Identification of an Autoinhibitory Domain of p21-activated Protein Kinase 5

The p21-activated protein kinases (Paks) are serine/threonine protein kinases activated by binding to Rho family small GTPases, Rac and Cdc42. Recently, Pak family members have been subdivided into two groups, I and II. Group II Paks, including Pak4, Pak5, and Pak6, does not contain the highly conserved autoinhibitory domain that is found in the group I Paks members, i.e. Pak1, Pak2, and Pak3. In the present study, we have purified the glutathione S-transferase fusion form of Pak5 and shown for the first time that Pak5 autophosphorylation can be activated by GTP bound form of Cdc42. Mutation of histidine residues 19 and 22 to leucine on the p21-binding domain of Pak5 completely abolished the binding of Cdc42 and the Cdc42-mediated autophosphorylation. On the other hand, mutation of tyrosine 40 to cysteine of Cdc42 did not knockout the binding of Pak5. Analysis of C-terminal deletion mutants has identified an autoinhibitory fragment of Pak5 that is absent from other group II Pak family members. Taken together, these results suggest that Pak5, like Pak1, contains an autoinhibitory domain and its activity is regulated by Cdc42.postprin

The tumor suppressive function of AMPK in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world. However, the molecular mechanism underlying the development of HCC is still unclear. AMP-activated protein kinase (AMPK), which is a serine/theronine protein kinase, originally found as a key regulator in glucose and lipid metabolism in response to cellular stress. Recent publications suggest that AMPK activation results in suppressing cell proliferation. Also, AMPK lies upstream and downstream of two tumor suppressors, TSC2 and LKB1, respectively, indicating that AMPK may also involve in carcinogenesis. In this project, we aim to study the molecular mechanism leading to the tumor suppressive function of AMPK in HCC, particularly relating to the p53 pathway. Our preliminary findings have shown that overexpression of AMPKα2 catalytic subunit in HCC cell line HepG2 suppress cell proliferation in focus formation assay. On the other hand, an increase in proliferation rate was observed in HCC cell with AMPKα2 stably knocked down by small hairpin RNA. Also, our data have demonstrated that expression of constitutive active form of AMPKα2 leads to p53 phosphorylation at serine 15 residue and acetylation at lysine 382 residue. In addition, in-vitro kinase assay has shown that AMPK directly phosphorylates p53. Our results suggest that AMPK may mediate its tumor suppression function through regulation of p53

regeneration of nucleus pulposus after disectomy by autologous mesenchymal stem cells: a rabbit model

Open Access JournalConference Theme: Spinal Motion Segment: From Basic Science to Clinical Applicationlink_to_subscribed_fulltex

The effect of severity of disc degeration on mesenchymal stem cell's ability to regenerate the intervertebral disc

Conference Theme: Spinal Motion Segment: From Basic Science to Clinical Applicatio

Overexpression of PAK4 in hepatocellular carcinoma (HCC)

p21-activated protein kinases (PAKs) are activated by the small Rho family GTPases, Cdc42 and Rac1, in response to various extracellular signals and act in a variety of cellular processes including cell proliferation, morphology, motility, death and survival. PAK-4 is a newly identified Group II member of the PAK family. Like the Group I PAKs, PAK-4 contains an N-terminal p21 binding domain (PBD) and a C-terminal kinase domain, but lacks the auto-inhibitory domain (AID) which is present in Group I PAKs. Previous studies in fibroblasts have demonstrated that expression of activated form of PAK-4 promotes cell proliferation, anchorage-independent growth and cell migration, which are the characteristics of malignant tumors. Besides, PAK-4 was found to be frequently overexpressed in tumor cell lines. However, it is still not clear whether PAK-4 plays a role in the pathogenesis of human cancer. Here we report that PAK-4 is frequently over-expressed in hepatocellular carcinomas (HCCs), using real-time quantitative PCR and Western Blotting. To investigate the function of PAK-4 in the development of HCC, we established PAK-4 knocked-down stable cell lines, using vector-based siRNA approach. We report that knocking down of PAK-4 led to decrease in cell migration by trans-well assay. Morphological changes have also been observed after PAK-4 is knocked down. In summary these results incidated a possible tumorigenic effect of PAK-4 in HCC.Further studies are needed to address this issue and provide the molecular mechanism by which PAK-4 activity is regulated

Functional characterization of C53 and its possible roles in tumorigenesis

Conference Theme: Oncogenes and Human Cancer- The next 25 year

P21-activated protein kinase is overexpressed in hepatocellular carcinoma and enhances cancer metastasis involving c-Jun NH2-terminal kinase activation and paxillin phosphorylation

Hepatocellular carcinoma (HCC) is one of the major malignancies in the world. The prognosis of HCC is poor, due to frequent intrahepatic metastasis and tumor recurrence. P21-activated protein kinase (Pak1), a main downstream effector of small Rho GTPases, Rac1 and Cdc42, plays an important role in the regulation of cell morphogenesis, motility, mitosis, and angiogenesis. Here, we show that Pak1 gene was overexpressed in human HCCs. Overexpression of Pak1 in human HCCs was associated with more aggressive tumor behavior in terms of more metastatic phenotype and more advanced tumor stages. In addition, HCC cell line stably expressing Pak1 displayed increased cell motility rates and, conversely, knockdown of endogenous Pak1 expression by small interfering RNA reduced the migration rates of HCC cells. In an established metastatic HCC cell line, we found that Pak1 was overexpressed compared with its primary HCC cell line and this overexpression was associated with higher cell motility. Importantly, we found that c-Jun NH2-terminal kinase (JNK) was activated in HCC cell lines overexpressing Pak1. Inhibition of the JNK activity by chemical inhibitor significantly reduced the migration rates of HCC cells via attenuation of paxillin phosphorylation at Ser178. In conclusion, our results document that Pak1 is overexpressed in HCCs and plays an important role in the metastasis of HCC. The mechanism by which Pak1 induces cancer metastasis may involve activation of JNK and phosphorylation of paxillin. ©2007 American Association for Cancer Research.link_to_OA_fulltex