Glioblastoma multiforme is the most aggressive form of primary brain tumor and remains largely incurable, in large part, due to its highly invasive nature. The phosphoinositide (PI) 3-kinase pathway is often constitutively active in these tumors due to activating mutations in the epidermal growth factor receptor, or deletion/loss of function of the tumor suppressor PTEN. Protein kinase C type iota (PKCiota), a member of the atypical protein kinase C family, is activated by the PI 3-kinase pathway and is an important downstream mediator. Here, we have assessed the role of PKCiota in glioblastoma cell invasion. Depletion of PKCiota with RNA interference caused an increase in actin stress fibers and a decrease in cell motility and invasion. Gene expression microarray analysis of U87MG cells showed that PKCiota repressed expression of mRNA for RhoB, which has previously been shown to have a role in actin stress fiber formation. Western blot analysis showed that both PKCiota depletion and pharmacological inhibition of PKCiota caused an increase in the protein levels of RhoB, as did inhibition of PI 3-kinase. Expression of RhoB from a constitutive promoter caused changes in actin stress fibers and cell invasion that were similar to those seen with PKCiota depletion. These data show that PKCiota, activated as a consequence of aberrant upstream PI 3-kinase signaling, mediates glioblastoma cell motility and invasion, and that repression of RhoB is key downstream event in PKCiota signaling leading to enhanced cell motility. In addition, constitutive expression of RhoB repressed PKCiota activity, as assessed by its phosphorylation status on Thr555. PKCiota and RhoB are, therefore, mutually antagonistic, potentially creating a sensitive switch between invasive and non-invasive phenotypes.

Genetic aberrations, such as gene amplification, deletions, and loss of heterozygosity, are hallmarks of cancer and are thought to be major contributors to the neoplastic process. Established cancer cell lines have been the primary in vitro and in vivo models for cancer for more than 2 decades; however, few such cell lines have been extensively characterized at the genomic level. Here, we present a high-resolution genome-wide chromosomal alteration and gene expression analyses of five of the most commonly used glioma cell lines and compare the findings with those observed in 83 primary human gliomas. Although genomic alterations known to occur in primary tumors were identified in the cell lines, we also observed several novel recurrent aberrations in the glioma cell lines that are not frequently represented in primary tumors. Additionally, a global gene expression cluster distinct from primary tumors was identified in the glioma cell lines. Our results indicate that established cell lines are generally a poor representation of primary tumor biology, presenting a host of genomic and gene expression changes not observed in primary tissues, although some discrete features of glioma biology were conserved in the established cell lines. Refined maps of genetic alterations and transcriptional divergence from the original tumor type, such as the one presented here, may help serve as a guideline for a more biologically rational and clinically relevant selection of the most appropriate glioma model for a given experiment. (Mol Cancer Res 2008;6(1):21–30)

Large-Scale Mutagenesis in p19ARF- and p53-Deficient Mice Identifies Cancer Genes and Their Collaborative Networks