GSK3ß phosphorylation of the KLF6 tumor suppressor promotes its transactivation of p21.

KLF6, a ubiquitously expressed Krüppel-like transcription factor, is frequently inactivated in human cancer and has significant roles in cellular proliferation, apoptosis, differentiation and development. A key mechanism of KLF6-mediated growth suppression is through p53-independent transactivation of p21. Several cancer-derived KLF6 mutants lead to the loss of p21-mediated growth suppression through an unknown mechanism. Because several colorectal cancer and hepatocellular carcinoma-derived KLF6 mutations affect a glycogen synthase kinase 3ß (GSK3ß) phosphorylation consensus site, we investigated the role of GSK3ß in the regulation of KLF6 function. Based on transient transfection, GSK3ß augments the transactivation of a p21 promoter luciferase by KLF6. Reciprocal co-immunoprecipitation of hemagglutinin (HA)-GSK3ß and Flag-KLF6 validated the interaction between these two proteins. KLF6 phosphorylation is augmented in the presence of GSK3ß based on in vitro and in vivo (32)P incorporation assays. Site-directed mutagenesis of the candidate phosphorylation sites to alanines ('KLF6-4A' phosphomutant) eliminated a higher molecular weight phosphorylated isoform of KLF6 based on western blot. GSK3ß augmented the transactivation by wild-type KLF6, but not KLF6-4A, towards the p21 promoter, and increased p21 protein. Functionally, GSK3ß enhanced KLF6-mediated growth suppression, which was abrogated by the KLF6-4A phosphomutant. These data establish that GSK3ß directly phosphorylates KLF6, which augments its induction of p21 and resultant growth suppression. This interaction may account for the growth-promoting effects of cancer-derived KLF6 mutants that lack tumor suppressor activity.

ATP-mediated protein kinase B Akt/mammalian target of rapamycin mTOR/p70 ribosomal S6 protein p70S6 kinase signaling pathway activation promotes improvement of locomotor function after spinal cord injury in rats.

The protein kinase B (Akt)/mammalian target of rapamycin (mTOR)/p70 ribosomal S6 protein kinase (p70S6K) signaling pathway, as a central controller of cell growth, proliferation, survival, and differentiation in response to extracellular signals, growth factors, nutrient availability, energy status of the cell, and stress, has recently gained attention in neuroscience. The effects of this signaling pathway on repair of spinal cord injury (SCI), however, have not been well elucidated. ATP is increasingly recognized as an important regulator of signal transduction pathways, and plays important roles in functional recovery after nervous system injury. In the present study, we examined the ATP-induced changes of the Akt/mTOR/p70S6K signaling pathway in injured spinal cord of adult rats and potential therapeutic effects of this pathway on SCI-induced locomotor dysfunction. SCI was produced by extradural weight-drop using modified Allen's stall with damage energy of 50 g-cm force. The rats were divided into four groups: SCI plus ATP, SCI plus saline, SCI plus ATP and rapamycin, and sham-operated. Using immunostaining studies, Western blot analyses and real-time qualitative RT-PCR analyses, we demonstrated that the Akt/mTOR/p70S6K signaling pathway is present in the injured spinal cord and the expression of its components at the protein and mRNA levels is significantly elevated by exogenous administration of ATP following SCI. We observed the effectiveness of the activated Akt/mTOR/p70S6K signaling pathway in improving locomotor recovery, significantly increasing the expression of nestin, neuronal nuclei (NeuN), neuron specific enolase (NSE), and neurofilament 200 (NF200), and relatively inhibiting excessive reactive astrogliosis after SCI in a rapamycin-sensitive manner. We concluded that ATP injection produced a significant activation of the Akt/mTOR/p70S6K signaling pathway in the injured spinal cord and that enhancement of rapamycin-sensitive signaling produces beneficial effects on SCI-induced motor function defects and repair potential. We suggest that modulation of this protein kinase signaling pathway activity should be considered as a potential therapeutic strategy for SCI.

Frequent mutations of NF2 and allelic loss from chromosome band 22q12 in malignant mesothelioma: evidence for a two-hit mechanism of NF2 inactivation.

We previously reported NF2 mutations in malignant mesothelioma (MM) cell lines and corresponding primary tumors. We have now generated polyclonal antibodies that specifically recognize the C-terminus of the NF2 protein. Western blot analysis was performed on 25 MM cell lines, 14 of which showed no NF2 expression. Single-strand conformation polymorphism and DNA sequence analyses revealed NF2 mutations in each of these 14 cell lines. To explore the mechanism of inactivation of NF2, loss of heterozygosity analysis was performed with two microsatellite markers located in the vicinity of the NF2 locus in chromosome band 22q12. Eighteen of the 25 cell lines (72%) showed losses at one or both loci tested. All cases exhibiting mutation and/or aberrant expression of NF2 showed allelic losses, suggesting that inactivation of NF2 in MM occurs via a two-hit mechanism.

Combined chromosome microdissection and comparative genomic hybridization detect multiple sites of amplification DNA in a human lung carcinoma cell line.

Chromosome microdissection-fluorescence in situ hybridization and comparative genomic hybridization (CGH) were performed in parallel to identify the native location of amplified DNA in a human non-small cell lung cancer (NSCLC) cell line exhibiting a homogeneously staining region (hsr) and double minutes (dmin). The native locations of microdissected DNA from the hsr and dmin were 7p12-13 and 8q24, respectively. Southern analysis revealed coamplification of EGFR (7p12) and MYC (8q24). CGH detected amplification of DNA not only from 7p12-13 and 8q24, but also from 9p24 and 10q22.