Protein PAK4 PDB 2bva.png
Available structures
PDBOrtholog search: PDBe RCSB
AliasesPAK4, p21 (RAC1) activated kinase 4
External IDsOMIM: 605451 MGI: 1917834 HomoloGene: 4300 GeneCards: PAK4
RefSeq (mRNA)


RefSeq (protein)



Location (UCSC)Chr 19: 39.13 – 39.18 MbChr 7: 28.26 – 28.3 Mb
PubMed search[3][4]
View/Edit HumanView/Edit Mouse

Serine/threonine-protein kinase PAK 4 is an enzyme that in humans is encoded by the PAK4 gene.[5][6][7]

PAK4 is one of six members of the PAK family of serine/threonine kinases which are divided into group I (PAK1, PAK2 and PAK3) and group II (PAK4, PAK6 and PAK5/7).[8][9] PAK4 localizes in sub-cellular domains of the cytoplasm and nucleus.[8][10][11] PAK4 regulates cytoskeleton remodeling, phenotypic signaling and gene expression, and affects directional motility, invasion, metastasis, and growth.[12] Similar to PAK1, PAK4-signaling-dependent cellular functions also regulate both physiologic and disease processes such as cancer, as PAK4 is overexpressed and/or hyperstimulated in human cancer, at-large.[13][14]


PAK4, the founding member of Group II PAK member, was cloned and identified by Minden A. and colleagues in 1998 using a PCR-based strategy from a cDNA library prepared from Jurkett cells.[8]

Gene and spliced variants

The group II PAKs have less coding exons compared with group I PAKs, highlights the potential structural and functional differences between two group of PAKs. The human PAK4 is about 57-kb in length with 13 exons. The PAK4 generates 12 transcripts of which 10 coding transcripts are predicted to code proteins of about 438 to 591 amino acids long, while remaining two transcripts are non-coding in nature. In contrast to human PAK4, murine PAK4 contains four transcripts - two coding for 593 amino acids long polypeptides and two are non-coding RNA transcripts.

Protein domains

The core domains of PAK4 include, a kinase domain in the C-terminal region, a p21-binding domain (PBD), and a newly defined auto-inhibitory domain (AID) [15] or an AID-like pseudosubstrate sequence (PS) domain.[16]


PAK4 activity is stimulated by upstream activators and signals, including by HGF,[17] PKD,[18][19] PKA,[20] CDK5RAP3,[21] and SH3RF2.[22]

In addition to other mechanisms, PAK4 functions are mediated though phosphorylation of its effector proteins, including, LIMK1-Thr508,[23] integrin β5-Ser759/Ser762,[24] p120-catenin-Ser288,[25] superior cervical ganglia 10 (SCG10)-Ser50,[26] GEF-H1-Ser810[11][27] β-catenin-Ser675,[10] and Smad2-Ser465.[28]

PAK4 and/or PAK4-dependent signals also modulate the expression of genomic targets, including MT1-MMP[29] and p57Kip2.[30]


The PAK4 activity and expression has been shown to be inhibited by chemical inhibitors such as PF-3758309,[31] LCH-7749944,[32] glaucarubinone,[33] KY-04031,[34] KY-04045,[35] 1-phenanthryl-tetrahydroisoquinoline derivatives,[36] (-)-β-hydrastine,[37] Inka1,[38] GL-1196,[39] GNE-2861,[40] and microRNAs such as miR-145,[41] miR-433,[42] and miR-126.[43]


PAK proteins, a family of serine/threonine p21-activating kinases, include PAK1, PAK2, PAK3 and PAK4. PAK proteins are critical effectors that link Rho GTPases to cytoskeleton reorganization and nuclear signaling. They serve as targets for the small GTP binding proteins Cdc42 and Rac and have been implicated in a wide range of biological activities. PAK4 interacts specifically with the GTP-bound form of Cdc42Hs and weakly activates the JNK family of MAP kinases. PAK4 is a mediator of filopodia formation and may play a role in the reorganization of the actin cytoskeleton. Multiple alternatively spliced transcript variants encoding distinct isoforms have been found for this gene.[7] PAK4 has been shown to be repressed at translational level by miR-24.[44]

PAK4 regulates cellular processes by its scaffolding activity and/or by phosphorylation of effector substrates, which in-turn, set-up a cascades of biochemical events cumulating into a cellular phenotypic response. Examples of PAK4-regulated cellular processes include, dynamic reorganization of actin,[23] and microtubule fibers,[26] anchorage-independent growth,[45] filopodium formation,[8] and cell motility</ref>


PAK4 has been shown to interact with:


The 2016 version of this article was updated by an external expert under a dual publication model. The corresponding academic peer reviewed article was published in Gene and can be cited cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free a,.mw-parser-output .citation .cs1-lock-free a{background:linear-gradient(transparent,transparent),url("//")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited a,.mw-parser-output .id-lock-registration a,.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:linear-gradient(transparent,transparent),url("//")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription a,.mw-parser-output .citation .cs1-lock-subscription a{background:linear-gradient(transparent,transparent),url("//")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:linear-gradient(transparent,transparent),url("//")right 0.1em center/12px no-repeat}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:#d33}.mw-parser-output .cs1-visible-error{color:#d33}.mw-parser-output .cs1-maint{display:none;color:#3a3;margin-left:0.3em}.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}Rakesh Kumar; Rahul Sanawar; Xiaodong Li; Feng Li (19 December 2016). "Structure, biochemistry, and biology of PAK kinases". Gene. Gene Wiki Review Series. 605: 20–31. doi:10.1016/J.GENE.2016.12.014. ISSN 0378-1119. PMC 5250584. PMID 28007610. Wikidata Q38779105.


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