# A computational analysis of the role of integrins and Rho-GTPases in the emergence and disruption of apical-basal polarization in renal epithelial cells

## TL;DR

This study uses a computational model to show how integrins and Rho-GTPases control the formation and stability of cell polarity in kidney cells.

## Contribution

A novel computational framework integrating protein interactions to reveal how integrins and Rho-GTPases regulate apical-basal polarization.

## Key findings

- Polarization requires a minimum concentration of integrins to initiate.
- Polarization is stable once formed and can only be disrupted by complete degradation of Rho and Cdc42.
- Reduced Rho-GTPase Rho levels coincide with epithelial-to-mesenchymal transition in experiments.

## Abstract

Apical-basal polarization in renal epithelial cells is crucial to renal function and an important trigger for tubule formation in kidney development. Loss of polarity can induce epithelial-to-mesenchymal transition (EMT), which can lead to kidney pathologies. Understanding the relative and combined roles of the involved proteins and their interactions that govern epithelial polarity may provide insights for controlling the process of polarization via chemical or mechanical manipulations in an in vitro or in vivo setting. Here, we developed a computational framework that integrates several known interactions between integrins, Rho-GTPases Rho, Rac and Cdc42, and polarity complexes Par and Scribble, to study their mutual roles in the emergence of polarization. The modeled protein interactions were shown to induce the emergence of polarized distributions of Rho-GTPases, which in turn led to the accumulation of apical and basal polarity complexes Par and Scribble at their respective poles, effectively recapitulating polarization. Our multiparametric sensitivity analysis suggested that polarization depends foremost on the mutual inhibition between Rac and Rho. Next, we used the computational framework to investigate the role of integrins and GTPases in the generation and disruption of polarization. We found that a minimum concentration of integrins is required to catalyze the process of polarization. Furthermore, loss of polarization was found to be only inducible via complete degradation of the Rho-GTPases Rho and Cdc42, suggesting that polarization is fairly stable once it is established. Comparison of our computational predictions against data from in vitro experiments in which we induced EMT in renal epithelial cells while quantifying the relative Rho-GTPase levels, displayed that EMT coincides with a large reduction in the Rho-GTPase Rho. Collectively, these results demonstrate the essential roles of integrins and Rho-GTPases in the establishment and disruption of apical-basal polarity and thereby provide handles for the in vitro or in vivo regulation of polarity.

Apical-basal polarization of renal epithelial cells lies at the foundation of the kidney’s biological function and is the catalyst for tubulogenesis during kidney development. Although individual parts of the polarization pathway have been extensively studied before, a deep understanding of the combined and relative roles of the different proteins and/or protein interactions that lead to the emergence of polarization remains lacking due to the complexity of the various and integrated pathways. To dissect the complexity, we constructed a computational model that integrates known mechanisms of the polarization pathway. We found that the emergence of polarization is heavily dependent on a specific subset of the interactions between the involved proteins (i.e. integrins, Rho-GTPases, and polarity proteins Par and Scribble). Specifically, we concluded from our model that polarization could only be initiated when the number of integrins exceeded a threshold value, while polarization could only be disrupted in our model by complete degradation of certain Rho-GTPases. Collectively, these results indicate that apical-basal polarization is a stable process once it has emerged. Our findings help in deepening the understanding of the polarization pathway and provide new insights for regulating apical-basal polarization.