Perturbation of the human T-cell antigen receptor-T3 complex leads to the production of inositol tetrakisphosphate: evidence for conversion from inositol trisphosphate.

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Abstract
Antibodies directed against the T-cell antigen receptor-T3 complex mimic antigen and lead to cellular changes consistent with activation. When cells of the human T-cell line Jurkat were stimulated with a monoclonal antibody directed against T3, inositol phosphates were produced. In addition to inositol trisphosphate, which is the product of phosphatidylinositol bisphosphate cleavage, a second inositol polyphosphate was formed. This compound was more polar than inositol trisphosphate but less polar than inositol pentakisphosphate. It cochromatographed with inositol tetrakisphosphate from ostrich erythrocytes. In permeabilized Jurkat cells, this compound was shown to be formed from inositol 1,4,5-trisphosphate, but only in the presence of ATP, and 32P was incorporated into it from [gamma-32P]ATP. There also was coincident formation of inositol 1,3,4-trisphosphate. We conclude that the more polar compound is inositol tetrakisphosphate, which is formed by phosphorylation of inositol 1,4,5-trisphosphate and may be the precursor of inositol 1,3,4-trisphosphate.

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