PTEN regulates colorectal epithelial apoptosis through Cdc42 signalling

Cisatracurium besylate rescues Mycobacterium Tuberculosis-infected macrophages from necroptosis and enhances the bactericidal effect of isoniazid

OBJECTIVE

Tuberculosis is the leading killer among the chronic single-source infectious diseases. Mycobacterium tuberculosis can induce necrotic-dominant multiple modes of cell death in macrophages, which accelerates bacterium dissemination and expands tissue injury in host lungs. Mining drugs to counteract Mycobacterium tuberculosis-induced cell death would be beneficial to tuberculosis patients.

METHODS

In this study, the protective drug was screened out from the FDA-approved drug library in Mycobacterium tuberculosis-infected macrophages with CCK-8 assay. The death mode regulated by the drug was identified using transcriptomic sequencing, cytomorphological observation, and in the experimental mouse Mycobacterium tuberculosis-infection model. The functional mechanism was explored using western blot, co-immunoprecipitation, and DARTS assay. The intracellular bacterial survival was detected using colony forming unit assays.

RESULTS

Cisatracurium besylate was identified to be highly protective for the viability of macrophages during Mycobacterium tuberculosis infection via inhibiting necroptosis. Cisatracurium besylate prevented RIPK3 to be associated with the executive molecule MLKL for forming the necroptotic complex, resulting in the inhibition of MLKL phosphorylation and pore formation on cell membrane. However, Cisatracurium besylate did not interfere with the association between RIPK3 with its upstream kinase RIPK1 or ZBP1 but regulated RIPK3 autophosphorylation. Moreover, Cisatracurium besylate significantly inhibited the expansion of intracellular Mycobacterium tuberculosis both in vitro and in vivo, which also displayed a strong auxiliary bacteriostatic effect to support the therapeutic efficacy of isoniazid and rifampicin, the first-line anti-tubercular drugs.

CONCLUSION

Cisatracurium besylate performs anti-Mycobacterium tuberculosis and anti-necroptotic roles, which potentiates its application to be an adjuvant drug for antituberculosis therapy to assist the battle against drug-resistant tuberculosis.

Molecular docking, molecular dynamics simulations and in vitro screening reveal cefixime and ceftriaxone as GSK3β covalent inhibitors

GSK3β is a serine/threonine kinase that has been suggested as a putative drug target for several diseases. Recent studies have reported the beneficial effects of cephalosporin antibiotics in cancer and Alzheimer's disease, implying potential inhibition of GSK3β. To investigate this mechanism, four cephalosporins, namely, cefixime, ceftriaxone, cephalexin and cefadroxil were docked into the GSK3β binding pocket. The third-generation cephalosporins, cefixime and ceftriaxone, exhibited the best docking scores due to the exclusive hydrogen bonding between their aminothiazole group and hinge residues of GSK3β. The stability of top-ranked poses and the possibility of covalent bond formation between the carbonyl carbon of the β-lactam ring and the nucleophilic thiol of Cys-199 were evaluated by molecular dynamics simulations and covalent docking. Finally, the in vitro inhibitory activities of the four cephalosporins were measured against GSK3β with and without preincubation. In agreement with the results of molecular docking, cefixime and ceftriaxone exhibited the best inhibitory activities with IC₅₀ values of 2.55 μM and 7.35 μM, respectively. After 60 minutes preincubation with GSK3β, the IC₅₀ values decreased to 0.55 μM for cefixime and 0.78 μM for ceftriaxone, supporting a covalent bond formation as suggested by molecular dynamics simulations and covalent docking. In conclusion, the third-generation cephalosporins are reported herein as GSK3β covalent inhibitors, offering insight into the mechanism behind their benefits in cancer and Alzheimer's disease.

Overactivated Cdc42 acts through Cdc42EP3/Borg2 and NCK to trigger DNA damage response signaling and sensitize cells to DNA-damaging agents

The small GTPase Cdc42, a member of the Rho family, regulates essential biological processes such as cytoskeleton remodeling, migration, vesicular trafficking and cell cycle. It was demonstrated that Cdc42 overactivation through different molecular strategies increases cell sensitivity to genotoxic stress and affects the phosphorylation status of DNA damage response proteins by unknown mechanisms. By using a combination of approaches including affinity purification/mass spectrometry (AP/MS) and colocalization microscopy analysis we were able to identify Cdc42EP3/Borg2 as a putative molecular effector of these molecular and cellular events that seem to be independent of cell line or DNA damage stimuli. We then investigated the influence of Cdc42EP3/Borg2 and other potential protein partners, such as the NCK and Septin2 proteins, which could mediate cellular responses to genotoxic stress under different backgrounds of Cdc42 activity. Clonogenic assays showed a reduced cell survival when ectopically expressing the Cdc42EP3/Borg2, NCK2 or Septin2 in an overactivated Cdc42-dependent background. Moreover, endogenous NCK appears to relocate into the nucleus upon Cdc42 overactivation, especially under genotoxic stress, and promotes the suppression of Chk1 phosphorylation. In sum, our findings reinforce Cdc42 as an important player involved in the DNA damage response acting through Cdc42EP3/Borg2 and NCK proteins following genomic instability conditions.

Glycogen Synthase Kinase 3β in Cancer Biology and Treatment

Glycogen synthase kinase (GSK)3β is a multifunctional serine/threonine protein kinase with more than 100 substrates and interacting molecules. GSK3β is normally active in cells and negative regulation of GSK3β activity via phosphorylation of its serine 9 residue is required for most normal cells to maintain homeostasis. Aberrant expression and activity of GSK3β contributes to the pathogenesis and progression of common recalcitrant diseases such as glucose intolerance, neurodegenerative disorders and cancer. Despite recognized roles against several proto-oncoproteins and mediators of the epithelial–mesenchymal transition, deregulated GSK3β also participates in tumor cell survival, evasion of apoptosis, proliferation and invasion, as well as sustaining cancer stemness and inducing therapy resistance. A therapeutic effect from GSK3β inhibition has been demonstrated in 25 different cancer types. Moreover, there is increasing evidence that GSK3β inhibition protects normal cells and tissues from the harmful effects associated with conventional cancer therapies. Here, we review the evidence supporting aberrant GSK3β as a hallmark property of cancer and highlight the beneficial effects of GSK3β inhibition on normal cells and tissues during cancer therapy. The biological rationale for targeting GSK3β in the treatment of cancer is also discussed at length.

Cloning and differential expression analyses of Cdc42 from sheep

Introduction

Serological diagnosis of brucellosis is still a great challenge due to the infeasibility of discriminating infected animals from vaccinated ones, so it is necessary to search for diagnostic biomarkers for differential diagnosis of brucellosis.

Material and Methods

Cell division cycle 42 (Cdc42) from sheep (Ovis aries) (OaCdc42) was cloned by rapid amplification of cDNA ends (RACE), and then tissue distribution and differential expression levels of OaCdc42 mRNA between infected and vaccinated sheep were analysed by RT-qPCR.

Results

The full-length cDNA of OaCdc42 was 1,609 bp containing an open reading frame (ORF) of 576 bp. OaCdc42 mRNAs were detected in the heart, liver, spleen, lung, kidneys, rumen, small intestine, skeletal muscles, and buffy coat, and the highest expression was detected in the small intestine. Compared to the control, the levels of OaCdc42 mRNA from sheep infected with Brucella melitensis or sheep vaccinated with Brucella suis S2 was significantly different (P < 0.01) after 40 and 30 days post-inoculation, respectively. However, the expression of OaCdc42 mRNA was significantly different between vaccinated and infected sheep (P < 0.05 or P < 0.01) on days: 14, 30, and 60 post-inoculation, whereas no significant difference (P > 0.05) was noted 40 days post-inoculation. Moreover, the expression of OaCdc42 from both infected and vaccinated sheep showed irregularity.

Conclusion

OaCdc42 is not a good potential diagnostic biomarker for differential diagnosis of brucellosis in sheep.

Cloning and Differential Expression Analyses of Cdc42 from Sheep

INTRODUCTION

Serological diagnosis of brucellosis is still a great challenge due to the infeasibility of discriminating infected animals from vaccinated ones, so it is necessary to search for diagnostic biomarkers for differential diagnosis of brucellosis.

MATERIAL AND METHODS

Cell division cycle 42 (Cdc42) from sheep (Ovis aries) (OaCdc42) was cloned by rapid amplification of cDNA ends (RACE), and then tissue distribution and differential expression levels of OaCdc42 mRNA between infected and vaccinated sheep were analysed by RT-qPCR.

RESULTS

The full-length cDNA of OaCdc42 was 1,609 bp containing an open reading frame (ORF) of 576 bp. OaCdc42 mRNAs were detected in the heart, liver, spleen, lung, kidneys, rumen, small intestine, skeletal muscles, and buffy coat, and the highest expression was detected in the small intestine. Compared to the control, the levels of OaCdc42 mRNA from sheep infected with Brucella melitensis or sheep vaccinated with Brucella suis S2 was significantly different (P < 0.01) after 40 and 30 days post-inoculation, respectively. However, the expression of OaCdc42 mRNA was significantly different between vaccinated and infected sheep (P < 0.05 or P < 0.01) on days: 14, 30, and 60 post-inoculation, whereas no significant difference (P > 0.05) was noted 40 days post-inoculation. Moreover, the expression of OaCdc42 from both infected and vaccinated sheep showed irregularity.

CONCLUSION

OaCdc42 is not a good potential diagnostic biomarker for differential diagnosis of brucellosis in sheep.

Reduced beta 2 glycoprotein I prevents high glucose-induced cell death in HUVECs through miR-21/PTEN

High serum beta 2 glycoprotein I (β2GPI) is associated with complications of type 2 diabetes mellitus (DM), and especially microvascular disorders. In contrast, reduced β2GPI (Rβ2GPI) can prevent diabetic vascular injury. This study aimed to investigate the protective function of Rβ2GPI in DM vascular disorders, and to assess the under lying mechanisms. High glucose-induced injury in human umbilical vein endothelial cells (HUVECs) was used to model hyperglycemia. Alow concentration of Rβ2GPI (0.5 μM), but not β2GPI, mitigated high glucose-induced cell injury. High glucose decreased miR-21 expression and Akt phosphorylation at 6 h, but facilitated their expression at 48 h. Moreover, high glucose decreased phosphatase and tensin homolog deleted on chromosome ten(PTEN) expression at 6 h, but facilitatedits expression at 48 h. Importantly, by promoting miR-21 expression, Rβ2GPI mitigated high glucose-induced PTEN expression, reduced Akt phosphorylation and nitric oxide synthase activity, and increased cyclooxygenase-2 activity and cell loss. Similar to Rβ2GPI, an miR-21 mimic (1 pM) and PTEN inhibition (1 μM bpV, or PTEN silencing) exerted protective action, while an Akt signaling pathway inhibitor (LY294002, 1 μM) aborted the effect of Rβ2GPI on high glucose-induced cell injury. Finally, Rβ2GPI inhibited high glucose-induced apoptosis via a mitochondria-dependent pathway. These data reveal that Rβ2GPI exerts protective action in high glucose-induced HUVEC injury. The mechanism is related to the miR-21-PTEN-Akt pathway and mitochondria-dependent apoptosis. This study provides in vitro data supporting the therapeutic effect of Rβ2GPI in diabetic vascular injury.

PTEN controls glandular morphogenesis through a juxtamembrane β-Arrestin1/ARHGAP21 scaffolding complex

PTEN controls three-dimensional (3D) glandular morphogenesis by coupling juxtamembrane signaling to mitotic spindle machinery. While molecular mechanisms remain unclear, PTEN interacts through its C2 membrane-binding domain with the scaffold protein β-Arrestin1. Because β-Arrestin1 binds and suppresses the Cdc42 GTPase-activating protein ARHGAP21, we hypothesize that PTEN controls Cdc42 -dependent morphogenic processes through a β-Arrestin1-ARHGAP21 complex. Here, we show that PTEN knockdown (KD) impairs β-Arrestin1 membrane localization, β-Arrestin1-ARHGAP21 interactions, Cdc42 activation, mitotic spindle orientation and 3D glandular morphogenesis. Effects of PTEN deficiency were phenocopied by β-Arrestin1 KD or inhibition of β-Arrestin1-ARHGAP21 interactions. Conversely, silencing of ARHGAP21 enhanced Cdc42 activation and rescued aberrant morphogenic processes of PTEN-deficient cultures. Expression of the PTEN C2 domain mimicked effects of full-length PTEN but a membrane-binding defective mutant of the C2 domain abrogated these properties. Our results show that PTEN controls multicellular assembly through a membrane-associated regulatory protein complex composed of β-Arrestin1, ARHGAP21 and Cdc42.

Vitamin D3 suppresses morphological evolution of the cribriform cancerous phenotype

Development of cribriform morphology (CM) heralds malignant change in human colon but lack of mechanistic understanding hampers preventive therapy. This study investigated CM pathobiology in three-dimensional (3D) Caco-2 culture models of colorectal glandular architecture, assessed translational relevance and tested effects of 1,25(OH)2D3,theactive form of vitamin D. CM evolution was driven by oncogenic perturbation of the apical polarity (AP) complex comprising PTEN, CDC42 and PRKCZ (phosphatase and tensin homolog, cell division cycle 42 and protein kinase C zeta). Suppression of AP genes initiated a spatiotemporal cascade of mitotic spindle misorientation, apical membrane misalignment and aberrant epithelial configuration. Collectively, these events promoted "Swiss cheese-like" cribriform morphology (CM) comprising multiple abnormal "back to back" lumens surrounded by atypical stratified epithelium, in 3D colorectal gland models. Intestinal cancer driven purely by PTEN-deficiency in transgenic mice developed CM and in human CRC, CM associated with PTEN and PRKCZ readouts. Treatment of PTEN-deficient 3D cultures with 1,25(OH)2D3 upregulated PTEN, rapidly activated CDC42 and PRKCZ, corrected mitotic spindle alignment and suppressed CM development. Conversely, mutationally-activated KRAS blocked1,25(OH)2D3 rescue of glandular architecture. We conclude that 1,25(OH)2D3 upregulates AP signalling to reverse CM in a KRAS wild type (wt), clinically predictive CRC model system. Vitamin D could be developed as therapy to suppress inception or progression of a subset of colorectal tumors.

CDC42 Gtpase Activation Affects Hela Cell DNA Repair and Proliferation Following UV Radiation-Induced Genotoxic Stress

Cell division control protein 42 (CDC42) homolog is a small Rho GTPase enzyme that participates in such processes as cell cycle progression, migration, polarity, adhesion, and transcription. Recent studies suggest that CDC42 is a potent tumor suppressor in different tissues and is related to aging processes. Although DNA damage is crucial in aging, a potential role for CDC42 in genotoxic stress remains to be explored. Migration, survival/proliferation and DNA damage/repair experiments were performed to demonstrate CDC42 involvement in the recovery of HeLa cells exposed to ultraviolet radiation-induced stress. Sub-lines of HeLa cells ectopically expressing the constitutively active CDC42-V12 mutant were generated to examine whether different CDC42-GTP backgrounds might reflect different sensitivities to UV radiation. Our results show that CDC42 constitutive activation does not interfere with HeLa cell migration after UV radiation. However, the minor DNA damage exhibited by the CDC42-V12 mutant exposed to UV radiation most likely results in cell cycle arrest at the G2/M checkpoint and reduced proliferation and survival. HeLa cells and Mock clones, which express endogenous wild-type CDC42 and show normal activity, are more resistant to UV radiation. None of these effects are altered by pharmacological CDC42 inhibition. Finally, the phosphorylation status of the DNA damage response proteins γ-H2AX and p-Chk1 was found to be delayed and attenuated, respectively, in CDC42-V12 clones. In conclusion, the sensitivity of HeLa cells to ultraviolet radiation increases with CDC42 over-activation due to inadequate DNA repair signaling, culminating in G2/M cell accumulation, which is translated into reduced cellular proliferation and survival.

A dynamic exchange of TCF3 and TCF4 transcription factors controls MYC expression in colorectal cancer cells

Deregulated Wnt/β-catenin signaling promotes colorectal cancer (CRC) by activating expression of the c-MYC proto-oncogene (MYC). In the nucleus, the β-catenin transcriptional co-activator binds T-cell factor (TCF) transcription factors, and together TCF/β-catenin complexes activate MYC expression through Wnt responsive DNA regulatory elements (WREs). The MYC 3' WRE maps 1.4-kb downstream from the MYC transcription stop site and binds TCF4/β-catenin transcription complexes to activate MYC. However, the underlying mechanisms for how this element operates are not fully understood. Here, we report that the TCF family member, TCF3, plays an important role in regulating MYC expression in CRCs. We demonstrate that TCF3 binds the MYC 3' WRE to repress MYC. When TCF3 is depleted using shRNAs, the MYC 3' WRE is more available to bind TCF4/β-catenin complexes. Stimulating downstream Wnt/β-catenin signaling by inhibiting GSK3β causes an exchange of TCF3 with TCF4/β-catenin complexes to activate MYC. Finally, this transcription factor switch at the MYC 3' WRE controls MYC expression as quiescent cells re-enter the cell cycle and progress to S phase. These results indicate that a dynamic interplay of TCF transcription factors governs MYC gene expression in CRCs.

Association of genetic polymorphisms in PTEN and additional interaction with alcohol consumption and smoking on colorectal cancer in Chinese population

AIMS

To investigate the association of phosphatase and tensin homologue deleted on chromosome ten (PTEN) gene rs3830675, and additional interaction with drinking and smoking on colorectal cancer (CRC), based on a hospital based Chinese case-control study.

METHODS

A total of 850 subjects (413 males and 437 females) were studied, including 422 colorectal cancer cases and 428 controls. Rs3830675 was selected for genotyping in the case-control study. Logistic regression model was used to examine the association between rs3830675 and colorectal cancer, and additional interaction with alcohol consumption and smoking.

RESULTS

The frequencies for rs3830675 (-) alleles was higher in cases than that in controls, (-) allele of rs3830675 was 24.4% in controls and 29.4% in CRC subjects (p=0.005). Logistic analysis showed that the carriers of (-) allele of rs3830675 revealed increased CRC risk than those with (+/+) genotype, adjusted OR (95% CI) was 1.35(1.12-1.98). We found a significant interaction between alcohol consumption and rs3830675, drinkers with (-/-) or (-/+) of rs3830675 genotype have highest colorectal cancer risk, compared to never drinking subjects with (+/+) genotype, OR (95% CI) was 2.57 (1.66-3.33), after covariates adjustment. In addition, we also found that smokers with (-/-) or (-/+) of rs3830675 genotype have highest colorectal cancer risk, compared to never smokers with (+/+) genotype, OR (95% CI) was 3.01 (1.58-6.05).

CONCLUSIONS

The (-) allele of rs3830675 was positively with colorectal cancer risk. There was a significant role of interaction of rs3830675 with alcohol consumption and smoking on colorectal cancer.

MicroRNA-mRNA regulatory network study and apoptosis analysis on bone marrow endothelial cells induced by liver cirrhosis serum

BACKGROUND AND OBJECTIVE

As important components of bone marrow microenvironment, bone marrow endothelial cells (BMECs) have important roles in regulating haematopoietic functions of the bone marrow. In preliminary study, we found the humoral inhibitor in liver cirrhosis (LC) could lead to ultrastructure alterations of the bone marrow endothelium. The present study aimed to investigate functional changes occurred in BMECs during LC.

METHODS

A multi-step approach combining microarray microRNA (miRNA) and mRNA expression profiling and bioinformatics analysis was used to generate a specific miRNA-mRNA regulatory network in BMECs treated with supplemented medium with 20% pooled sera from 26 patients with LC or 10 healthy volunteers as a control group for 48h.

RESULTS

A total of 372 differentially expressed miRNAs and 1872 differentially expressed mRNAs were identified by miRNA and mRNA microarray, respectively. Twenty-one dysregulated miRNAs and their 23 dysregulated target mRNAs confirmed by experiment (31 miRNA-mRNA interactions) were screened based on databases miRecords and miRTarBase. Bioinformatics analysis revealed that the functions of these miRNA-mRNA interactions were involved in the positive regulation of apoptosis, negative regulation of cell proliferation, cell cycle arrest and so on. The results of flow cytometry analysis showed that the LC serum treated-BMECs had a higher apoptosis percentage (17.57±1.84%) compared to the control group (10.2±1.55%). (P<0.05) CONCLUSIONS: Thirty-one miRNA-mRNA pairs combined with 21 dysregulated miRNAs and their 23 target mRNAs identified by the multi-step approach are involved in BMECs treated with LC serum. The results indicated that LC serum-induced apoptosis in BMECs were regulated by a complicated miRNA-mRNA regulatory network.

PTEN phosphatase-independent maintenance of glandular morphology in a predictive colorectal cancer model system

Organotypic models may provide mechanistic insight into colorectal cancer (CRC) morphology. Three-dimensional (3D) colorectal gland formation is regulated by phosphatase and tensin homologue deleted on chromosome 10 (PTEN) coupling of cell division cycle 42 (cdc42) to atypical protein kinase C (aPKC). This study investigated PTEN phosphatase-dependent and phosphatase-independent morphogenic functions in 3D models and assessed translational relevance in human studies. Isogenic PTEN-expressing or PTEN-deficient 3D colorectal cultures were used. In translational studies, apical aPKC activity readout was assessed against apical membrane (AM) orientation and gland morphology in 3D models and human CRC. We found that catalytically active or inactive PTEN constructs containing an intact C2 domain enhanced cdc42 activity, whereas mutants of the C2 domain calcium binding region 3 membrane-binding loop (M-CBR3) were ineffective. The isolated PTEN C2 domain (C2) accumulated in membrane fractions, but C2 M-CBR3 remained in cytosol. Transfection of C2 but not C2 M-CBR3 rescued defective AM orientation and 3D morphogenesis of PTEN-deficient Caco-2 cultures. The signal intensity of apical phospho-aPKC correlated with that of Na(+)/H(+) exchanger regulatory factor-1 (NHERF-1) in the 3D model. Apical NHERF-1 intensity thus provided readout of apical aPKC activity and associated with glandular morphology in the model system and human colon. Low apical NHERF-1 intensity in CRC associated with disruption of glandular architecture, high cancer grade, and metastatic dissemination. We conclude that the membrane-binding function of the catalytically inert PTEN C2 domain influences cdc42/aPKC-dependent AM dynamics and gland formation in a highly relevant 3D CRC morphogenesis model system.

Anti-miRNA-221 sensitizes human colorectal carcinoma cells to radiation by upregulating PTEN

AIM: To investigate the regulative effect of miRNA (miR)-221 on colorectal carcinoma (CRC) cell radiosensitivity and the underlying mechanisms.

METHODS: A human CRC-derived cell line was cultured conventionally and exposed to different doses of X-rays (0, 2, 4, 6 and 8 Gy). The total RNA and protein of the cells were extracted 24 h after irradiation, and the alteration of miR-221 and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) gene mRNA expression was detected by real-time reverse transcriptase polymerase chain reaction (PCR). The protein alteration of PTEN in the cells was detected by Western blotting. Caco2 cells were pretreated with or without anti-PTEN-siRNA prior to the addition of pre-miR-221 or anti-miR-221 using Lipofectamine 2000. Colony formation assay and flow cytometry analysis were used to measure the surviving cell fraction and the sensitizing enhancement ratio after irradiation. Additionally, PTEN 3′-untranslated region fragment was PCR amplified and inserted into a luciferase reporter plasmid. The luciferase reporter plasmid construct was then transfected into CRC cells together with pre-miR-221 or anti-miR-221, and the luciferase activity in the transfected cells was detected.

RESULTS: The X-ray radiation dose had a significant effect on the expression of miR-221 and PTEN protein in human Caco2 cells in a dose-dependent manner. The miR-221 expression level improved gradually with the increase in irradiation dose, while the PTEN protein expression level reduced gradually. miR-221 expression was significantly reduced in the anti-miR-221 group compared with the pre-miR-221 and negative control groups (P < 0.01). Anti-miR-221 upregulated expression of PTEN protein and enhanced the radiosensitivity of Caco2 cells (P < 0.01). Moreover, the inhibitory effect was dramatically abolished by pretreatment with anti-PTEN-siRNA, suggesting that the enhancement of radiosensitivity was indeed mediated by PTEN. A significant increase of luciferase activity was detected in CRC cells that were cotransfected with the luciferase reporter plasmid construct and anti-miR-221 (P < 0.01).

CONCLUSION: Anti-miR-221 can enhance the radiosensitivity of CRC cells by upregulating PTEN.

PTEN regulation of ERK1/2 signaling in cancer

Since its discovery, the tumor suppressor phosphatase and tensin homolog (PTEN) has become a molecule with a wide spectrum of functions, which is typically meditated through its lipid phosphatase activity; however, PTEN also functions in a phosphatase-independent manner. It is well established that PTEN regulates several signaling pathways, such as phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT), janus kinase (JAK)/signal transducers and activators of transcription (STAT), focal adhesion kinase (FAK), and more recent, extracellular signal-regulated kinase (ERK)1/2, where activation of these pathways typically leads to cancer development and progression. In regard to most of these pathways, the underlining molecular mechanism of PTEN-mediated regulation is well established, but not so much for the ERK1/2 pathway. Indeed, accumulating evidence has shown an inverse correlation between PTEN expression and ERK1/2 in several malignancies. However, the detailed mechanism by which PTEN regulates ERK1/2 is poorly understood. In this review, we discuss the role of PTEN in regulating ERK1/2 by directly targeting shc/Raf/MEK and PI3K/AKT cascades, and a putative cross-talk between the two.

Rescue of glandular dysmorphogenesis in PTEN-deficient colorectal cancer epithelium by PPARγ-targeted therapy

Disruption of glandular architecture associates with poor clinical outcome in high-grade colorectal cancer (CRC). Phosphatase and tensin homolog deleted on chromosome ten (PTEN) regulates morphogenic growth of benign MDCK (Madin Darby Canine Kidney) cells through effects on the Rho-like GTPase cdc42 (cell division cycle 42). This study investigates PTEN-dependent morphogenesis in a CRC model. Stable short hairpin RNA knockdown of PTEN in Caco-2 cells influenced expression or localization of cdc42 guanine nucleotide exchange factors and inhibited cdc42 activation. Parental Caco-2 cells formed regular hollow gland-like structures (glands) with a single central lumen, in three-dimensional (3D) cultures. Conversely, PTEN-deficient Caco-2 ShPTEN cells formed irregular glands with multiple abnormal lumens as well as intra- and/or intercellular vacuoles evocative of the high-grade CRC phenotype. Effects of targeted treatment were investigated. Phosphatidinylinositol 3-kinase (PI3K) modulating treatment did not affect gland morphogenesis but did influence gland number, gland size and/or cell size within glands. As PTEN may be regulated by the nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ), cultures were treated with the PPARγ ligand rosiglitazone. This treatment enhanced PTEN expression, cdc42 activation and rescued dysmorphogenesis by restoring single lumen formation in Caco-2 ShPTEN glands. Rosiglitazone effects on cdc42 activation and Caco-2 ShPTEN gland development were attenuated by cotreatment with GW9662, a PPARγ antagonist. Taken together, these studies show PTEN-cdc42 regulation of lumen formation in a 3D model of human CRC glandular morphogenesis. Treatment by the PPARγ ligand rosiglitazone, but not PI3K modulators, rescued colorectal glandular dysmorphogenesis of PTEN deficiency.