Negative regulation of PKB/Akt-dependent cell survival by the tumor suppressor PTEN

PTEN is a tumor suppressor with sequence homology to protein tyrosine phosphatases and the cytoskeletal protein tensin. mPTEN-mutant mouse embryos display regions of increased proliferation. In contrast, mPTEN-deficient immortalized mouse embryonic fibroblasts exhibit decreased sensitivity to cell death in response to a number of apoptotic stimuli, accompanied by constitutively elevated activity and phosphorylation of protein kinase B/Akt, a crucial regulator of cell survival. Expression of exogenous PTEN in mutant cells restores both their sensitivity to agonist-induced apoptosis and normal pattern of PKB/Akt phosphorylation. Furthermore, PTEN negatively regulates intracellular levels of phosphatidylinositol (3,4,5) trisphosphate in cells and dephosphorylates it in vitro. Our results show that PTEN may exert its role as a tumor suppressor by negatively regulating the PI3'K/PKB/Akt signaling pathway.

Localization of brain electrical activity via linearly constrained minimum variance spatial filtering

A spatial filtering method for localizing sources of brain electrical activity from surface recordings is described and analyzed. The spatial filters are implemented as a weighted sum of the data recorded at different sites. The weights are chosen to minimize the filter output power subject to a linear constraint. The linear constraint forces the filter to pass brain electrical activity from a specified location, while the power minimization attenuates activity originating at other locations. The estimated output power as a function of location is normalized by the estimated noise power as a function of location to obtain a neural activity index map. Locations of source activity correspond to maxima in the neural activity index map. The method does not require any prior assumptions about the number of active sources of their geometry because it exploits the spatial covariance of the source electrical activity. This paper presents a development and analysis of the method and explores its sensitivity to deviations between actual and assumed data models. The effect on the algorithm of covariance matrix estimation, correlation between sources, and choice of reference is discussed. Simulated and measured data is used to illustrate the efficacy of the approach.

Function of PI3Kgamma in thymocyte development, T cell activation, and neutrophil migration

Phosphoinositide 3-kinases (PI3Ks) regulate fundamental cellular responses such as proliferation, apoptosis, cell motility, and adhesion. Viable gene-targeted mice lacking the p110 catalytic subunit of PI3Kgamma were generated. We show that PI3Kgamma controls thymocyte survival and activation of mature T cells but has no role in the development or function of B cells. PI3Kgamma-deficient neutrophils exhibited severe defects in migration and respiratory burst in response to heterotrimeric GTP-binding protein (G protein)-coupled receptor (GPCR) agonists and chemotactic agents. PI3Kgamma links GPCR stimulation to the formation of phosphatidylinositol 3,4,5-triphosphate and the activation of protein kinase B, ribosomal protein S6 kinase, and extracellular signal-regulated kinases 1 and 2. Thus, PI3Kgamma regulates thymocyte development, T cell activation, neutrophil migration, and the oxidative burst.

Genome evolution in the allotetraploid frog Xenopus laevis

To explore the origins and consequences of tetraploidy in the African clawed frog, we sequenced the Xenopus laevis genome and compared it to the related diploid X. tropicalis genome. We demonstrate the allotetraploid origin of X. laevis by partitioning its genome into two homeologous subgenomes, marked by distinct families of “fossil” transposable elements. Based on the activity of these elements and the age of hundreds of unitary pseudogenes, we estimate that the two diploid progenitor species diverged ~34 million years ago (Mya) and combined to form an allotetraploid ~17–18 Mya. 56% of all genes are retained in two homeologous copies. Protein function, gene expression, and the amount of flanking conserved sequence all correlate with retention rates. The subgenomes have evolved asymmetrically, with one chromosome set more often preserving the ancestral state and the other experiencing more gene loss, deletion, rearrangement, and reduced gene expression.

High cancer susceptibility and embryonic lethality associated with mutation of the PTEN tumor suppressor gene in mice

BACKGROUND

Germ-line and sporadic mutations in the tumor suppressor gene PTEN (also known as MMAC or TEP1), which encodes a dual-specificity phosphatase, cause a variety of cancers such as Cowden disease, glioblastoma, endometrial carcinoma and prostatic cancer. PTEN is widely expressed, and Cowden disease consistently affects various organ systems, suggesting that the PTEN protein must have an important, although as yet poorly understood, function in cellular physiology.

RESULTS

Homozygous mutant mice lacking exons 3-5 of the PTEN gene (mPTEN3-5) had severely expanded and abnormally patterned cephalic and caudal regions at day 8.5 of gestation. Embryonic death occurred by day 9.5 and was associated with defective chorio-allantoic development. Heterozygous mPTEN3-5 mice had an increased incidence of tumors, especially T-cell lymphomas; gamma-irradiation reduced the time lapse of tumor formation. DNA analysis of these tumors revealed the deletion of the mPTEN gene due to loss of heterozygosity of the wild-type allele. Tumors associated with loss of heterozygosity in mPTEN showed elevated phosphorylation of protein kinase B (PKB, also known as Akt kinase), thus providing a functional connection between mPTEN and a murine proto-oncogene (c-Akt) involved in the development of lymphomas.

CONCLUSIONS

The mPTEN gene is fundamental for embryonic development in mice, as mPTEN3-5 mutant embryos died by day 9.5 of gestation, with patterning defects in cephalic and caudal regions and defective placentation. Heterozygous mice developed lymphomas associated with loss of heterozygosity of the wild-type mPTEN allele, and tumor appearance was accelerated by gamma-irradiation. These lymphomas had high levels of activated Akt/PKB, the protein product of a murine proto-oncogene with anti-apoptotic function, associated with thymic lymphomas. This suggests that tumors associated with mPTEN loss of heterozygosity may arise as a consequence of an acquired survival advantage. We provide direct evidence of the role of mPTEN as a tumor suppressor gene in mice, and establish the mPTEN mutant mouse as an experimental model for investigating the role of PTEN in cancer progression.

Bmpr encodes a type I bone morphogenetic protein receptor that is essential for gastrulation during mouse embryogenesis

Bone morphogenetic proteins (BMPs) are secreted proteins that interact with cell-surface receptors and are believed to play a variety of important roles during vertebrate embryogenesis. Bmpr, also known as ALK-3 and Brk-1, encodes a type I transforming growth factor-beta (TGF-beta) family receptor for BMP-2 and BMP-4. Bmpr is expressed ubiquitously during early mouse embryogenesis and in most adult mouse tissues. To study the function of Bmpr during mammalian development, we generated Bmpr-mutant mice. After embryonic day 9.5 (E9.5), no homozygous mutants were recovered from heterozygote matings. Homozygous mutants with morphological defects were first detected at E7.0 and were smaller than normal. Morphological and molecular examination demonstrated that no mesoderm had formed in the mutant embryos. The growth characteristics of homozygous mutant blastocysts cultured in vitro were indistinguishable from those of controls; however, embryonic ectoderm (epiblast) cell proliferation was reduced in all homozygous mutants at E6.5 before morphological abnormalities had become prominent. Teratomas arising from E7.0 mutant embryos contained derivatives from all three germ layers but were smaller and gave rise to fewer mesodermal cell types, such as muscle and cartilage, than controls. These results suggest that signaling through this type I BMP-2/4 receptor is not necessary for preimplantation or for initial postimplantation development but may be essential for the inductive events that lead to the formation of mesoderm during gastrulation and later for the differentiation of a subset of mesodermal cell types.

The PAR-aPKC system: lessons in polarity

Ten years ago, par-1 and par-3 were cloned as two of the six par genes essential for the asymmetric division of the Caenorhabditis elegans zygote. PAR-1 is a protein kinase, whereas PAR-3 is a PDZ-domain-containing scaffold protein. Work over the past decade has shown that they are part of an evolutionarily conserved PAR-aPKC system involved in cell polarity in various biological contexts. Recent progress has illustrated the common principle that the PAR-aPKC system is the molecular machinery that converts initial polarity cues in the establishment of complementary membrane domains along the polarity axis. In most cases, this is achieved by mutually antagonistic interactions between the aPKC-PAR-3-PAR-6 complex and PAR-1 or PAR2 located opposite. However, accumulating evidence has also revealed that mechanisms by which the asymmetrically localized components of the PAR-aPKC system are linked with other cellular machinery for developing polarity are divergent depending on the cell type.

T cell-specific loss of Pten leads to defects in central and peripheral tolerance

PTEN, a tumor suppressor gene, is essential for embryogenesis. We used the Cre-loxP system to generate a T cell-specific deletion of the Pten gene (Pten(flox/-) mice). All Pten(flox/-) mice develop CD4+ T cell lymphomas by 17 weeks. Pten(flox/-) mice show increased thymic cellularity due in part to a defect in thymic negative selection. Pten(flox/-) mice exhibit elevated levels of B cells and CD4+ T cells in the periphery, spontaneous activation of CD4+ T cells, autoantibody production, and hypergammaglobulinemia. Pten(flox/-) T cells hyperproliferate, are autoreactive, secrete increased levels of Th1/Th2 cytokines, resist apoptosis, and show increased phosphorylation of PKB/Akt and ERK. Peripheral tolerance to SEB is also impaired in Pten(flox/-) mice. PTEN is thus an important regulator of T cell homeostasis and self-tolerance.

Protein kinase C activates the MEK-ERK pathway in a manner independent of Ras and dependent on Raf

Although the involvement of protein kinase C (PKC) in the activation of the mitogen-activated protein (MAP) kinase pathway has been implicated through experiments using 12-O-tetradecanoylphorbol-13-acetate (TPA), there has been no direct demonstration that PKC activates the MAP kinase pathway. A Raf-dependent intact cell assay system for monitoring the activation of MAPK/ERK kinase (MEK) and extracellular signal-related kinase (ERK) permitted us to evaluate the role of PKC isotypes in MAP kinase activation. Treatment of cells with TPA or epidermal growth factor resulted in the activation of MEK and ERK. The activation of the MAP kinase pathway triggered by epidermal growth factor was completely inhibited by dominant-negative Ras (RasN17), whereas the activation triggered by TPA was not, consistent with previous observations. The introduction of an activated point mutant of PKCdelta, but not PKCalpha or PKCepsilon, resulted in the activation of the MAP kinase pathway. The activation of MEK and ERK by an activated form of PKCdelta requires the presence of c-Raf and is independent of RasN17. These results demonstrate that activation of PKCdelta is sufficient for the activation of MEK and ERK and that the pathway operates in a manner dependent on c-Raf and independent of Ras.

Musashi1: an evolutionally conserved marker for CNS progenitor cells including neural stem cells

In situ detection of neural progenitor cells including stem-like cells is essential for studying the basic mechanisms of the generation of cellular diversity in the CNS, upon which therapeutic treatments for CNS injuries, degenerative diseases, and brain tumors may be based. We have generated rat monoclonal antibodies (Mab 14H1 and 14B8) that recognize an RNA-binding protein Musashi1, but not a Musashi1-related protein, Musashi2. The amino acid sequences at the epitope sites of these anti-Musashi1 Mabs are remarkably conserved among the human, mouse, and Xenopus proteins. Spatiotemporal patterns of Musashi1 immunoreactivity in the developing and/or adult CNS tissues of frogs, birds, rodents, and humans indicated that our anti-Musashi1 Mabs reacted with undifferentiated, proliferative cells in the CNS of all the vertebrates tested. Double or triple immunostaining of embryonic mouse brain cells in monolayer cultures demonstrated strong Musashi1 expression in Nestin(+)/RC2(+) cells. The relative number of Musashi1(+)/Nestin(+)/RC2(+) cells increased fivefold when embryonic forebrain cells were cultured to form 'neurospheres' in which stem-like cells are known to be enriched through their self-renewing mode of growth. Nestin(+)/RC2(-) cells, which included Talpha1-GFP(+) neuronal progenitor cells and GLAST(+) astroglial precursor cells, were also Musashi1(+), as were GFAP(+) astrocytes. Young neurons showed a trace of Musashi1 expression. Cells committed to the oligodendroglial lineage were Musashi(-). Musashi1 was localized to the perikarya of CNS stem-like cells and non-oligodendroglial progenitor cells without shifting to cell processes or endfeet, and is therefore advantageous for identifying each cell and counting cells in situ.

Helicobacter pylori CagA targets PAR1/MARK kinase to disrupt epithelial cell polarity

Helicobacter pylori cagA-positive strains are associated with gastritis, ulcerations and gastric adenocarcinoma. CagA is delivered into gastric epithelial cells and, on tyrosine phosphorylation, specifically binds and activates the SHP2 oncoprotein, thereby inducing the formation of an elongated cell shape known as the 'hummingbird' phenotype. In polarized epithelial cells, CagA also disrupts the tight junction and causes loss of apical-basolateral polarity. We show here that H. pylori CagA specifically interacts with PAR1/MARK kinase, which has an essential role in epithelial cell polarity. Association of CagA inhibits PAR1 kinase activity and prevents atypical protein kinase C (aPKC)-mediated PAR1 phosphorylation, which dissociates PAR1 from the membrane, collectively causing junctional and polarity defects. Because of the multimeric nature of PAR1 (ref. 14), PAR1 also promotes CagA multimerization, which stabilizes the CagA-SHP2 interaction. Furthermore, induction of the hummingbird phenotype by CagA-activated SHP2 requires simultaneous inhibition of PAR1 kinase activity by CagA. Thus, the CagA-PAR1 interaction not only elicits the junctional and polarity defects but also promotes the morphogenetic activity of CagA. Our findings revealed that PAR1 is a key target of H. pylori CagA in the disorganization of gastric epithelial architecture underlying mucosal damage, inflammation and carcinogenesis.

Deletion of Pten in mouse brain causes seizures, ataxia and defects in soma size resembling Lhermitte-Duclos disease

Initially identified in high-grade gliomas, mutations in the PTEN tumor-suppressor are also found in many sporadic cancers and a few related autosomal dominant hamartoma syndromes. PTEN is a 3'-specific phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P3) phosphatase and functions as a negative regulator of PI3K signaling. We generated a tissue-specific deletion of the mouse homolog Pten to address its role in brain function. Mice homozygous for this deletion (PtenloxP/loxP;Gfap-cre), developed seizures and ataxia by 9 wk and died by 29 wk. Histological analysis showed brain enlargement in PtenloxP/loxP;Gfap-cre mice as a consequence of primary granule-cell dysplasia in the cerebellum and dentate gyrus. Pten mutant cells showed a cell-autonomous increase in soma size and elevated phosphorylation of Akt. These data represent the first evidence for the role of Pten and Akt in cell size regulation in mammals and provide an animal model for a human phakomatosis condition, Lhermitte-Duclos disease (LDD).

A truncated bone morphogenetic protein receptor affects dorsal-ventral patterning in the early Xenopus embryo

Bone morphogenetic proteins (BMPs), which are members of the transforming growth factor beta (TGF-beta) superfamily, have been implicated in bone formation and the regulation of early development. To better understand the roles of BMPs in Xenopus laevis embryogenesis, we have cloned a cDNA coding for a serine/threonine kinase receptor that binds BMP-2 and BMP-4. To analyze its function, we attempted to block the BMP signaling pathway in Xenopus embryos by using a dominant-negative mutant of the BMP receptor. When the mutant receptor lacking the putative serine/threonine kinase domain was expressed in ventral blastomeres of Xenopus embryos, these blastomeres were respecified to dorsal mesoderm, eventually resulting in the formation of a secondary body axis. These findings suggest that endogenous BMP-2 and BMP-4 are involved in the dorsal-ventral specification in the embryo and that ventral fate requires induction rather than resulting from an absence of dorsal specification.

Atypical protein kinase C is involved in the evolutionarily conserved par protein complex and plays a critical role in establishing epithelia-specific junctional structures

We have previously shown that during early Caenorhabditis elegans embryogenesis PKC-3, a C. elegans atypical PKC (aPKC), plays critical roles in the establishment of cell polarity required for subsequent asymmetric cleavage by interacting with PAR-3 [Tabuse, Y., Y. Izumi, F. Piano, K.J. Kemphues, J. Miwa, and S. Ohno. 1998. Development (Camb.). 125:3607--3614]. Together with the fact that aPKC and a mammalian PAR-3 homologue, aPKC-specific interacting protein (ASIP), colocalize at the tight junctions of polarized epithelial cells (Izumi, Y., H. Hirose, Y. Tamai, S.-I. Hirai, Y. Nagashima, T. Fujimoto, Y. Tabuse, K.J. Kemphues, and S. Ohno. 1998. J. Cell Biol. 143:95--106), this suggests a ubiquitous role for aPKC in establishing cell polarity in multicellular organisms. Here, we show that the overexpression of a dominant-negative mutant of aPKC (aPKCkn) in MDCK II cells causes mislocalization of ASIP/PAR-3. Immunocytochemical analyses, as well as measurements of paracellular diffusion of ions or nonionic solutes, demonstrate that the biogenesis of the tight junction structure itself is severely affected in aPKCkn-expressing cells. Furthermore, these cells show increased interdomain diffusion of fluorescent lipid and disruption of the polarized distribution of Na(+),K(+)-ATPase, suggesting that epithelial cell surface polarity is severely impaired in these cells. On the other hand, we also found that aPKC associates not only with ASIP/PAR-3, but also with a mammalian homologue of C. elegans PAR-6 (mPAR-6), and thereby mediates the formation of an aPKC-ASIP/PAR-3-PAR-6 ternary complex that localizes to the apical junctional region of MDCK cells. These results indicate that aPKC is involved in the evolutionarily conserved PAR protein complex, and plays critical roles in the development of the junctional structures and apico-basal polarization of mammalian epithelial cells.

Junctional adhesion molecules (JAMs): more molecules with dual functions?

Junctional adhesion molecules (JAMs) are members of an immunoglobulin subfamily expressed by leukocytes and platelets as well as by epithelial and endothelial cells, in which they localize to cell-cell contacts and are specifically enriched at tight junctions. The recent identification of extracellular ligands and intracellular binding proteins for JAMs suggests two functions for JAMs. JAMs associate through their extracellular domains with the leukocyte beta2 integrins LFA-1 and Mac-1 as well as with the beta1 integrin alpha4beta1. All three integrins are involved in the regulation of leukocyte-endothelial cell interactions. Through their cytoplasmic domains, JAMs directly associate with various tight junction-associated proteins including ZO-1, AF-6, MUPP1 and the cell polarity protein PAR-3. PAR-3 is part of a ternary protein complex that contains PAR-3, atypical protein kinase C and PAR-6. This complex is highly conserved through evolution and is involved in the regulation of cell polarity in organisms from Caenorhabditis elegans and Drosophila to vertebrates. These findings point to dual functions for JAMs: they appear to regulate both leukocyte/platelet/endothelial cell interactions in the immune system and tight junction formation in epithelial and endothelial cells during the acquisition of cell polarity.

Polarity-dependent distribution of angiomotin localizes Hippo signaling in preimplantation embryos

BACKGROUND

In preimplantation mouse embryos, the first cell fate specification to the trophectoderm or inner cell mass occurs by the early blastocyst stage. The cell fate is controlled by cell position-dependent Hippo signaling, although the mechanisms underlying position-dependent Hippo signaling are unknown.

RESULTS

We show that a combination of cell polarity and cell-cell adhesion establishes position-dependent Hippo signaling, where the outer and inner cells are polar and nonpolar, respectively. The junction-associated proteins angiomotin (Amot) and angiomotin-like 2 (Amotl2) are essential for Hippo pathway activation and appropriate cell fate specification. In the nonpolar inner cells, Amot localizes to adherens junctions (AJs), and cell-cell adhesion activates the Hippo pathway. In the outer cells, the cell polarity sequesters Amot from basolateral AJs to apical domains, thereby suppressing Hippo signaling. The N-terminal domain of Amot is required for actin binding, Nf2/Merlin-mediated association with the E-cadherin complex, and interaction with Lats protein kinase. In AJs, S176 in the N-terminal domain of Amot is phosphorylated by Lats, which inhibits the actin-binding activity, thereby stabilizing the Amot-Lats interaction to activate the Hippo pathway.

CONCLUSIONS

We propose that the phosphorylation of S176 in Amot is a critical step for activation of the Hippo pathway in AJs and that cell polarity disconnects the Hippo pathway from cell-cell adhesion by sequestering Amot from AJs. This mechanism converts positional information into differential Hippo signaling, thereby leading to differential cell fates.

A phase II study of CPT-11, a new derivative of camptothecin, for previously untreated non-small-cell lung cancer

PURPOSE

Camptothecin-11 (CPT-11) is a new semisynthetic derivative of CPT, and has been shown to inhibit DNA topoisomerase I and to have a strong antitumor activity with low toxicity in murine tumors. To evaluate the effectiveness of CPT-11 in patients with non-small-cell lung cancer (NSCLC), a phase II study was conducted between April 1989 and February 1990.

PATIENTS AND METHODS

Seventy-three patients were entered onto the study. All patients had had no previous therapy and had measurable disease. Their median age was 67 years (range, 34 to 75 years). Fifty-four patients had a performance status (PS) of 0 or 1 on the Eastern Cooperative Oncology Group (ECOG) scale, and 19 had a PS of 2. CPT-11 was given at a dose of 100 mg/m2 by intravenous 90-minute infusion once a week. The dose of CPT-11 was modified based on the WBC count obtained on the day of drug administration.

RESULTS

Of 72 assessable patients, 23 (31.9%) showed a partial response (95% confidence interval, 20.2% to 43.6%). Of 40 patients with a stage IV disease, 13 (32.5%) responded. Response rates for patients with PS 0 or 1 and those with PS 2 did not differ (34.0% and 26.3%, respectively). The median duration of response in patients showing a PR was 15 weeks. The median survival time for all patients was 42 weeks. The major toxicities were leukopenia and diarrhea. Grade 3 or 4 leukopenia and diarrhea occurred in 18 patients (25%) and 15 patients (21%), respectively. These toxicities were unpredictable. Other toxicities of greater than or equal to grade 3 included nausea/vomiting (22%), anemia (15%), alopecia (4%) and pneumonitis (3%). One patient died of pulmonary toxicity (interstitial pneumonitis).

CONCLUSIONS

CPT-11 is a very active agent for NSCLC with acceptable toxicities. Further trials in combination with other agents for this disease are warranted.

Cytokine-inducible SH2 protein-3 (CIS3/SOCS3) inhibits Janus tyrosine kinase by binding through the N-terminal kinase inhibitory region as well as SH2 domain

BACKGROUND

The Janus family of protein tyrosine kinases (JAKs) regulate cellular processes involved in cell growth, differentiation and transformation through their association with cytokine receptors. We have recently identified the JAK-binding protein, JAB that inhibits various cytokine-dependent JAK signalling pathways. JAB inhibits JAK2 tyrosine kinase activity by binding to the kinase domain (JH1 domain) through the N-terminal kinase inhibitory region (KIR) and the SH2 domain. The SH2 domain of JAB has been shown to bind to the phosphorylated Y1007 in the activation loop of JH1. We also identified another JAK-binding protein, CIS3 (cytokine-inducible SH2-protein 3, or SOCS3) that inhibits signalling of various cytokines. However, the mechanism of JAK signal inhibition by CIS3 has not been clarified.

RESULTS

We showed that endogenous CIS3 bound to JAK2 in intact cells. The CIS3-SH2 domain bound to the phosphorylated Y1007 of JH1, and inhibited tyrosine kinase activity through the N-terminal KIR. Therefore, CIS3 and JAB inhibit JAK2 tyrosine kinase activity by an essentially similar mechanism. However, we found that the affinity of the SH2 domain of CIS3 to Y1007 was weaker than that of JAB. In contrast, the KIR of CIS3 showed stronger potential for both binding to JH1 and inhibition of JAK kinase activity than that of JAB. Consistent with this notion, chimeras containing CIS3-KIR and JAB-SH2 domain inhibited JAK2 kinase activity more efficiently than the wild-type CIS3 or JAB.

CONCLUSION

CIS3 inhibits JAK2 kinase activity by binding to the activation loop through the SH2 domain, and KIR is necessary for kinase inhibition. Although the inhibitory mechanism by CIS3 is similar to that by JAB, the contributions of the SH2 domain and KIR for binding are different between JAB and CIS3. Our study defined the inhibitory mechanism of CIS3 and provides a useful information for creating a novel tyrosine kinase inhibitor.

The molecular basis for the absence of N-glycolylneuraminic acid in humans

N-Glycolylneuraminic acid (NeuGc) is abundantly expressed in most mammals, but it is not detectable in humans. The expression of NeuGc is controlled by cytidine monophospho-N-acetylneuraminic acid (CMP-NeuAc) hydroxylase activity. We previously cloned a cDNA for mouse CMP-NeuAc hydroxylase and found that the human genome contains a homologue. We report here the molecular basis for the absence of NeuGc in humans. We cloned a cDNA for human CMP-NeuAc hydroxylase from a HeLa cell cDNA library. The cDNA encodes a 486-amino acid protein, and its deduced amino acid sequence lacks a domain corresponding to the N-terminal 104 amino acids of the mouse CMP-NeuAc hydroxylase protein, although the human protein is highly identical (93%) to the rest of the mouse hydroxylase protein. The N-terminal truncation of the human hydroxylase is caused by deletion of a 92-base pair-long exon in human genomic DNA. The human hydroxylase expressed in COS-7 cells exhibited no enzymatic activity, and a mouse hydroxylase mutant, which lacks the N-terminal domain, was also inactive. A chimera composed of the human hydroxylase and the N-terminal domain of the mouse hydroxylase displayed the enzyme activity. These results indicate that the human homologue of CMP-NeuAc hydroxylase is inactive because it lacks an N-terminal domain that is essential for enzyme activity. The absence of NeuGc in human glycoconjugates is due to a partial deletion in the gene that encodes CMP-NeuAc hydroxylase.

Experimental investigation of geologically produced antineutrinos with KamLAND

The detection of electron antineutrinos produced by natural radioactivity in the Earth could yield important geophysical information. The Kamioka liquid scintillator antineutrino detector (KamLAND) has the sensitivity to detect electron antineutrinos produced by the decay of 238U and 232Th within the Earth. Earth composition models suggest that the radiogenic power from these isotope decays is 16 TW, approximately half of the total measured heat dissipation rate from the Earth. Here we present results from a search for geoneutrinos with KamLAND. Assuming a Th/U mass concentration ratio of 3.9, the 90 per cent confidence interval for the total number of geoneutrinos detected is 4.5 to 54.2. This result is consistent with the central value of 19 predicted by geophysical models. Although our present data have limited statistical power, they nevertheless provide by direct means an upper limit (60 TW) for the radiogenic power of U and Th in the Earth, a quantity that is currently poorly constrained.

The cell polarity protein ASIP/PAR-3 directly associates with junctional adhesion molecule (JAM)

The establishment and maintenance of cellular polarity are critical for the development of multicellular organisms. PAR (partitioning-defective) proteins were identified in Caenorhabditis elegans as determinants of asymmetric cell division and polarized cell growth. Recently, vertebrate orthologues of two of these proteins, ASIP/PAR-3 and PAR-6, were found to form a signalling complex with the small GTPases Cdc42/Rac1 and with atypical protein kinase C (PKC). Here we show that ASIP/PAR-3 associates with the tight-junction-associated protein junctional adhesion molecule (JAM) in vitro and in vivo. No binding was observed with claudin-1, -4 or -5. In fibroblasts and CHO cells overexpressing JAM, endogenous ASIP is recruited to JAM at sites of cell-cell contact. Over expression of truncated JAM lacking the extracellular part disrupts ASIP/PAR-3 localization at intercellular junctions and delays ASIP/PAR-3 recruitment to newly formed cell junctions. During junction formation, JAM appears early in primordial forms of junctions. Our data suggest that the ASIP/PAR-3-aPKC complex is tethered to tight junctions via its association with JAM, indicating a potential role for JAM in the generation of cell polarity in epithelial cells.

Ca 2+ -specific removal of Z lines from rabbit skeletal muscle

Removal of rabbit psoas strips immediately after death and incubation in a saline solution containing 1 mM Ca(2+) and 5 nM Mg(2+) for 9 hr at 37 degrees C and pH 7.1 causes complete Z-line removal but has no ultrastructurally detectable effect on other parts of the myofibril. Z lines remain ultrastructurally intact if 1 mM 1,2-bis-(2-dicarboxymethylaminoethoxy)-ethane (EGTA) is substituted for 1 mM Ca(2+) and the other conditions remain unchanged. Z lines are broadened and amorphous but are still present after incubation for 9 hr at 37 degrees C if 1 mM ethylenediaminetetraacetate (EDTA) is substituted for 1 mM Ca(2+) and 5 mM Mg(2+) in the saline solution. A protein fraction that causes Z-line removal from myofibrils in the presence of Ca(2+) at pH 7.0 can be isolated by extraction of ground muscle with 4 mM EDTA at pH 7.0-7.6 followed by isoelectric precipitation and fractionation between 0 and 40% ammonium sulfate saturation. Z-line removal by this protein fraction requires Ca(2+) levels higher than 0.1 mM, but Z lines are removed without causing any other ultrastructurally detectable degradation of the myofibril. This is the first report of a protein endogenous to muscle that is able to catalyze degradation of the myofibril. The very low level of unbound Ca(2+) in muscle cells in vivo may regulate activity of this protein fraction, or alternatively, this protein fraction may be localized in lysosomes.

Mammalian Lgl forms a protein complex with PAR-6 and aPKC independently of PAR-3 to regulate epithelial cell polarity

BACKGROUND

Epithelial cells have apicobasal polarity and an asymmetric junctional complex that provides the bases for development and tissue maintenance. In both vertebrates and invertebrates, the evolutionarily conserved protein complex, PAR-6/aPKC/PAR-3, localizes to the subapical region and plays critical roles in the establishment of a junctional complex and cell polarity. In Drosophila, another set of proteins called tumor suppressors, such as Lgl, which localize separately to the basolateral membrane domain but genetically interact with the subapical proteins, also contribute to the establishment of cell polarity. However, how physically separated proteins interact remains to be clarified.

RESULTS

We show that mammalian Lgl competes for PAR-3 in forming an independent complex with PAR-6/aPKC. During cell polarization, mLgl initially colocalizes with PAR-6/aPKC at the cell-cell contact region and is phosphorylated by aPKC, followed by segregation from apical PAR-6/aPKC to the basolateral membrane after cells are polarized. Overexpression studies establish that increased amounts of the mLgl/PAR-6/aPKC complex suppress the formation of epithelial junctions; this contrasts with the previous observation that the complex containing PAR-3 promotes it.

CONCLUSIONS

These results indicate that PAR-6/aPKC selectively interacts with either mLgl or PAR-3 under the control of aPKC activity to regulate epithelial cell polarity.

Resistance to Fas-mediated apoptosis: activation of caspase 3 is regulated by cell cycle regulator p21WAF1 and IAP gene family ILP

The death receptor Fas transduces apoptotic death signaling mediated by caspases. In the present study, human hepatoma HepG2 cells showed the Fas-mediated apoptosis mediated by caspase, especially caspase 3, only in the presence of actinomycin D. Interestingly, cytosolic proteins extracted from intact HepG2 cells induced caspase 3 inactivation. Our results reveal that this inactivation was triggered by the direct inhibition of activated caspase 3 by IAP gene family ILP. In addition, a 53 kDa protein was co-immunoprecipitated with anti-human caspase 3 antibody from intact HepG2 cells. This protein was a complex-protein of procaspase 3 and the cell cycle regulator p21WAF1 (p21). P21 bound to only procaspase 3, but not to activated caspase 3. We also demonstrate that p21 protein-loaded HepG2 cells resist to Fas-mediated apoptosis even in the presence of actinomycin D. Here we report that caspase 3 inactivation for the resistance to Fas-mediated apoptosis is induced by a procaspase 3/p21 complex formation and direct inhibition of activated caspase 3 by ILP.