Atsuko Sehara-Fujisawa

A metalloprotease-disintegrin, MDC9/meltrin-gamma/ADAM9 and PKCdelta are involved in TPA-induced ectodomain shedding of membrane-anchored heparin-binding EGF-like growth factor.

The ectodomains of many proteins located at the cell surface are shed upon cell stimulation. One such protein is the heparin‐binding EGF‐like growth factor (HB‐EGF) that exists in a membrane‐anchored form which is converted to a soluble form upon cell stimulation with TPA, an activator of protein kinase C (PKC). We show that PKCδ binds in vivo and in vitro to the cytoplasmic domain of MDC9/meltrin‐γ/ADAM9, a member of the metalloprotease–disintegrin family. Furthermore, the presence of constitutively active PKCδ or MDC9 results in the shedding of the ectodomain of proHB‐EGF, whereas MDC9 mutants lacking the metalloprotease domain, as well as kinase‐negative PKCδ, suppress the TPA‐induced shedding of the ectodomain. These results suggest that MDC9 and PKCδ are involved in the stimulus‐coupled shedding of the proHB‐EGF ectodomain.

Phosphorylation of cofilin by LIM-kinase is necessary for semaphorin 3A-induced growth cone collapse

Semaphorin 3A is a chemorepulsive axonal guidance molecule that depolymerizes the actin cytoskeleton and collapses growth cones of dorsal root ganglia neurons. Here we investigate the role of LIM-kinase 1, which phosphorylates an actin-depolymerizing protein, cofilin, in semaphorin 3A-induced growth cone collapse. Semaphorin 3A induced phosphorylation and dephosphorylation of cofilin at growth cones sequentially. A synthetic cell-permeable peptide containing a cofilin phosphorylation site inhibited LIM-kinase in vitro and in vivo, and essentially suppressed semaphorin 3A-induced growth cone collapse. A dominant-negative LIM kinase, which could not be activated by PAK or ROCK, suppressed the collapsing activity of semaphorin 3A. Phosphorylation of cofilin by LIM-kinase may be a critical signaling event in growth cone collapse by semaphorin 3A.

RGD-independent Binding of Integrin α9β1 to the ADAM-12 and -15 Disintegrin Domains Mediates Cell-Cell Interaction

ADAMs (a disintegrinand metalloproteases) mediate several important processes (e.g. tumor necrosis factor-α release, fertilization, and myoblast fusion). The ADAM disintegrin domains generally lack RGD motifs, and their receptors are virtually unknown. Here we show that integrin α9β1specifically interacts with the recombinant ADAMs-12 and -15 disintegrin domains in an RGD-independent manner. We also show that interaction between ADAM-12 or -15 and α9β1supports cell-cell interaction. Interestingly, the cation requirement and integrin activation status required for α9β1/ADAM-mediated cell adhesion and cell-cell interaction is similar to those required for known integrin-extracellular matrix interaction. These results are quite different from recent reports that ADAM-2/α6β1 interaction during sperm/egg fusion requires an integrin activation status distinct from that for extracellular matrix interaction. These results suggest that α9β1 may be a major receptor for ADAMs that lack RGD motifs, and that, considering a wide distribution of ADAMs and α9β1, this interaction may be of potential biological and pathological significance.

ADAM10 is a principal 'sheddase' of the low-affinity immunoglobulin E receptor CD23

CD23, the low-affinity immunoglobulin E receptor, is an important modulator of the allergic response and of diseases such as rheumatoid arthritis. The proteolytic release of CD23 from cells is considered a key event in the allergic response. Here we used loss-of-function and gain-of-function experiments with cells lacking or overexpressing candidate CD23-releasing enzymes (ADAM8, ADAM9, ADAM10, ADAM12, ADAM15, ADAM17, ADAM19 and ADAM33), ADAM-knockout mice and a selective inhibitor to identify ADAM10 as the main CD23-releasing enzyme in vivo. Our findings provide a likely target for the treatment of allergic reactions and set the stage for further studies of the involvement of ADAM10 in CD23-dependent pathologies.

Phenotypic Analysis of Meltrin α (ADAM12)-Deficient Mice: Involvement of Meltrin α in Adipogenesis and Myogenesis

ABSTRACT Meltrin α (ADAM12) is a metalloprotease-disintegrin whose specific expression patterns during development suggest that it is involved in myogenesis and the development of other organs. To determine the roles Meltrin α plays in vivo, we generated Meltrin α-deficient mice by gene targeting. Although the number of homozygous embryos are close to the expected Mendelian ratio at embryonic days 17 to 18, ca. 30% of the null pups born die before weaning, mostly within 1 week of birth. The viable homozygous mutants appear normal and are fertile. Most of the muscles in the homozygous mutants appear normal, and regeneration in experimentally damaged skeletal muscle is unimpeded. In some Meltrin α-deficient pups, the interscapular brown adipose tissue is reduced, although the penetrance of this phenotype is low. Impaired formation of the neck and interscapular muscles is also seen in some homozygotes. These observations suggest Meltrin α may be involved in regulating adipogenesis and myogenesis through a linked developmental pathway. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a candidate substrate of Meltrin α, and we found that TPA (12-O-tetradecanoylphorbol-13-acetate)-induced ectodomain shedding of HB-EGF is markedly reduced in embryonic fibroblasts prepared from Meltrin α-deficient mice. We also report here the chromosomal locations of Meltrin α in the mouse and rat.

Proteolytic Processing of Delta-like 1 by ADAM Proteases

Delta-like 1 (Dll1) is a mammalian ligand for Notch receptors. Interactions between Dll1 and Notch in trans activate the Notch pathway, whereas Dll1 binding to Notch in cis inhibits Notch signaling. Dll1 undergoes proteolytic processing in its extracellular domain by ADAM10. In this work we demonstrate that Dll1 represents a substrate for several other members of the ADAM family. In co-transfected cells, Dll1 is constitutively cleaved by ADAM12, and the N-terminal fragment of Dll1 is released to medium. ADAM12-mediated cleavage of Dll1 is cell density-dependent, takes place in cis orientation, and does not require the presence of the cytoplasmic domain of ADAM12. Full-length Dll1, but not its N- or C-terminal proteolytic fragment, co-immunoprecipitates with ADAM12. By using a Notch reporter construct, we show that Dll1 processing by ADAM12 increases Notch signaling in a cell-autonomous manner. Furthermore, ADAM9 and ADAM17 have the ability to process Dll1. In contrast, ADAM15 does not cleave Dll1, although the two proteins still co-immunoprecipitate with each other. Asn-353 present in the catalytic motif of ADAM12 and other Dll1-processing ADAMs, but absent in ADAM15, is necessary for Dll1 cleavage. Dll1 cleavage is reduced in ADAM9/12/15-/- mouse embryonic fibroblasts (MEFs), suggesting that the endogenous ADAM9 and/or ADAM12 present in wild type MEFs contribute to Dll1 processing. Finally, the endogenous Dll1 present in primary mouse myoblasts undergoes cleavage in confluent, differentiating myoblast cultures, and this cleavage is decreased by ADAM12 small interfering RNAs. Our findings expand the role of ADAM proteins in the regulation of Notch signaling.

Efficient and Reproducible Myogenic Differentiation from Human iPS Cells: Prospects for Modeling Miyoshi Myopathy In Vitro

The establishment of human induced pluripotent stem cells (hiPSCs) has enabled the production of in vitro, patient-specific cell models of human disease. In vitro recreation of disease pathology from patient-derived hiPSCs depends on efficient differentiation protocols producing relevant adult cell types. However, myogenic differentiation of hiPSCs has faced obstacles, namely, low efficiency and/or poor reproducibility. Here, we report the rapid, efficient, and reproducible differentiation of hiPSCs into mature myocytes. We demonstrated that inducible expression of myogenic differentiation1 (MYOD1) in immature hiPSCs for at least 5 days drives cells along the myogenic lineage, with efficiencies reaching 70–90%. Myogenic differentiation driven by MYOD1 occurred even in immature, almost completely undifferentiated hiPSCs, without mesodermal transition. Myocytes induced in this manner reach maturity within 2 weeks of differentiation as assessed by marker gene expression and functional properties, including in vitro and in vivo cell fusion and twitching in response to electrical stimulation. Miyoshi Myopathy (MM) is a congenital distal myopathy caused by defective muscle membrane repair due to mutations in DYSFERLIN. Using our induced differentiation technique, we successfully recreated the pathological condition of MM in vitro, demonstrating defective membrane repair in hiPSC-derived myotubes from an MM patient and phenotypic rescue by expression of full-length DYSFERLIN (DYSF). These findings not only facilitate the pathological investigation of MM, but could potentially be applied in modeling of other human muscular diseases by using patient-derived hiPSCs.

ADAM12 is highly expressed in carcinoma-associated stroma and is required for mouse prostate tumor progression

The interaction between stromal cells and tumor cells is emerging as a critical aspect of tumor progression. Yet there is a paucity of molecular markers for cells participating in such interactions, and only few genes are known to play a critical role in this process. Here, we describe the identification of ADAM12 (a disintegrin and metalloprotease 12) as a novel marker for a subpopulation of stromal cells that are adjacent to epithelial tumor cells in three mouse carcinoma models (models for prostate, breast and colon cancer). Moreover, we show that ADAM12 is essential for tumor development and progression in the W10 mouse model for prostate cancer. These results suggest that ADAM12 might be a useful marker for stromal cells in mouse tumors that are likely to participate in stromal/tumor cell crosstalk, and that ADAM12 is a potential target for design of drugs that prevent carcinoma growth.

ERK5 Regulates Muscle Cell Fusion through Klf Transcription Factors

In skeletal muscle differentiation, muscle-specific genes are regulated by two groups of transcription factors, the MyoD and MEF2 families, which work together to drive the differentiation process. Here, we show that ERK5 regulates muscle cell fusion through Klf transcription factors. The inhibition of ERK5 activity suppresses muscle cell fusion with minimal effects on the expression of MyoD, MEF2, and their target genes. Promoter analysis coupled to microarray assay reveals that Klf-binding motifs are highly enriched in the promoter regions of ERK5-dependent upregulated genes. Remarkably, Klf2 and Klf4 expression are also upregulated during differentiation in an ERK5-dependent manner, and knockdown of Klf2 or Klf4 specifically suppresses muscle cell fusion. Moreover, we show that Sp1 transcription factor links ERK5 to Klf2/4, and that nephronectin, a Klf transcriptional target, is involved in muscle cell fusion. Therefore, an ERK5/Sp1/Klf module plays a key role in the fusion process during skeletal muscle differentiation.

Meltrin β/ADAM19 mediates ectodomain shedding of Neuregulin β1 in the Golgi apparatus : fluorescence correlation spectroscopic observation of the dynamics of ectodomain shedding in living cells

Membrane‐anchored Neuregulin β1 sheds its ectodomain as soluble factors. Two proteases that belong to a disintegrin and metalloprotease (ADAM) family are known to cleave Neuregulin β1. One is tumor necrosis factor‐α converting enzyme (TACE/ADAM17). The other is Meltrin β (ADAM19). Against our expectation that shedding by ADAM proteases occurs at the cell surface, here we found that Meltrin β mediates the ectodomain shedding of Neuregulin β1 in the Golgi apparatus. Meltrin β was localized in and around the Golgi apparatus in developing sensory neurons. Subcellular fractionation revealed that Meltrin β generated soluble Neuregulin β1 in Golgi‐enriched fractions while TACE‐cleaved Neuregulin β1 was recovered in lighter fractions. To examine whether Meltrin β‐mediated ectodomain shedding occurs in the Golgi apparatus in living cells, we took advantage of different diffusion properties of cleavage products from those of membrane‐anchored precursor proteins. Fluorescence correlation spectroscopy (FCS) is the most sensitive method to determine milli∼submillisecond diffusion in vivo. Protease‐active Meltrin β caused a shift in autocorrelation function in FCS of green fluorescent protein (GFP)‐tagged Neuregulin β1 in the Golgi apparatus, suggesting a conversion of Neuregulin β1 molecules from membrane‐anchored to soluble forms in that organelle. The Golgi apparatus is a site of processing Neuregulin β1 by Meltrin β.