Biology subjects

Ullo, M. F.

Publications and source records attributed to Ullo, M. F..

4 recordsLinked to original sources

bioRxiv2026

An intrinsically disordered adaptor protein controls the size and composition of EGFR condensates on membranes

Receptor phase separation is common in signaling pathways, yet mechanisms that limit condensate size and drive their dissolution remain poorly understood. For example, phosphorylated EGFR forms large micron-scale condensates in vitro, but assembles into smaller nanoscale clusters in cells, suggesting cellular regulation of condensate size. Here, we show that the intrinsically disordered adaptor protein GAB1 actively dissolves EGFR condensates and re-nucleates smaller, compositionally distinct assemblies in reconstituted supported lipid bilayers and simulations. Dissolution requires unphosphorylated tyrosines within the GAB1 intrinsically disordered region, and tyrosine phosphorylation acts as a regulatory switch that abolishes this activity. GAB1-nucleated assemblies require PH domain-driven oligomerization, which is inhibited by phosphoinositide lipids, linking membrane composition to nucleation. These results uncover two unexpected regulatory features in signaling pathways. First, unphosphorylated tyrosines may function broadly to regulate condensate size or stability, since similar tyrosine-based sequence features are found across hundreds of proteins, including many that function in signal transduction. Additionally, PH domains may play a broader role in protein oligomerization and receptor organization, as an AlphaFold screen reveals dozens of additional PH domains predicted to self-associate. Together, these results establish general mechanisms that function as modular tools for reprogramming signaling through receptor reorganization and may enable new approaches to target such pathways in disease.

biophysics↗

bioRxiv2023

The amoeboid migration of monocytes in confining channels requires the local remodeling of the cortical actin cytoskeleton by cofilin-1

Within the bloodstream, monocytes must traverse the microvasculature to prevent leukostasis, which is the entrapment of monocytes within the confines of the microvasculature. Using the model cell line, THP-1, and VCAM-1 coated channels to simulate the microvasculature surface, we demonstrate that monocytes predominantly adopt an amoeboid phenotype, which is characterized by the formation of blebs. As opposed to cortical actin flow in leader blebs, cell movement is correlated with myosin contraction at the cell rear. It was previously documented that cofilin-1 promotes cortical actin turnover at leader bleb necks in melanoma cells. In monocytes, our data suggest that cofilin-1 promotes the local upregulation of myosin contractility through actin cytoskeleton remodeling. In support of this concept, cofilin-1 is found to localize to a single cell edge. Moreover, the widespread upregulation of myosin contractility was found to inhibit migration. Thus, monocytes within the microvasculature may avoid entrapment by adopting an amoeboid mode of migration. Summary StatementIn confining channels, monocytes largely adopt an amoeboid migrating phenotype, which is found to depend on the upregulation of myosin contractility at the cell rear and cortical actin remodeling by cofilin-1.

cell biology↗

bioRxiv2021

ADF and cofilin-1 collaborate to promote cortical actin flow and the leader bleb-based migration of confined cells

Melanoma cells have been shown to undergo fast amoeboid (leader bleb-based) migration, requiring a single large bleb for migration. In leader blebs, is a rapid flow of cortical actin that drives the cell forward. Using RNAi, we find that co-depleting cofilin-1 and ADF led to a large increase in cortical actin, suggesting that both proteins regulate cortical actin. Furthermore, severing factors can promote contractility through the regulation of actin architecture. However, RNAi of cofilin-1 but not ADF led to a significant decrease in cell stiffness. We found cofilin-1 to be enriched at leader bleb necks, whereas RNAi of cofilin-1 and ADF reduced bleb sizes and the frequency of motile cells. Strikingly, cells without cofilin-1 and ADF had blebs with abnormally long necks. Many of these blebs failed to retract and displayed slow actin turnover. Collectively, our data identifies cofilin-1 and ADF as actin remodeling factors required for fast amoeboid migration.

cell biology↗

bioRxiv2020

Emerin regulation of nuclear stiffness is required for the amoeboid migration of cancer cells in confining environments

When metastasizing, tumor cells must traverse environments with diverse physicochemical properties. Recently, the cell nucleus has emerged as a major regulator of the transition from mesenchymal to fast amoeboid (leader bleb-based) migration. Here, in melanoma cells, we demonstrate that increasing nuclear stiffness through elevating Lamin A, inhibits fast amoeboid migration. Importantly, nuclei may respond to force through stiffening. A key factor in this process is the inner nuclear membrane (INM) protein, emerin. Accordingly, we determined the role of emerin in regulating fast amoeboid migration. Strikingly, we found that both the up- and down-regulation of emerin results in an inhibition of fast amoeboid migration. However, when key Src phosphorylation sites were removed, up-regulation of emerin no longer inhibited fast amoeboid migration. Interestingly, in confined cells, Src activity was low, as measured by a Src biosensor. Thus, the fast amoeboid migration of melanoma cells depends on the precise calibration of emerin activity. Summary StatementIn mechanically constrictive microenvironments, amoeboid migrating melanoma cells require emerin for the precise calibration of nuclear stiffness.

cell biology↗