Activation of p53 After Irradiation Impairs the Regenerative Capacity of the Mouse Liver.

Radiation therapy is one of the treatment methods for hepatocellular carcinoma. However, radiation tolerance of the liver is low, and the detailed effect of radiation on liver regeneration has not been clarified. C57BL/6J mice or hepatocyte-specific p53 knockout (KO) mice (albumin [Alb]-Cre Trp53flox/flox ) were irradiated with a single fraction of 10 Gy localized to the upper abdomen. We performed 70% partial hepatectomy (PHx) 24 hours after irradiation. Liver regeneration was assessed by proliferation cell nuclear antigen (PCNA)- and Ki-67-positive hepatocyte ratios and liver-to-body weight ratio after PHx. To establish a fibrosis model, CCl4 was orally administered for 8 weeks. The murine hepatocyte cell line BNL CL.2 (CL2) was irradiated with 10 Gy. Irradiation activated p53, induced downstream p21 in the liver, and delayed liver regeneration after PHx. While PHx increased hepatocyte growth factor (HGF) levels and activated Met with or without irradiation in the regenerative liver, it activated Akt and extracellular kinase 1 and 2 (Erk 1/2) less in irradiated mice than in nonirradiated mice. In CL2 cells cultured with HGF, irradiation suppressed cell growth by decreasing phosphorylated Akt and Erk 1/2 levels, which was abolished by small interfering RNA-mediated p53 knockdown but not by p21 knockdown. Hepatocyte-specific knockout of p53 in mice abolished the irradiation-induced suppression of both liver regeneration and Akt and Erk 1/2 activation after PHx. In the fibrotic mouse model, the survival rate after PHx of irradiated p53 KO mice was higher than that of wild-type mice. Conclusion: p53 but not p21 is involved in the impaired regenerative ability of the irradiated liver.

Prognostic significance of PAK family kinases in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a clonal and heterogeneous disease characterized by a myriad of genetic defects. Genetic abnormalities are powerful prognostic factors. P21-activated kinases (PAKs) are a kind of serine/threonine protein kinases, which is regulator of plenty of oncogenic signaling pathways. The clinical and prognostic value of PAKs in AML is unclear. A total of 155 AML patients with PAK expression data from The Cancer Genome Atlas database were enrolled in this study. Eighty-four patients underwent chemotherapy only, 71 also underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT). In the chemotherapy-only group, high PAK3 and PAK7 expression were both bound up with poor EFS and OS (all P < 0.05). However, high PAK2 expressers had better EFS and OS (all P < 0.05). Multivariate analysis demonstrated that high PAK7 expression was an adverse independent prognostic factor in patients who received chemotherapy only. PAKs have no influence in EFS and OS in patients who underwent allo-HSCT. In conclusion, high PAK2 expression is a favorable prognostic factor, as to the high expression of PAK3 and PAK7, they are poor prognostic factors, and PAK7 has better prognostic value, but their prognostic effects can be offset by allo-HSCT.

PAK4, a target of miR-9-5p, promotes cell proliferation and inhibits apoptosis in colorectal cancer.

BACKGROUND: Colorectal cancer (CRC) is a leading cause of cancer-related death worldwide. P21-activated kinase 4 (PAK4) and miR-9-5p have emerged as attractive therapeutic targets in several tumor types, but in CRC, the regulation of their biological function and their target association remain unclear. METHODS: The expression of PAK4 in CRC tissues was determined using quantitative real-time PCR and immunohistochemistry analyses. The targeted regulation between miR-9-5p and PAK4 was predicted and confirmed with bioinformatics analysis and the dual-luciferase reporter assay. Functional experiments, including the MTT assay and flow cytometry, were performed to investigate the impact of PAK4 knockdown and miR-9-5p overexpression on cell proliferation and apoptosis in CRC cells. RESULTS: We found that the expression of PAK4 was upregulated in CRC tissues. PAK4 knockdown significantly suppressed cell proliferation and promoted apoptosis in cells of the CRC cell lines HCT116 and SW1116. We also found that miR-9-5p directly targeted the 3'-UTR of PAK4 mRNA and negatively regulated its expression. The degree of downregulation of miR-9-5p inversely correlated with PAK4 expression. Intriguingly, enforced expression of miR-9-5p suppressed cell proliferation and promoted apoptosis. This could be partially reversed by PAK4 overexpression. CONCLUSION: These results suggest that miR-9-5p targeting of PAK4 could have therapeutic potential for CRC treatment.

A stemness screen reveals C3orf54/INKA1 as a promoter of human leukemia stem cell latency.

There is a growing body of evidence that the molecular properties of leukemia stem cells (LSCs) are associated with clinical outcomes in acute myeloid leukemia (AML), and LSCs have been linked to therapy failure and relapse. Thus, a better understanding of the molecular mechanisms that contribute to the persistence and regenerative potential of LSCs is expected to result in the development of more effective therapies. We therefore interrogated functionally validated data sets of LSC-specific genes together with their known protein interactors and selected 64 candidates for a competitive in vivo gain-of-function screen to identify genes that enhanced stemness in human cord blood hematopoietic stem and progenitor cells. A consistent effect observed for the top hits was the ability to restrain early repopulation kinetics while preserving regenerative potential. Overexpression (OE) of the most promising candidate, the orphan gene C3orf54/INKA1, in a patient-derived AML model (8227) promoted the retention of LSCs in a primitive state manifested by relative expansion of CD34+ cells, accumulation of cells in G0, and reduced output of differentiated progeny. Despite delayed early repopulation, at later times, INKA1-OE resulted in the expansion of self-renewing LSCs. In contrast, INKA1 silencing in primary AML reduced regenerative potential. Mechanistically, our multidimensional confocal analysis found that INKA1 regulates G0 exit by interfering with nuclear localization of its target PAK4, with concomitant reduction of global H4K16ac levels. These data identify INKA1 as a novel regulator of LSC latency and reveal a link between the regulation of stem cell kinetics and pool size during regeneration.

[Expression and clinical significance of MIIP and PAK1 in endometrial carcinoma].

Objective: To investigate the expressions of migration and invasion inhibitory protein (MIIP) and p21-activated kinase 1 (PAK1) in endometrial carcinoma (EC) and their correlation with clinicopathological features. Methods: The protein levels of MIIP and PAK1 in 135 paraffin-embedded EC tissues, 55 atypical hyperplasia of endometrium (AHE) and 88 normal endometrium (NE) tissues were quantified by immunohistochemistry, the clincial significance and the relationship of these two proteins were also analyzed. Results: The positive rates of MIIP expression in NE, AHE and EC tissues were 52.3%(46/88), 41.8% (23/55) and 34.8% (47/135), respectively. The expression of MIIP in EC was significantly lower than that of MIIP in NE (P<0.05). The positive rates of PAK1 expression in NE, AHE and EC tissues were 45.5% (40/88), 50.9% (28/55) and 62.2% (84/135), respectively. The expression of PAK1 in EC tissues was significantly higher than that of PAK1 in NE tissues (P<0.05). The expression of MIIP in EC tissues was significantly associated with myometrial invasion, International Federation of Gynaecology and Obstetrics (FIGO) stage and lymph node metastasis (P<0.05). The expression of PAK1 in EC tissues was significantly related with differentiation, myometrial invasion, FIGO stage and lymph node metastasis (P<0.05). The expressions of MIIP and PAK1 in EC tissues were marginally related with the overall survival of patients (P=0.092, P=0.052). The expression of MIIP in EC was negatively correlated with PAK1 (r=-0.329, P<0.001). Conclusions: The down-regulation of MIIP and up-regualtion of PAK1 paticipate in the initiation and development of EC, which are correlated with the poor prognosis of EC. The protein expression of MIIP is inversely related with PAK1 in EC.

Prognostic value of p21-activated kinase 4 in resected pancreatic cancer.

Resectable pancreatic cancer has a high recurrence rate after curative surgery. Biomarkers are needed for distinguishing patients who may benefit from curative resection. In this study, we sought to analyze the prognostic value of p21-activated kinase 1 (PAK1), p21-activated kinase 4 (PAK4), human equilibrative nucleoside transporter 1 (hENT1), and thymidylate synthase (TS) in surgically resected pancreatic ductal adenocarcinomas. A total of 160 pancreatic cancer patients who underwent surgery with curative intent were retrospectively reviewed. Tissue microarrays were constructed and immunohistochemical stains were performed for PAK1, PAK4, hENT1, and TS. The absence of PAK4 expression in pancreatic adenocarcinomas was associated with poorer histologic differentiation (p < 0.001), shorter overall survival [hazard ratio (HR) = 2.86, 95% confidence interval (CI) 1.43-5.71; p = 0.003], and disease-free survival (HR = 2.29, 95% CI: 1.11-4.74; p = 0.025) on univariate analyses. In addition, more frequent venous invasion and lymph node metastases were seen in PAK4-negative tumors although not statistically significant. PAK1, hENT1, and TS expression status did not have significant influences on patient survival. In conclusion, PAK4 of the markers tested in this study may be a potential prognostic biomarker for pancreatic adenocarcinomas.

PAK4 Phosphorylates p53 at Serine 215 to Promote Liver Cancer Metastasis.

PAK4 kinase contributes to signaling pathways controlling cancer cell transformation, invasion, and survival, but its clinicopathological impact has begun to emerge only recently. Here we report that PAK4 overexpression in hepatocellular carcinoma (HCC) conveys aggressive metastatic properties. A novel nuclear splice isoform of PAK4 lacking exon 2 sequences was isolated as part of our studies. By stably overexpressing or silencing PAK4 in HCC cells, we showed that it was critical for their migration. Mechanistic investigations in this setting revealed that PAK4 directly phosphorylated p53 at S215, which not only attenuated transcriptional transactivation activity but also inhibited p53-mediated suppression of HCC cell invasion. Taken together, our results showed how PAK4 overexpression in HCC promotes metastatic invasion by regulating p53 phosphorylation. Cancer Res; 76(19); 5732-42. ©2016 AACR.

Shenhua Tablet inhibits mesangial cell proliferation in rats with chronic anti-Thy-1 nephritis.

BACKGROUND: In China, mesangial proliferative glomerulonephritis (MsPGN) is one of the most common kidney diseases. In this study, we treated a rat model of chronic anti-Thy-1 MsPGN with Shenhua Tablet and evaluated whether the tablet was able to protect the kidney function. Thirty-six Wistar rats were randomly divided into six groups: (1) Sham surgery (Sham); (2) anti-Thy-1 nephritis model (Thy-1); (3) anti-Thy-1 nephritis model + irbesartan-treated (Irb); (4) anti-Thy-1 nephritis model + low-dose of Shenhua Tablet (SHL); (5) anti-Thy-1 nephritis model + medium-dose of Shenhua Tablet (SHM); (6) anti-Thy-1 nephritis model + high-dose of Shenhua Tablet (SHH). RESULTS: Thirteen weeks after drug treatment, urinary proteins were quantified and renal pathological changes were thoroughly examined at the time point of 24 h. Meanwhile, the expression levels of p-Erk1/2, cyclin D1 and p21 at the renal cortex were also tested. The levels of urinary proteins and total cholesterol in the blood were significantly reduced in rats treated with any drug tested in this study. The level of triglyceride was significantly reduced in all three Shenhua Tablet-treated groups. Renal pathomorphological scores were significantly improved in groups of Irb, SHM and SHH. Mesangial cell proliferation was significantly inhibited in any drug-treated group. p-Erk1/2 and cyclin D1 were downregulated whereas p21 was upregulated in the renal cortex. CONCLUSIONS: Our study indicated that Shenhua Tablet is able to inhibit the abnormal proliferation of mesangial cells and to prevent kidney damage, which is likely associated with downregulation of p-Erk1/2 and reduced activity of its downstream target-cyclin D1.

Shenhua Tablet inhibits mesangial cell proliferation in rats with chronic anti-Thy-1 nephritis

BACKGROUND: In China, mesangial proliferative glomerulonephritis (MsPGN) is one of the most common kidney diseases. In this study, we treated a rat model of chronic anti-Thy-1 MsPGN with Shenhua Tablet and evaluated whether the tablet was able to protect the kidney function. Thirty-six Wistar rats were randomly divided into six groups: (1) Sham surgery (Sham); (2) anti-Thy-1 nephritis model (Thy-1); (3) anti-Thy-1 nephritis model + irbesartan-treated (Irb); (4) anti-Thy-1 nephritis model + low-dose of Shenhua Tablet (SHL); (5) anti-Thy-1 nephritis model + medium-dose of Shenhua Tablet (SHM); (6) anti-Thy-1 nephritis model + high-dose of Shenhua Tablet (SHH). RESULTS: Thirteen weeks after drug treatment, urinary proteins were quantified and renal pathological changes were thoroughly examined at the time point of 24 h. Meanwhile, the expression levels of p-Erk1/2, cyclin D1 and p21 at the renal cortex were also tested. The levels of urinary proteins and total cholesterol in the blood were significantly reduced in rats treated with any drug tested in this study. The level of triglyceride was significantly reduced in all three Shenhua Tablet-treated groups. Renal pathomorphological scores were significantly improved in groups of Irb, SHM and SHH. Mesangial cell proliferation was significantly inhibited in any drug-treated group. p-Erk1/2 and cyclin D1 were downregulated whereas p21 was upregulated in the renal cortex. CONCLUSIONS: Our study indicated that Shenhua Tablet is able to inhibit the abnormal proliferation of mesangial cells and to prevent kidney damage, which is likely associated with downregulation of p-Erk1/2 and reduced activity of its downstream target-cyclin D1.

Expression of immunohistochemical markers of progression in pre-cancerous and cancerous human colon: correlation with serum vitamin D levels.

BACKGROUND/AIM: We aimed to evaluate vitamin D levels in blood, as well as the immunohistological expression of ß-catenin, p21 activated kinase (PAK1), p53 and Ki67 in relation to histological type and grading of colonic tumors. RESULTS were compared to the expression in normal and adenomatous colon. MATERIALS AND METHODS: We analyzed colorectal specimens from 20 patients with colorectal tumors for expression of ß-catenin, PAK1, p53 and Ki67. Associations between the expression of these markers and levels of vitamin D in serum were analyzed. RESULTS: The average 25-hydroxy-vitamin D (25OHD) level in a healthy population was 20.53 ng/ml, while that in patients with colorectal cancer was 5.99 ng/ml. The average vitamin D level in patients with positive nuclear ß-catenin was 4.58 ng/ml, which was lower than that of patients with negative nuclear ß-catenin expression. Patients with positive nuclear PAK1 also had low vitamin D levels in their blood (4.51 ng/ml). Patients with positive nuclear p53 had significantly lower vitamin D levels (4.18 ng/ml), compared to patients without nuclear p53 expression. In patients with Ki67 expression in at least 50% of cells, the average vitamin D level was 6.27 ng/ml, while in patients with Ki67 staining in fewer than 50% of cells, the average vitamin D levels in serum was double (13.42 ng/ml).

Overexpression of PAK-1 is an independent predictor of disease recurrence in colorectal carcinoma.

BACKGROUND: Colorectal carcinoma (CRC) is a significant cause of major morbidity and mortality. PAK-1 is a protein that regulates cytoskeletal dynamics and cell motility. The purpose of the present study is to investigate the relationship between PAK-1 immunoexpression and CRC progression and its validity as an independent prognostic factor. PATIENTS AND METHODS: Paraffin blocks of 103 primary CRCs and 37 nodal metastases were retrieved and tissue microarrays were constructed. Immunohistochemistry was performed using anti-PAK-1 antibody. Immunostaining was scored and results were analysed in relation to clinicopathological parameters. RESULTS: PAK-1 was overexpressed in primary CRC (P<0.001). No difference between low and high expression in nodal metastasis (P=0.139). There was no difference between PAK-1 immunoexpression in primary and nodal metastasis (P=0.275). High PAK-1 immunoexpression was associated with disease recurrence (P=0.03). However, there was no association with most clinicopathological parameters. PAK-1 overexpression was detected as an independent predictor of disease recurrence (P=0.05). No association was found between PAK-1 immunoexpression and disease free survival (log-rank =1.287, P=0.257). CONCLUSION: PAK-1 overexpression may be involved in CRC progression and could be considered an independent predictor of disease recurrence. Further in vivo and in vitro molecular studies are needed to investigate the role of PAK-1 in colorectal carcinogenesis.

Clinical significance of p21-activated kinase 1 expression level in patients with upper urinary tract urothelial carcinoma.

OBJECTIVE: The p21-activated kinase serine/threonine kinases have been outlined as the main cytoskeletal remolding regulators. The same holds true for cell proliferation and motility. They additionally have a part in cellular invasion and carcinogenesis, but the effect of p21-activated kinase 1 expression on the progression of upper urinary tract urothelial carcinoma remains unclear. Therefore, we assessed the relation of p21-activated kinase 1 positivity level to clinicopathological features in patients with upper urinary tract urothelial carcinoma. METHODS: Immunohistochemical staining was performed using formalin-fixed and paraffin-embedded specimens, which were all from 124 patients with upper urinary tract urothelial carcinoma. The determination of staining level was based on the intensity of the staining along with portion of cells stained. Correlation of p21-activated kinase 1 positivity with clinicopathological parameters, including disease-specific or extravesical-recurrence-free survival, was evaluated. RESULTS: Statistically significant association was observed between moderate or more than moderate p21-activated kinase 1 positivity and higher tumor grade, pathological T stage, lymphovascular invasion, history of adjuvant chemotherapy and extravesical recurrence. Positivity for p21-activated kinase 1 had a significant association with shortened disease-specific survival in a multivariate analysis among clinicopathological parameters. Strongly positive p21-activated kinase 1 expression was also one of the independent factors for shortened extravesical-recurrence-free survival time in N0M0 upper urinary tract urothelial carcinoma patients in another multivariate analysis as well as histology and lymphovascular invasion (P = 0.0304, hazard ratio = 4.425). CONCLUSIONS: We conclude that our findings can help us continue a careful follow-up for upper urinary tract urothelial carcinoma patients with high p21-activated kinase 1 expression in surgical specimens.

Remarkable reductions of PAKs in the brain tissues of scrapie-infected rodent possibly linked closely with neuron loss.

Prion diseases are irreversible progressive neurodegenerative diseases characterized in the brain by PrP(Sc) deposits, neuronal degeneration, gliosis and by cognitive, behavioral and physical impairments, leading to severe incapacity and inevitable death. Proteins of the p21-activated kinase (PAK) family are noted for roles in gene transcription, cytoskeletal dynamics, cell cycle progression and survival signaling. In the present study, we aimed to identify the potential roles of PAKs during prion infection, utilizing the brains of scrapie agent-infected hamsters. Western blots and immunohistochemical assays showed that brain levels of PAK3 and PAK1, as well as their upstream activator Rac/cdc42 and downstream substrate Raf1, were remarkably reduced at terminal stage. Double-stained immunofluorescent assay demonstrated that PAK3 was expressed mainly in neurons. Dynamic analyses of the brain samples collected at the different time points during the incubation period illustrated successive decreases of PAK3, PAK1 and Raf1, especially phosphor Raf1, which correlated well with neuron loss. Rac/cdc42 in the brain tissues increased at early stage and reached to the top at mid-late stage, but diminished at final stage. Unlike the alteration of PAKs in vivo, PAK3 and PAK1, as well as Rac/cdc42 and Raf1 in the prion-infected cell line SMB-S15 remained unchanged compared with those of its normal cell line SMB-PS. Our data here indicate that the functions of PAKs and their associated signaling pathways are seriously affected in the brains of prion disease, which appear to associate closely with the extensive neuron loss.

Prognostic significance of p21-activated kinase 6 expression in patients with clear cell renal cell carcinoma.

PURPOSE: To investigate prognostic values of intratumoral p21-activated kinase 6 (PAK6) expression in patients with clear cell renal cell carcinoma (ccRCC). METHODS: Immunohistochemistry in tissue microarray was used to evaluate the expression of PAK6 in 104 patients who had undergone nephrectomy at Zhongshan Hospital of Fudan University. Prognostic value and clinical outcomes were evaluated. RESULTS: Intratumoral PAK6 expression was significantly lower than nontumoral tissues (P < 0.001). Moreover, low expression of PAK6 was associated with unfavorable overall survival (OS) (P = 0.001) and recurrence-free survival (RFS) (P = 0.001). In the subgroup of patients with tumor, node, metastasis classification system (TNM) stage I + II disease, those with low expression of PAK6 were prone to have poor OS (P = 0.014) and RFS (P = 0.037). Intratumoral PAK6 low expression was correlated with tumor size (P = 0.001) and TNM stage (P = 0.006), and was identified as an independent prognostic factor for OS (hazard ratio 4.109, P = 0.002) and RFS (hazard ratio 3.175, P = 0.002). Use of an extended TNM staging system with intratumoral PAK6 expression showed a better prognostic value for OS [area under the receiver operating characteristic curve (AUC) 0.790, P = 0.022] and RFS (AUC 0.769, P = 0.040). The c-index of a Cox-based model combined with Eastern Cooperative Oncology Group performance status, TNM stage, Fuhrman grade, and PAK6 was 0.83 for OS and 0.80 for RFS. CONCLUSIONS: Intratumoral PAK6 could be a potential prognosticator for OS and RFS in ccRCC patients after nephrectomy. Further external validation and functional analysis should be pursued to assess its potential prognostic and therapeutic values for ccRCC patients.

Protein kinase D-mediated phosphorylation at Ser99 regulates localization of p21-activated kinase 4.

PAKs (p21-activated kinases) are effectors of RhoGTPases. PAK4 contributes to regulation of cofilin at the leading edge of migrating cells through activation of LIMK (Lin-11/Isl-1/Mec-3 kinase). PAK4 activity is regulated by an autoinhibitory domain that is released upon RhoGTPase binding as well as phosphorylation at Ser474 in the activation loop of the kinase domain. In the present study, we add another level of complexity to PAK4 regulation by showing that phosphorylation at Ser99 is required for its targeting to the leading edge. This phosphorylation is mediated by PKD1 (protein kinase D1). Phosphorylation of PAK4 at Ser99 also mediates binding to 14-3-3 protein, and is required for the formation of a PAK4-LIMK-PKD1 complex that regulates cofilin activity and directed cell migration.

Proteomics-based strategy to delineate the molecular mechanisms of RhoGDI2-induced metastasis and drug resistance in gastric cancer.

Rho GDP dissociation inhibitor 2 (RhoGDI2) was initially identified as a regulator of the Rho family of GTPases. Our recent works suggest that RhoGDI2 promotes tumor growth and malignant progression, as well as enhances chemoresistance in gastric cancer. Here, we delineate the mechanism by which RhoGDI2 promotes gastric cancer cell invasion and chemoresistance using two-dimensional gel electrophoresis (2-DE) on proteins derived from a RhoGDI2-overexpressing SNU-484 human gastric cancer cell line and control cells. Differentially expressed proteins were identified using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF-MS). In total, 47 differential protein spots were identified; 33 were upregulated, and 14 were downregulated by RhoGDI2 overexpression. Upregulation of SAE1, Cathepsin D, Cofilin1, CIAPIN1, and PAK2 proteins was validated by Western blot analysis. Loss-of-function analysis using small interference RNA (siRNA) directed against candidate genes reveals the need for CIAPIN1 and PAK2 in RhoGDI2-induced cancer cell invasion and Cathepsin D and PAK2 in RhoGDI2-mediated chemoresistance in gastric cancer cells. These data extend our understanding of the genes that act downstream of RhoGDI2 during the progression of gastric cancer and the acquisition of chemoresistance.

The pathogenesis of chronic hypersensitivity pneumonitis in common with idiopathic pulmonary fibrosis: expression of apoptotic markers.

Previous studies showed that apoptotic epithelial cells were involved in the pathogenesis of idiopathic pulmonary fibrosis (IPF)/usual interstitial pneumonia (UIP); however, little is known about apoptosis in chronic hypersensitivity pneumonitis (HP). This study was performed to examine whether apoptosis has a role in chronic HP. We performed immunohistochemical studies for p53, p21, Fas, Fas ligand, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labeling methods on surgical lung specimens. The expression of Fas and Fas ligand was up-regulated in UIP-like lesions compared with nonspecific interstitial pneumonia (NSIP)-like lesions. The expression of p53 and p21 on epithelial cells increased significantly in UIP-like lesions compared with fibrotic NSIP-like lesions and in fibrotic NSIP-like lesions compared with normal lung tissues. These results confirm that apoptotic epithelial cells are present in chronic HP as seen in IPF. Augmented epithelial apoptosis may contribute much more to UIP-like lesions than to NSIP-like lesions in chronic HP.

WAVE2 targeting to phosphatidylinositol 3,4,5-triphosphate mediated by insulin receptor substrate p53 through a complex with WAVE2.

Membrane targeting of WAVE2 along microtubules to phosphatidylinositol 3,4,5-triphosphate (PIP(3)) in response to an extracellular stimulus requires Rac1, Pak1, stathmin, and EB1. However, whether WAVE2 interacts directly with PIP(3) or not remains unclear. We demonstrate that insulin-like growth factor I (IGF-I) induces WAVE2 membrane targeting, accompanied by phosphorylation of Pak1 at serine 199/204 (Ser199/204) and stathmin at Ser38 in the inner cytoplasmic region. This is spatially independent of the membrane region where the IGF-I receptor (IGF-IR) is locally activated. WAVE2, phosphorylated Pak1, and phosphorylated stathmin located at the microtubule ends began to accumulate at the leading edge of cells in close proximity to PIP(3) that was produced in a phosphatidylinositol 3-kinase (PI 3-kinase)-dependent manner. The PIP(3)-beads binding assay revealed that insulin receptor substrate p53 (IRSp53) and actin rather than WAVE2 bound to PIP(3). IRSp53 constitutively associated with WAVE2 and these two proteins colocalized with PIP(3) at the leading edge after IGF-I stimulation. Suppression of IRSp53 expression by two independent small interfering RNAs (siRNAs) completely inhibited IGF-I-induced membrane targeting and local accumulation of WAVE2 at the leading edge of cells. We propose that IRSp53 constitutively forms a complex with WAVE2 and is crucial for membrane targeting followed by local accumulation of WAVE2 at the leading edge of cells through linking WAVE2 to PIP(3) that is produced near locally activated IGF-IR in response to IGF-I.

Increased Rac1 activity and Pak1 overexpression are associated with lymphovascular invasion and lymph node metastasis of upper urinary tract cancer.

BACKGROUND: Lymphovascular invasion (LVI) and lymph node metastasis are conventional pathological factors associated with an unfavorable prognosis of urothelial carcinoma of the upper urinary tract (UC-UUT), but little is known about the molecular mechanisms underlying LVI and nodal metastasis in this disease. Rac1 small GTPase (Rac1) is essential for tumor metastasis. Activated GTP-bound Rac1 (Rac1 activity) plays a key role in activating downstream effectors known as Pak (21-activated kinase), which are key regulators of cytoskeletal remolding, cell motility, and cell proliferation, and thus have a role in both carcinogenesis and tumor invasion. METHODS: We analyzed Rac1 activity and Pak1 protein expression in matched sets of tumor tissue, non-tumor tissue, and metastatic lymph node tissue obtained from the surgical specimens of 108 Japanese patients with UC-UUT. RESULTS: Rac1 activity and Pak1 protein levels were higher in tumor tissue and metastatic lymph node tissue than in non-tumor tissue (both P < 0.0001). A high level of Rac1 activity and Pak1 protein expression in the primary tumor was related to poor differentiation (P < 0.05), muscle invasion (P < 0.01), LVI (P < 0.0001), and lymph node metastasis (P < 0.0001). Kaplan-Meier survival analysis showed that an increase of Rac1 activity and Pak1 protein was associated with a shorter disease-free survival time (P < 0.01) and shorter overall survival (P < 0.001). Cox proportional hazards analysis revealed that high Rac1 activity, Pak1 protein expression and LVI were independent prognostic factors for shorter overall and disease-free survival times (P < 0.01) on univariate analysis, although only Pak1 and LVI had an influence (P < 0.05) according to multivariate analysis. CONCLUSIONS: These findings suggest that Rac1 activity and Pak1 are involved in LVI and lymph node metastasis of UC-UUT, and may be prognostic markers for this disease.

MicroRNA-7, a homeobox D10 target, inhibits p21-activated kinase 1 and regulates its functions.

MicroRNAs are noncoding RNAs that inhibit the expression of their targets in a sequence-specific manner and play crucial roles during oncogenesis. Here we show that microRNA-7 (miR-7) inhibits p21-activated kinase 1 (Pak1) expression, a widely up-regulated signaling kinase in multiple human cancers, by targeting the 3'-untranslated region (UTR) of Pak1 mRNA. We noticed an inverse correlation between the levels of endogenous miR-7 and Pak1 expression in human cancer cells. We discovered that endogenous miR-7 expression is positively regulated by a homeodomain transcription factor, HoxD10, the loss of which leads to an increased invasiveness. HoxD10 directly interacts with the miR-7 chromatin. Accordingly, the levels of Pak1 protein are progressively up-regulated whereas those of miR-7 and its upstream activator HoxD10 are progressively down-regulated in a cellular model of breast cancer progression from low to highly invasive phenotypes. Furthermore, HoxD10 expression in highly invasive breast cancer cells resulted in an increased miR-7 expression but reduced Pak1 3'-UTR-luciferase activity and reduced Pak1 protein. Finally, we show that miR-7 introduction inhibits the motility, invasiveness, anchorage-independent growth, and tumorigenic potential of highly invasive breast cancer cells. Collectively, these findings establish for the first time that Pak1 is a target of miR-7 and that HoxD10 plays a regulatory role in modifying the expression of miR-7 and, consequently, the functions of the miR-7-Pak1 pathway in human cancer cells.