Detection of active fraction of glycogen synthase kinase 3beta in cancer cells by nonradioisotopic in vitro kinase assay

Glycogen synthase kinase 3β: the nexus of chemoresistance, invasive capacity, and cancer stemness in pancreatic cancer

The treatment of pancreatic cancer remains a significant clinical challenge due to the limited number of patients eligible for curative (R0) surgery, failures in the clinical development of targeted and immune therapies, and the pervasive acquisition of chemotherapeutic resistance. Refractory pancreatic cancer is typified by high invasiveness and resistance to therapy, with both attributes related to tumor cell stemness. These malignant characteristics mutually enhance each other, leading to rapid cancer progression. Over the past two decades, numerous studies have produced evidence of the pivotal role of glycogen synthase kinase (GSK)3β in the progression of over 25 different cancer types, including pancreatic cancer. In this review, we synthesize the current knowledge on the pathological roles of aberrant GSK3β in supporting tumor cell proliferation and invasion, as well as its contribution to gemcitabine resistance in pancreatic cancer. Importantly, we discuss the central role of GSK3β as a molecular hub that mechanistically connects chemoresistance, tumor cell invasion, and stemness in pancreatic cancer. We also discuss the involvement of GSK3β in the formation of desmoplastic tumor stroma and in promoting anti-cancer immune evasion, both of which constitute major obstacles to successful cancer treatment. Overall, GSK3β has characteristics of a promising therapeutic target to overcome chemoresistance in pancreatic cancer.

Downregulation of microRNA-6125 promotes colorectal cancer growth through YTHDF2-dependent recognition of N6-methyladenosine-modified GSK3β

BACKGROUND

MicroRNAs (miRNAs), the key regulator of gene expression, and N6-methyladenosine (m6A) RNA modification play a significant role in tumour progression. However, regulation of m6A-modified mRNAs by miRNAs in colorectal cancer (CRC), and its effect on progression of CRC, remains to be investigated.

METHODS

Expression of miR-6125 and YTH Domain-Containing Family Protein 2 (YTHDF2) was detected by western blotting and immunohistochemistry. The effects of miR-6125 and YTHDF2 on proliferative capacity of CRC cells were analysed using soft agar, ATP, CCK8 and EdU assays, and in animal experiments.

RESULTS

MiR-6125 expression was downregulated markedly in CRC, and expression correlated negatively with tumour size and prognosis. MiR-6125 targeted the 3'-UTR of YTHDF2 and downregulated the YTHDF2 protein, thereby increasing the stability of m6A-modified glycogen synthase kinase 3 beta (GSK3β) mRNA. Increased GSK3β protein levels inhibited the expression of Wnt/β-catenin/Cyclin D1 pathway-related proteins, leading to G0-G1 phase arrest and ultimately inhibiting the proliferation of CRC cells.

CONCLUSIONS

MiR-6125 regulates YTHDF2 and thus plays a critical role in regulating the Wnt/β-catenin pathway, thereby affecting the growth of CRC. Collectively, these results suggest that miR-6125 and YTHDF2 are potential targets for treatment of CRC.

Knockdown of ISOC1 inhibits the proliferation and migration and induces the apoptosis of colon cancer cells through the AKT/GSK-3β pathway

Isochorismatase domain-containing 1 (ISOC1) is a coding gene that contains an isochorismatase domain. The precise functions of ISOC1 in humans have not been clarified; however, studies have speculated that it may be involved in unknown metabolic pathways. Currently, it is reported that ISOC1 is associated with breast cancer. In this research, the aim is to investigate the critical role of ISOC1 in colorectal cancer (CRC) and to explore its biological function and mechanism in colon cancer cells. In 106 paired clinical samples, we found that the levels of ISOC1 expression were widely increased in cancer tissues compared with matched adjacent non-tumor tissues and that increased expression of ISOC1 was significantly associated with tumor size, tumor invasion, local lymph node metastasis and Tumor, Node and Metastasis (TNM) stage. Moreover, higher expression levels of ISOC1 were correlated with shorter disease-free survival in patients 2 years after surgery. In vitro, ISOC1 knockdown inhibited the proliferation and migration and induced the apoptosis of colon cancer cells, and in vivo, the xenograft tumors were also inhibited by ISOC1 silencing. We also used MTS, Transwell and cell apoptosis assays to confirm that ISOC1 plays a critical role in regulating the biological functions of colon cancer cells through the AKT/GSK-3β pathway. Additionally, the results of confocal microscopy and western blot analysis indicated that ISOC1 knockdown could promote p-STAT1 translocation to the nucleus.

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.

Nerigoside suppresses colorectal cancer cell growth and metastatic potential through inhibition of ERK/GSK3β/β-catenin signaling pathway

BACKGROUND

Nerigoside (NG), a cardenolide isolated from a commonfolk medicine, Nerium oleander Linn. (Apocynaceae), has not been explored for its biological effects. To date, cardenolides have received considerable attention in pharmacology studies due to their direct effects of apoptosis-induction or growth-inhibitory against tumor in vitro and in vivo. Whether and how NG exerts anticancer effects against colorectal cancer remains to be elucidated.

PURPOSE

The aim of this study was to investigate the anticancer effect of NG in human colorectal cancer cells.

METHODS

To test anticancer effect, we compared potency of NG in two colorectal cancer cell lines, HT29 and SW620 by WST-1 and colony proliferation assays. And we investigated mechanism of anticancer activities by analyzing players in apoptotic and ERK/GSK3β/β-catenin signaling pathways in HT29 and SW620 cells treated with NG.

RESULTS

In this study, we showed that NG markedly suppressed the cell viability and colony formation of colorectal cancer cells HT29 and SW620, with no significant toxic effect on non-cancer cells NCM460. Annexin V-FITC/PI and CFSE labeling results revealed that NG suppressed cell proliferation in low concentration, along with reducing expression of PCNA, while NG induced apoptosis in high concentration,. Meanwhile, NG significantly arrested cell migration by reversal of EMT and cell cycle on G2/M. Then, we found that the ERK and GSK3β/β-catenin signaling pathway were noticeably blocked in CRC cells after treatment with NG. According to western blot, NG upregulated the expression of p-GSK3β/GSK3β and decreased especially the expression of β-catenin in nuclear. In addition, Wnt signaling and its target genes were suppressed in response to NG. Then, the Ser9 phosphorylation of GSK3β can be reduced / raised by GÖ 6983 / LiCl, respectively. Thus, we further confirmed that the GSK3β/β-catenin axis is involved in NG-prevented cell proliferation.

CONCLUSION

NG inhibited the growth of colorectal cancer cells by suppressing ERK/GSK3β/β-catenin signaling pathway. And the GSK3β/β-catenin axis is involved in preventing cell proliferation and migration by NG-treatment. These results suggest that NG may be used to treat colorectal cancer, with better outcome by combining with GSK3β inhibitor to block Wnt pathway.

Brain ischemic preconditioning protects against ischemic injury and preserves the blood-brain barrier via oxidative signaling and Nrf2 activation

Brain ischemic preconditioning (IPC) with mild ischemic episodes is well known to protect the brain against subsequent ischemic challenges. However, the underlying mechanisms are poorly understood. Here we demonstrate the critical role of the master redox transcription factor, nuclear factor (erythroid-derived 2)-like 2 (Nrf2), in IPC-mediated neuroprotection and blood-brain barrier (BBB) preservation. We report that IPC causes generation of endogenous lipid electrophiles, including 4-hydroxy-2-nonenal (4-HNE), which release Nrf2 from inhibition by Keap1 (via Keap1-C288) and inhibition by glycogen synthase kinase 3β (via GSK3β-C199). Nrf2 then induces expression of its target genes, including a new target, cadherin 5, a key component of adherens junctions of the BBB. These effects culminate in mitigation of BBB leakage and of neurological deficits after stroke. Collectively, these studies are the first to demonstrate that IPC protects the BBB against ischemic injury by generation of endogenous electrophiles and activation of the Nrf2 pathway through inhibition of Keap1- and GSK3β-dependent Nrf2 degradation.

Identification of two potential glycogen synthase kinase 3β inhibitors for the treatment of osteosarcoma

Osteosarcoma is the most common primary malignant bone tumor among adolescents worldwide with high mortality rate. Glycogen synthase kinase 3β (GSK3β) is a serine/threonine kinase and is considered as a validated target in osteosarcoma therapy. Therefore, the study of GSK3β inhibitors is one of the most popular fields in anti-osteosarcoma drug development. Here, the tools of bioinformatics were used to screen novel effective inhibitors of GSK3β from ZINC Drug Database. The molecular docking, molecular dynamic simulations, MM/GBSA, and energy decomposition analysis were performed to identify the inhibitors. Finally, ZINC08383479 and ZINC08441251 were selected as potential GSK3β inhibitors. These two inhibitors were evaluated by GSK3β kinase inhibition assay in vitro. The inhibition of cell proliferation was tested in osteosarcoma cell lines U2OS and MG63 in vitro. The result showed that ZINC08383479 and ZINC08441251 had high inhibition activity against GSK3β. We found that CHIR99021 (a known GSK3β inhibitor), ZINC08383479, and ZINC08441251 had significant inhibition activity in U2OS cells and MG63 cells. These findings may provide new ideas for the design of more potent GSK3β inhibitors and therapeutic targets for osteosarcoma.

Colorectal cancer cells require glycogen synthase kinase-3β for sustaining mitosis via translocated promoter region (TPR)-dynein interaction

Glycogen synthase kinase (GSK) 3β, which mediates fundamental cellular signaling pathways, has emerged as a potential therapeutic target for many types of cancer including colorectal cancer (CRC). During mitosis, GSK3β localizes in mitotic spindles and centrosomes, however its function is largely unknown. We previously demonstrated that translocated promoter region (TPR, a nuclear pore component) and dynein (a molecular motor) cooperatively contribute to mitotic spindle formation. Such knowledge encouraged us to investigate putative functional interactions among GSK3β, TPR, and dynein in the mitotic machinery of CRC cells. Here, we show that inhibition of GSK3β attenuated proliferation, induced cell cycle arrest at G2/M phase, and increased apoptosis of CRC cells. Morphologically, GSK3β inhibition disrupted chromosome segregation, mitotic spindle assembly, and centrosome maturation during mitosis, ultimately resulting in mitotic cell death. These changes in CRC cells were associated with decreased expression of TPR and dynein, as well as disruption of their functional colocalization with GSK3β in mitotic spindles and centrosomes. Clinically, we showed that TPR expression was increased in CRC databases and primary tumors of CRC patients. Furthermore, TPR expression in SW480 cells xenografted into mice was reduced following treatment with GSK3β inhibitors. Together, these results indicate that GSK3β sustains steady mitotic processes for proliferation of CRC cells via interaction with TPR and dynein, thereby suggesting that the therapeutic effect of GSK3β inhibition depends on induction of mitotic catastrophe in CRC cells.

Glycogen synthase kinase-3β is a pivotal mediator of cancer invasion and resistance to therapy

Tumor cell invasion and resistance to therapy are the most intractable biological characteristics of cancer and, therefore, the most challenging for current cancer research and treatment paradigms. Refractory cancers, including pancreatic cancer and glioblastoma, show an inextricable association between the highly invasive behavior of tumor cells and their resistance to chemotherapy, radiotherapy and targeted therapies. These aggressive properties of cancer share distinct cellular pathways that are connected to each other by several molecular hubs. There is increasing evidence to show that glycogen synthase kinase (GSK)‐3β is aberrantly activated in various cancer types and this has emerged as a potential therapeutic target. In many but not all cancer types, aberrant GSK3β sustains the survival, immortalization, proliferation and invasion of tumor cells, while also rendering them insensitive or resistant to chemotherapeutic agents and radiation. Here we review studies that describe associations between therapeutic stimuli/resistance and the induction of pro‐invasive phenotypes in various cancer types. Such cancers are largely responsive to treatment that targets GSK3β. This review focuses on the role of GSK3β as a molecular hub that connects pathways responsible for tumor invasion and resistance to therapy, thus highlighting its potential as a major cancer therapeutic target. We also discuss the putative involvement of GSK3β in determining tumor cell stemness that underpins both tumor invasion and therapy resistance, leading to intractable and refractory cancer with dismal patient outcomes.

Upregulation of C-C chemokine receptor type 7 expression by membrane-associated prostaglandin E synthase-1/prostaglandin E2 requires glycogen synthase kinase 3β-mediated signal transduction in colon cancer cells

C-C chemokine receptor type 7 (CCR7) is involved in the development and progressions of chronic inflammatory diseases and cancer; therefore, signaling pathways that regulate CCR7 expression may represent novel molecular therapeutic targets. Previous studies by our group revealed that CCR7 is important in colon cancer progression and a is linked with cyclooxygenase (COX)‑2‑derived prostaglandin (PG)E2. Induction of COX‑2 and membrane‑associated PGE synthase 1 (mPGES‑1), which are overexpressed in numerous cancer types, cooperatively enhance PGE2 expression, which contributes to carcinogenesis and cancer progression. The present study investigated whether CCR7 expression is associated with the levels of mPGES‑1-derived PGE2. The results showed that mPGES‑1‑dependent release of PGE2 was markedly induced in colon cancer cells after transient transfection with mPGES‑1 overexpression vector, accompanied by elevated CCR7 expression. PGE2 levels and CCR7 expression were markedly attenuated in colon cancer cells in which mPGES‑1 was blocked, which identified mPGES‑1 as a potential therapeutic target for the regulation of CCR7 expression. Finally, overexpression of CCR7 was partly mediated through the AKT/glycogen synthase kinase 3β signaling pathway dependent on the binding of mPGES‑1-derived PGE2 to the prostaglandin EP4 receptor. Thus, in addition to inhibitors of mPGES‑1 expression, EP4 antagonists and AKT/GSK-3β inhibitors may emerge as potential therapeutics to reduce CCR7 expression in colon cancer.

Ser9-phosphorylated GSK3β induced by 14-3-3ζ actively antagonizes cell apoptosis in a NF-κB dependent manner

The activity of glycogen synthase kinase beta (GSK3β) is mainly regulated by its Ser9 phosphorylation. It has been believed for a long time that Ser9 phosphorylation regulates the functions of GSK3β through inhibition of its kinase activity. In this study, we have confirmed the interaction of Ser9-phosphorylated GSK3β with 14-3-3ζ by using GST pull-down assays. We show that 14-3-3ζ enhances Ser9 phosphorylation of GSK3β by PKC. Surprisingly, using a NF-κB luciferase reporter system, we find that Ser9-phosphorylation of GSK3β promoted by 14-3-3ζ is critical for the activation of NF-κB pathway, which may thwart the pro-apoptotic activity of GSK3β. Inhibition of either NF-κB or GSK3β significantly abolishes the anti-apoptotic effect of 14-3-3ζ and Ser9-phosphorylated GSK3β, suggesting that Ser9-phosphorylated GSK3β actively antagonizes cell apoptosis in a NF-κB dependent manner.

Aberrant glycogen synthase kinase 3β is involved in pancreatic cancer cell invasion and resistance to therapy

Background and Purpose

The major obstacles to treatment of pancreatic cancer are the highly invasive capacity and resistance to chemo- and radiotherapy. Glycogen synthase kinase 3β (GSK3β) regulates multiple cellular pathways and is implicated in various diseases including cancer. Here we investigate a pathological role for GSK3β in the invasive and treatment resistant phenotype of pancreatic cancer.

Methods

Pancreatic cancer cells were examined for GSK3β expression, phosphorylation and activity using Western blotting and in vitro kinase assay. The effects of GSK3β inhibition on cancer cell survival, proliferation, invasive ability and susceptibility to gemcitabine and radiation were examined following treatment with a pharmacological inhibitor or by RNA interference. Effects of GSK3β inhibition on cancer cell xenografts were also examined.

Results

Pancreatic cancer cells showed higher expression and activity of GSK3β than non-neoplastic cells, which were associated with changes in its differential phosphorylation. Inhibition of GSK3β significantly reduced the proliferation and survival of cancer cells, sensitized them to gemcitabine and ionizing radiation, and attenuated their migration and invasion. These effects were associated with decreases in cyclin D1 expression and Rb phosphorylation. Inhibition of GSK3β also altered the subcellular localization of Rac1 and F-actin and the cellular microarchitecture, including lamellipodia. Coincident with these changes were the reduced secretion of matrix metalloproteinase-2 (MMP-2) and decreased phosphorylation of focal adhesion kinase (FAK). The effects of GSK3β inhibition on tumor invasion, susceptibility to gemcitabine, MMP-2 expression and FAK phosphorylation were observed in tumor xenografts.

Conclusion

The targeting of GSK3β represents an effective strategy to overcome the dual challenges of invasiveness and treatment resistance in pancreatic cancer.

Glycogen synthase kinase 3β inhibition sensitizes pancreatic cancer cells to gemcitabine

BACKGROUND

Pancreatic cancer is obstinate and resistant to gemcitabine, a standard chemotherapeutic agent for the disease. We previously showed a therapeutic effect of glycogen synthase kinase-3β (GSK3β) inhibition against gastrointestinal cancer and glioblastoma. Here, we investigated the effect of GSK3β inhibition on pancreatic cancer cell sensitivity to gemcitabine and the underlying molecular mechanism.

METHODS

Expression, phosphorylation, and activity of GSK3β in pancreatic cancer cells (PANC-1) were examined by Western immunoblotting and in vitro kinase assay. The combined effect of gemcitabine and a GSK3β inhibitor (AR-A014418) against PANC-1 cells was examined by isobologram and PANC-1 xenografts in mice. Changes in gene expression in PANC-1 cells following GSK3β inhibition were studied by cDNA microarray and reverse transcription (RT)-PCR.

RESULTS

PANC-1 cells showed increased GSK3β expression, phosphorylation at tyrosine 216 (active form), and activity compared with non-neoplastic HEK293 cells. Administration of AR-A014418 at pharmacological doses attenuated proliferation of PANC-1 cells and xenografts, and significantly sensitized them to gemcitabine. Isobologram analysis determined that the combined effect was synergistic. DNA microarray analysis detected GSK3β inhibition-associated changes in gene expression in gemcitabine-treated PANC-1 cells. Among these changes, RT-PCR and Western blotting showed that expression of tumor protein 53-induced nuclear protein 1, a gene regulating cell death and DNA repair, was increased by gemcitabine treatment and substantially decreased by GSK3β inhibition.

CONCLUSIONS

The results indicate that GSK3β inhibition sensitizes pancreatic cancer cells to gemcitabine with altered expression of genes involved in DNA repair. This study provides insight into the molecular mechanism of gemcitabine resistance and thus a new strategy for pancreatic cancer chemotherapy.

Inhibition of glycogen synthase kinase-3 activity triggers an apoptotic response in pancreatic cancer cells through JNK-dependent mechanisms

Recent evidences suggest that the activity of glycogen synthase kinase-3 (GSK3) contributes to the tumorigenic potential of pancreatic cancer cells through modulation of cell proliferation and survival. However, further investigations are needed to identify GSK3-dependent mechanisms involved in the control of pancreatic cancer cell proliferation and survival. This study was undertaken to provide further support for a role of GSK3 in pancreatic cancer cell growth as well as to identify new cellular and molecular mechanisms involved. Herein, we demonstrate that prolonged inhibition of GSK3 triggers an apoptotic response only in human pancreatic cancer cells but not in human non-transformed pancreatic epithelial cells. We show that prolonged inhibition of GSK3 activity increases Bim messenger RNA and protein expressions. Moreover, we provide evidence that activation of the c-jun N-terminal kinase (JNK) pathway is necessary for the GSK3 inhibition-mediated increase in Bim expression and apoptotic response. Finally, we demonstrate that concomitant inhibition of GSK3 potentiates the death ligand-induced apoptotic response in pancreatic cancer cells but not in non-transformed pancreatic epithelial cells and that this effect also requires JNK activity. Considering that different approaches leading to stimulation of death receptor signaling are under clinical trials for treatment of unresectable or metastatic pancreatic cancer, inhibition of GSK3 could represent an attractive new avenue to improve their effectiveness.

Emerging roles of glycogen synthase kinase 3 in the treatment of brain tumors

The constitutively active protein glycogen synthase kinase 3 (GSK3), a serine/threonine kinase, acts paradoxically as a tumor suppressor in some cancers while potentiates growth in others. Deciphering what governs its actions is vital for understanding many pathological conditions, including brain cancer. What are seemingly disparate roles of GSK3 stems from the complex regulation of many cellular functions by GSK3. This review focuses on the regulation of GSK3, its role in survival, apoptosis and DNA damage, and finally its potential therapeutic impact in brain cancer. A thorough understanding of this versatile protein is critical for improving the outcome of various diseases, especially cancer.

GSK-3β: a key regulator in the initiation and progression of colorectal cancer

The Wnt/β-catenin signal transduction pathway plays an important role in the initiation and progression of colorectal cancer. Glycogen synthase kinase-3beta (GSK-3β) is a multi-functional serine/threonine kinase that plays an important regulatory role in the Wnt/β-catenin signal transduction pathway. However, there are two opposing views on the role of GSK-3β in the pathogenesis of colorectal cancer. On one hand, some researchers believe that inhibition of GSK-3β can promote tumor initiation and progression, and tumor growth will be inhibited if GSK-3β is activated. On the other hand, some other researchers hold the view that inhibition of GSK-3β can prevent tumor development, and the initiation and progression of tumors will be promoted if GSK-3β is activated. In this paper, we will review the roles that the Wnt/β-catenin signal transduction pathway and GSK-3β play in the pathogenesis of colorectal cancer.

Constitutive activation of glycogen synthase kinase-3beta correlates with better prognosis and cyclin-dependent kinase inhibitors in human gastric cancer

Background

Aberrant regulation of glycogen synthase kinase-3β (GSK-3β) has been implicated in several human cancers; however, it has not been reported in the gastric cancer tissues to date. The present study was performed to determine the expression status of active form of GSK-3β phosphorylated at Tyr²¹⁶ (pGSK-3β) and its relationship with other tumor-associated proteins in human gastric cancers.

Methods

Immunohistochemistry was performed on tissue array slides containing 281 human gastric carcinoma specimens. In addition, gastric cancer cells were cultured and treated with a GSK-3β inhibitor lithium chloride (LiCl) for immunoblot analysis.

Results

We found that pGSK-3β was expressed in 129 (46%) of 281 cases examined, and was higher in the early-stages of pathologic tumor-node-metastasis (P < 0.001). The expression of pGSK-3β inversely correlated with lymphatic invasion (P < 0.001) and lymph node metastasis (P < 0.001) and correlated with a longer patient survival (P < 0.001). In addition, pGSK-3β expression positively correlated with that of p16, p21, p27, p53, APC, PTEN, MGMT, SMAD4, or KAI1 (P < 0.05), but not with that of cyclin D1. This was confirmed by immunoblot analysis using SNU-668 gastric cancer cells treated with LiCl.

Conclusions

GSK-3β activation was frequently observed in early-stage gastric carcinoma and was significantly correlated with better prognosis. Thus, these findings suggest that GSK-3β activation is a useful prognostic marker for the early-stage gastric cancer.

Glycogen synthase kinase 3 beta: can it be a target for oral cancer

Despite progress in treatment approaches for oral cancer, there has been only modest improvement in patient outcomes in the past three decades. The frequent treatment failure is due to the failure to control tumor recurrence and metastasis. These failures suggest that new targets should be identified to reverse oral epithelial dysplastic lesions. Recent developments suggest an active role of glycogen synthase kinase 3 beta (GSK3 β) in various human cancers either as a tumor suppressor or as a tumor promoter. GSK3β is a Ser/Thr protein kinase, and there is emerging evidence that it is a tumor suppressor in oral cancer. The evidence suggests a link between key players in oral cancer that control transcription, accelerated cell cycle progression, activation of invasion/metastasis and anti-apoptosis, and regulation of these factors by GSK3β. Moreover, the major upstream kinases of GSK3β and their oncogenic activation by several etiological agents of oral cancer support this hypothesis. In spite of all this evidence, a detailed analysis of the role of GSK3β in oral cancer and of its therapeutic potential has yet to be conducted by the scientific community. The focus of this review is to discuss the multitude of roles of GSK3β, its possible role in controlling different oncogenic events and how it can be targeted in oral cancer.

Deregulated GSK3{beta} sustains gastrointestinal cancer cells survival by modulating human telomerase reverse transcriptase and telomerase

PURPOSE

Glycogen synthase kinase-3beta (GSK3beta) regulates multiple cell signaling pathways and has been implicated in glucose intolerance, neurodegenerative disorders, and inflammation. We investigated the expression, activity, and putative pathologic role of GSK3beta in gastrointestinal, pancreatic, and liver cancers.

EXPERIMENTAL DESIGN

Colon, stomach, pancreatic, and liver cancer cell lines; nonneoplastic HEK293 cells; and matched pairs of normal and tumor tissues of stomach and colon cancer patients were examined for GSK3beta expression and its phosphorylation at serine 9 (inactive form) and tyrosine 216 (active form) by Western immunoblotting and for GSK3beta activity by in vitro kinase assay. The effects of small-molecule GSK3beta inhibitors and of RNA interference on cell survival, proliferation, and apoptosis were examined in vitro and on human colon cancer cell xenografts in athymic mice. The effects of GSK3beta inhibition on human telomerase reverse transcriptase (hTERT) expression and telomerase activity were compared between colon cancer and HEK293 cells.

RESULTS

Cancer cell lines and most cancer tissues showed increased GSK3beta expression and increased tyrosine 216 phosphorylation and activity but decreased serine 9 phosphorylation compared with HEK293 cells and nonneoplastic tissues. Inhibition of GSK3beta resulted in attenuated cell survival and proliferation and increased apoptosis in most cancer cell lines and in HT-29 xenografts in rodents but not in HEK293 cells. GSK3beta inhibition in colon cancer cells was associated with decreased hTERT expression and telomerase activity.

CONCLUSION

The results indicate that deregulated GSK3beta sustains gastrointestinal cancer cells survival through modulation of hTERT and telomerase.

Potential therapeutic effect of glycogen synthase kinase 3beta inhibition against human glioblastoma

PURPOSE

Glioblastoma represents the malignant brain tumor that is most refractory to treatment and in which the identification of molecular target(s) is urgently required. We investigated the expression, activity, and putative pathologic role of glycogen synthase kinase 3beta (GSK3beta), an emerging therapeutic target for neurodegenerative diseases, in human glioblastoma.

EXPERIMENTAL DESIGN

The active fraction of GSK3beta that is phosphorylated at the tyrosine 216 residue (pGSK3betaY216) was identified in glioblastoma cell lines. GSK3beta activity for phosphorylating its substrate was detected in these cells by nonradioisotopic in vitro kinase assay.

RESULTS

Higher expression levels of GSK3beta and pGSK3betaY216 were frequently detected in glioblastomas compared with nonneoplastic brain tissues. Inhibition of GSK3beta activity by escalating doses of a small-molecule inhibitor (AR-A014418) or inhibition of its expression by RNA interference induced the apoptosis and attenuated the survival and proliferation of glioblastoma cells in vitro. Inhibition of GSK3beta was associated with increased expression of p53 and p21 in glioblastoma cells with wild-type p53 and with decreased Rb phosphorylation and expression of cyclin-dependent kinase 6 in all glioblastoma cell lines. Administration of AR-A014418 at a low dose significantly sensitized glioblastoma cells to temozolomide and 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea, chemotherapeutic agents used in the clinical setting, as well as to ionizing radiation.

CONCLUSION

These results indicate that GSK3beta exerts a pathologic role by promoting the survival and proliferation of glioblastoma cells and by protecting them from apoptosis via the inactivation of p53- and/or Rb-mediated pathways. Consequently, we propose that GSK3beta provides a potential therapeutic target in glioblastoma.

From a natural product lead to the identification of potent and selective benzofuran-3-yl-(indol-3-yl)maleimides as glycogen synthase kinase 3beta inhibitors that suppress proliferation and survival of pancreatic cancer cells

Recent studies have demonstrated that glycogen synthase kinase 3beta (GSK-3beta) is overexpressed in human colon and pancreatic carcinomas, contributing to cancer cell proliferation and survival. Here, we report the design, synthesis, and biological evaluation of benzofuran-3-yl-(indol-3-yl)maleimides, potent GSK-3beta inhibitors. Some of these compounds show picomolar inhibitory activity toward GSK-3beta and an enhanced selectivity against cyclin-dependent kinase 2 (CDK-2). Selected GSK-3beta inhibitors were tested in the pancreatic cancer cell lines MiaPaCa-2, BXPC-3, and HupT3. We determined that some of these compounds, namely compounds 5, 6, 11, 20, and 26, demonstrate antiproliferative activity against some or all of the pancreatic cancer cells at low micromolar to nanomolar concentrations. We found that the treatment of pancreatic cancer cells with GSK-3beta inhibitors 5 and 26 resulted in suppression of GSK-3beta activity and a distinct decrease of the X-linked inhibitor of apoptosis (XIAP) expression, leading to significant apoptosis. The present data suggest a possible role for GSK-3beta inhibitors in cancer therapy, in addition to their more prominent applications in CNS disorders.