Materials Research Science and Engineering Center

Ricki Levitus

Brandeis / Biochemistry
Hosted by Goode's Lab

“Closing the GAP Between IQGAP1 and its Yeast Homologue”

Ricki Levitus, Greg Hoeprich, Bruce Goode

Abstract

IQGAP1 is actin binding protein localized to the leading edge of mammalian cells and plays an important role in cell migration. This process is common to many healthy cells including epithelial cells and neurons, but abnormal cell migration is a key contributor to metastasis of cancerous cells.
Understanding the molecular basis of actin regulation during cell migration has the potential to shed light on how these cancerous abnormalities arise. Previous studies have shown increasing actin density when IQGAP1 is knocked down. This phenotype is consistent with knocking down Capping Protein, which blocks actin assembly.

We hypothesize IQGAP1 similarly blocks actin assembly. To test this, we investigated the functions of mammalian IQGAP1 on actin assembly in vitro. Using total internal reflection fluorescence (TIRF) microscopy and bulk fluorescence assays we measured actin assembly in the presence of IQGAP1 to assess its effects. We show for the first time IQGAP1 attenuating actin elongation on single actin filaments. Our results are also consistent with the current working hypothesis that mammalian IQGAP1 attenuates actin elongation rates through a capping mechanism. Further, we provide evidence that mammalian IQGAP1 bundles actin filaments in vitro, validating previous results. Lastly, the protein Iqg1 was identified in the yeast model organism S. cerevisiae with sequence homology to mammalian IQGAP1.

Yeast is an ideal model organism for answering fundamental questions about the function of IQGAP1 in vivo as this project expands, but in vitro functional studies are required first to show similarity between yeast Iqg1 and mammalian IQGAP1. Moving forward, we plan to repeat the in vitro experiments above with the yeast homologue to confirm that the functions of mammalian IQGAP1 are evolutionarily conserved across species.

Support: SMURF (Summer MRSEC Undergrad Research Fellowship)