Kinase-Deficient Pak1 Mutants Inhibit Ras Transformation of Rat-1 Fibroblasts

Chen, Zunxuan; Ambrose, Diane; Liu, Jianhua; Gibbs, Jackson B.; Chernoff, Jonathan; Field, Jeffrey

doi:10.1128/mcb.17.8.4454

Cited by 195 publications

(148 citation statements)

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“…As another downstream effector of Rac1, PAK1 would likely be activated through K-Ras/Rac1, suggesting that a potential K-Ras/Rac1/PAK1 cascade may exist in colon cancer cells. This is consistent with the previous finding that PAK1 functions downstream of Ras in promoting cell proliferation and transformation (Tang et al, 1997;Nheu et al, 2004). In our Rac1 knockdown cells, nuclear clearance of b-catenin staining (the staining intensity in the nucleus and cytosol became the same) was observed, confirming the previous report (Phelps et al, 2009).…”

Section: Discussionsupporting

confidence: 94%

A Rac1/PAK1 cascade controls β-catenin activation in colon cancer cells

et al. 2011

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P21-activated kinase 1 (PAK1) is associated with colon cancer progression and metastasis, whereas the molecular mechanism remains elusive. Here, we show that downregulation of PAK1 in colon cancer cells reduces total b-catenin level, as well as cell proliferation. Mechanistically, PAK1 directly phosphorylates b-catenin proteins at Ser675 site and this leads to more stable and transcriptional active b-catenin. Corroborating these results, PAK1 is required for full Wnt signaling, and superactivation of b-catenin is achieved by simultaneous knockdown of adenomatous polyposis coli protein and activation of PAK1. Moreover, we show that Rac1 functions upstream of PAK1 in colon cancer cells and contributes to b-catenin phosphorylation and accumulation. We conclude that a Rac1/PAK1 cascade controls b-catenin S675 phosphorylation and full activation in colon cancer cells. Supporting this conclusion, overexpression of PAK1 is observed in 70% of colon cancer samples and is correlated with massive b-catenin accumulation.

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Section: Discussionsupporting

confidence: 94%

A Rac1/PAK1 cascade controls β-catenin activation in colon cancer cells

et al. 2011

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“…Our suggestion that MEK-ERK acts as a downstream effector of PAK-1 is consistent with a previous observation that group A PAKs (PAK-1, PAK-2 and PAK-3) are required for ERK activation and transformation by Ras (Tang et al, 1997). Furthermore, MEK-1 and C-Raf have been shown to be direct substrates of PAK (King et al, 1998;Li et al, 2001;Sundberg-Smith et al, 2005;Park et al, 2007).…”

Section: Discussionsupporting

confidence: 92%

“…Functional knockdown of PAK-1 reduces insulinstimulated proto-oncogene expression and insulin induced b-cat binding to human c-Myc gene promoter To examine whether PAK-1 has a role in insulinstimulated proto-oncogene expression, we first used a plasmid construct that expresses a Myc-tagged dominant negative (DN) form of human PAK-1 (K299R) (Tang et al, 1997(Tang et al, , 1998 to inhibit PAK-1 function in the HT29 cell line. We also used and assessed the expression of a constitutively active form of PAK-1 (T423E).…”

Section: Insulin Stimulates Pak-1 Phosphorylation In Intestinal Cellsmentioning

confidence: 99%

“…We also used and assessed the expression of a constitutively active form of PAK-1 (T423E). The DN PAK-1 mutant was initially shown to inhibit Ras-mediated transformation of Rat-1 fibroblasts and Schwann cells (Tang et al, 1997(Tang et al, , 1998, and has been used by several other studies that required functional knockdown of PAK-1 (Adam et al, 2000;Yoshii et al, 2001). The constitutively active PAK-1 mutant was shown to stimulate Raf-1 phosphorylation at Ser338, thereby enhancing its mitochondrial localization .…”

Section: Insulin Stimulates Pak-1 Phosphorylation In Intestinal Cellsmentioning

confidence: 99%

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P-21-activated protein kinase-1 functions as a linker between insulin and Wnt signaling pathways in the intestine

et al. 2009

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Hyperinsulinemia and type II diabetes are associated with an increased risk of developing colorectal tumors. We found previously that in intestinal cells, insulin or insulinlike growth factor-1 stimulates c-Myc and cyclin D1 protein expression through both Akt-dependent and Aktindependent mechanisms. The effect of Akt is attributed to the stimulation of c-Myc translation by mammalian target of rapamycin. However, Akt-independent stimulation was, associated with an increase in b-catenin (b-cat) in the nucleus and an increased association between b-cat and T-cell factor binding sites on the c-Myc promoter, detected by chromatin immunoprecipitation. In this study, we show that insulin stimulated the phosphorylation/ activation of p-21-activated protein kinase-1 (PAK-1) in an Akt-independent manner in vitro and in an in vivo hyperinsulinemic mouse model. Significantly, shRNA (small hairpin RNA)-mediated PAK-1 knockdown attenuated both basal and insulin-stimulated c-Myc and cyclin D1 expression, associated with a marked reduction in extracellular signal-regulated kinase activation and b-cat phosphorylation at Ser675. Furthermore, PAK-1 silencing led to a complete blockade of insulin-stimulated b-cat binding to the c-Myc promoter and cellular growth. Finally, inhibition of MEK, a downstream target of PAK-1, blocked insulin-stimulated nuclear b-cat accumulation and c-Myc expression. Our observations suggest that PAK-1 serves as an important linker between insulin and Wnt signaling pathways.

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“…To date, evidence has accumulated from many labs suggesting that PAK isoforms from both group A and B promote cell transformation. Tang et al first showed that expression of dominant negative PAK1 blocked Ras transformation of Rat-1 fibroblasts 5 and Schwann cells. 6 Expression of dominant negative PAK1 in a highly invasive breast cancer cell line also suppressed its invasiveness and motility, 7 although PAK2 may be more relevant in breast cancer.…”

Section: Commentarymentioning

confidence: 99%

Targeting PAK etk…

Zhou

Field²

2004

Cancer Biology & Therapy

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B i o s c i e n c e . N o t f o r d i s t r i b u t i o n .[Cancer Biology & Targeting PAK etk… PAK kinases are versatile proteins that have been shown to be involved in many cellular signaling pathways including regulation of cytoskeletal reorganization, cell transformation, and survival. Though the first p21-activated kinase member (PAK1) was identified less than 10 years ago, 1 our understanding of these kinases has increased tremendously since then. The PAKs are a family of serine-threonine kinases with six known isoforms. They can be divided into two groups based on structural similarities. Group A includes PAK1 (αPAK), PAK2(γPAK) and PAK3(βPAK), and group B consists of PAK4, PAK5 and PAK6. Group A PAKs contain an N-terminal regulatory domain and a C-terminal kinase domain. Within the N-terminal domain is the p21-binding domain (PBD), which binds the small GTPases Rac and Cdc42 to activate the kinase domain by releasing it from autoinhibition. Flanking the PBD domain are two SH3-binding regions which bind the adaptor protein Nck 2 and a Rac GEF Pix, 3 respectively. Like group A PAKs, group B PAKs also contain the PBD domain and C-terminal kinase domain, but they do not have SH3-binding regions for Nck and Pix. 4 Furthermore, the PBD and kinase domains of group B PAKs only have relatively low (about 50%) sequence identity with group A PAKs. In addition to activation by small GTPases, PAKs are activated by p21-independent mechanisms. The p21-dependent mechanism, as suggested by the naming of PAK, is the one by which PAK was first identified 1 and probably represents the main mechanism for PAK activation.Because Rac and Cdc42 are two Rho family members downstream of the Ras oncogene, there has been a keen interest in determining if PAK is involved in oncogenic transformation especially since Ras is one of the most frequently mutated oncogenes. To date, evidence has accumulated from many labs suggesting that PAK isoforms from both group A and B promote cell transformation. Tang et al. first showed that expression of dominant negative PAK1 blocked Ras transformation of Rat-1 fibroblasts 5 and Schwann cells. 6 Expression of dominant negative PAK1 in a highly invasive breast cancer cell line also suppressed its invasiveness and motility, 7 although PAK2 may be more relevant in breast cancer. 8 PAK4 is overexpressed in about 75% of tumor cell lines and dominant negative mutants of PAK4 also inhibit cell transformation. 9,10 Both group A and B family members also protect cells by inhibiting apoptosis. The mechanism of protection involves crosstalk to the Akt pathway. [11][12][13][14] Together, these studies suggest PAK is important for oncogenic cell transformation and has the potential to be a molecular target for suppressing cell transformation caused by Ras and related genes.Ras itself and intermediates in two major Ras effector pathways (PI 3K cascade and Raf/MEK/MAPK cascade) have been considered as potential pharmacologic targets of Ras-induced cell transformation. Another category of drugs are farnesyl transf...

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Kinase-Deficient Pak1 Mutants Inhibit Ras Transformation of Rat-1 Fibroblasts

Abstract: , while neither mutant inhibited Raf activation of ERK. These results suggest that Pak1 interacts with components essential for Ras transformation and that inhibition can be uncoupled from JNK but not ERK signaling.

Cited by 195 publications

References 59 publications

A Rac1/PAK1 cascade controls β-catenin activation in colon cancer cells

A Rac1/PAK1 cascade controls β-catenin activation in colon cancer cells

P-21-activated protein kinase-1 functions as a linker between insulin and Wnt signaling pathways in the intestine

Targeting PAK etk…

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