OBJECTIVETo observe the localization of p53(301-393)(residues 301-393) in p53 positive/negative cells and its effect on cell mitosis.

METHODSThe protein expression of p53-GFP and p53(301-393)-GFP was checked by immunoblotting after transfection. Immunofluorescence staining was performed to detect the localization of wide type and mutant in Hela cells (p53 positive) and H1299 cells (p53 negative). The cell morphology of H1299 cells transfected of p53(301-393)-GFP and the cells in mitotic phase were observed. Cell cycle was analyzed by flow cytometry and p53 protein level in HeLa cells was evaluated by Western blot after transfection of p53-GFP and p53(301-393)-GFP.

RESULTSThe protein expression of p53-GFP and p53(301-393)-GFP was verified, p53-GFP was about 90 kMr and p53(301-393)-GFP about 40 kMr. Immunofluorescence microscopy demonstrated that both proteins were diffusely located in the nuclei of HeLa cells and H1299 cells. But different from the p53-GFP, the p53(301-393)-GFP was distributed in the nucleolus of HeLa cells. After transfection of the two plasmids, mitosis was inhibited in H1299 cells and some cells underwent apoptosis. G2/M progression of HeLa cells could be blocked by transfection of p53(301-393)-GFP, but endogenous p53 protein level was not changed.

CONCLUSIONp53(301-393)has a different localization in the p53 positive and p53 negative cells and could inhibit mitosis and cause the cell cycle arrest in G2/M.

Green Fluorescent Proteins ; genetics ; metabolism ; HeLa Cells ; Humans ; Immunoblotting ; Microscopy, Fluorescence ; Mitosis ; genetics ; physiology ; Mutant Proteins ; metabolism ; physiology ; Mutation ; Recombinant Fusion Proteins ; genetics ; metabolism ; Transfection ; Tumor Suppressor Protein p53 ; genetics ; metabolism ; physiology

The Met tyrosine kinase receptor is a widely expressed molecule, which mediates pleiotropic cellular responses following activation by its ligand, hepatocyte growth factor/scatter factor (HGF/SF). Previously, one of the authors identified an alternatively spliced form of Met (Met-SM) that lacked a single exon of a 47-amino-acid segment in the juxtamembrane domain. Here we report that Met-SM is a potent transforming gene in NIH3T3 mouse fibroblast cells. Met-SM-transfected NIH3T3 cells show stronger foci-forming activity than wild type-Met-transfected ones. In addition, Met-SM-transfected NIH3T3 cells form colonies in soft agar and are tumorigenic in athymic nu/nu mice. Furthermore, HGF/SF significantly increases the focus-forming activity of Met-SM comparing to wild type Met. The amount of protein and of tyrosine kinase activity of Met-SM accumulates to a high level following HGF/SF treatment. The accumulation of Met-SM correlated well with its delayed ubiquitination and increased stability. These results are consistent with the important role of the juxtamembrane domain in protein stability of Met receptor and suggest that the alternatively-spliced form may contribute to the development and progression of human cancer.
Proto-Oncogene Proteins c-met/*metabolism/*physiology ; Protein Isoforms/metabolism/physiology ; NIH 3T3 Cells ; Mutant Proteins/metabolism/physiology ; Mice, Nude ; Mice ; Hepatocyte Growth Factor/pharmacology ; Female ; Down-Regulation ; Carcinogens/*metabolism ; Carcinogenicity Tests ; Animals ; *Alternative Splicing

I kappa B kinase beta (IKK beta) subunit of IKK complex is essential for the activation of NF-kappa B in response to various proinflammatory signals. Cys-179 in the activation loop of IKK beta is known to be the target site for IKK inhibitors such as cyclopentenone prostaglandins, arsenite, and antirheumatic gold compounds. Here we show that a mutant IKK beta in which Cys-179 is substituted with alanine had decreased activity when it was expressed in HEK-293 cells, and TNF stimulation did not restore the activity. Phosphorylation of activation loop serines (Ser-177 and Ser-181) which is required for IKK beta activation was reduced in the IKK beta (C179A) mutant. The activity of IKK beta (C179A) was partially recovered when its phosphorylation was enforced by coexpression with mitogen-activated protein kinase kinase kinases (MAPKKK) such as NF-kappa B inducing kinase (NIK) and MAPK/extracellular signal-regulated kinase kinase kinase 1(MEKK1) or when the serine residues were replaced with phospho-mimetic glutamate. The IKK beta (C179A) mutant was normal in dimer formation, while its activity abnormally responded to the change in the concentration of substrate ATP in reaction mixture. Our results suggest that Cys-179 of IKK beta plays a critical role in enzyme activation by promoting phosphorylation of activation-loop serines and interaction with ATP.
Transfection ; Serine/*metabolism ; Protein Binding ; Phosphorylation ; Mutant Proteins/chemistry ; MAP Kinase Kinase Kinases/metabolism ; I-kappa B Kinase/*chemistry ; Humans ; Hela Cells ; Enzyme Activation/*physiology ; Cysteine/*physiology ; Cells, Cultured ; Catalytic Domain ; Amino Acid Substitution/physiology ; Adenosine Triphosphate/metabolism

Sequential activation of the JNK pathway components, including Rac1/Cdc42, MLKs (mixed-lineage kinases), MKK4/7 and JNKs, plays a required role in many cell death paradigms. Those components are organized by a scaffold protein, POSH (Plenty of SH3's), to ensure the effective activation of the JNK pathway and cell death upon apoptotic stimuli. We have shown recently that the expression of POSH and MLK family proteins are regulated through protein stability. By generating a variety of mutants, we provide evidence here that the Nterminal half of POSH is accountable for its stability regulation and its over-expression-induced cell death. In addition, POSH's ability to induce apoptosis is correlated with its stability as well as its MLK binding ability. MLK family's stability, like that of POSH, requires activation of JNKs. However, we were surprised to find out that the widely used dominant negative (d/n) form of c-Jun could down-regulate MLK's stability, indicating that peptide from d/n c-Jun can be potentially developed into a therapeutical drug.
Adaptor Proteins, Signal Transducing ; genetics ; metabolism ; Animals ; Apoptosis ; physiology ; Base Sequence ; Cell Line ; DNA Primers ; genetics ; Humans ; JNK Mitogen-Activated Protein Kinases ; antagonists & inhibitors ; genetics ; metabolism ; MAP Kinase Kinase Kinases ; genetics ; metabolism ; Mutant Proteins ; genetics ; metabolism ; Nuclear Proteins ; genetics ; metabolism ; PC12 Cells ; Peptide Fragments ; genetics ; metabolism ; Protein Stability ; Rats ; Recombinant Proteins ; genetics ; metabolism ; Signal Transduction ; physiology ; Transfection ; Ubiquitin-Protein Ligases ; genetics ; metabolism

CD98, a disulfide-linked 125-kDa heterodimeric type II transmembrane glycoprotein, regulates beta 1 integrin- mediated cell adhesion. However, the molecular mechanisms underlying CD98-mediated activation of beta 1 integrin are presently unclear. In this study, the effects of CD98 signaling on the expression and clustering of beta 1 integrin were investigated. Activation of CD98 augmented surface expression of beta 1 integrin on MCF-7 cells. Cross-linking CD98 induced clustering of beta 1 integrins. Inhibition of phosphorylation of focal adhesion kimase (FAK) by PP2, an inhibitor of Src family kinase, reduced cell-extracellular matrix adhesion, but not surface expression and clustering of beta1 integrin on MCF-7 cells. This result was confirmed by over-expression of dominant negative forms of FAK. In addition, phalloidin or cytochalasin D inhibited CD98-mediated induction of cell-ECM adhesion, but not surface expression and clustering of b1 integrins. The inhibitory effects of PP2, cytochalasin D or phalloidin on CD98-stimulated cell adhesion were diminished by pretreatment of cells with Mn2+, which is shown to induce conformational change of integrins. These results provide the first evidence that CD98 activation increases not only beta1 integrin affinity but also its surface expression and clustering and the latter is independent of FAK/Src and cytoskeleton.
Antigens, CD29/*biosynthesis/genetics ; Antigens, CD98/agonists/*metabolism ; Cell Line, Tumor ; Cytochalasin D/pharmacology ; Cytoskeleton/drug effects/enzymology ; Focal Adhesion Kinase 2/genetics/*metabolism ; Focal Adhesions/drug effects/enzymology ; Humans ; Microscopy, Confocal ; Multiprotein Complexes/*biosynthesis/genetics ; Mutant Proteins/genetics/metabolism ; Phalloidine/pharmacology ; Phosphorylation/drug effects ; Protein Binding ; Pyrimidines/pharmacology ; Signal Transduction/physiology ; Transfection

BACKGROUNDStudies indicated that Mer might be the main contributor to the specific internalization of photoreceptor outer segments (POS) in retinal pigment epithelium (RPE). It is very important to understand the mechanism of POS phagocytosis under the pathway of Mer and its ligands. The objective of this study was to identify changes in gene expression profiles caused by Mer gene knockout (Mer-/-) during phagocytosis of POS in RPE.

METHODSRPE from both Mer-/- and wild-type (WT) mice were isolated and cultured to the 3rd passage. POS were subjected to culture medium with 20 nmol/L Gas6 and protein S to activate specific mer-mediated phagocytosis. RPE phagocytosis was evaluated by phagocytosis assays and differential gene expression identified by microarray at 3 and 12 hours; the 0-hour time point served as the control. Three independent samples for each Mer-/- or WT RPE were subjected to the same protocol of microarray. Five genes were confirmed by real-time quantitative PCR (QPCR).

RESULTSThe Mer-/- RPE had less internalized POS than WT RPE after both 3 and 12 hours in phagocytosis assay. Compared to WT RPE and the 0-hour control, 38 and 45 different known genes were increased and 68 and 59 known genes were decreased in Mer-/- RPE after 3 and 12 hours, respectively. Abnormal POS phagocytosis in Mer-/- RPE was associated with significant gene expression changes in, for example, signal transduction (WNT, MAPK), phagocytosis (Vav3, Hsd11b1), cytoskeleton components (Myo7a), and metabolism, in a time-specific manner. QPCR results showed Vav3, Hsd11b1, Myo7a, Rtn2 and Itga8 in those independent samples were consistent with microarray.

CONCLUSIONGene expression profiles modulated in a time-specific manner in Mer-/- RPE indicate a possible internalization mechanism for abnormal POS phagocytosis, which gives insight into the mechanism of retinitis pigmentosa caused by the mutation of MerTK in humans.

Animals ; Gene Expression Profiling ; Mice ; Mice, Knockout ; Mice, Mutant Strains ; Oligonucleotide Array Sequence Analysis ; Phagocytosis ; genetics ; physiology ; Proto-Oncogene Proteins ; genetics ; metabolism ; Receptor Protein-Tyrosine Kinases ; genetics ; metabolism ; Retinal Pigment Epithelium ; cytology ; Reverse Transcriptase Polymerase Chain Reaction ; Tissue Culture Techniques ; c-Mer Tyrosine Kinase

Mutations in LR RK2 (Leucine rich repeat kinase 2) are a major cause of Parkinson's disease (PD). We and others reported recently that expression of the pathogenic gainof-function mutant form of LRRK2, LRRK2 G2019S, induces mitochondrial fission in neurons through DLP1. Here we provide evidence that expression of LRRK2 G2019S stimulates mitochondria loss or mitophagy. We have characterized several LRRK2 interacting proteins and found that LRRK2 interacts with ULK1 which plays an essential role in autophagy. Knockdown of either ULK1 or DLP1 expression with shRNAs suppresses LRRK2 G2019S expression-induced mitochondrial clearance, suggesting that LRRK2 G2019S expression induces mitochondrial fission through DLP1 followed by mitophagy via an ULK1 dependent pathway. In addition to ULK1, we found that LRRK2 interacts with the endogenous MKK4/7, JIP3 and coordinates with them in the activation of JNK signaling. Interestingly, LRRK2 G2019S-induced loss of mitochondria can also be suppressed by 3 different JNK inhibitors, implying the involvement of the JNK pathway in the pathogenic mechanism of mutated LRRK2. Thus our findings may provide an insight into the complicated pathogenesis of PD as well as some clues to the development of novel therapeutic strategies.
Amino Acid Substitution ; Autophagosomes ; metabolism ; pathology ; Autophagy-Related Protein-1 Homolog ; chemistry ; genetics ; metabolism ; GTP Phosphohydrolases ; antagonists & inhibitors ; genetics ; metabolism ; Gene Knockdown Techniques ; HeLa Cells ; Humans ; Intracellular Signaling Peptides and Proteins ; chemistry ; genetics ; metabolism ; Leucine-Rich Repeat Serine-Threonine Protein Kinase-2 ; chemistry ; genetics ; metabolism ; MAP Kinase Signaling System ; Microtubule-Associated Proteins ; antagonists & inhibitors ; genetics ; metabolism ; Mitochondrial Degradation ; genetics ; physiology ; Mitochondrial Proteins ; antagonists & inhibitors ; genetics ; metabolism ; Mutant Proteins ; chemistry ; genetics ; metabolism ; Mutation ; Parkinson Disease ; genetics ; metabolism ; pathology ; Protein Interaction Domains and Motifs ; Recombinant Proteins ; chemistry ; genetics ; metabolism