A novel monoclonal antibody cross-reactive with both human and mouse α9 integrin useful for therapy against rheumatoid arthritis.

This study introduces a novel monoclonal anti-α9 integrin antibody (MA9-413) with human variable regions, isolated by phage display technology. MA9-413 specifically binds to both human and mouse α9 integrin by recognizing a conserved loop region designated as L1 (amino acids 104-122 of human α9 integrin). MA9-413 inhibits human and mouse α9 integrin-dependent cell adhesion to ligands and suppresses synovial inflammation and osteoclast activation in a mouse model of arthritis. This is the first monoclonal anti-α9 integrin antibody that can react with and functionally inhibit both human and mouse α9 integrin. MA9-413 allows data acquisition both in animal and human pharmacological studies without resorting to surrogate antibodies. Since MA9-413 showed certain therapeutic effects in the mouse arthritis model, it can be considered as a useful therapy against rheumatoid arthritis and other α9 integrin-associated diseases.

Constitutive Activation of Integrin α9 Augments Self-Directed Hyperplastic and Proinflammatory Properties of Fibroblast-like Synoviocytes of Rheumatoid Arthritis.

Despite advances in the treatment of rheumatoid arthritis (RA), currently approved medications can have significant side effects due to their direct immunosuppressive activities. Additionally, current therapies do not address residual synovial inflammation. In this study, we evaluated the role of integrin α9 and its ligand, tenascin-C (Tn-C), on the proliferative and inflammatory response of fibroblast-like synoviocytes (FLSs) from RA patients grown in three-dimensional (3D)-micromass culture. FLSs from osteoarthritis patients, when grown in the 3D-culture system, formed self-directed lining-like structures, whereas FLSs from RA tissues (RA-FLSs) developed an abnormal structure of condensed cellular accumulation reflective of the pathogenic features of RA synovial tissues. Additionally, RA-FLSs grown in 3D culture showed autonomous production of proinflammatory mediators. Predominant expression of α9 and Tn-C was observed in the condensed lining, and knockdown of these molecules abrogated the abnormal lining-like structure formation and suppressed the spontaneous expression of matrix metalloproteinases, IL-6, TNFSF11/RANKL, and cadherin-11. Disruption of α9 also inhibited expression of Tn-C, suggesting existence of a positive feedback loop in which the engagement of α9 with Tn-C self-amplifies its own signaling and promotes progression of synovial hyperplasia. Depletion of α9 also suppressed the platelet-derived growth factor-induced hyperplastic response of RA-FLSs and blunted the TNF-α-induced expression of matrix metalloproteinases and IL-6. Finally, α9-blocking Ab also suppressed the formation of the condensed cellular lining by RA-FLSs in 3D cultures in a concentration-related manner. This study demonstrates the central role of α9 in pathogenic behaviors of RA-FLSs and highlights the potential of α9-blocking agents as a nonimmunosuppressive treatment for RA-associated synovitis.

Rapostlin is a novel effector of Rnd2 GTPase inducing neurite branching.

Rho family GTPases are central regulators of neuronal morphology. Recently, Rnd proteins, Rnd1, Rnd2, and Rnd3/RhoE, have been identified as new members of Rho family GTPases. Of these, Rnd2 is specifically expressed in neurons in brain; however, the signaling pathways of Rnd2 are not known. Here we have performed a yeast two-hybrid screen using Rnd2 as a bait and identified a novel Rnd2-effector protein, expressed predominantly in brain. We named it Rapostlin (apostle of Rnd2). Rapostlin has two functional domains, Fer-CIP4 homology (FCH) domain at the amino terminus and SH3 (Src homology 3) domain at the carboxyl terminus. In in vitro binding assays, Rapostlin specifically binds to Rnd2 among the Rho family GTPases in a GTP-dependent manner, and the Rnd2-binding domain of Rapostlin is localized between FCH and SH3 domains. Rapostlin directly binds to microtubules, and the amino-terminal region containing the FCH domain of Rapostlin is essential for this interaction. In PC12 cells, Rapostlin induces neurite branching in response to Rnd2, and at least the amino-terminal region of Rapostlin is necessary for this activity. Therefore, Rapostlin is the first effector of Rnd2, regulating neurite branch formation.

Vps4-A (vacuolar protein sorting 4-A) is a binding partner for a novel Rho family GTPase, Rnd2.

Rho family GTPases are implicated in a variety of biological activities, including endocytic vesicle trafficking. Rnd2 is a new member of Rho family GTPases, but its biological functions are not known. In the present study, we have performed a yeast two-hybrid screening using Rnd2 as bait and revealed that Rnd2 binds specifically to Vps4-A (where Vsp4-A is vacuolar protein sorting 4-A), a member of the AAA ATPase family and a central regulator for early endosome trafficking. This interaction was determined by the yeast two-hybrid system, in vitro binding and co-immunoprecipitation studies. Vps4-A associated with both guanosine 5'-[beta-thio]triphosphate-bound active and guanosine 5'-[beta-thio]diphosphate-bound inactive forms of Rnd2. An ATPase-defective Vps4-A mutant, Vps4-A(E228Q), expressed in HeLa cells was accumulated in the early endosomes. When Rnd2 was co-expressed with Vps4-A(E228Q), Rnd2 was recruited to the Vps4-A-bound early endosomes. These results suggest that Rnd2 is involved in the regulation of endosomal trafficking via direct binding to Vps4-A.