SIGNAL-TRANSDUCTION PATHWAYS INVOLVED IN THE MITOGENIC ACTIVITY OF PLEIOTROPHIN - IMPLICATION OF MITOGEN-ACTIVATED PROTEIN-KINASE AND PHOSPHOINOSITIDE 3-KINASE PATHWAYS

Pleiotrophin (PTN) is a developmentally regulated protein which exhibi ts neurite-outgrowth, mitogenic, and angiogenic properties. It has als o been shown to be involved in tumor growth and metastasis, Here we us ed primary BEL (bovine epithelial lens) cells to investigate the signa l transduction pathways involved in the mitogenic activity of recombin ant PTN. PTN was purified from conditioned media of SW-13 cells transf ected with the human PTN cDNA. We show that inhibitors of tyrosine kin ase, mitogen-activated protein kinase, or phosphoinositide (PI) 3-kina se inhibit DNA synthesis stimulated by PTN. Analysis of tyrosine-phosp horylated proteins following PTN stimulation showed phosphorylation of two novel 190- and 215-kDa proteins in addition to SHC, ERK1, and ERK 2. A mobility shift of phosphorylated ERK1 and ERK2 was detected with a panERK antibody confirming the phosphorylation of the two ERKs. Furt hermore, in vitro immunocomplex kinase assay with Akt1, a natural subs trate of PI 3-kinase, showed an activation of the kinase following PTN stimulation and a reversal by the PI 3-kinase inhibitor wortmannin, W e conclude that the mitogenic activity of PTN is dependent on tyrosine kinase activation and utilizes the mitogen-activated protein kinase a nd the PI 3-kinase pathways to transduce a mitogenic signal.