Mechanical Forces Regulate Nucleocytoplasmic Transport in Cell Monolayers Independently of Cell Density

Core Concepts

Nucleocytoplasmic transport responds to mechanical stimuli, such as osmotic shocks and inhibition of cell contractility, but not to cell-cell contacts in cell monolayers.

Abstract

The study demonstrates that nucleocytoplasmic transport (NCT) in cell monolayers is regulated by mechanical forces, independent of cell density. Using a fluorescent sensor of NCT called Sencyt, the authors show that:

Hypo-osmotic shocks increase nuclear volume, nuclear envelope tension, and Sencyt nuclear localization, while hyper-osmotic shocks have the opposite effects. This indicates that NCT responds to changes in nuclear mechanics.

Inhibition of cell contractility by blocking myosin II and Arp2/3 decreases Sencyt nuclear localization, even without visible changes in nuclear volume or shape. This suggests that NCT can be affected by mechanical perturbations without requiring large nuclear deformations.

In cell monolayers with varying densities, Sencyt nuclear localization correlates better with nuclear shape (solidity index) than with cell density.

In contrast, the localization of the transcription factor YAP correlates strongly with cell density, in addition to nuclear shape. This indicates that the regulation of YAP by both mechanics and cell-cell contacts operates through distinct mechanisms from the mechanical regulation of NCT.

The results demonstrate the generality of the mechanical regulation of NCT in multicellular systems and its separation from other mechanosensitive pathways like the Hippo-YAP axis. The Sencyt sensor provides a valuable tool to study NCT regulation in complex cellular environments.

Stats

Nuclear volume increased by 50% in MCF7 and 30% in C26 cells under hypo-osmotic shock.
Nuclear volume decreased by up to 40% in both cell lines under hyper-osmotic shock.
Sencyt nuclear localization increased under hypo-osmotic shock and decreased under hyper-osmotic shock.
Inhibition of myosin II and Arp2/3 decreased Sencyt nuclear localization.

Quotes

"Cells sense and respond to their mechanical context in a process called mechanotransduction."
"Force applied to the nucleus increases nuclear membrane tension, NPC diameter, and diffusion through NPCs."
"Mechanically induced changes in NCT can occur both with nuclear deformation (in response to osmotic shocks) and without (in response to contractility inhibition)."

Key Insights Distilled From

Nucleocytoplasmic transport senses mechanics independently of cell density in cell monolayers

by Granero-Moya... at www.biorxiv.org 01-12-2024

https://www.biorxiv.org/content/10.1101/2024.01.11.575167v1

Deeper Inquiries

How do different mechanical stimuli, such as substrate stiffness or cell-cell adhesion forces, affect nucleocytoplasmic transport in multicellular systems

In multicellular systems, nucleocytoplasmic transport (NCT) can be influenced by various mechanical stimuli, including substrate stiffness and cell-cell adhesion forces. Substrate stiffness affects NCT by altering the transmission of mechanical forces to the cell nucleus, which in turn impacts the nuclear envelope tension, NPC diameter, and the diffusion of molecules through NPCs. Higher substrate stiffness can lead to increased nuclear membrane tension, affecting the passive and active transport of molecules through the nuclear pores. On the other hand, cell-cell adhesion forces regulate NCT by influencing the localization and activity of transcriptional regulators like YAP. These forces can modulate the mechanotransduction pathways that control NCT, leading to changes in nuclear localization of specific proteins based on the mechanical environment of the cell.

What are the potential implications of the decoupled regulation of nucleocytoplasmic transport and YAP localization for cellular processes like proliferation and differentiation

The decoupled regulation of nucleocytoplasmic transport (NCT) and YAP localization in cellular processes like proliferation and differentiation has significant implications for understanding mechanotransduction mechanisms. While NCT responds primarily to mechanical stimuli, YAP localization is influenced by both mechanical cues and biochemical signaling pathways, such as the Hippo pathway. The differential responses of NCT and YAP to mechanical and biochemical signals suggest that cells have evolved distinct mechanisms to sense and respond to their mechanical and biochemical environments. This separation allows for fine-tuned control of cellular processes, where NCT may play a more direct role in translating mechanical cues into changes in gene expression and cellular behavior, while YAP integrates multiple signaling inputs to regulate proliferation and differentiation.

Could the Sencyt sensor be used to identify other mechanosensitive transcriptional regulators that are primarily regulated by nucleocytoplasmic transport rather than biochemical signaling pathways

The Sencyt sensor, designed to monitor nucleocytoplasmic transport (NCT) in response to mechanical forces, holds great potential for identifying other mechanosensitive transcriptional regulators that are primarily regulated by NCT rather than biochemical signaling pathways. By using Sencyt in combination with live imaging and image analysis techniques, researchers can track the nuclear localization of specific proteins in response to mechanical stimuli, providing insights into how NCT regulates gene expression and cellular functions. This approach could help uncover novel transcriptional regulators that are sensitive to changes in nuclear mechanics and could shed light on the intricate interplay between mechanical forces and gene regulation in multicellular systems.