EXPRESSION OF A CONSTITUTIVELY ACTIVE PHOSPHATIDYLINOSITOL 3-KINASE INDUCES PROCESS FORMATION IN RAT PC12 CELLS - USE OF CRE LOXP RECOMBINATION SYSTEM/

It has been shown that inhibition of phosphatidylinositol (PI) S-kinas e blocks neurite outgrowth of PC12 cells stimulated with nerve growth factor. To further assess the role of PI S-kinase, the active form of PI 3-kinase was expressed in PC12 cells by the adenovirus mediated int roduction of a site-specific recombinase, Cre. After expression of the active PI S-kinase, elevation of the levels of PI 3,4-diphosphate and PI 3,4,5-trisphosphate as well as formation of neurite-like processes was observed. The process formation was inhibited by wortmannin, a se lective inhibitor of PI 3-kinase, which suggests that a high activity of PI 3-kinase was responsible for the formation of these processes. T he processes lacked accumulation of F-actin and GAP43 at the growth co ne, which suggests that the processes were incomplete compared with ne urites. Instead, the bundling of microtubules was enhanced, which sugg ests that organization of the microtubules might be driving the proces s of elongation in the cells expressing the active PI 3-kinase. Induct ion of active PI 3-kinase resulted in activation of Jun N-terminal kin ase but not of mitogen-activated protein kinase or protein kinase B/Ra c protein kinase/Akt. These results suggest that PI 3-kinase is involv ed in neurite outgrowth in PC12 cells and that activation of Jun N-ter minal kinase cascade may be involved in the cell response.