Phosphatidylinositol 3-Kinase Mediates Epidermal Growth Factor-Induced Activation of the c-Jun N-Terminal Kinase Signaling Pathway

Abstract

The signaling events which mediate activation of c-Jun N-terminal kinase (JNK) are not yet well characterized. To broaden our understanding of upstream mediators which link extracellular signals to the JNK pathway, we investigated the role of phosphatidylinositol (PI) 3-kinase in epidermal growth factor (EGF)-mediated JNK activation. In this report we demonstrate that a dominant negative form of PI 3-kinase as well as the inhibitor wortmannin blocks EGF-induced JNK activation dramatically. However, wortmannin does not have an effect on JNK activation induced by UV irradiation or osmotic shock. In addition, a membranetargeted, constitutively active PI 3-kinase (p110␤) was shown to produce in vivo products and to activate JNK, while a kinase-mutated form of this protein showed no activation. On the basis of these experiments, we propose that PI 3-kinase activity plays a role in EGF-induced JNK activation in these cells.Phosphatidylinositol (PI) 3-kinases have been implicated in such biologically diverse processes as mitogenesis, membrane trafficking, insulin-stimulated glucose transport, and cell survival (for reviews, see references 22, 38, and 40). A scenario in which one enzyme activity could play a role in all these processes seems unlikely but may be clarified by the recent realization that there are multiple isoforms of PI 3-kinase, which belong to different families with respect to their substrate specificities and mechanisms of activation. The p110␣ and p110␤ PI 3-kinase isoforms both bind p85 regulatory subunits and are stimulated by both receptor and nonreceptor protein tyrosine kinases. The N-terminal region of p110 has been shown to bind to the region of p85 which separates two src homology (SH2) domains (inter-SH2 region) (10,20,23). p85 mediates the interaction of PI 3-kinase with other proteins via an SH3 domain (35) and two SH2 domains which bind proline-rich regions and tyrosine phosphoproteins, including activated growth factor receptors, respectively. Another PI 3-kinase isoform, p110␥, does not bind p85 and is stimulated by G proteins (41). All three enzymes phosphorylate the 3Ј position of the inositol ring and contribute to the rapid cellular accumulation of PI 3,4-diphosphate (PI 3,4-P 2 ) and PI 3,4,5-triphosphate (PI 3,4,5-P 3 ) upon appropriate stimulation. On the other hand, resting cells have a constitutive pool of PI 3-phosphate (PI 3-P), possibly due to the activity of kinases such as PI 3-kinase p100, (46) which can phosphorylate PI to produce PI 3-P but not PI 4-P or PI 4,5-P 2 to produce PI 3,4-P 2 or PI 3,4,5-P 3 .Variations in the domain structures of PI 3-kinases suggest different modes of interaction with lipids or proteins. For example, while p110␣ and p110␤ are probably localized to the plasma membrane via p85, a p170 PI 3-kinase may be localized by an intrinsic C2 domain, previously identified in membraneassociated proteins (31, 45). Such variety in protein structure suggests variation in the way PI 3-kinases will function as signaling molecules.Little is understood regardi...

The oncogenic TEL/PDGFRβ fusion protein induces cell death through JNK/SAPK pathway

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“…However, the signalling pathways through which these growth factors and oncogenes activate JNK/SAPK pathway are still unde®ned. Recently, it has been reported that a dominant negative form of PI-3 kinase as well as PI-3 kinase inhibitors block EGF-induced JNK/SAPK activation, although these inhibitors had no e ect on JNK/SAPK activation induced by UV irradiation, osmotic shock, or TNFa (Logan et al, 1997). Furthermore, both PI-3 kinase and JNK/SAPK pathway activation has been shown to be involved in the transforming potential of the human leukaemia oncogene, BCR/ABL (Skorski et al, 1997;Raitano et al, 1995).…”

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“…Several growth factors have been shown to activate the c-Jun terminal kinase (JNK), through PI3K (Logan et al, 1997;Minden and Karin, 1997;Minden et al, 1995). To determine whether JNK is activated by Gas6-dependent survival signalling, JNK activity was measured at various times after induction of cell death and Gas6 addition.…”

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