ABSTRACT
This study shows that the lateral mobility of CD4, an important plasma-membrane immune receptor, can be modulated by intracellular application of an anti-CD4 antibody. For this purpose, (i) full-length CD4 and a truncated CD4 mutant, lacking a 32-residue-long C-terminal intracellularly exposed domain, were expressed in Spodoptera frugiperda (Sf9) insect cells, (ii) a monoclonal antibody, C6, with specificity for the C-terminal domain was generated, and (iii) a versatile apparatus for fluorescence microphotolysis (FM) studies was constructed. By these means it was found that the commercial anti-CD4 antibody Leu3a-PE, in contrast with several other anti-CD4 antibodies, could be used as a fluorescent label of CD4 without interfering greatly with CD4 mobility. Labelled by Leu3a-PE, full-length CD4 had a lateral diffusion coefficient of D = (4.7 +/- 1.9) x 10(-10) cm2/s and a mobile fraction of fm = 80 +/- 16% (room temperature). Within experimental accuracy the truncated CD4 had the same mobility as full-length CD4. Introduction of the C6 antibody into Sf9 cells by microinjection or by fusion with C6-loaded liposomes decreased the mobility of full-length CD4 (fm = 40%) but not of truncated CD4 (fm = 80%). Treatment of Sf9 cells with phorbol ester also reduced the mobility of full-length CD4 (fm = 50%) but not truncated CD4 (fm = 90%). A calmodulin inhibitor but not a protein kinase C (PKC) inhibitor abolished the phorbol ester effect.
Subject(s)
Antibodies, Monoclonal/immunology , CD4 Antigens/metabolism , Cell Membrane/immunology , Amino Acid Sequence , Animals , Antibody Specificity , Baculoviridae/genetics , CD4 Antigens/genetics , CD4 Antigens/immunology , Calmodulin/antagonists & inhibitors , Cell Line , Humans , Liposomes , Microinjections , Microscopy, Fluorescence , Microscopy, Phase-Contrast , Molecular Sequence Data , Mutagenesis/genetics , Protein Kinase C/antagonists & inhibitors , Spodoptera , Sulfonamides/pharmacology , Tetradecanoylphorbol Acetate/pharmacologyABSTRACT
The baculovirus-insect cell system is reliable in expressing a variety of recombinant proteins. A recombinant baculovirus encoding the full length human CD4 has been used to infect Spodoptera frugiperda 9 cells in 6-L-airlift fermentors. The procedured described in this report permitted a 6.5-fold enhancement of rCD4 expression as compared to standard procedures previously published. The increase of rCD4 expression on the cell surface was achieved by using the following steps: (1) Optimal seeding density of 0.8 x 10(6) cells/mL used to multiply cells at a maximum exponential growth of 4.5 x 10(6); (2) high multiplicity of infection (MOI) of 580 PFU/cell; (3) addition of medium at time of infection. In addition to full-length rCD4, a "short" rCD4 with largely deleted cytoplasmic sequence (last 31 C-terminal amino acids) was also efficiently expressed.