Construction of a high-resolution 2.5-Mb transcript map of the human 6p21.2-6p21.3 region immediately centromeric of the major histocompatibility complex

DEF6(differentially exprehomolog) exacerbates pathological cardiac hypertrophy via RAC1

Pathological cardiac hypertrophy involves multiple regulators and several signal transduction pathways. Currently, the mechanisms of it are not well understood. Differentially expressed in FDCP 6 homolog (DEF6) was reported to participate in immunity, bone remodeling, and cancers. The effects of DEF6 on pathological cardiac hypertrophy, however, have not yet been fully characterized. We initially determined the expression profile of DEF6 and found that DEF6 was upregulated in hypertrophic hearts and cardiomyocytes. Our in vivo results revealed that DEF6 deficiency in mice alleviated transverse aortic constriction (TAC)-induced cardiac hypertrophy, fibrosis, dilation and dysfunction of left ventricle. Conversely, cardiomyocyte-specific DEF6-overexpression aggravated the hypertrophic phenotype in mice under chronic pressure overload. Similar to the animal experiments, the in vitro data showed that adenovirus-mediated knockdown of DEF6 remarkably inhibited phenylephrine (PE)-induced cardiomyocyte hypertrophy, whereas DEF6 overexpression exerted the opposite effects. Mechanistically, exploration of the signal pathways showed that the mitogen-activated extracellular signal-regulated kinase 1/2 (MEK1/2)-extracellular signal-regulated kinase 1/2 (ERK1/2) cascade might be involved in the prohypertrophic effect of DEF6. Coimmunoprecipitation and GST (glutathione S-transferase) pulldown analyses demonstrated that DEF6 can directly interact with small GTPase Ras-related C3 botulinum toxin substrate 1 (Rac1), and the Rac1 activity assay revealed that the activity of Rac1 is altered with DEF6 expression in TAC-cardiac hypertrophy and PE-triggered cardiomyocyte hypertrophy. In the end, western blot and rescue experiments using Rac1 inhibitor NSC23766 and the constitutively active mutant Rac1(G12V) verified the requirement of Rac1 and MEK1/2-ERK1/2 activation for DEF6-mediated pathological cardiac hypertrophy. Our study substantiates that DEF6 acts as a deleterious regulator of cardiac hypertrophy by activating the Rac1 and MEK1/2-ERK1/2 signaling pathways, and suggests that DEF6 may be a potential treatment target for heart failure.

Regulation of NDR2 protein kinase by multi-site phosphorylation and the S100B calcium-binding protein

Nuclear Dbf2-related (NDR) protein kinases are a family of AGC group kinases that are involved in the regulation of cell division and cell morphology. We describe the cloning and characterization of the human and mouse NDR2, a second mammalian isoform of NDR protein kinase. NDR1 and NDR2 share 86% amino acid identity and are highly conserved between human and mouse. However, they differ in expression pattern; mouse Ndr1 is expressed mainly in spleen, lung and thymus, whereas mouse Ndr2 shows highest expression in the gastrointestinal tract. NDR2 is potently activated in cells following treatment with the protein phosphatase 2A inhibitor okadaic acid, which also results in phosphorylation on the activation segment residue Ser-282 and the hydrophobic motif residue Thr-442. We show that Ser-282 becomes autophosphorylated in vivo, whereas Thr-442 is targeted by an upstream kinase. This phosphorylation can be mimicked by replacing the hydrophobic motif of NDR2 with a PRK2-derived sequence, resulting in a constitutively active kinase. Similar to NDR1, the autophosphorylation of NDR2 protein kinase was stimulated in vitro by S100B, an EF-hand Ca(2+)-binding protein of the S100 family, suggesting that the two isoforms are regulated by the same mechanisms. Further we show a predominant cytoplasmic localization of ectopically expressed NDR2.

Molecular cloning of IBP, a SWAP-70 homologous GEF, which is highly expressed in the immune system

Rho GTPases play a fundamental role in a variety of biological processes ranging from the reorganization of the actin cytoskeleton to the regulation of cell proliferation. The activation of Rho GTPases is regulated by guanine nucleotide exchange factors (GEFs) belonging to the Dbl family of proteins. The hallmark of this large family of GEFs is the presence of a tandem DH-PH module in which a pleckstrin-homology (PH) domain is located at the C-terminus of a Dbl-homology (DH) domain. Recent studies have demonstrated that SWAP-70 constitutes a novel class of Rac-GEF, in which the PH domain is located at the N-terminus, rather than the C terminus, of the DH domain. Here we report the molecular cloning of human IBP (IRF-4 binding protein), a new member of this novel family of GEFs. The IBP gene maps to human chromosome 6p21.31 centromeric to the MHC locus. Isolation of the murine IBP cDNA reveals a very high degree of homology with the human IBP cDNA suggesting that IBP is evolutionarily conserved. The 5' portion of the murine IBP cDNA is furthermore identical to the Def-6 cDNA fragment, which was identified in the course of a search for genes differentially expressed in the murine hematopoietic system. IBP is broadly expressed in the immune system and can be detected in both T and B cell compartments in contrast to SWAP-70 whose expression is primarily restricted to B cells. Taken together these findings indicate that IBP is a novel type of GEF, which participates in the activation of Rho GTPases in lymphoid tissues.

Mechanism of Ca2+-mediated regulation of NDR protein kinase through autophosphorylation and phosphorylation by an upstream kinase

NDR1 (nuclear Dbf2-related) is a serine/threonine protein kinase belonging to subfamily of kinases implicated in the regulation of cell division and morphology. Previously, we demonstrated that the activity of NDR1 is controlled by phosphorylation of two regulatory residues, Ser-281 and Thr-444. Moreover, we found that NDR1 becomes activated through a direct interaction with EF-hand Ca(2+)-binding proteins of the S100 family. In this work, we characterize this regulatory mechanism in detail. We found that NDR1 autophosphorylates in vitro predominantly on Ser-281 and to a lesser extent on Thr-74 and Thr-444. All of these residues proved to be crucial also for NDR1 activity in vivo; however, in contrast to Ser-281 and Thr-444, Thr-74 seems to be involved only in binding to S100B rather than directly regulating NDR1 activity per se. When we added Ca(2+)/S100B, we observed an increased autophosphorylation on Ser-281 and Thr-444, resulting in stimulation of NDR1 activity in vitro. Using phosphospecific antibodies, we found that Ser-281 also becomes autophosphorylated in vivo, whereas Thr-444 is targeted predominantly by an as yet unidentified upstream kinase. Significantly, the Ca(2+)-chelating agent BAPTA-AM suppressed the activity and phosphorylation of NDR1 on both Ser-281 and Thr-444, and specifically, these effects were reversed when we added the sarcoplasmic-endoplasmic reticulum Ca(2+) ATPase pump inhibitor thapsigargin.

Mapping genes on an integrated sorghum genetic and physical map using cDNA selection technology

Sorghum is an important target of plant genomics. This cereal has unusual tolerance to adverse environments, a small genome (750 Mbp) relative to most other grasses, a diverse germplasm, and utility for comparative genomics with rice, maize and other grasses. In this study, a modified cDNA selection protocol was developed to aid the discovery and mapping of genes across an integrated genetic and physical map of the sorghum genome. BAC DNA from the sorghum genome map was isolated and covalently bound in arrayed tubes for efficient liquid handling. Amplifiable cDNA sequence tags were isolated by hybridization to individual sorghum BACs, cloned and sequenced. Analysis of a fully sequenced sorghum BAC indicated that about 80% of known or predicted genes were detected in the sequence tags, including multiple tags from different regions of individual genes. Data from cDNA selection using the fully sequenced BAC indicate that the occurrence of mislocated cDNA tags is very low. Analysis of 35 BACs (5.25 Mb) from sorghum linkage group B revealed (and therefore mapped) two sorghum genes and 58 sorghum ESTs. Additionally, 31 cDNA tags that had significant homologies to genes from other species were also isolated. The modified cDNA selection procedure described here will be useful for genome-wide gene discovery and EST mapping in sorghum, and for comparative genomics of sorghum, rice, maize and other grasses.

Isolation of a cDNA representing the Fanconi anemia complementation group E gene

Fanconi anemia (FA) is an autosomal recessive chromosomal instability syndrome with at least seven different complementation groups. Four FA genes (FANCA, FANCC, FANCF, and FANCG) have been identified, and two other FA genes (FANCD and FANCE) have been mapped. Here we report the identification, by complementation cloning, of the gene mutated in FA complementation group E (FANCE). FANCE has 10 exons and encodes a novel 536-amino acid protein with two potential nuclear localization signals.