10298

PAK4

p21 protein (Cdc42/Rac)-activated kinase 4;PAK4;p21 protein (Cdc42/Rac)-activated kinase 4

PAK-4|p21(CDKN1A)-activated kinase 4|p21-activated kinase 4|protein kinase related to S. cerevisiae STE20, effector for Cdc42Hs|serine/threonine-protein kinase PAK 4

19q13.2

protein-coding

OBJECTIVE: To study the role of p21-activated kinase-4 (PAK4) in the occurrence, progression and metastasis of breast cancer. METHOD: PAK4 expression was detected in 35 cases of normal breast, 22 breast cystic hyperplasia, 28 breast adenofibroma, 37 breast cancer (including 7 non-invasive cancer, 9 early invasive cancer and 21 invasive cancer) and 13 metastatic breast cancer tissues using immunohistochemistry for a comparison of PAK4 expression and distribution. RESULTS: PAK4 was expressed mainly in the cytoplasm of the cancer cells, occasionally in the cell nuclei, and virtually not expressed in the matrix surrounding the breast cells. PAK4 positivity rates increased in the order of normal breast tissues, benign changes (including breast cystic hyperplasea and breast adenoma), breast cancer and metastatic cancer tissues; in the cancer tissues, the positivity rates increased in the order of non-invasive breast tumor, early invasive tumor and invasive tumor tissues. CONCLUSION: PAK4 is closely correlated to the progression and metastasis of breast cancer and may become a new diagnostic and therapeutic target of breast cancer.

The CDK5 kinase regulatory subunit-associated protein 3 (CDK5RAP3 or C53/LZAP) regulates apoptosis induced by genotoxic stress. Although CDK5RAP3 has been implicated in cancer progression, its exact role in carcinogenesis is not well established. In this article, we report that CDK5RAP3 has an important prometastatic function in hepatocarcinogenesis. An examination of human hepatocellular carcinoma (HCC) samples revealed at least twofold overexpression of CDK5RAP3 transcripts in 58% (39/67) of HCC specimens when compared with corresponding nontumorous livers. CDK5RAP3 overexpression was associated with more aggressive biological behavior. In HCC cell lines, stable overexpression of CDK5RAP3 promoted, and small interfering RNA-mediated knockdown inhibited, tumorigenic activity and metastatic potential. We found that overexpression of CDK5RAP3 and p21-activated protein kinase 4 (PAK4) correlated in human HCCs, and that CDK5RAP3 was a novel binding partner of PAK4, and this binding enhanced PAK4 activity. siRNA-mediated knockdown of PAK4 in CDK5RAP3-expressing HCC cells reversed the enhanced cell invasiveness mediated by CDK5RAP3 overexpression, implying that PAK4 is essential for CDK5RAP3 function. Taken together, our findings reveal that CDK5RAP3 is widely overexpressed in HCC and that overexpression of CDK5RAP3 promotes HCC metastasis through PAK4 activation.

Migration and invasion comprise key steps in cancer metastasis. Through the migration and invasion into and out of lymphatic and/or blood vessels, cancer cells can be spread out into the tissues in remote site from the origin. Degradation of extracellular matrix (ECM) must be preceded prior to the metastasis of cancer cells. Matrix metalloproteinases (MMP) can degrade ECM, thus allow cells to migrate from the original site. Among MMPs, two gelatinase MMP-2 and MMP-9 play particularly important roles in ECM degradation. Here, we report that recently developed p21-activated kinase 4 inhibitor PF-3758309 shows anti-metastatic effect in A549 human lung cancer cell. PF-3758309 suppresses CREB, NF-kappaB, and beta-catenin pathways, which are well known to be closely related with cell migration. This leads to the downregulation of MMP-2/MMP-9 expressions and the inhibition of A549 lung cancer metastasis.

Hepatocyte growth factor (HGF) and its receptor (c-Met) are associated with cancer cell motility and invasiveness. p21-activated kinase 4 (PAK4), a potential therapeutic target, is recruited to and activated by c-Met. In response, PAK4 phosphorylates LIM kinase 1 (LIMK1) in an HGF-dependent manner in metastatic prostate carcinoma cells. PAK4 overexpression is known to induce increased cell migration speed but the requirement for kinase activity has not been established. We have used a panel of PAK4 truncations and mutations in a combination of overexpression and RNAi rescue experiments to determine the requirement for PAK4 kinase activity during carcinoma cell motility downstream of HGF. We find that neither the kinase domain alone nor a PAK4 mutant unable to bind Cdc42 is able to fully rescue cell motility in a PAK4-deficient background. Nevertheless, we find that PAK4 kinase activity and associated LIMK1 activity are essential for carcinoma cell motility, highlighting PAK4 as a potential anti-metastatic therapeutic target. We also show here that overexpression of PAK4 harbouring a somatic mutation, E329K, increased the HGF-driven motility of metastatic prostate carcinoma cells. E329 lies within the glycine-rich loop region of the kinase. Our data suggest that E329K mutation leads to a modest increase in kinase activity, conferring resistance to competitive ATP inhibitors in addition to promoting cell migration. The existence of such a mutation may have implications for the development of PAK4-specific competitive ATP inhibitors should PAK4 be further explored for clinical inhibition.