Binding studies with six purified plant lectins were used to investigate membrane alterations that occur in lymphocyte transformation. Normal human peripheral blood lymphocytes transformed with E-Phytohemagglutinin (E-PHA) or concanavalin-A (Con-A) generally possessed increased numbers of lectin receptors. When this increase was corrected for the expanded surface area of transformed lymphocytes, it appeared that E-PHA and ConA each produced a unique and complex reorganization of cell surface topography. Surface alterations occurred independently of DNA synthesis, cell proliferation, and microtubule or microfilament function. Puromycin inhibited emergence of new lectin receptors on cells transformed with E-PHA, but not with ConA. Lymphocytes incubated with either lectin showed increased incorporation of [14C]galactose into trypsin-sensitive cell surface glycoproteins. This incorporation was abolished by puromycin in cells stimulated by E-PHA but not by ConA. These studies demonstrate that although both lectins induce similar morphological alterations in human lymphocytes, at the molecular level the structural changes induced in the cell membrane by these two lectins differ considerably. Furthermore, these structural alterations are mediated via different mechanisms in the two groups of cells. De novo protein synthesis is required for cell surface reorganization in PHA-stimulated cells, but not in cells stimulated by ConA. The effect of ConA appears to be to enhance attachment of saccharide structures to pre-synthesized membrane proteins.
ASJC Scopus subject areas
- Cell Biology