Cofilin activity during insulin-like growth factor I-stimulated neuroblastoma cell motility

Insulin-like growth factor I (IGF-I) is a potent stimulator of neuroblastoma cell motility. Cell motility requires lamellipodium extension at the leading edge of the cell through organized actin polymerization, and IGF-I stimulates lamellipodial elaboration in human neuroblastoma cells. Rac is a Rho GTPase that stimulates lamellipodial formation via the regulation of actin polymerization. In this study, we show that IGF-I-stimulated phosphatidylinositol 3-kinase (PI-3K) activity promotes rac activation and subsequent activation of the down- stream effectors LIM kinase and cofilin. Overexpression of wild-type LIM kinase and wild-type Xenopus ADF/cofilin (XAC) suppresses IGF-I-stimulated motility in SH-SY5Y cells, while expression of dominant negative LIM kinase and constitutively active XAC increases SH-SY5Y motility in the absence of IGF-I stimulation. These results suggest that regulation by cofilin of actin depolymerization is important in the process of neuroblastoma cell motility, and IGF-I regulates cofilin activity in part through PI-3K, rac, and LIM kinase.Received 18 October 2004; received after revision 3 December 2004; accepted 16 December 2004     

An olivine-free mantle source of Hawaiian shield basalts

More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent with a deep olivine-bearing source, because this mineral together with pyroxene buffers both nickel and silicon at lower levels. This can be resolved if the olivine of the mantle peridotite is consumed by reaction with melts derived from recycled oceanic crust, to form a secondary pyroxenitic source. Our modelling shows that more than half of Hawaiian magmas formed during the past 1 Myr came from this source. In addition, we estimate that the proportion of recycled (oceanic) crust varies from 30 per cent near the plume centre to insignificant levels at the plume edge. These results are also consistent with volcano volumes, magma volume flux and seismological observations.     

A mechanosensory complex that mediates the endothelial cell response to fluid shear stress

Shear stress is a fundamental determinant of vascular homeostasis, regulating vascular remodelling, cardiac development and atherogenesis, but the mechanisms of transduction are poorly understood. Previous work showed that the conversion of integrins to a high-affinity state mediates a subset of shear responses, including cell alignment and gene expression. Here we investigate the pathway upstream of integrin activation. PECAM-1 (which directly transmits mechanical force), vascular endothelial cell cadherin (which functions as an adaptor) and VEGFR2 (which activates phosphatidylinositol-3-OH kinase) comprise a mechanosensory complex. Together, these receptors are sufficient to confer responsiveness to flow in heterologous cells. In support of the relevance of this pathway in vivo, PECAM-1-knockout mice do not activate NF-kappaB and downstream inflammatory genes in regions of disturbed flow. Therefore, this mechanosensing pathway is required for the earliest-known events in atherogenesis.     

The phylogenetic position of the 'giant deer' Megaloceros giganteus

The giant deer, or 'Irish elk', has featured extensively in debates on adaptation, sexual selection, and extinction. Its huge antlers--the largest of any deer species, living or extinct--formed a focus of much past work. Yet the phylogenetic position of the giant deer has remained an enigma. On the basis of its flattened antlers, the species was previously regarded as closely related to the living fallow deer. Recent morphological studies, however, have challenged that view and placed the giant deer closer to the living red deer or wapiti. Here we present a new phylogenetic analysis encompassing morphological and DNA sequence evidence, and find that both sets of data independently support a sister-group relationship of giant and fallow deer. Our results include the successful extraction and sequencing of DNA from this extinct species, and highlight the value of a joint molecular and morphological approach.     

T-cell receptor triggering is critically dependent on the dimensions of its peptide-MHC ligand

The binding of a T-cell antigen receptor (TCR) to peptide antigen presented by major histocompatibility antigens (pMHC) on antigen-presenting cells (APCs) is a central event in adaptive immune responses. The mechanism by which TCR-pMHC ligation initiates signalling, a process termed TCR triggering, remains controversial. It has been proposed that TCR triggering is promoted by segregation at the T cell-APC interface of cell-surface molecules with small ectodomains (such as TCR-pMHC and accessory receptors) from molecules with large ectodomains (such as the receptor protein tyrosine phosphatases CD45 and CD148). Here we show that increasing the dimensions of the TCR-pMHC interaction by elongating the pMHC ectodomain greatly reduces TCR triggering without affecting TCR-pMHC ligation. A similar dependence on receptor-ligand complex dimensions was observed with artificial TCR-ligand systems that span the same dimensions as the TCR-pMHC complex. Interfaces between T cells and APCs expressing elongated pMHC showed an increased intermembrane separation distance and less depletion of CD45. These results show the importance of the small size of the TCR-pMHC complex and support a role for size-based segregation of cell-surface molecules in TCR triggering.     

Localization and analysis of nonpolar regions in onconase

A detailed analysis of the composition and properties of hydrophobic nuclei and microclusters has been carried out for onconase. Two main hydrophobic nuclei in the onconase structure were detected. Their composition and shape were found to be very similar to those of RNase A, in accordance with the predictions made. The nuclei in onconase are more compact, the side-chain atoms of residues included in the nuclei in onconase form more contacts with the environment than in RNase A. The hydrophobic nuclei should be considered as individual structural units along with elements of the secondary structure. Differences in composition and conformation of exposed loops between onconase and RNase A were found. The additional hydrophobic clusters attached to the nuclei in onconase might be involved in the fixation of an appropriate conformation of site(s) for manifestation of the biological activity of onconase. A comparison of amphibian representatives of the RNase A superfamily was also made. The results obtained suggest that the availability of nonpolar residues in established key positions of amino acid sequences determines the characteristic fold of homologous proteins and the structure of the active site cleft.     

A new gene involved in X-linked mental retardation identified by analysis of an X;2 balanced translocation

X-linked forms of mental retardation (MR) affect approximately 1 in 600 males and are likely to be highly heterogeneous. They can be categorized into syndromic (MRXS) and nonspecific (MRX) forms. In MRX forms, affected patients have no distinctive clinical or biochemical features. At least five MRX genes have been identified by positional cloning, but each accounts for only 0.5%-1.0% of MRX cases. Here we show that the gene TM4SF2 at Xp11.4 is inactivated by the X breakpoint of an X;2 balanced translocation in a patient with MR. Further investigation led to identification of TM4SF2 mutations in 2 of 33 other MRX families. RNA in situ hybridization showed that TM4SF2 is highly expressed in the central nervous system, including the cerebral cortex and hippocampus. TM4SF2 encodes a member of the tetraspanin family of proteins, which are known to contribute in molecular complexes including beta-1 integrins. We speculate that through this interaction, TM4SF2 might have a role in the control of neurite outgrowth.