The NESH/Abi-3-based WAVE2 complex is functionally distinct from the Abi-1-based WAVE2 complex

Abstract

BackgroundAbl interactor (Abi) family proteins play significant roles in actin cytoskeleton organization through participation in the WAVE complex. Mammals possess three Abi proteins: Abi-1, Abi-2, and NESH/Abi-3. Abi-1 and Abi-2 were originally identified as Abl tyrosine kinase-binding proteins. It has been disclosed that Abi-1 acts as a bridge between c-Abl and WAVE2, and c-Abl-mediated WAVE2 phosphorylation promotes actin remodeling. We showed previously that NESH/Abi-3 is present in the WAVE2 complex, but neither binds to c-Abl nor promotes c-Abl-mediated phosphorylation of WAVE2.ResultsIn this study, we characterized NESH/Abi-3 in more detail, and compared its properties with those of Abi-1 and Abi-2. NESH/Abi-3 was ectopically expressed in NIH3T3 cells, in which Abi-1, but not NESH/Abi-3, is expressed. The expression of NESH/Abi-3 caused degradation of endogenous Abi-1, which led to the formation of a NESH/Abi-3-based WAVE2 complex. When these cells were plated on fibronectin-coated dishes, the translocation of WAVE2 to the plasma membrane was significantly reduced and the formation of peripheral lamellipodial structures was disturbed, suggesting that the NESH/Abi-3-based WAVE2 complex was unable to help produce lamellipodial protrusions. Next, Abi-1, Abi-2, or NESH/Abi-3 was expressed in v-src-transformed NIH3T3 cells. Only in NESH/Abi-3-expressed cells did treatment with an Abl kinase inhibitor, imatinib mesylate, or siRNA-mediated knockdown of c-Abl promote the formation of invadopodia, which are ventral membrane protrusions with extracellular matrix degradation activity. Structural studies showed that a linker region between the proline-rich regions and the Src homology 3 (SH3) domain of Abi-1 is crucial for its interaction with c-Abl and c-Abl-mediated phosphorylation of WAVE2.ConclusionsThe NESH/Abi-3-based WAVE2 complex is functionally distinct from the Abi-1-based one, and NESH/Abi-3 may be involved in the formation of ventral protrusions under certain conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12964-015-0119-5) contains supplementary material, which is available to authorized users.

Microglia express ABI3 in the brains of Alzheimer's disease and Nasu-Hakola disease

“…WRC regulates Arp2/3-mediated actin filament nucleation and actin network assembly in response to the Rac GTPase. WRC containing ABI3 is functionally distinct from that containing ABI1 (17,18). Both ABI1 and ABI2 but not ABI3 promote the c-ABL-mediated phosphorylation of WAVE2, since ABI3 does not directly interact with c-ABL (17,18).…”

“…WRC containing ABI3 is functionally distinct from that containing ABI1 (17,18). Both ABI1 and ABI2 but not ABI3 promote the c-ABL-mediated phosphorylation of WAVE2, since ABI3 does not directly interact with c-ABL (17,18). WAVE2 phosphorylation by c-ABL activates WRC, leading to formation of lamellipodial membrane protrusions.…”

“…Members of ABI family encode a protein containing an aminoterminal homeodomain homologous region (HHR), a proline-rich (PR) region, and a carboxy-terminal SH3 domain. They constitute the WAVE regulatory complex (WRC) that regulates actin cytoskeleton organization (17,18). WRC is a macromolecular complex, composed of five-subunit proteins that include ABI (ABI1, ABI2 or ABI3), WAVE (WAVE1, WAVE2 or WAVE3), Nap1, PIR121/Sra1, and HSPC300 (19).…”

“…WAVE2 phosphorylation by c-ABL activates WRC, leading to formation of lamellipodial membrane protrusions. A linker region between the PR region and the SH3 domain of ABI1 is crucial for its interaction with c-ABL (18).…”

“…Forced expression of ABI3 in v-src-transformed NIH3T3 (SRD) cells, thyroid cancer cells, or colon cancer cells inhibits cell growth, invasiveness and migration, and enhances cellular senescence in vitro and reduces the tumor growth and metastasis in vivo, indicating that ABI3 acts as a tumor suppressor gene (20,22). In contrast, treatment of SRD cells overexpressing ABI3 with a tyrosine kinase inhibitor imatinib mesylate markedly promotes formation of invadopodia, actin-rich ventral membrane protrusions with extracellular matrix-degrading activity, and enhances the metastatic potential (18,23). Microglia, along with macrophages, are capable of producing podosomes, a matrix-degrading ventral cell surface structure similar to invadopodia (24).…”