PI 3-kinase, an enzyme responsible for the phosphorylation of the D3 position of the inositol ring of phosphatidylinositol (PI), is recognized 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, oncoproteins and ultraviolet light. Here we report the subcellular distribution and

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... he phosphorylative pattern of p85 a subunit of PI 3-kinase in Burkitt lymphomacells exposed to R interferon a treatment. Immunocytochemical analysis of this enzyme, performed by con focal microscopy, revealed an increased expression of this protein at cytoplasmic level after 90 min of interferon a treatment. Western blotting analyses performed on nuclear and cytoplasmic fractions confirmed the overexpression found by con focal microscopy at cytoplasmic level in the 90 min interferon a treated cells still persisting in the 24 hr treated samples. Such an overexpression was paralleled by an increase of tyrosine phosphorylation both at cytoplasmic and nuclear level suggesting that an enhanced requirement for cytoplasmic expression and phosphorylation of PI 3-kinase might be necessary to the cell for regulating some cytoplasmic-nuclear cross talk involved in the control of Burkitt lymphomacell metabolism following interferon a treatment.