Journal P21 (1) Eja.docx

Biochimica et Biophysica Acta 1833 (2013) 33–39

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Review

p21-activated kinases and g astrointestinal cancer Hong He, Graham S. Baldwin ⁎ Department of Surgery, University of Melbourne, Austin Health, Melbourne, Victoria 3084, Australia

article fo

A r Receive d 6 Se ptember 2012 Received in revis ed form 15 Octo ber 2012 A c c e p t e d 1 5

in

abstrac t p21-activated kinases (PA Ks) were initially identifie d as effector proteins dow nstream from GTPases of the

Rho family. To date, six membe rs of the PAK family have been discovered in mammalian cells. PAKs play important roles in growth factor sign alling, cytoskeletal remodelling, ge ne transcription, cell proliferation a nd oncogenic transformation. A large body of research has demonstrated that PAKs are up-regulated in seve ral human cancers, and that their ove rexpression is linked to tumour p rogression and resistance to thera py.

O c t o b e r 2 0 1 2 Availabl e online 22 Oct ober 20 12 K e P A

S i

Liv er can cer

Structural and biochemic al studies have revealed the mechanisms involved in PAK signalling, and opened the way to the developme nt of PAK-targeted thera pies for cancer treatment. Here we summarise rece nt findings from biological and clinical research on the r ole of PAKs in gastroint estinal cancer, and discus s the current status of PAKtargeted anticancer t herapies. ©

Gastric cancer Colorectal cancer

1 The PAK family of 6 seri Since Manser and collea ne/threonine kinases are cl gues discovered the fi assified into two member of the family of p21-activated groups based on sequence, ses (PAKs), PAK1, in 1994 structuralhomology and res [1], a tremendous ponse to activated amount of work has revealed the roles of PAKs in diverse cellular proGTPases (Fig. 1). Both grou p I (PAKs 1–3) and group II (PAKs 4–6) PAKs cesses, including cytoskel are characterised by an Netal reorganisation, gene terminal regulatory domain transcription, cell and a conserved proliferation and survival, C-terminal kinase domain [ and oncogenic transformat 3]. Group I PAKs are appro ion (for reviews ximately 70% idensee [2–4]).Members of tical in sequence overall, b p21-activated kinase famil ut share greater than 90% i y are key effectors dentity in their kiof the Rho family of GTPa nase is however only ap ses,which act as regulatory ns. There proximately 50% id switches that conentity trol cell proliferation andm between the kinase domains otility [3–5]. PAKs are of group I and II PAKs [4]. er up-regulated or Binding of the achyper-activated in a variet tivated forms of the GTPase y of human cancers ands Cdc42 or Rac to the regu bundant evidence latory domain actipoints to roles for PAKs vatesPAKs1,2and3[6,7]. in tumourigenesis (for Signals from growth factor iews see [2,3]). receptor tyrosine Here recent findings regarding the biological function s of PAK signalling kinases and G proteincoupled receptors lead to the activation of PAKs in gastrointestinal cancers via both GTPase-dependent are summarised. The focus and independent mechanis is on themolecums. In particular, lar pathways activated by oncogenic Ras often act s in the context of four gastro ivates PAK in cancers [ intestinal 8]. cancers: hepatocellular Structural studies have r arcinoma (HCC), pancre evealed that group I PA atic cancer, gastric Ks have a kinase cance domain, a p21 r and -binding domai colore n (PBD) and ctal ca an autorcino inhibitory dom ma (C ain RC). (AID) which overlaps with the PBD [9]. Bindi ng of an activated GTPase to a group I PAK disrupts PAK dimerisatio n leading to a series of conformational changes that unfold the AID, w hich in turn dissociates from the catalytic domain of the other mol ecule in the dimer [9–12]. All group I PAKs contain a threonine res idue in their kinase Abbreviations: AID, autodomain, and dissociation inhibitory domain; CDK5RA of the AID permits this t P3, CDK5 kinase regulatory subunit-associated protein hreonine residue C, colorectal carcinoma; EGFR, to be autophosphorylated, pithelial growth factor

which is necessary for ful l kinase activity receptor; GAP, GTPase-activating [13]. Group I PAKs also protein; HBV, hepatitis B virus; have an N-terminal domai HBx, HBV X protein; n which binds to HCC, hepatocellular carcinoma; PAK, p21-activated kinase; PIX, an important downs tream effector [14]. Unlik p21-binding domain;

e group I PAKs,

P S D ,

p s e u d o

2

s u b s t r a t e d o m a i n

PAKs 4–6 do not have PI X-binding domains. Like th e AID in group I PAKs, the group II PAKs 4 –6 contain within their N -terminal regions an auto-inhibitory pseud osubstrate domain (PSD) , which inhibits

⁎ Corresponding author at: of Surgery, University of urne, Austin Health, Studley Rd., Heidelberg, Victoria 3084, Australia. Tel.: +61 96 5592; fax: +61 3 9 4 5 8 1 6 5 0 . E-mail address: grahamsb@unim elb.edu.au (G.S. Baldwin).

the kinase activity of group II PAKs in the absence of any GTPa se (Fig. 1)

0167-4889/$ – see front matter © 2012 Elsevier B.V. All right s reserved. http://dx.doi.org/10.1016/j.bbamcr.2012.10.015 3 H. He, G.S. Baldwin / 4 Biochimica et Biophysica Acta 1833 (2013) 33–39

survival, angiogenesis [38] , the epithelial– [15,16]. Structural compariso n of the kinase domainsmesenchymal transition PAKs 4–6with PAK1 revealed plasticity [39] and anchoragethe catalytic domain of independent growth [40,4 e group II PAKs, 1]. PAKs enhance tuand suggested that theremour development by d e a number of possible own-regulation of severa ovements allowed l pro-apoptotic within the kinase domain during catalysis [17]. I ndeed, group I and pathways, as discussed in the previous paragraph. The role of PAKs group II PAKs have distinct in the regulation of cytos substrate specificities [1 keletal dynamics contribut ecatalyticdoes significantly main of PAK1 has a to their effects on cancer al kinase fold containinginvasion and metastasis. N- and C-terminal Knockdown of lobes connected by a hinge PAK1 leads to decreased region which forms a pocket phosphorylation of myosi for ATP binding n light chain in and substrate catalysis breast epithelial cells whil 9]. Although the initial st transfection with a plas h for PAK inhibimid encoding a tors focussed on ATP compe mutated inactive PAK1 bl titors, because of the highocks the invasiveness of b gree of similarity reast cancer cells between the ATP-binding[42]. Expression of PA ockets of kinases such K1 increases hepatocyte pounds often have growth factorpoor selectivity, and therefor induced migration of prost e cause unwanted side ate cancer cells [43]. PAK s. PAK inhibitors s have also been that target other regions implicated in cell adhesio the molecule have also n. PAK1 phosphorylates a n developed, and nd stimulates the will zinc finger pro be d tein, snail, wh iscu ich in turn re ssed presses Elate cadherin prom r in otthis revi ew.

er activity, causing cells to detach and migrate [4 4]. 3 Amongst t . he six PA K isoforms , the role o B f PAK1 in i human can o cer has l o g i c a l a c t i v i t i e s o f P A K s beenmost thoroughly investigated. The PAK1 gene isamplified in bladThe PAK kinase familyder, ovarian, and breast can lays important roles cers [45,46]. PAK1 expressi any biological on is increased in activities, including stimulati 55% of human breast cance on of cell proliferation, rs and overexpression corre ility and survival lates with breast [2–4]. Deregulation of cancer invasiveness [2]. P cellular processes initiates AK1 promotes proliferatio nd promotes carn and survival of cinogenesis. PAKs stimulate breast cancer cells by activ cell proliferation throughation of nuclear factor kap hancing the actipa B (NFκB) and vation of the MAP kinase cyclin D1, and transgenic m pathway, and thereby ice with a constitutively acti moting cell cycle ve PAK1 develop progression. PAK1 phosph malignant mammary glan orylates two mediators d tumours [47]. PAK1 e the MAP kinase xpression also inpathway, MEK1 and Raf1 [20–22], and facilitates t he activation of these creases with progression through the adenoma to carcinoma sequence kinases by their upstream in CRC [48]. PAK1 is criti ctivators Raf1 and Ras, cally important for the mal pectively. The kiignant growth of nase activity of PAK1 both neurofibromatosis typ s at entry into mitosis es 1 and 2, which are do remains sustained minantly inherited during mitotic progression. autosomal diseases caused PAKs also promote cell by loss-of-function mutatio le progression by ns of the tumour regulati suppressor gene on of c s NF1 and N yclin D F2, respectively. 1 expre Mutation carri ssion [2 ers are 3,24]. PAKs regulate cell motility predisposed to the develop by changing cytoskeletalment of multiple tumours i ynamics. PAKs n the central and function as downstreamperipheral nervous system. ectors of Rac/Cdc42 Neurofibromin, the prod regulation of the uct of the NF1 actin cytoskeleton and gene, acts as a GTPasee stimulate cellmotility activating protein (GAP) for invasion. Growth Ras by accelerating

factors and other cell the intrinsic GTPase activit li cause the redistributiony of Ras, leading to inacti f PAK1 from the vation of Ras and cytoplasm into cortical eventually to inhibition of P tin structures and focalAK1 activity. Merlin, the pr dhesions [25,26]. oduct of the NF2 PAK1 then interacts with gene, inhibits PAK1 activ and phosphorylates cytoske ation by direct interactio letal proteins, inn with the Raccluding myosin light binding domain of PAK1 [49 n kinase [27,28], LIM- ,50]. Loss of either the NF1 kinase [29], and the or NF2 gene prodp41-Arc subunit of the Arp2/3 uct leads to abnormal complex [30], and thereby activation of PAK1. ulates re The other or PAK isofor g ms may al a so be upni regulated a s nd/or hype at rio n o f th e c yt o s k el et o n. PAKs also stimulate activated in many human c l survival by inhibition ancers, including breast, ov of apoptosis arian, colorectal (i.e. programmed cell and pancreatic cancers [2] ). Both PAK1 and PAK5. The PAK4 gene is ampli hosphorylate Bad, fied in colorectal a pro-apoptotic protein, and pancreatic cancers [51 ducing its binding to ,52]. PAK5 expression is al inhibition of the so increased in a two anti-apoptotic proteins Bcl-2 and Bcl-xL, and thereby leading to panel of CRC cell lines [5 3], whilst increased expression of PAK6 has enhancement of cell surviv been detected in both prost al [31–34]. PAK1 also ate cancer cells and breast sphorylates BimL, tumours [54,55]. another pro-apoptotic protein, and prevents it fr om binding to and inhibiting Bcl-2 [35]. In rhabdomyosarcoma PAK 1 additionally phosphorylates the transcription 5. PAKs in gastroin r forkhead homolog, and suppre testinal cancers sses its ability to activate pro-apoptotic target genes [ 36]. Amongst group II PAKs, PAK4 is a key Gastrointestinal cancer r ector for Cdc42 and medi efers to cancers that affe ates downstream sigct the digestive sysnals that control cel tem, and thus includes l motility, proliferati cancers of the oesoph on and survival [37] agus, gallbladder, liver . , pancreas, stomach and bowel. Amplification of the genes encoding 4 PAKs a . nd ove rexpres sion of PAK pr oteins h ave bee n found in gastr ointestinal cancers as listed in Table 1 [56]. The import ance of PAKs in canThe PAK kinase familycers of the liver, pancreas, s as a variety of effects tomach, colon and rectum t promote carciwill be reviewed

nogenesis including stimulation l proliferation, motility,

of here.

Kinase domain PAK1-3 Nck

PAK4-6

PBD

AID

Kinase dom ain

P I X

PBD

PSD Fig. 1. Structures of PAKs. The kinase domains of group I PAKs ( PAKs 1–3) and group II PAKs (PAKs 4–6) are approximately 50 % identical. PAKs from both groups also contain a p21 binding domain (PBD). The group I PAKs contain an autoinhibitory domain (AID), and binding motifs for PIX and Nck. F or group I PAKs binding of an activated GTPase such as Rac or Cdc42 to the PBD disrupts PAK dimerisation leading to a series of conformational changes that unfold the AID, which then dissociates from the kinase domain of the other molecule in the dimer. Dissociation of the AID permits a co nserved threonine residue in the kinase domain to be autopho sphorylated, which is necessary for full kinase activity [13]. The phosphorylation sites in the activation loop differ b etween individual PAKs and are therefore not shown. The gr oup II PAKs contain an autoinhibitory pseudosubstrate domain (PSD). Binding of activated Rac or Cdc42 to the PBD of group II PAKs causes conformational changes in the PSD wh ich lead to increased kinase activity [15,16]. H. He, G.S. Baldwin / Biochimica et Biophysica Acta 1833 (2013) 33–39

2

5 .

PAK1

✓

PAK1 PAK4

✓ ✓

CDK5 RAP3 binds to and activa tes PA K4, a nd tha t over express ion of

CDK5RAP3 promotes HCC metastasis [66]. Hepatocellular carcinoma (HCC) is the most co mmon malignant primary cancer in the liver. The 5.2. Pancreatic c ity of cases of HCC arise in the ancer setting of cirrhosis, which may be caused by vario us factors including chronic hepatitis B or Pancreatic cancer has th infection, or alcohole highest mortality rate induced liver damage. amongst all carciHepatocarcinogenesis is a multistep process, assoc iated with changes nomas, with an overall 5year survival rate of less than 5%. The high in multiple molecular mortality has been attrib nalling pathways includin uted to the lack of reli g Wnt/β-catenin able methods for and Ras, and up to 50%early detection and to the HCC carry mutations molecular mechanisms un e genes encoding derlying the agcomponents of the Wnt/β-catenin pathway [57]. Overexpression of gressive pathogenesis [67] . Activating mutations of KRas are amongst Ras proteins has been the most common genetic in cirrhotic livers and in alterations in pancreatic c C [58], although ancer with an inRas mutations are not cidence of approximately mon in HCC. BRaf and 100% [68,69], and oncoge osphatidylinositol [60] nic Ras activates 3-kinase (PI3K) mutations [51]also found both PAK1 and PAK4. PA have been K4 gene amplification is fo CC patients, and und in pancreatic BRaf mutations are signi cancer, and is associated cantly correlated with with significantly higher k her proliferation inase activity of r 9]. a

3 5

t h PAK1, activated by via PI3K-dependent dependent path-

and invasion [70]. MUC1 3, a transmembrane muci n, has recently ways, is overexpressed in HCC patients with mo re advanced tumours been found to be overe xpressed in pancreatic cancer, and increased and more metastatic expression of MUC13 in otypes [60]. The PAK1 pancreatic cancer cell lines ne is also amplistimulated xenofied in HCC, and PAK1 graft growth, and was cor mulates HCC cell migration related with increased exp by activation of ression and actic-Jun NH -terminal kinase (JNK) and phosphoryla tion of paxillin. In vation of PAK1 [71]. Conv ersely Smad4, which is a tumour suppressor human HCCsamples, increased levels of PAK1 corr elatedwith poor proggene frequently mutate d in human pancreatic cancer, induces cell nosis, hepatitis B virus death by suppression of PA V) infection, and portal K1 [72]. Although the effec tumour thrombot of PAK1 knocksis [61]. Thehuman HBV out on pancreatic tumouri rotein (HBx) is involved genesis in mice has not b he viral life cycle een reported, the and exerts a direct hepatoca importance of PAK1 in pan rcinogenic effect in the creatic physiology is highli elopment of HCC ghted by the ob[62]. HBx induces mitocho servation− mice are deficien ndrial translocation of slets fromt in the second kinase by oxida1 tive stress. This mitochondrial sustained phase of in ranslocation of Raf1 is depende sulin secretion [73]. nt on the phosphorylation of In the past two decades, af1 at Ser338/339 and pancreatic cancer therap yr340/341 by PAK1 y has focussed on and Src kinase, respectivel several signallingmolecul y [63]. In HCC cells es, with particular interest up-regulates PAK1, inmembrane reconfers resistance to anoikis ceptors such as the epithel (a specialised form of ial growth factor receptor ptosis that occurs (EGFR) [74]. The in cells because of inadequ EGFR acts, at least in part, ate or inappropriate interact thorough Ras, and the outc ion with the celome of clinical lular matrix), and promote trials with EGFR inhibitor s growth of xenografted s in pancreatic cancer is umours in mice. dependent on the HBx-induced activation of PAK1 contributes to prog ression of HCC in pamutation status of Ras. A single Kras mutation, which is the most tie common gen nt etic alteratio s n in pancreat wi ic cancer, is th able to circu ch mvent ro ni c H B V inf ec tio n. Currently partial resection or complete resection with liver transthe anti-tumour activity of anti-EGFR therapies as mutant forms plantation offers the only of KRas are constitutively ossibility oflong-term active independently of the ival for HCC paEGFR. Since ontients. In the case of cogenic Ras activates PAK1 al resection recurrences and PAK4, both of which cur in more than are overexpressed two-thirds of these patien and hyper-activated in panc ts. Wang and coworkers reatic cancer [51,70,71], PA have discovered K inhibitors, espethat early recurrent HCCt increased expresumours have significantly

cially when combined ugs, may provide classic chemotherapeutic sion of Rac GTPasea promising therapeutic activating protein 1 (RACGA strategy for pancreatic c P1) [64]. Although ancer. RACGAP1 overexpression contributes to aggre ssive recurrence of HCC [64], inactivation of Rac would5.3. Gastric can be expected to lead to inactivacer tion of PAK1. Further work will therefore be re quired to clarify the possible involvement of Gastric cancer is one of AK1 in HCC recurrence. the most common cause In this context it is s of cancer-related interesting to note that down-regulation of cyc lin D1, associated death. In Asian countries including China, Japan and Korea, the morwith decreased levels of p38 MAP kinase, AKT and PAK1, inhibits probidity and mortality of ga stric cancer are the highest amongst maligliferation an nant carcinomas [ d survival o 75]. The majority o f liver canc f gastric cancers in er cells [65 the East Asian ]. Although PAK1 is clearly population are associated nvolved inmultiple signallin with infection by virulent s g pathways that trains of the gassignificantly contribute tric bacterium Helicobacte he progression of liver r pylori [76,77]. The strai cer, the effects of ns carry unique other members of the PAK variants of the bacterial pr amily remain to be explored. otein CagA, which activate Recent observas PAK1 in host tions suggest that the cells through PIX, a PAK15 kinase regulatory subunitactivating SH3 adaptor prot associated protein ein (as shown in 3(CDK5RAP3)isoverexpres Fig. 1). Hence PIX-specific sedinmore than 50% of siRNA blocks the activati C specimens, that on of PAK1 by CagA [77]. Activated PAK1 in turn has been show n to activate NF-κB, which triggers the release of proinflammatory cyto kines [78,79]. T a b l e

Both PAK1 a nd PAK4 are overexpressed in gastric can cer and play important roles i n its metastasis [ 80–82]. In huma n gastric cancer c ell

1 Genetic alte rations of P AKs in gast rointestinal cancers. Cancer locatio n PA Ks A lteratio n

lines, PAK1 regulates the expression and activity of cyclins D1 and B1 via NF-κB, and inhibition of PAK1 suppresses prolif eration and migra-

Gene amplification Protein overexp ression

tion by decreasing the ex pression of cyclins D1 an d B1 [83,84]. In

Oesophagus P A K 4 Liver

✓

gastric cancer patients, o verexpression of PAK1 is associated with adPAK1 ✓

Pancreas Stomach

Colon

PAK4 ✓ ✓

vanced and metastatic tum our stages, and increased P AK1 activity is [71] related to reduced survival [81]. PAK1 affects metasta sis of gastric [80,81] cancer cells by activation of ERK and JNK [81], whilst P [82,85] AK4 stimulates themigration of gastric can cer cells via activation ofLi m kinase 1 [85]. PAK1

✓ PAK4 ✓ P A K 5 3 6

[ 4

capecitabine/cisplatin treat ment and have poor surv ival [82]. Given their important roles in th e viability and mobility o f gastric cancer

H. He, G.S. Baldwin / Biochimica et Biophysica Acta 1833 (2013) 33–39

[102]. The conclusions of this study are definitive b cells, PAKs are becomin g attractive therapeuticecause the cells argets, especially − since the outcome of used were mice and hence, rent chemotherapy remain ived fromalthough being s disappointing, K with the median survival more expensive to generat ranging between 9 e, will not have the off11 months only target effects asso[ ci 8 at ed w ith si R N Atre at ed c ell s. Ta ke nt og et he r, t he se re su lts in di ca te that instead of combination therapies targeting both ERK with a MEK 5 inhibitor a . nd AKT with a PI3 K inhibito r, targetin g PAK1 al one could be an alternative approach in CRC treatment. We h ave further reported Colorectal carcinoma that PAK1 associates with C) arises and progresses β-catenin in CRC cells, a result of cuand that PAK1 mulative genetic and epigenetic changes intumour cells.Mutations in knockdown inhibited β-HIF-1 catenin activation by reducing the expression the genes encoding comp of β-catenin and c-myc (o onents of the Ras andWnt ne of the downstream tar /β-catenin signalgets of β-catenin ling pathways occur in signalling) and by suppres and 90% of CRCs [87,88] sing β-catenin/TCF4 trans n animalmodels criptional activity constitutive activation ofWnt/β-catenin signalling initiates growth of [99]. Consistent with our findings, Zhu and coworkers have shown benign adenomas. Mutatio that PAK1 phosphorylated ns in KRas, BRaf β-catenin at Ser675 leadin related pathways g to a more stastimulate adenoma growth and contribute to inva sive and other mable and transcriptionally active β-catenin in CRC cells [103]. Together

lignant behaviours. Despi these results indicate that P te the high frequency AK1 is required for βnt/β-catenin mucatenin activation in tations in CRC, no therapy CRC and plays a key role targeted to the Wnt pathw in mediating the cross-talk ay has yet been between Ras and developed because of Wnt/β-catenin signalling. ack of suitable enzyme However a recent report th gets in this pathat PAK1 negativew . a

l y Activation of KRas by [104] indicates that PAK1 utation increases cell may act differently in diff iferation and erent species. motility, and KRas muta To summarise, oncogeni tions are clinically assoc c Ras activates PAK1, a iated with a poor nd enhances Wnt/ prognosis of CRC [90] β-catenin signalling in CR activates multiple signallin C initiation and progression g pathways, invia activation of cluding PAKs, the Raf/ME ERK- and AKT-pathways. K/MAPK/ERK cascade PAK1 is required for the a PI3K/AKT [91]. ctivation of ERK, Mutations of KRas, BRaf and PI3K occur in 50%, 10% and 15% of CRC reAKT and β-catenin signalli ng in CRC cells, and is critical for CRC growth spectively [92]. Whereasandmetastasis in vivo (Fig. KRas mutations do not 2). These findings indicate t ally occur in CRC hat PAK1 acts as cells that have BRaf a convergence point in mul ions, they may coexist tiple signalling pathways i h PI3K mutations mportant for CRC [92]. Because of the inhibitory effects development. ween the PI3K and Raf/MEK/ MARK/ERK pathways [93], blocking one signal alo ne may increase the signalfrom the other pathway. 6. Perspectives in P Thereforecombined inhibition AK-targeted therapy of both PI3K andRaf/MEK/MARP/ERK is necessary when considering targeted t T h h e c o n cl u si o n th at P A K s in g e n er al , a n d P A K 1 in p ar ti c ul ar , a ct a s KRas mutations are central nodes in multiple ten associated with signalling pathways that c tations that activate ontrol cell prolifthe Wnt/β-catenin pathwa eration, mobility, survival y [94]. Synchronous and transformation, makes them attractive tion of activated KRas and of nuclear β targets in the treatment of catenin, the hallmark diseases including cancers ctive Wnt signalling, . Functional inidentifies a group of hibition of PAK1 has be ents with poor prognosis en achieved experimentall and resistance to y using several

chemotherapy [95]. Most forms of dominantCRC contain collections negativemutants, RNA int mutations, most erference and a number frequently in Ras, Raf, of chemical inhibitors wit K andcomponents of h various degrees of spec nt/β-catenin sigificity (Table 2). nalling pathway. Although Several small molecule inhi advanced knowledge bitors such as CEP-1347, a e signalling netnd the SRC and work involved in these pathways has provided us eful information for the development of targeted therapy, the clinical benefits so far have been limited, indicating a need for improvement in the rational design of new therapies. In CRC, expression Prolife A of PAK1 increases ration K with progression thr T ough the adenoma to carcinoma sequence, with the mo st dramatic increases i n invasive and metastatic CRCRAS S u [48]. PAK1 phosphorylates r af and facilv itates the Ras/Raf/MAPK RAF ER i ignalling pathway which, K v s mentioned a l above, plays a crucial role M in CRC development [88,96 ig ]. Conversely ra PAK1 knockdown downregul ti ates JNK and cyclin D1 o n ]. A kinaseI n v a s i o n Transfo rmation

inactive PAK4 blocks oncogenic Ras-induced tra nsformation and inhibits the a nchor ageindep enden t gro wth o f HC T116 colon cancer

C R

h

cells [ 40]. T he PA K4 ge ne is also a mplifie d in CRC patient sampl es

&

s

[52]. PAK5 is overexpressed during CRC progression d regulates Wnt CRC cell adhesion and migrat ion [53], and apoptosis [31] catenin The expression of PAK2 in hepatic te cells has been suggested o contribute t o

Proliferati on migrati on

l i v e r m e t a s t a s i s o f C R C c e l l s [ 9 8 ] . Recently we S have reported a that knockdo n wn of PAK1 abrogates growth and metast asis of CRC cell lines in xenograft and liver metastasis models in mice [99]. PAK1 is also required f or the proliferation, survival, migration, and GF secretion of CRC cells Fig. 2. PAK1 mediates cross-talk harbouring mutabetween Ras and Wnt/β-catenin tions in Ras, PI3K andsignalling in CRC and progression. Onco pc [100]. Furthermore initiation genic Ras activates PAK1, whic AK1 knockdown h in turn stimulates inhibited growth, survivalthe proliferation, survival, and mi nd migration of CRC gration/invasion of CRC cells via activation of ERKines by inactivation of ERK and AKT, and AKT-dependent pathways, whi downstream targets of ch are critical for CRC progressio n. The Wnt-β-catenin [100]. This observation is consistent withpathway also stimulates CRC cell he report by Li and proliferation andmigration under n ormoxia, via formation rkers that PAK1 regulates CRC metastasis also required for KRasthrough ERK-dependentdriven skin cancer, and phosphorylation that inhibition of of FAK [101]. Interestingly PAK1 causes tumour regre , a recent report has ssion and loss of activity wn that PAK1 is of ERK and AKT

stimulate survival and angiogen of a complex between β-catenin esis. PAK1 provides a critical nd the transcription factor TCF4 connection between n the nucleus. Under hypoxia, β-catenin interacts Ras and Wnt-β-catenin pathwa th hypoxia-inducible factor ys by associating with βcatenin and promoting (HIF-1) instead, to β-catenin/TCF4 activity. H. He, G.S. Baldwin / Biochimica et Biophysica Acta 1833 (2013) 33–39

R e

T a PAK inhibitors. Inhibi tor

PAK1

C o

K

P A

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50

50

3 7

C a [ 3 CEP1347

OSU03012 FL1 72

ar, PAK signaling in oncog enesis, Oncogene 28 (2009) 2545–2555.

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PF375830 9

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PAK4, a novel effector f or Cdc42Hs, is implicate d in the reorganization o f the actin cytoskeleton and in the formation of fil opodia, EMBO J. 17 (1 998) 6 5 2 7 – 6 5 4 0 .

I P A 3

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motes neurite outgrowt h in N1E-115 cells, M ol. Cell. Biol. 22 (200 2) 567–577. [8] D. Bar-Sagi, A. Hall, Ras a nd Rho GTPases: a family reuni on, Cell 103 (2000) 227–238. [9] M. Lei, W. Lu, W. Meng, M.C. Parrini, M.J. Eck, B.J. M ayer, S.C. Harrison, Structure of PAK1 in an autoinhibite d conformation reveals am ultistage activation switch, C e l l 1 0 2 ( 2 0 0 0 ) 3 8 7 – 3 9 7 .

[ 1 0 2 ] .

[10] G.E. Benner, P.B. Dennis, R.A. Masaracchia, Activation of an S6/H4 kinase (PAK 65) from human placenta by intramolecular and int ermolecular autophosphorylation, J. Biol. Chem. 270 (1995) 21121–21128. [11] Z.S. Zhao, E. Manser, X.Q. Chen, C. Chong, T. Leung, L. Li m, A conserved negative regulatory region in alphaPAK: inhibition of PAK kinases reve als their morpho-

ETK tyrosine kinase inhibi tors AG 879 and FK228, respectively, have been shown to inhibit activity [105–107]. The ganometallic compound FL172 inhibits 1 kinase activity with C of 110 nM by

logical roles downstream of Cdc42 and Rac1, Mo l. Cell. Biol. 18 (1998) 2 1 5 3 – 2 1 6 3

. [12] A. Morreale, M. Venkatesan, H.R. Mott, D. Owen, D. Nietlisp ach, P.N. Lowe, E.D.

blocking the ATP-binding site [108], and LCH7749944 suppresses PAK4 kinase activity with n IC of 15 μM [109] recentlydeveloped group I-selective bitor FRAX597 not only hibits PAK1 activi-

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