MISP regulates the IQGAP1/Cdc42 complex to collectively orchestrate spindle orientation and mitotic progression

Barbara Vodicska,Elmar Schiebel,Berati Cerikan,Ingrid Hoffmann

doi:10.1038/s41598-018-24682-8

Barbara Vodicska, Elmar Schiebel + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-24682-8

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Abstract

Precise mitotic spindle orientation is essential for both cell fate and tissue organization while defects in this process are associated with tumorigenesis and other diseases. In most animal cell types, the dynein motor complex is anchored at the cell cortex and exerts pulling forces on astral microtubules to position the spindle. The actin-binding protein MISP controls spindle orientation and mitotic progression in human cells. However, the exact underlying mechanism remains to be elucidated. Here we report that MISP interacts with the multidomain scaffolding protein IQGAP1. We further show that MISP binds to the active form of Cdc42 through IQGAP1. Depletion of MISP promotes increased accumulation of IQGAP1 at the cell cortex and a decrease in its Cdc42-binding capacity leading to reduced active Cdc42 levels. Interestingly, overexpression of IQGAP1 can rescue mitotic defects caused by MISP downregulation including spindle misorientation, loss of astral microtubules and prolonged mitosis and also restores active Cdc42 levels. Importantly, we find that IQGAP1 acts downsteam of MISP in regulating astral microtubule dynamics and the localization of the dynactin subunit p150glued that is crucial for proper spindle positioning. We propose that MISP regulates IQGAP1 and Cdc42 to ensure proper mitotic progression and correct spindle orientation.

Highlights

Orientation of the mitotic spindle is a fundamental process in all multicellular organisms crucial for both symmetrical and asymmetrical cell divisions
We further show that overexpresion of IQGAP1 can rescue mitotic defects including spindle misorientation, loss of astral microtubules and prolonged mitosis caused by MISP downregulation while it restores active Cdc[42] levels
Using co-immunoprecipitation followed by mass spectrometry analysis with MISP as bait in mitotically blocked HeLa cells we identified the scaffolding protein IQGAP1 (Supplementary Fig. 1a), which has already been indicated in a previous screen as a potential interaction partner of MISP16 and which was shown to be involved in spindle orientation[5]

Summary

Introduction

Orientation of the mitotic spindle is a fundamental process in all multicellular organisms crucial for both symmetrical and asymmetrical cell divisions. Lack of MISP leads to mitotic defects including spindle orientation and positioning disorders, loss of astral microtubules, prolonged metaphases accompanied by SAC activation, chromosome misalignment, disrupted poles and increased mitotic index[2]. IQGAP1 was shown to be involved in regulating spindle orientation through restricting the distribution of NuMA to the basolateral membrane[5] and it regulates the capture and stabilization of astral MTs at the cell cortex in collaboration with its binding partner CLIP-1706,7. One of the best-characterized interaction partners of IQGAP1 is the small GTPase Cdc[42]. Together they regulate crosslinking of actin filaments, MT dynamics and E-cadherin-mediated cell–cell adhesion[8]. We further show that overexpresion of IQGAP1 can rescue mitotic defects including spindle misorientation, loss of astral microtubules and prolonged mitosis caused by MISP downregulation while it restores active Cdc[42] levels. Our results suggest that MISP collaborates with IQGAP1 and Cdc[42] to collectively orchestrate spindle orientation and mitotic progression

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