AKAP350 targets to the centrosome and scaffolds a novel transforming acidic coiled-coil protein, TACC4

Abstract

AKAP350 is a multiply-spliced scaffolding protein that localizes to the centrosome -and Golgi apparatus. Two important characteristics of AKAP350 are its ability to interact with multiple signaling partners and to target to specific cellular structures. Here, we have identi_fied a novel interacting partner of AKAP350 from the Transforming Acidic Coiled-Coil protein family, TACC4. Localization of fusion GFP-TACC4 proteins to the centrosome in interphase Jurkat cells required AKAP350 interaction. During mitosis, GFP-TACC4 expression targeted to the spindle apparatus and delayed cell cycle progression. Multiple GFP-TACC4 transfected HeLa cells displayed Mad2-positive kinetochore staining suggesting GFP-TACC4 expression prolonged activation of the spindle checkpoint. AKAP350 localizes to the centrosome by a specific targeting sequence in its carboxyl terminus known as the PACT domain. Expression of GFP-PACT altered structures of the mitotic apparatus in Jurkat • cells. In interphase cells, hypertrophied centrosomes, fragmented centrosomes, and supernumerary centrosomes were increased with GFP-PACT expression. Mitotic cells displayed increased tripolar and multipolar spindle apparatuses. Expression of GFP-PACT in rat intestinal epithelial (RIE-1) cells altered its morphologic growth characteristics in a manner indicative of cellular transformation. We propose that AKAP350 scaffolds a multivalent complex to the centrosome that may play role in signaling pathways important for cellular transformation. Therefore, AKAP350 may provide further evidence that centrosome alterations are important in the biology of cancer.