Abstract
Assembly of F-actin that links with β1-integrin during the G1 phase of cell cycle is released from β1-integrin and disrupted at mitosis. However, it remains unclear how F-actin assembly to which β1-integrin anchors is cell cycle-dependently regulated. We show that β1-integrin was co-immunoprecipitated and co-localized with a small GTPase Rac and its effector IQGAP1, along with PP2A-AC, in HME cells during G1. When the cells were accumulated to G2/M, the co-immunoprecipitation or co-localization of IQGAP1 and PP2A-AC with β1-integrin was lost, leaving Rac bound to β1-integrin. The dissociated IQGAP1 was co-immunoprecipitated with the concomitantly dissociated PP2A-A and -C, indicating the complex formation among the proteins in G2/M cells. Falling ball viscometric assays revealed that only IQGAP1-bound β1-integrin-Rac in G1 cells exhibited an enhanced F-actin cross-linking activity. The results suggest that the mitotic loss of F-actin assembly to which β1-integrin anchors is due to PP2A-mediated dissociation of IQGAP1 from Rac-bound β1-integrin.
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