The Small GTP-binding Protein Rho Activates c-Jun N-terminal Kinases/Stress-activated Protein Kinases in Human Kidney 293T Cells

Abstract

Work from a number of laboratories has established a role for certain small GTP-binding proteins in controlling the enzymatic activity of a family of serine-threonine kinases known as mitogen-activated protein kinases (MAPKs). MAPKs have been classified into three subfamilies: extracellular signal-regulated kinases (ERKs), also known as MAPKs; c-Jun N-terminal kinases (JNKs); and p38 kinase. Whereas Ras controls the activation of MAPKs, we and others have recently observed that in certain cells, the small GTP-binding proteins Rac1 and Cdc42 but not Rho regulate the activity of JNKs. Furthermore, because Rac1 and Cdc42 but not Rho bind and activate a kinase known as Pak1, it has been suggested that Pak1 is the most upstream component of the pathway linking these GTPases to JNK. However, in both yeast and mammalian cells, Rho1p, a Rho homologue, and RhoA, respectively, directly interact with a number of proteins, including kinases related to protein kinase C. In addition, in yeast, Rho1p controls the activity of a MAPK cascade involved in bud formation. Considering this diversity of target molecules for small GTP-binding proteins, their likely tissue specific distribution, and the potential role for Rho in signaling to a kinase cascade, we decided to extend our initial analysis, exploring the ability of Ras and Rho-related GTP-binding proteins to activate MAPK or JNK in a variety of cell lines. We found that in the human kidney epithelial cell line, 293T, Cdc42 and all Rho proteins, RhoA, RhoB, and RhoC, but not Rac or Ras can induce activation of JNK. Furthermore, we provide evidence that signaling from Rho proteins to JNK in 293T cells does not involve Pak1. Taken together these findings demonstrate that Rho signals to JNK in a cell type-specific manner and suggest the existence of a novel, Pak1-independent signaling route communicating the Rho family of small GTP-binding proteins to the JNK pathway.

The Src family tyrosine kinase is involved in Rho-dependent activation of c-Jun N-terminal kinase by Gα12

“…These results suggest that Rho is involved in the signaling pathways from Ga 12 to JNK in various cell types. Activated mutants of RhoA, RhoB and RhoC have been shown to elevate JNK activity in 293T cells (Teramoto et al, 1996). In Saccharomyces cerevisiae, Rho1p, a homologue of the mammalian RhoA, leads to the activation of the mitogen-activated protein kinase (MAPK) cascade involved in bud formation through Pkc1p, a homologue of the mammalian protein kinase C (Nonaka et al, 1995).…”

JNK and ROKα function in the noncanonical Wnt/RhoA signaling pathway to regulate Xenopus convergent extension movements

“…RhoA activates JNK in human culture cells in a G ␣12 -and G i -dependent (Nagao et al, 1999;Yamauchi et al, 2000) or Pak-independent manner (Teramoto et al, 1996), and Rac1 and Cdc42 mediate the activation of JNK by several stimuli (Davis, 2000; Gallo Johnson, 2002). Recently, it has been known that the Wnt/PCP pathway is an important signal cascade for JNK activation (Veeman et al, 2003b).…”

Signaling by dual specificity kinases

“…Recent studies indicate that in the speci®c instances in which Ras is involved in the activation of JNKK/JNK module, it appears that Rac or CDC42 is downstream of Ras mediating the`true' coupling (Coso et al, 1995;Minden et al, 1995). In addition to Ras, Rac, and CDC 42 there has been reports that Rho also mediates the activation of JNK through a PAK-independent pathway (Teramoto et al, 1996;. Furthermore, a role for ceramide in mediating the apoptotic signals from TNFa to JNK signaling pathway via MKK4 has been shown (Verheij et al, 1996).…”