Biology subjects

Bulgakova, N. A.

Publications and source records attributed to Bulgakova, N. A..

8 recordsLinked to original sources

bioRxiv2024

E-cadherin endocytosis promotes non-canonical EGFR:STAT signalling to induce cell death and inhibit heterochromatinisation

Signalling molecules often contribute to several signalling pathways that produce distinct transcriptional outputs and cellular phenotypes. One of the major unanswered questions in cell biology is how multiple activities of signalling molecules are coordinated in space and time in vivo. Here, we focus on the Signal Transducer and Activator of Transcription (STAT) protein as a paradigm of signalling molecules involved in several independent signalling pathways. In addition to the canonical pathways, whereby STAT is phosphorylated and activated by Janus Kinases, STAT is involved in at least two non-canonical pathways. In one pathway, STAT is activated by the Epidermal Growth Factor Receptor (EGFR) promoting apoptosis. In another, it binds the Heterochromatin Protein 1 (HP1) to enhance heterochromatin formation. Using Drosophila wing discs as an epithelial system, we demonstrate that all three STAT activities coexist in this tissue. We provide evidence that while the canonical STAT signalling is dominant over non-canonical pathways, EGFR:STAT and HP1:STAT pathways compete for the availability of unphosphorylated STAT. We also describe the role of the cell-cell adhesion protein E-cadherin in EGFR:STAT signalling. Both EGFR and STAT colocalise with E-cadherin at cell-cell junctions and on intracellular vesicles. Elevated intracellular E-cadherin promotes EGFR:STAT pathway leading to apoptosis, whereas blocking E-cadherin endocytosis prevents apoptosis induction. Altogether, we propose that E-cadherin endocytosis controls the balance between two non-canonical STAT activities in a potential tumour-suppressive mechanism - junctional disassembly in dysregulated epithelial-to-mesenchymal transitions would shift this balance towards the EGFR:STAT signalling to promote apoptosis.

cell biology↗

bioRxiv2021

Multifaceted control of E-cadherin dynamics by the Adaptor Protein Complex 1 during epithelial morphogenesis

Intracellular trafficking regulates the distribution of transmembrane proteins including the key determinants of epithelial polarity and adhesion. The Adaptor Protein 1 (AP-1) complex is the key regulator of vesicle sorting, which binds many specific cargos. We examined roles of the AP-1 complex in epithelial morphogenesis, using the Drosophila wing as a paradigm. We found that AP-1 knockdown leads to ectopic tissue folding, which is consistent with the observed defects in integrin targeting to the basal cell-extracellular matrix adhesion sites. This occurs concurrently with an integrin-independent induction of cell death, which counteracts elevated proliferation and prevents hyperplasia. We discovered a distinct pool of AP-1, which localizes at the subapical Adherens Junctions. Upon AP-1 knockdown, E-cadherin is hyperinternalized from these junctions and becomes enriched at the Golgi and recycling endosomes. We then provide evidence that E-cadherin hyperinternalization acts upstream of cell death in a potential tumour-suppressive mechanism. Simultaneously, cells compensate for elevated internalization of E-cadherin by increasing its expression to maintain cell-cell adhesion. Author SummaryThe epithelium is one of the four types of tissues found in animals and is essential for the normal development and maintenance of multicellular organisms. In this tissue, the adhesion protein E-cadherin helps keep cells together and facilitates the coordination of their behaviours. E-cadherin is highly dynamic and undergoes constant turnover by intracellular trafficking machinery. Here, we describe the contributions of one of the core components of intracellular trafficking, the AP-1 complex to E-cadherin dynamics. Using epithelial cells from Drosophila melanogaster, we discover that the AP-1 complex limits E-cadherin internalization from the plasma membrane, which is consistent with the localization of a distinct pool of the AP-1 complex at the sites of E-cadherin cell-cell adhesion. We also show that increased E-cadherin internalization triggers programmed cell death, preventing the tissue from hyperplastic overgrowth in a potential tumour-suppressive mechanism. At the same time, cells compensate for the reduction in the membrane presentation of E-cadherin by increasing its expression, therefore protecting tissue integrity.

cell biology↗

bioRxiv2020

The Adaptor Protein Complex 1 limits E-cadherin endocytosis during epithelial morphogenesis

cell biology↗

bioRxiv2019

The walkoff effect: cargo distribution implies motor type in bidirectional microtubule bundles

Cells rely on molecular motors moving along an ever-shifting network of polymers (microtubules) for the targeted delivery of cell organelles to biologically-relevant locations. We present a stochastic model for a molecular motor stepping along a bidirectional bundle of microtubules, as well as a tractable analytical model. Using these models, we investigate how the preferred stepping direction of the motor (parallel or antiparallel to the microtubule growth, corresponding to kinesin and dynein motor families) quantitatively and qualitatively affects the cargo delivery. We predict which motor type is responsible for which cargo type, given the experimental distribution of cargo in the cell, and report experimental findings which support this guideline for motor classification.

cell biology↗

bioRxiv2019

Cellular crowding guides and debundles the microtubule cytoskeleton

Cytoplasm is densely packed with macromolecules causing cellular crowding, which alters interactions inside cells and differs between biological systems. Here we investigate the impact of crowding on microtubule cytoskeleton organization. Using mathematical modelling, we find that only anisotropic crowding affects the mean microtubule direction, but any crowding reduces the number of microtubules that form bundles. We validate these predictions in vivo using Drosophila follicular epithelium. Since cellular components are transported along microtubules, our results identify cellular crowding as a novel regulator of this transport and cell organization.

cell biology↗

bioRxiv2019

Robustness of bidirectional microtubule network self-organization

Robustness of biological systems is crucial for their survival, however, for many systems its origin is an open question. Here we analyze one sub-cellular level system, the microtubule cytoskeleton. Microtubules self-organize into a network, along which cellular components are delivered to their biologically relevant locations. While individual microtubule are highly dynamic with their dynamics depends on the organism environment and genetics, network sensitivity to this dynamics would result in pathologies. Combining mathematical modelling with genetic manipulations in Drosophila, we show that the microtubule self-organization indeed does not depend on dynamics of individual microtubules, and thus is robust on the tissue level. We demonstrate the origin of this robustness via a mathematical model, suggesting this being a generic mechanism.

cell biology↗

bioRxiv2019

Interplay between cortical actin and E-cadherin dynamics regulates cell shape in the Drosophila embryonic epidermis

Precise regulation of cell shape is vital for building functional tissues. Here, we study the mechanisms which lead to the formation of highly elongated anisotropic epithelial cells in the Drosophila epidermis. We demonstrate that this cell shape is the result of two counteracting mechanisms at the cell surface: actomyosin, which inhibits cell elongation downstream of RhoA signalling, and intercellular adhesion, modulated via clathrin-mediated endocytosis of E-cadherin, which promotes cell elongation downstream of the GTPase Arf1. We show that these two mechanisms are interconnected, with RhoA signalling activity reducing Arf1 recruitment to the plasma membrane. Additionally, cell adhesion itself regulates both mechanisms: p120-catenin, a regulator of intercellular adhesion, promotes the activity of both Arf1 and RhoA. Altogether, we uncover a complex network of interactions between cell-cell adhesion, the endocytic machinery, and the actomyosin cortex, and demonstrate how this network regulates cell shape in an epithelial tissue in vivo.

developmental biology↗

bioRxiv2018

E-cadherin endocytosis is modulated by p120-catenin through the opposing actions of RhoA and Arf1

The regulation of E-cadherin at the plasma membrane by endocytosis is of vital importance for developmental and disease. p120-catenin, which binds to the E-cadherin C-terminus, can both promote and inhibit E-cadherin endocytosis. However, little is known about what determines the directionality of p120-catenin activity, and the molecules downstream. Here, we have discovered that p120-catenin fine-tunes the clathrin-mediated endocytosis of E-cadherin in Drosophila embryonic epidermal cells. It simultaneously activated two actin-remodelling pathways with opposing effects: RhoA, which stabilized E-cadherin at the membrane, and Arf1, which promoted internalization. Epistasis experiments revealed that RhoA additionally inhibited Arf1. E-cadherin was efficiently endocytosed only in the presence of intermediate p120-catenin amounts with too little and too much p120-catenin inhibiting E-cadherin endocytosis. Finally, we found that p120-catenin levels altered the tension of the plasma membrane. Altogether, this shows that p120-catenin is a central hub which co-ordinates cell adhesion, endocytosis, and actin dynamics with tissue tension.

cell biology↗