We report the identification of βIV spectrin, a novel spectrin isolated as an interactor of the receptor tyrosine phosphatase-like protein ICA512. The βIV spectrin gene is located on human and mouse chromosomes 19q13.13 and 7b2, respectively. Alternative splicing of βIV spectrin generates at least four distinct isoforms, numbered βIVΣ1–βIVΣ4 spectrin. The longest isoform (βIVΣ1 spectrin) includes an actin-binding domain, followed by 17 spectrin repeats, a specific domain in which the amino acid sequence ERQES is repeated four times, several putative SH3-binding sites and a pleckstrin homology domain. βIVΣ2 and βIVΣ3 spectrin encompass the NH2- and COOH-terminal halves of βIVΣ1 spectrin, respectively, while βIVΣ4 spectrin lacks the ERQES and the pleckstrin homology domain. Northern blots revealed an abundant expression of βIV spectrin transcripts in brain and pancreatic islets. By immunoblotting, βIVΣ1 spectrin is recognized as a protein of 250 kD. Anti–βIV spectrin antibodies also react with two additional isoforms of 160 and 140 kD. These isoforms differ from βIVΣ1 spectrin in terms of their distribution on subcellular fractionation, detergent extractability, and phosphorylation. In islets, the immunoreactivity for βIV spectrin is more prominent in α than in β cells. In brain, βIV spectrin is enriched in myelinated neurons, where it colocalizes with ankyrinG 480/270-kD at axon initial segments and nodes of Ranvier. Likewise, βIV spectrin is concentrated at the nodes of Ranvier in the rat sciatic nerve. In the rat hippocampus, βIVΣ1 spectrin is detectable from embryonic day 19, concomitantly with the appearance of immunoreactivity at the initial segments. Thus, we suggest that βIVΣ1 spectrin interacts with ankyrinG 480/270-kD and participates in the clustering of voltage-gated Na+ channels and cell-adhesion molecules at initial segments and nodes of Ranvier.

Abstract. Ankyrins are a family of large, membraneassociated proteins that mediate the linkage of the cytoskeleton to a variety of membrane transport and receptor proteins. A repetitive 33-residue motif characteristic of domain

Problem-Among pregnant women, acquired viral infections with a concurrent bacterial infection is a detrimental factor associated to poor prognosis. We evaluate the effect of a viral infection that does not lead to pre-term labor on the response to low doses of lipopolysaccharide (LPS). Our objectives were (i) to characterize the effect of a viral infection concurrent with exposure to microbial products on pregnancy outcome and (ii) to characterize the placental and fetal immune responses to the viral sensitization to LPS.Method-C57B/6 wild-type mice were injected with murine gammaherpesvirus 68 (MHV68) at E8.5. Either PBS or LPS was injected i.p. at E15.5. Pregnancy outcome and cytokine / chemokine profile from implantation sites were analyzed by multiplex.Results-LPS treatment of MHV-68-infected animals induced pre-term delivery and fetal death in 100% of the mice. Pre-term labor was characterized by a upregulation of pro-inflammatory cytokines and chemokines in both placenta and decidua. Similar profiles were observed from MHV-68-infected human primary trophoblast and trophoblast cell lines in response to LPS.Conclusion-We describe for the first time that a sub-clinical viral infection in pregnant mice might sensitize to a bacterial infection leading to pre-term delivery. We propose the 'Double Hit Hypothesis' where the presence of a viral infection enhances the effect of bacterial products during pregnancy leading not only to pre-term labor but likely larger adverse outcomes.

Spectrin is an important structural component of the plasma membrane skeleton. Heretoforeunidentified isoforms of spectrin also associate with Golgi and other organelles. We have discovered another member of the ␤-spectrin gene family by homology searches of the GenBank databases and by 5 rapid amplification of cDNA ends of human brain cDNAs. Collectively, 7,938 nucleotides of contiguous clones are predicted to encode a 271,294-Da protein, called ␤III spectrin, with conserved actin-, protein 4.1-, and ankyrin-binding domains, membrane association domains 1 and 2, a spectrin dimer self-association site, and a pleckstrinhomology domain. ␤III spectrin transcripts are concentrated in the brain and present in the kidneys, liver, and testes and the prostate, pituitary, adrenal, and salivary glands. All of the tested tissues contain major 9.0-kb and minor 11.3-kb transcripts. The human ␤III spectrin gene (SPTBN2) maps to chromosome 11q13 and the mouse gene (Spnb3) maps to a syntenic region close to the centromere on chromosome 19. Indirect immunof luorescence studies of cultured cells using antisera specific to human ␤III spectrin reveal a Golgiassociated and punctate cytoplasmic vesicle-like distribution, suggesting that ␤III spectrin associates with intracellular organelles. This distribution overlaps that of several Golgi and vesicle markers, including mannosidase II, p58, transGolgi network (TGN)38, and ␤-COP and is distinct from the endoplasmic reticulum markers calnexin and Bip. Liver Golgi membranes and other vesicular compartment markers cosediment in vitro with ␤III spectrin. ␤III spectrin thus constitutes a major component of the Golgi and vesicular membrane skeletons.

Spectrin (␤I⌺‫)ء‬ and ankyrin (Ank G119 ) associate with Golgi membranes and the dynactin complex, but their role in vesicle trafficking remains uncertain. We find that the actin-binding domain and membrane-association domain 1 (MAD1) of ␤I spectrin together form a constitutive Golgi targeting signal in transfected MDCK cells. Expression of this signal in transfected cells disrupts the endogenous Golgi spectrin skeleton and blocks transport of ␣-and ␤-Na,K-ATPase and vesicular stomatitis virus-G protein from the endoplasmic reticulum (ER) but does not disrupt the formation of Golgi stacks, the distribution of ␤-COP, or the transport and surface display of E-cadherin. The Golgi spectrin skeleton is thus required for the transport of a subset of membrane proteins from the ER to the Golgi. We postulate that together with polyfunctional adapter proteins such as Ank G119 , Golgi spectrin forms a docking complex that acts prior to the cis-Golgi, presumably with vesicular-tubular clusters (VTCs or ERGIC), to sequester specific membrane proteins into vesicles transiting between the ER and Golgi, and subsequently (probably involving other isoforms of spectrin and ankyrin) to mediate cargo transport within the Golgi and to other membrane compartments. We hypothesize that this vesicular spectrin-ankyrin adapter-protein trafficking (or tethering) system (SAATS) mediates the capture and transport of many membrane proteins and acts in conjunction with vesicle-targeting molecules to effect the efficient transport of cargo proteins.

Diseases of ectopic calcification of the vascular wall range from lethal orphan diseases such as generalized arterial calcification of infancy (GACI), to common diseases such as hardening of the arteries associated with aging and calciphylaxis of chronic kidney disease (CKD). GACI is a lethal orphan disease in which infants calcify the internal elastic lamina of their medium and large arteries and expire of cardiac failure as neonates, while calciphylaxis of CKD is a ubiquitous vascular calcification in patients with renal failure. Both disorders are characterized by vascular Mönckeburg's sclerosis accompanied by decreased concentrations of plasma inorganic pyrophosphate (PPi). Here we demonstrate that subcutaneous administration of an ENPP1-Fc fusion protein prevents the mortality, vascular calcifications and sequela of disease in animal models of GACI, and is accompanied by a complete clinical and biomarker response. Our findings have implications for the treatment of rare and common diseases of ectopic vascular calcification.

Homologues of two major components of the well-characterized erythrocyte plasma-membrane-skeleton, spectrin (a not-yet-cloned isoform, ␤I⌺* spectrin) and ankyrin (Ank G119 and an Ϸ195-kDa ankyrin), associate with the Golgi complex. ADP ribosylation factor (ARF) is a small G protein that controls the architecture and dynamics of the Golgi by mechanisms that remain incompletely understood. We find that activated ARF stimulates the in vitro association of ␤I⌺* spectrin with a Golgi fraction, that the Golgiassociated ␤I⌺* spectrin contains epitopes characteristic of the ␤I⌺2 spectrin pleckstrin homology (PH) domain known to bind phosphatidylinositol 4,5-bisphosphate (PtdInsP 2 ), and that ARF recruits ␤I⌺* spectrin by inducing increased PtdInsP 2 levels in the Golgi. The stimulation of spectrin binding by ARF is independent of its ability to stimulate phospholipase D or to recruit coat proteins (COP)-I and can be blocked by agents that sequester PtdInsP 2 . We postulate that a PH domain within ␤I⌺* Golgi spectrin binds PtdInsP 2 and acts as a regulated docking site for spectrin on the Golgi. Agents that block the binding of spectrin to the Golgi, either by blocking the PH domain interaction or a constitutive Golgi binding site within spectrin's membrane association domain I, inhibit the transport of vesicular stomatitis virus G protein from endoplasmic reticulum to the medial compartment of the Golgi complex. Collectively, these results suggest that the Golgi-spectrin skeleton plays a central role in regulating the structure and function of this organelle.Despite the early recognition of a key role for the small G protein ADP ribosylation factor (ARF) among the molecules controlling the architecture of the Golgi complex (1), and recent advances in identifying structural components of this organelle (2-3), the mechanisms by which such control is effected remain obscure. Recently, homologues of two major components of the well-characterized erythrocyte plasmamembrane-skeleton, spectrin (a not-yet-cloned isoform, hence designed as ␤I⌺* spectrin) and ankyrin (Ank G119 and a Ϸ195-kDa ankyrin) have been identified in the Golgi complex (4-7), and a Golgi-targeting sequence has been identified in spectrin (7). The molecular mechanisms controlling such localization and its functional role remain incompletely understood.We now demonstrate a mechanism controlling Golgi spectrin association and investigate the acute effects of the loss of Golgi spectrin binding on intracellular membrane traffic. Spectrin uses at least two sites to bind to Golgi fractions in vitro. One site involves spectrin's membrane association domain (MAD) 1, in accord with studies identifying a Golgitargeting sequence in ␤I⌺* spectrin (7). The other site involves a pleckstrin homology (PH) domain within the MAD2 of ␤I⌺* spectrin. Binding at MAD2 is regulated by ARF, which recruits spectrin by increasing Golgi phosphatidylinositol 4,5-bisphosphate (PtdInsP 2 ) levels. Inhibitors of spectrin binding to Golgi block endoplasmic reticulum (ER) to Golgi t...

SummarySpectrin a2 (aII-spectrin) is a scaffolding protein encoded by the Spna2 gene and constitutively expressed in most tissues. Exon trapping of Spna2 in C57BL/6 mice allowed targeted disruption of aII-spectrin. Heterozygous animals displayed no phenotype by 2 years of age. Homozygous deletion of Spna2 was embryonic lethal at embryonic day 12.5 to 16.5 with retarded intrauterine growth, and craniofacial, neural tube and cardiac anomalies. The loss of aII-spectrin did not alter the levels of aI-or bI-spectrin, or the transcriptional levels of any b-spectrin or any ankyrin, but secondarily reduced by about 80% the steady state protein levels of bII-and bIII-spectrin. Residual bII-and bIII-spectrin and ankyrins B and G were concentrated at the apical membrane of bronchial and renal epithelial cells, without impacting cell morphology. Neuroepithelial cells in the developing brain were more concentrated and more proliferative in the ventricular zone than normal; axon formation was also impaired. Embryonic fibroblasts cultured on fibronectin from E14.5 (Spna2 2/2 ) animals displayed impaired growth and spreading, a spiky morphology, and sparse lamellipodia without cortical actin. These data indicate that the spectrin-ankyrin scaffold is crucial in vertebrates for cell spreading, tissue patterning and organ development, particularly in the developing brain and heart, but is not required for cell viability.