Biology subjects

Fokin, A.

Publications and source records attributed to Fokin, A..

3 recordsLinked to original sources

bioRxiv2026

Coordinated Assembly of WAVE and WASH complexes

WAVE and WASH polymerize Arp2/3-mediated branched actin at the leading edge of migrating cells and on the surface of endosomes, respectively. These two proteins are regulated within similar multiprotein complexes, the assembly mechanism of which remains poorly understood. Here we found using mass spectrometry that the two smallest subunits, BRK1 of the WAVE complex and CCDC53 of the WASH complex, interact with each other and with the assembly factor HSBP1. HSBP1 promotes WAVE and WASH assemblies and their respective activities, migration persistence and endosomal branched actin. Reduced levels of WAVE and WASH complexes caused by HSBP1 depletion can be corrected by providing cells with an excess of BRK1 or CCDC53 to assemble their specific complex. Unexpectedly, endogenous levels of BRK1 cross-regulate WASH assembly, whereas those of CCDC53 cross-regulate WAVE assembly. We found that various oligomers comprising BRK1, CCDC53 and HSBP1, including a heterotrimer containing one molecule of each, are formed through their promiscuous coiled coils. These oligomers play a coordinating role in the assembly of WAVE and WASH complexes.

cell biology↗

bioRxiv2020

CYFIP2 containing WAVE complexes inhibit cell migration

Branched actin networks polymerized by the Arp2/3 complex are critical for cell migration. The WAVE complex is the machinery that activates Arp2/3 in a RAC1-dependent manner at the leading edge of migrating cells. Multiple WAVE complexes are assembled in a cell through various combinations of paralogous subunits. Here we report the surprising phenotype associated with loss-of-function of CYFIP2, a subunit of the WAVE complex. In three different human mammary cell lines and in prechordal plate cells of gastrulating zebrafish embryos, CYFIP2 depletion promoted, rather than impaired, membrane protrusions and migration persistence. CYFIP2, however, assembled WAVE complexes that polymerize branched actin at the cell cortex and rescued membrane protrusions of CYFIP1/2 double knock-out cells, although less efficiently than CYFIP1. Point mutations of CYFIP2 associated with intellectual disability in children were gain-of-function, as they made CYFIP2 as active as CYFIP1 in this rescue experiment. Biochemical reconstitutions of CYFIP2-containing WAVE complexes showed that they bound equally well to active RAC1 as CYFIP1-containing WAVE complexes, yet they were poorly activated in response to RAC1 binding. Together these results suggest that CYFIP2-containing WAVE complexes titrate active RAC1 and thereby prevent efficient CYFIP1-containing complexes from being activated. In this context, where cell migration is governed by the balance of CYFIP1/2 expression, releasing the restrained activity of CYFIP2-containing WAVE complexes leads to pathology.

cell biology↗

bioRxiv2019

Low Carbohydrate and Low Fat Diets with Equal Protein Content Lead to Similar Improvements in Body Composition and Glucose Tolerance in Obese Mice subjected to Caloric Restriction

BackgroundReported differences in effects of low and high carbohydrate diets on weight control and metabolic health are controversial. We aimed to examine if such diets induce different improvements in body composition and glucose tolerance under conditions of caloric restriction (CR) in obese mice. MethodsMale C57BL/6J mice (n = 20) were fed obesogenic diet (45 and 17.5% kcal from fat and sugar) ad libitum for 18 weeks and then subjected to 6-week CR which progressively increased up to 40% using either Low Fat diet (20, 60, 20% kcal from fat, carbohydrate, protein, n = 10) or Low Carb diet (20, 60, 20% kcal from carbohydrate, fat, protein, n = 10). Mice fed regular chow diet ad libitum served as controls (n = 10). Body mass, hind limb muscle mass, fat mass, energy expenditure and glucose tolerance were compared between the groups. ResultsLow Fat and Low Carb groups had similar body mass (p > 0.05) prior to CR which was 30% greater compared to control group (p < 0.001). CR resulted in weight loss with no differences between Low Fat and Low Carb groups (30.0 {+/-} 5.6 and 23.8 {+/-} 7.5%, p > 0.05). Weight loss was mainly due to fat loss in both groups. Energy expenditure of freely moving mice did not differ between the groups (p > 0.05). Intraperitoneal glucose tolerance test improved compared to control group (p < 0.05) and values before CR (p < 0.01) but without differences between Low Fat and Low Carb groups (p > 0.05). ConclusionsDietary carbohydrate or fat content when protein is equated does not play a significant role for body composition and metabolic health benefits of caloric restriction in obese mice.

physiology↗