Interleukin-4 receptor expression on AIDS-associated Kaposi's sarcoma cells and their targeting by a chimeric protein comprised of circularly permuted interleukin-4 and Pseudomonas exotoxin.
BACKGROUND
AIDS-associated Kaposi's sarcoma (AIDS-KS) represents one of the most common malignancies associated with human immunodeficiency virus infection. To target effective therapeutic agents to AIDS-KS, we have identified a new target in the form of interleukin-4 receptors (IL-4R).


METHODS
The expression of IL-4R on AIDS-KS cells and their subunit structure was determined by radioligand receptor binding, cross-linking and Northern and RT-PCR analyses. The in vitro effect of IL-4 and recombinant fusion protein made up of circularly permuted IL-4 and a mutated form of Pseudomonas exotoxin, IL-4(38-37)-PE38KDEL, was examined by clonogenic and protein synthesis inhibition assays.


RESULTS
Five AIDS-KS cell lines expressed high-affinity IL-4R with a Kd of 23.5-219 pM. IL-4 appeared to cross-link to one major protein corresponding to 140 kDa and a broad band corresponding to 60-70 kDa. Both cross-linked proteins were immunoprecipitated with an antibody to human IL-4R beta chain. AIDS-KS cells exhibited IL-4R beta-specific mRNA. IL-4 caused a modest inhibition (31-34%) of colony formation in two AIDS-KS cell lines tested. IL-4(38-37)-PE38KDEL was found to be highly effective in inhibiting the protein synthesis in all five AIDS-KS examined. The IC50 ranged from 32 to 1225 pM. The cytotoxic action of IL-4 toxin was blocked by an excess of IL-4, exhibiting the specificity of IL-4(38-37)-PE38KDEL. The cytotoxicity of IL-4 toxin observed by a clonogenic assay corroborated well with the IC50 obtained by protein synthesis inhibition assay. Normal human endothelial cells expressed a negligible number of IL-4R (< 50 sites/cell) and were less sensitive or not sensitive to IL-4(38-37)-PE38KDEL.


CONCLUSIONS
The presence of a new plasma membrane protein in the form of IL-4R on AIDS-KS cells may be targeted by IL-4(38-37)-PE38KDEL for its potential implication in the treatment of AIDS-KS.
Husain
S R
SR
Laboratory of Molecular Tumor Biology, Food and Drug Administration, Bethesda, Maryland 20892, USA.
Gill
P
P
Kreitman
R J
RJ
Pastan
I
I
Puri
R K
RK
D017088:AIDS-Related Opportunistic Infections / Q000235:genetics / Q000378:metabolism*; D015703:Antigens, CD / Q000235:genetics*; D001667:Binding, Competitive; D015152:Blotting, Northern; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D003432:Cross-Linking Reagents; D005098:Exotoxins / Q000235:genetics / Q000494:pharmacology; D015870:Gene Expression; D006801:Humans; D000922:Immunotoxins / Q000235:genetics / Q000494:pharmacology*; D015847:Interleukin-4 / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D011549:Pseudomonas / Q000235:genetics; D012333:RNA, Messenger; D012194:RNA-Directed DNA Polymerase; D018123:Receptors, Interleukin / Q000235:genetics*; D019948:Receptors, Interleukin-4; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D012514:Sarcoma, Kaposi / Q000235:genetics / Q000378:metabolism*
D015703:Antigens, CD; D003432:Cross-Linking Reagents; D005098:Exotoxins; D000922:Immunotoxins; D012333:RNA, Messenger; D018123:Receptors, Interleukin; D019948:Receptors, Interleukin-4; D011993:Recombinant Fusion Proteins; D015847:Interleukin-4; D012194:RNA-Directed DNA Polymerase