Purpose: Glycogen synthase kinase-3β (GSK3β) 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 GSK3β 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 GSK3β expression and its phosphorylation at serine 9 (inactive form) and tyrosine 216 (active form) by Western immunoblotting and for GSK3β activity by in vitro kinase assay. The effects of small-molecule GSK3β 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 GSK3β 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 GSK3β expression and increased tyrosine 216 phosphorylation and activity but decreased serine 9 phosphorylation compared with HEK293 cells and nonneoplastic tissues. Inhibition of GSK3β 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. GSK3β inhibition in colon cancer cells was associated with decreased hTERT expression and telomerase activity. Conclusion:The results indicate that deregulated GSK3β sustains gastrointestinal cancer cells survival through modulation of hTERT and telomerase. (Clin Cancer Res 2009;15(22):6810-9)

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 3h (GSK3h), an emerging therapeutic target for neurodegenerative diseases, in human glioblastoma. Experimental Design: The active fraction of GSK3h that is phosphorylated at the tyrosine 216 residue ( pGSK3h Y216 ) was identified in glioblastoma cell lines. GSK3h activity for phosphorylating its substrate was detected in these cells by nonradioisotopic in vitro kinase assay. Results: Higher expression levels of GSK3h and pGSK3h Y216 were frequently detected in glioblastomas compared with nonneoplastic brain tissues. Inhibition of GSK3h 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 GSK3h 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 GSK3h 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 GSK3h provides a potential therapeutic target in glioblastoma.