Cell membrane lipid fluidity and receptor expression in Moloney- and Friend virus-transformed cells

Normal and malignant cells show differences in cell membrane lipid fluidity (CMF) which influence the expression of membrane receptors and may interfere with cell function. Friend virus (FLV) and Moloney virus (MLV) infected hematopoietic and lymphoid cells were monitored for CMF (fluorescence polarization) and for transferrin (TFC) and thymic (Thy) receptors (FITC-labelled monoclonal antibodies). CMF was modulated with cholesterol hemisuccinate (CHS), phospholipids (PL) and DMSO. Erythropoietic stem cells exhibit an increased persistent CMF within minutes after FLV infection; transferrin receptors are expressed, yet no hemoglobin is synthesized. CHS rigidification reduces TFC expression with differentiation of cells and hemoglobin synthesis, yet transformed cell populations do not react uniformly. Thymic lymphocytes, instead, do not exhibit changes in Thy expression upon CHS treatment although cell membranes become rigidified. Separate experiments showed these cells not being 'transformed' per se but blocked in differentiation because of viral distruction of thymic epithelial cells with loss of thymopoietin in vivo. Thus viral cell transformation is followed by non-rigid but persistent membrane fluidization interfering with only selective receptor expression.