Regulation of the urokinase-type plasminogen activator gene by the oncogene Tpr-Met involves GRB2

Abstract

The oncogene Tpr-Met is a constitutively active form of the hepatocyte growth factor/scatter factor (HGF/SF) receptor Met. It comprises the intracellular moiety of Met linked to the dimerization domain of the nuclear envelope protein Tpr, thus functioning as a constitutively activated Met. HGF/SF is responsible for various biological processes including angiogenesis and wound healing, in which secreted serine protease urokinase-type plasminogen activator (uPA) is implicated. The action of HGF/SF on cells is mediated by the autophosphorylation of Met on two carboxyterminal tyrosine residues, Y¹³⁴⁹VHVNATVY¹³⁵⁶VNV. The two tyrosine residues provide docking sites for various effector molecules, suggesting that multiple signaling pathways are activated to exert biological effects of HGF/SF [Ponzetto et al., Cell (1994) 77: 261]. We found that Tpr-Met efficiently activates the uPA gene via a SOS/Ras/extracellular signal regulated kinase (ERK)-dependent signaling pathway. Mutation of Y¹³⁵⁶, which abrogates GRB2 binding, reduced the induction to half of the control level, while mutation of Y¹³⁴⁹ showed little effect on uPA induction, suggesting an important but partly replaceable role for GRB2 in Met-dependent uPA gene induction. Mutation of both Y¹³⁴⁹VHV and Y¹³⁵⁶VNV into optimal PI 3-kinase sites resulted in a residual induction of about one quarter of the control level, suggesting a potential role for PI 3-kinase. Dose-response analysis of the Tpr-Met showed a biphasic curve. These results suggest that the interplay among different signaling molecules on the receptor is important for full induction of the pathway leading to the activation of the uPA gene.