoeba histolytica/chemistry , Fibronectins/metabolism , Protozoan Proteins/isolation & purification , Amino Acid Sequence , Animals , Antibody Specificity , Carrier Proteins/metabolism , Chromatography, Affinity , Chromatography, DEAE-Cellulose , Entamoeba histolytica/growth & development , Entamoeba histolytica/metabolism , Integrins , Molecular Sequence Data , Molecular Weight , Peptide Fragments/immunology , Protozoan Proteins/metabolismABSTRACT
Entamoeba histolytica cells secrete electron-dense granules (EDGs) that have collagenase activity. To study the possible involvement of calmodulin (CaM) on EDG secretion, the effect of several CaM antagonists (TFP, R24571, W-7, W-5, dibucaine and DL-propranolol) was tested on this cellular function. Except for W-5 and dibucaine, the rest of these compounds inhibited EDG secretion. Transmission electron microscopy of collagen-activated trophozoites showed numerous EDGs located in or near the surface membrane. In contrast, trophozoites incubated with TFP showed no EDGs. Protein kinase C inhibitors (H-7, ML-9) had no effect on EDG secretion, suggesting that CaM antagonists acted by selectively inhibiting CaM. These results suggest that a CaM-dependent process is involved in EDG secretion.
