Dual specificity kinase DYRK3 regulates cell migration by influencing the stability of protrusions.

Plasma membrane-associated platforms (PMAPs) form at specific sites of plasma membrane by scaffolds including ERC1 and Liprin-α1. We identify a mechanism regulating PMAPs assembly, with consequences on motility/invasion. Silencing Ser/Thr kinase DYRK3 in invasive breast cancer cells inhibits their motility and invasive capacity. Similar effects on motility were observed by increasing DYRK3 levels, while kinase-dead DYRK3 had limited effects. DYRK3 overexpression inhibits PMAPs formation and has negative effects on stability of lamellipodia and adhesions in migrating cells. Liprin-α1 depletion results in unstable lamellipodia and impaired cell motility. DYRK3 causes increased Liprin-α1 phosphorylation. Increasing levels of Liprin-α1 rescue the inhibitory effects of DYRK3 on cell spreading, suggesting that an equilibrium between Liprin-α1 and DYRK3 levels is required for lamellipodia stability and tumor cell motility. Our results show that DYRK3 is relevant to tumor cell motility, and identify a PMAP target of the kinase, highlighting a new mechanism regulating cell edge dynamics.

DYRK3 enables secretory trafficking by maintaining the liquid-like state of ER exit sites.

The dual-specificity kinase DYRK3 controls the formation and dissolution of multiple biomolecular condensates, regulating processes including stress recovery and mitotic progression. Here, we report that DYRK3 functionally interacts with proteins associated with endoplasmic reticulum (ER) exit sites (ERESs) and that inhibition of DYRK3 perturbs the organization of the ERES-Golgi interface and secretory trafficking. DYRK3-mediated regulation of ERES depends on the N-terminal intrinsically disordered region (IDR) of the peripheral membrane protein SEC16A, which co-phase separates with ERES components to form liquid-like condensates on the surface of the ER. By modulating the liquid-like properties of ERES, we show that their physical state is essential for functional cargo trafficking through the early secretory pathway. Our findings support a mechanism whereby phosphorylation by DYRK3 and its reversal by serine-threonine phosphatases regulate the material properties of ERES to create a favorable physicochemical environment for directional membrane traffic in eukaryotic cells.

Kinase-controlled phase transition of membraneless organelles in mitosis.

Liquid-liquid phase separation has been shown to underlie the formation and disassembly of membraneless organelles in cells, but the cellular mechanisms that control this phenomenon are poorly understood. A prominent example of regulated and reversible segregation of liquid phases may occur during mitosis, when membraneless organelles disappear upon nuclear-envelope breakdown and reappear as mitosis is completed. Here we show that the dual-specificity kinase DYRK3 acts as a central dissolvase of several types of membraneless organelle during mitosis. DYRK3 kinase activity is essential to prevent the unmixing of the mitotic cytoplasm into aberrant liquid-like hybrid organelles and the over-nucleation of spindle bodies. Our work supports a mechanism in which the dilution of phase-separating proteins during nuclear-envelope breakdown and the DYRK3-dependent degree of their solubility combine to allow cells to dissolve and condense several membraneless organelles during mitosis.

Tug-of-war between dissimilar teams of microtubule motors regulates transport and fission of endosomes.

Intracellular transport is interspersed with frequent reversals in direction due to the presence of opposing kinesin and dynein motors on organelles that are carried as cargo. The cause and the mechanism of reversals are unknown, but are a key to understanding how cargos are delivered in a regulated manner to specific cellular locations. Unlike established single-motor biophysical assays, this problem requires understanding of the cooperative behavior of multiple interacting motors. Here we present measurements inside live Dictyostelium cells, in a cell extract and with purified motors to quantify such an ensemble function of motors. We show through precise motion analysis that reversals during endosome motion are caused by a tug-of-war between kinesin and dynein. Further, we use a combination of optical trap-based force measurements and Monte Carlo simulations to make the surprising discovery that endosome transport uses many (approximately four to eight) weak and detachment-prone dyneins in a tug-of-war against a single strong and tenacious kinesin. We elucidate how this clever choice of dissimilar motors and motor teams achieves net transport together with endosome fission, both of which are important in controlling the balance of endocytic sorting. To the best of our knowledge, this is a unique demonstration that dynein and kinesin function differently at the molecular level inside cells and of how this difference is used in a specific cellular process, namely endosome biogenesis. Our work may provide a platform to understand intracellular transport of a variety of organelles in terms of measurable quantities.