14-3-3γ Prevents Centrosome Amplification and Neoplastic Progression.

More than 80% of malignant tumors show centrosome amplification and clustering. Centrosome amplification results from aberrations in the centrosome duplication cycle, which is strictly coordinated with DNA-replication-cycle. However, the relationship between cell-cycle regulators and centrosome duplicating factors is not well understood.

14-3-3γ-Mediated transport of plakoglobin to the cell border is required for the initiation of desmosome assembly in vitro and in vivo.

The regulation of cell-cell adhesion is important for the processes of tissue formation and morphogenesis. Here, we report that loss of 14-3-3γ leads to a decrease in cell-cell adhesion and a defect in the transport of plakoglobin and other desmosomal proteins to the cell border in HCT116 cells and cells of the mouse testis. 14-3-3γ binds to plakoglobin in a PKCμ-dependent fashion, resulting in microtubule-dependent transport of plakoglobin to cell borders.

Inhibition of T-type calcium channels disrupts Akt signaling and promotes apoptosis in glioblastoma cells.

Glioblastoma multiforme (GBM) are brain tumors that are exceptionally resistant to both radio- and chemotherapy regimens and novel approaches to treatment are needed. T-type calcium channels are one type of low voltage-gated channel (LVCC) involved in embryonic cell proliferation and differentiation; however they are often over-expressed in tumors, including GBM. In this study, we found that inhibition of T-type Ca(2+) channels in GBM cells significantly reduced their survival and resistance to therapy.

PP6 regulatory subunit R1 is bidentate anchor for targeting protein phosphatase-6 to DNA-dependent protein kinase.

DNA-dependent protein kinase (DNA-PK) becomes activated in response to DNA double strand breaks, initiating repair by the non-homologous end joining pathway. DNA·PK complexes with the regulatory subunit SAPSR1 (R1) of protein phosphatase-6 (PP6). Knockdown of either R1 or PP6c prevents DNA-PK activation in response to ionizing radiation-induced DNA damage and radiosensitizes glioblastoma cells.

A novel pocket in 14-3-3epsilon is required to mediate specific complex formation with cdc25C and to inhibit cell cycle progression upon activation of checkpoint pathways.

Mitotic progression requires the activity of the dual specificity phosphatase, cdc25C. Cdc25C function is inhibited by complex formation with two 14-3-3 isoforms, 14-3-3epsilon and 14-3-3gamma. To understand the molecular basis of specific complex formation between 14-3-3 proteins and their ligands, chimeric 14-3-3 proteins were tested for their ability to form a complex with cdc25C in vivo.

14-3-3 Gamma is required to enforce both the incomplete S phase and G2 DNA damage checkpoints.

Checkpoint pathways inhibit mitotic progression by inducing the phosphorylation of serine 216 in cdc25C resulting in the generation of a 14-3-3 binding site on cdc25C. Two 14-3-3 isoforms, 14-3-3epsilon and 14-3-3gamma form a complex with cdc25C and inhibit cdc25C function. To examine the contribution of 14-3-3gamma to checkpoint regulation, the expression of 14-3-3gamma was inhibited in HCT116 cells using vector based RNA interference.

Plakophilin3 downregulation leads to a decrease in cell adhesion and promotes metastasis.

Plakophilin3 is a desmosomal plaque protein whose levels are reduced in poorly differentiated tumors of the oropharyngeal cavity and in invasive colon carcinomas. To test the hypothesis that plakophilin3 loss stimulates neoplastic progression, plakophilin3 expression was inhibited by DNA vector driven RNA interference in 3 epithelial cell lines, HCT116, HaCaT and fetal buccal mucosa. The plakophilin3-knockdown clones showed a decrease in cell-cell adhesion as assessed in a hanging drop assay, which was accompanied by an increase in cell migration.