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Biomedical subjects

Naoyuki Nishiya

Publications and source records attributed to Naoyuki Nishiya.

5 recordsLinked to original sources
PubMed2005

An alpha4 integrin-paxillin-Arf-GAP complex restricts Rac activation to the leading edge of migrating cells.

Formation of a stable lamellipodium at the front of migrating cells requires localization of Rac activation to the leading edge. Restriction of alpha4 integrin phosphorylation to the leading edge limits the interaction of alpha4 with paxillin to the sides and rear of a migrating cell. The alpha4-paxillin complex inhibits stable lamellipodia, thus confining lamellipod formation to the cell anterior. Here we report that binding of paxillin to the alpha4 integrin subunit inhibits adhesion-dependent lamellipodium formation by blocking Rac activation. The paxillin LD4 domain mediates this reduction in Rac activity by recruiting an ADP-ribosylation factor GTPase-activating protein (Arf-GAP) that decreases Arf activity, thereby inhibiting Rac. Finally, the localized formation of the alpha4-paxillin-Arf-GAP complex mediates the polarization of Rac activity and promotes directional cell migration. These findings establish a mechanism for the spatial localization of Rac activity to enhance cell migration.

ADP-Ribosylation Factors↗
PubMed2004

CD98hc (SLC3A2) mediates integrin signaling.

Integrins regulate cellular behaviors through signaling pathways, including Rho GTPases and kinases. CD98 heterodimers, comprised of a heavy chain (CD98hc, SLC3A2) and one of several light chains, interact with integrins through CD98hc. CD98hc overexpression leads to anchorage-independent cell growth and tumorigenesis in 3T3 fibroblasts and activates certain integrin-regulated signaling pathways. To establish the biological function of CD98hc, we disrupted the gene and analyzed CD98hc-null cells. Here we report that CD98hc contributes to integrin-dependent cell spreading, cell migration, and protection from apoptosis. Furthermore, CD98hc is required for efficient adhesion-induced activation of Akt and Rac GTPase, major contributors to the integrin-dependent signals involved in cell survival and cell migration. CD98 promotes amino acid transport through its light chains; however, a CD98hc mutant that interacts with beta1 integrins, but not CD98 light chains, restored integrin-dependent signaling and protection from apoptosis. beta1 integrins are involved in the pathogenesis of certain cancers. CD98hc deletion markedly impaired the ability of embryonic stem cells to form teratocarcinomas in mice; teratocarcinoma formation was reconstituted by reexpression of CD98hc or of the mutant that interacts exclusively with integrins. Thus, CD98hc is an integrin-associated protein that mediates integrin-dependent signals, which promote tumorigenesis.

Animals↗
PubMed2002

Hic-5 interacts with GIT1 with a different binding mode from paxillin.

Hic-5, a member of the paxillin family of adaptor molecules, is localized at focal adhesion and implicated in integrin-mediated signaling. Hic-5 and paxillin exhibit structural homology and share interacting factors, however, diverse functions are suggested for them. In this study, we carried out yeast two-hybrid screening to identify Hic-5 interacting factors using its LD3-4 region, which includes the Hic-5-specific amino acid sequence, as a bait. Through the screening, we identified GIT1, an Arf GTPase-activating protein, as a Hic-5 binding protein. The interaction of these two proteins was mediated by the LD3 motif of Hic-5 and the C-terminal region, which includes a paxillin-binding subdomain, of GIT1. Although GIT1 is known as a paxillin-binding protein, we only observed weak association of paxillin with GIT1 in the overexpression system. In contrast, Hic-5 firmly bound to GIT1 under the same conditions. In addition, the paxillin/GIT1 complex contained PIX, a guanine nucleotide exchange factor, whereas the Hic-5/GIT1 complex contained a smaller amount of PIX. These results suggested that paxillin and Hic-5 associate with GIT1 with different binding modes, and that the Hic-5 complex possesses static features compared with the paxillin complex, which contains both positive and negative regulators of GTPases involved in actin dynamics. Moreover, Hic-5-mediated inhibition of cell spreading was restored by co-expression of the C-terminal fragment of GIT1, which perturbs the interaction of Hic-5 with endogenous GIT1. Thus, it was demonstrated that Hic-5 and GIT1 interact functionally in addition to showing a physical association.

3T3 Cells↗