Nernst Sign Reversal in the Hexatic Vortex Phase of Weakly Disordered a-MoGe Thin Films.

The hexatic phase is an intermediate stage in the melting process of a 2D crystal due to topological defects. Recently, this exotic phase was experimentally identified in the vortex lattice of 2D weakly disordered superconducting MoGe by scanning tunneling microscopic measurements. Here, we study this vortex state by the Nernst effect, which is an effective and sensitive tool to detect vortex motion, especially in the superconducting fluctuation regime. We find a surprising Nernst sign reversal at the melting transition of the hexatic phase. We propose that they are a consequence of vortex dislocations in the hexatic state which diffuse preferably from the cold to hot.

Seatbelt: a double-edged sword.

Intra-abdominal vascular injury due to blunt trauma is unusual in children. Due to its rarity, detailed reports dealing with its management are scarce in paediatric literature. Diagnosis of these injuries is challenging, and a high degree of awareness is necessary for rapid identification and treatment of these injuries. We report the case of a child with seatbelt sign and mesenteric vein injury due to blunt trauma to the abdomen during a motor vehicle accident where the seatbelt was incorrectly placed. She also sustained cervical vertebral injury. The pattern of injuries in children in these situations may differ from that found in adults. While seatbelts have undoubtedly saved many lives, awareness about correct placement of these restraints is extremely necessary.

Prospective study of antenatally diagnosed congenital cystic adenomatoid malformations.

PURPOSE: Congenital cystic adenomatoid malformations (CCAMs) are increasingly diagnosed in recent years due to the routine usage of antenatal ultrasound. The aim of this study was to present the natural course and outcome of antenatally diagnosed cystic lung diseases, which were prospectively studied. METHODS: Between the period June 2004 and June 2010, 25 fetuses with suspected CCAMs were seen in a single tertiary maternal fetal unit. One child was excluded as the fetal MRI suggested congenital diaphragmatic hernia. Data were prospectively entered into a database including antenatal and postnatal findings which were then analyzed. RESULTS: Mean gestational age at the time of diagnosis was 20.8 weeks (range 17-29). Fetal interventions included amnioreduction (n = 2) and fetal thoracocentesis (n = 3) in one child. The mean gestational age at delivery was 38.5 weeks (range 31.6-40.6). None of the mothers underwent termination of pregnancy or spontaneous abortion. All patients underwent postnatal radiological assessment. Of the 24 cases, 5 children were symptomatic in the immediate neonatal period and 19 were asymptomatic. Anatomical surgical resection was undertaken in all symptomatic cases. There was one death in this group due to severe pre-existing pulmonary hypoplasia. Among the 19 asymptomatic cases, 5 children were managed conservatively as the lesions were not significant and the remaining 14 (73%) underwent surgical resection. The mean age at surgery was 11.1 months (range 3.3-34 months). Postnatal pathology confirmed CCAM in all operated cases, except one who had pulmonary sequestration. CONCLUSION: Antenatally diagnosed CCAMs have an excellent prognosis except in children with a large lesion and associated with lung hypoplasia. Postnatal investigations are required in all cases to confirm the diagnosis. Symptomatic CCAMs require immediate surgery in the neonatal period with a good outcome. Asymptomatic CCAMs can be safely operated between 9 and 12 months of age.

ARF-induced downregulation of Mip130/LIN-9 protein levels mediates a positive feedback that leads to increased expression of p16Ink4a and p19Arf.

The ARF-MDM2-p53 pathway constitutes one of the most important mechanisms of surveillance against oncogenic transformation, and its inactivation occurs in a large proportion of cancers. Here, we show that ARF regulates Mip130/LIN-9 by inducing its translocation to the nucleolus and decreasing the expression of the Mip130/LIN-9 protein through a post-transcriptional mechanism. The knockdown of Mip130/LIN-9 in p53(-/-) and Arf(-/-) mouse embryonic fibroblasts (MEFs) mimics some effects of ARF, such as the downregulation of B-Myb, impaired induction of G2/M genes, and a decrease in cell proliferation. Importantly, although the knockdown of Mip130/LIN-9 reduced the proliferation of p53 or Arf-null MEFs, only p53(-/-) MEFs showed a senescence-like state and an increase in the expression of Arf and p16. Interestingly, the increase in p16 and ARF is indirect because the Mip130/LIN-9 knockdown decreased the transcription of negative regulators of the Ink4a/Arf locus, such as BUBR1 and CDC6. Chromatin immunoprecipitation assays also reveal that Mip130/LIN-9 occupies the promoters of the BubR1 and cdc6 genes, suggesting that Mip130/LIN-9 is necessary for the expression of these genes. Altogether, these results indicate that there is a feedback mechanism between ARF and Mip130/LIN-9 in which either the increase of ARF or the decrease in Mip130/LIN-9 causes a further increase in the expression of Arf and p16.

Proliferation defects and genome instability in cells lacking Cul4A.

The Cul4A gene, which encodes a core component of a cullin-based E3 ubiquitin ligase complex, is overexpressed in breast and hepatocellular cancers. In breast cancers, overexpression of Cul4A strongly correlates with poor prognosis. In addition, Cul4A is required for early embryonic development. The early lethality of mouse embryos prevented a detailed analysis of the functions of Cul4A. Here, we used a strain of mice carrying floxed alleles of Cul4A to study its role in cell division, in vitro and in vivo. Embryonic fibroblasts (MEFs) show a severe deficiency in cell proliferation after deletion of Cul4A. We observed that the Cul4A protein is abundantly expressed in the brain, liver and the mammary tissue of pregnant mice. Deletion of Cul4A in the liver impairs hepatocyte proliferation during regeneration after carbon tetrachloride (CCl(4))-induced injury. The Cul4A-deleted cells are slow in entering the S phase, and are deficient in progressing through the early M phase. Several cell-cycle regulators, including p53 and p27Kip1, are deregulated in the Cul4A-deleted cells. Expression of a dominant negative mutant of p53 causes significant reversal of the proliferation defects in Cul4A-deleted cells. The Cul4A-deleted cells show an aberrant number of centrosome, multipolar spindles and micronuclei formation. Furthermore, those cells are sensitive to UV irradiation and show reduced levels of unscheduled DNA synthesis (UDS). Together, our observations indicate that Cul4A is required for efficient cell proliferation, control of centrosome amplification and genome stability.

Approaches in type 1 diabetes research: A status report.

Type 1 diabetes is a multifactorial disease with an early age of onset, in which the insulin producing beta cell of the pancreas are destroyed because of autoimmunity. It is the second most common chronic disease in children and account for 5% to 10% of all diagnosed cases of diabetes. India is having an incidence of 10.6 cases/year/100,000, and recent studies indicate that the prevalence of type 1 diabetes in India is increasing. However in view of poor health care network, there is no monitoring system in the country. Of the 18 genomic intervals implicated for the risk to develop type 1 diabetes, the major histocompatibility complex (MHC) region on chromosome 6p21.31 has been the major contributor estimated to account for 40-50%, followed by 10% frequency of INS-VNTR at 5' flanking region of the insulin gene on chromosome 11p15.5. However, population studies suggest that > 95% of type 1 diabetes have HLA-DR3 or DR4, or both, and in family studies, sibling pairs affected with type 1 diabetes have a non-random distribution of shared HLA haplotypes. As predisposing genetic factors such as HLA alleles are known, immunological interventions to prevent type 1 diabetes are of great interest. In the present study we have reviewed the status of molecular genetics of the disease and the approaches that need to be adopted in terms of developing patient and suitable control cohorts in the country.

An N-terminal inhibitory domain modulates activity of FoxM1 during cell cycle.

The FoxM1 transcription factor plays critical roles in the expression of genes that are essential for cell proliferation. FoxM1 null or depleted cells fail to progress through mitosis, as expression of several mitotic genes depends upon FoxM1. The transcriptional activity of FoxM1 is stimulated by cyclin-cdk-mediated phosphorylation at a site within the transcriptional activation domain. Here, we characterize the role of an N-terminal inhibitory domain in the transcriptional activity of FoxM1. Deletion of the N-terminal 232 amino-acid residues increases the transcriptional and transforming activities of FoxM1. Moreover, while the activity of the full-length FoxM1 is stimulated by growth factors, the activity of the N-terminal deletion mutant is constitutively high in all phases of the cell cycle. The N-terminal deletion also eliminates the requirement for cyclin-cdk to activate FoxM1. We provide evidence that the N-terminal domain interacts with the C-terminal half of the transcription factor to attenuate its transcriptional activity. Moreover, the N-terminal fragment inhibits the transcriptional activity of FoxM1 in G1/S cells, but not in G2/M cells. Our results suggest that cyclin-cdk phosphorylates FoxM1 to counteract the inhibition by the N-terminal domain to fully activate FoxM1 in G2/M phase.

Evidence of gap anisotropy in superconducting YNi2B2C using directional point-contact spectroscopy.

We present a study of the anisotropy in the superconducting energy gap in a single crystal of YNi2B2C (T(c) approximately 14.6 K) using directional point-contact spectroscopy. The superconducting energy gap at 2.7 K, when measured for I||c, is 4.5 times larger than that for I||a. The energy gaps in the two directions also have different temperature dependences. Our results support a scenario with s + g like symmetry.

Observation of minority spin character of the new electron doped manganite La0.7Ce0.3MnO3 from tunneling magnetoresistance.

We report the magnetotransport characteristics of a trilayer ferromagnetic tunnel junction built of an electron doped manganite (La0.7Ce0.3MnO3) and a hole doped manganite (La0.7Ca0.3MnO3). At low temperatures the junction exhibits a large positive tunneling magnetoresistance (TMR), irrespective of the bias voltage. At intermediate temperatures below T(C) the sign of the TMR is dependent on the bias voltage across the junction. The magnetoresistive characteristics of the junction strongly suggest that La0.7Ce0.3MnO3 is a minority spin carrier ferromagnet with a high degree of spin polarization, i.e., a transport half-metal.

Sensitivity to disorder of the metallic state in the ruthenates.

We report the results of transport measurements on SrRuO3, Sr3Ru2O7, and CaRuO3. In SrRuO3 and Sr3Ru2O7, our findings are consistent with the predictions of Fermi liquid theory, in contrast to previous reports based on samples with much shorter mean free paths. In CaRuO3, however, a T1.5 power law is seen in the resistivity in the high purity samples studied here. Our work gives concrete evidence that even the metallic state of the ruthenates is highly sensitive to disorder.

DDB2 induces nuclear accumulation of the hepatitis B virus X protein independently of binding to DDB1.

The hepatitis B virus (HBV) X protein (HBx) is critical for the life cycle of the virus. HBx associates with several host cell proteins including the DDB1 subunit of the damaged-DNA binding protein DDB. Recent studies on the X protein encoded by the woodchuck hepadnavirus have provided correlative evidence indicating that the interaction with DDB1 is important for establishment of infection by the virus. In addition, the interaction with DDB1 has been implicated in the nuclear localization of HBx. Because the DDB2 subunit of DDB is required for the nuclear accumulation of DDB1, we investigated the role of DDB2 in the nuclear accumulation of HBx. Here we show that expression of DDB2 increases the nuclear levels of HBx. Several C-terminal deletion mutants of DDB2 that fail to bind DDB1 are able to associate with HBx, suggesting that DDB2 may associate with HBx independently of binding to DDB1. We also show that DDB2 enhances the nuclear accumulation of HBx independently of binding to DDB1, since a mutant that does not bind DDB1 is able to enhance the nuclear accumulation of HBx. HBV infection is associated with liver pathogenesis. We show that the nuclear levels of DDB1 and DDB2 are tightly regulated in hepatocytes. Studies with regenerating mouse liver indicate that during late G1 phase the nuclear levels of both subunits of DDB are transiently increased, followed by a sharp decrease in S phase. Taken together, these results suggest that DDB1 and DDB2 would participate in the nuclear functions of HBx effectively only during the late-G1 phase of the cell cycle.

The xeroderma pigmentosum group E gene product DDB2 is a specific target of cullin 4A in mammalian cells.

The damaged-DNA binding protein DDB consists of two subunits, DDB1 (127 kDa) and DDB2 (48 kDa). Mutations in the DDB2 subunit have been detected in patients suffering from the repair deficiency disease xeroderma pigmentosum (group E). In addition, recent studies suggested a role for DDB2 in global genomic repair. DDB2 also exhibits transcriptional activity. We showed that expression of DDB1 and DDB2 stimulated the activity of the cell cycle regulatory transcription factor E2F1. Here we show that DDB2 is a cell cycle-regulated protein. It is present at a low level in growth-arrested primary fibroblasts, and after release the level peaks at the G(1)/S boundary. The cell cycle regulation of DDB2 involves posttranscriptional mechanisms. Moreover, we find that an inhibitor of 26S proteasome increases the level of DDB2, suggesting that it is regulated by the ubiquitin-proteasome pathway. Our previous study indicated that the cullin family protein Cul-4A associates with the DDB2 subunit. Because cullins are involved in the ubiquitin-proteasome pathway, we investigated the role of Cul-4A in regulating DDB2. Here we show that DDB2 is a specific target of Cul-4A. Coexpression of Cul-4A, but not Cul-1 or other highly related cullins, increases the ubiquitination and the decay rate of DDB2. A naturally occurring mutant of DDB2 (2RO), which does not bind Cul-4A, is not affected by coexpression of Cul-4A. Studies presented here identify a specific function of the Cul-4A gene, which is amplified and overexpressed in breast cancers.

Both Rb and E7 are regulated by the ubiquitin proteasome pathway in HPV-containing cervical tumor cells.

High-risk human papillomaviruses (HPVs) are etiologically linked to human cervical and oral cancers. The E6 and E7 oncoproteins encoded by HPV target host cell tumor suppressor proteins. E6 induces proteolysis of p53 through the ubiquitin-proteasome pathway. Recent studies showed that overexpression of E7 caused proteolytic degradation of the tumor suppressor Rb. However, unlike p53, Rb is not regulated by proteolysis in normal cells. In addition, it was unclear whether in its natural context E7 regulates Rb through the ubiquitin-proteasome pathway. Therefore, we sought to determine whether Rb is regulated by the ubiquitin-proteasome pathway in HPV-containing tumor cells. We carried out a detailed analysis in Caski cells, that are derived from HPV-containing cervical cancer tissues. Studies with various protease inhibitors revealed that Rb is regulated specifically by the ubiquitin-proteasome pathway in HPV-containing cervical tumor cells. Several inhibitors of the 26S proteasome significantly increased the level of Rb in the Caski cells. Rb controls cell growth by forming complexes with the E2F-family transcription factors. Surprisingly, in spite of a significant accumulation of the hypophosphorylated form of Rb, no Rb/E2F complex was detectable in the proteasome inhibitor treated cells. Further analysis revealed that there was an increased accumulation of the E7 oncoprotein. We showed that the proteasome inhibitors simultaneously blocked the proteolysis of E7 and Rb, suggesting that E7 is also regulated by the ubiquitin-dependent proteolysis in cervical cancer cells. Taken together, this study suggests that targeted inhibition of Rb proteolysis will be required for restoring Rb function in HPV-containing cervical cancer cells.

The p48 subunit of the damaged-DNA binding protein DDB associates with the CBP/p300 family of histone acetyltransferase.

DDB has been implicated in DNA repair as well as transcription. Mutations in DDB have been correlated with the repair-deficiency disease, xeroderma pigmentosum group E (XP-E). The XP-E cells exhibit deficiencies in global genomic repair, suggesting a role for DDB in that process. DDB also possesses a transcription stimulatory activity. We showed that DDB could function as a transcriptional partner of E2F1. But the mechanism by which DDB stimulates E2F-regulated transcription or carry out its DNA repair function is not understood. To investigate the mechanisms, we looked for nuclear proteins that interact with DDB. Here we show that DDB associates with the CBP/p300 family of proteins, in vivo and in vitro. We suggest that DDB participates in global genomic repair by recruiting CBP/p300 to the damaged-chromatin. It is possible that the histone acetyltransferase activities of the CBP/p300 proteins induce chromatin remodeling at the damaged-sites to allow recruitment of the repair complexes. The observation offers insights into both transcription and repair functions of DDB.

Mechanism of melphalan-induced B7-1 gene expression in P815 tumor cells.

We have previously shown that exposure of P815 tumor cells to melphalan (L-phenylalanine mustard; L-PAM) leads to up-regulation of B7-1 surface expression, and this L-PAM-induced up-regulation requires de novo RNA synthesis and is associated with accumulation of B7-1 mRNA. Here we show that the effect of L-PAM on B7-1 surface expression can be mimicked by exposing P815 tumor cells to oxidative stress but not to heat shock. Moreover, the antioxidant N-acetyl-L-cysteine prevented the L-PAM-induced accumulation of B7-1 mRNA in P815 tumor cells, suggesting that reactive oxygen species are involved in the transcriptional regulation of L-PAM-induced B7-1 gene expression. Although AP-1 and NF-kappaB are regarded as redox-sensitive transcription factors and the promoter/enhancer region of the B7-1 gene contains an AP-1 and an NF-kappaB binding site, exposure of P815 tumor cells to L-PAM led to rapid and transient activation only of NF-kappaB, but not AP-1, that bound specifically to a probe containing the respective binding site in the murine or human B7-1 gene. Moreover, exposure of P815 tumor cells to a cell-permeable peptide that selectively inhibits NF-kappaB activation by blocking the activation of the IkappaB-kinase complex was found to inhibit the L-PAM-induced B7-1 mRNA accumulation, indicating that NF-kappaB activation is essential for the L-PAM-induced B7-1 gene expression. Taken together, these results indicate that L-PAM leads to activation of B7-1 gene expression by activating NF-kappaB via a pathway that involves reactive oxygen species.

Cullin 4A associates with the UV-damaged DNA-binding protein DDB.

The damaged DNA-binding protein (DDB) is believed to be involved in DNA repair, and it has been linked to the repair deficiency disease xeroderma pigmentosum. DDB also exhibits transcriptional activities. DDB binds to the activation domain of E2F1 and stimulates E2F1-activated transcription. Here we provide evidence that DDB or DDB-associated proteins are targets of cullin 4A (CUL-4A). CUL-4A is a member of the cullin family of proteins, which are believed to be ubiquitin-protein isopeptide ligases (type E3). The CUL-4A gene has been shown to be amplified and up-regulated in breast carcinomas. In this study, we identify CUL-4A as one of the DDB-associated proteins. CUL-4A co-immunoprecipitates with DDB, but not with a naturally occurring mutant of DDB. Moreover, CUL-4A in HeLa nuclear extracts co-purifies with DDB, suggesting they are parts of the same complex. The observation provides insights how CUL-4A, through an interaction with DDB, might be playing a role in the development of breast carcinomas.

Functional interaction between human topoisomerase IIalpha and retinoblastoma protein.

DNA topoisomerase II-an essential nuclear enzyme in DNA replication and transcription, chromatin segregation, and cell cycle progression-is also a target of clinically useful anticancer drugs. Preliminary observations of a positive correlation between the expression of topoisomerase (topo) IIalpha and the retinoblastoma protein (Rb) in a series of rhabdomyosarcoma cells prompted us to ask whether these two proteins interact in vivo. Using human rhabdomyosarcoma and leukemic cell lines, we found a physical association between topo IIalpha and Rb protein by reciprocal immunoprecipitation and immunoblotting, in which topo IIalpha appeared to interact primarily with the underphosphorylated form of Rb. Experiments with truncated glutathione S-transferase-Rb fusion proteins and nuclear extracts of Rh1 rhabdomyosarcoma cells indicated that topo IIalpha binds avidly to the A/B pocket domain of Rb, which contains the intact spacer amino acid sequence. To determine whether this interaction has functional consequences in vivo, we expressed wild-type and mutant Rb in human cervical carcinoma cells lacking functional Rb. Wild-type, but not mutant, Rb inhibited topo II activity in nuclear extracts of these transfected cells. Moreover, purified wild-type Rb inhibited the activity of purified human topo IIalpha, indicating a direct interaction between these two proteins. We conclude that topo IIalpha associates physically with Rb in interactions that appear to have functional significance.

The naturally occurring mutants of DDB are impaired in stimulating nuclear import of the p125 subunit and E2F1-activated transcription.

The human UV-damaged-DNA binding protein DDB has been linked to the repair deficiency disease xeroderma pigmentosum group E (XP-E), because a subset of XP-E patients lack the damaged-DNA binding function of DDB. Moreover, the microinjection of purified DDB complements the repair deficiency in XP-E cells lacking DDB. Two naturally occurring XP-E mutations of DDB, 82TO and 2RO, have been characterized. They have single amino acid substitutions (K244E and R273H) within the WD motif of the p48 subunit of DDB, and the mutated proteins lack the damaged-DNA binding activity. In this report, we describe a new function of the p48 subunit of DDB, which reveals additional defects in the function of the XP-E mutants. We show that when the subunits of DDB were expressed individually, p48 localized in the nucleus and p125 localized in the cytoplasm. The coexpression of p125 with p48 resulted in an increased accumulation of p125 in the nucleus, indicating that p48 plays a critical role in the nuclear localization of p125. The mutant forms of p48, 2RO and 82TO, are deficient in stimulating the nuclear accumulation of the p125 subunit of DDB. In addition, the mutant 2RO fails to form a stable complex with the p125 subunit of DDB. Our previous studies indicated that DDB can associate with the transcription factor E2F1 and can function as a transcriptional partner of E2F1. Here we show that the two mutants, while they associate with E2F1 as efficiently as wild-type p48, are severely impaired in stimulating E2F1-activated transcription. This is consistent with our observation that both subunits of DDB are required to stimulate E2F1-activated transcription. The results provide insights into the functions of the subunits of DDB and suggest a possible link between the role of DDB in E2F1-activated transcription and the repair deficiency disease XP-E.