IMMUNOCYTOCHEMICAL DETECTION OF PHOSPHATIDYLINOSITOL-3 KINASE IN BURKITT-LYMPHOMA CELLS

PI 3-kinase, an enzyme responsible for the phosphorylation of the D3 p osition of the inositol ring of phosphatidylinositol (PI), is recogniz ed to be involved in the regulation of many cellular processes such as mitogenic signalling, inhibition of apoptosis, intracellular vesicle trafficking/secretion, regulation of actin and integrin functions and regulation of protein kinases induced by tumour necrosis factor, oncop roteins and ultraviolet light. Here we report the subcellular distribu tion and the phosphorylative pattern of p85 alpha subunit of PI 3-kina se in Burkitt lymphoma cells exposed to R interferon alpha treatment. Immunocytochemical analysis of this enzyme, performed by confocal micr oscopy, revealed an increased expression of this protein at cytoplasmi c level after 90 min of interferon a treatment. Western blotting analy ses performed on nuclear and cytoplasmic fractions confirmed the overe xpression found by confocal microscopy at cytoplasmic level in the 90 min interferon alpha treated cells still persisting in the 24 hr treat ed samples. Such an overexpression was paralleled by an increase of ty rosine phosphorylation both at cytoplasmic and nuclear level suggestin g that an enhanced requirement for cytoplasmic expression and phosphor ylation of PI 3-kinase might be necessary to the cell for regulating s ome cytoplasmic-nuclear cross talk involved in the control of Burkitt lymphoma cell metabolism following interferon alpha treatment.