Myosin 1g regulates cytoskeleton plasticity, cell migration, exocytosis, and endocytosis in B lymphocytes

Abstract

Myosin 1g (Myo1g) is a hematopoietic-specific myosin expressed mainly by lymphocytes. Here, we report the localization of Myo1g in B-cell membrane compartments such as lipid rafts, microvilli, and membrane extensions formed during spreading. By using Myo1g-deficient mouse B cells, we detected abnormalities in the adhesion ability and chemokineinduced directed migration of these lymphocytes. We also assessed a role for Myo1g in phagocytosis and exocytosis processes, as these were also irregular in Myo1g-deficient B cells. Taken together, our results show that Myo1g acts as a main regulator of different membrane/cytoskeleton-dependent processes in B lymphocytes.Keywords: B lymphocyte r Chemotaxis r Cytoskeleton r Exo-endocytosis r Myosin Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionMyosin I refers to a class of single-headed and actin-dependent molecular motors, which regulates a number of cellular functions, including intracellular transport, formation of cell-surface projections, regulation of the cytoskeleton, and regulation of membranerelated events, which includes exocytosis, endocytosis, and phagocytosis [1][2][3].Members of myosin I family contain a single heavy chain of 110-140 kDa [4,5], are monomeric, and do not form filaments unlike muscular/conventional myosin II. The single heavy chain is divided into the head (or motor), neck, and tail domains. The motor domain contains the ATP-binding (where ATP is adenosine triphosphate) site and the actin-binding site. This domain is Correspondence: Dr. Leopoldo Santos-Argumedo e-mail: lesantos@cinvestav.mx followed by the neck domain, which is involved in the binding of myosin light chains; molecules identified as calmodulin in vertebrate and yeast class I myosins [6]. Following the neck domain is the C-terminal tail region, which is enriched in basic residues and is involved in the binding of membrane phosphoinositides [7,8]. In humans and mice, eight different genes encode the eight heavy chains of class I myosins and are named Myo1a to Myo1h [2].Myosin 1g (Myo1g) is a vertebrate class I myosin, which is highly represented in leukocytes, according to microarray databases [9][10][11]. Immunoblot analyses of different tissues and cell lines recently identified this protein as being an exclusively hematopoietic motor protein [12,13].Mass spectrometric proteomic profiling of lymphocyte proteins indicates that Myo1g is the most abundant class I myosin * These authors contributed equally to this work. 878José L. Maravillas-Montero et al. Eur. J. Immunol. 2014. 44: 877-886 expressed by T lymphocytes [13]. Immunofluorescence assays showed that Myo1g localizes to the plasma membrane linked to phosphatidylinositol 4,5-bisphosphate and phosphatidylinositol 3,4,5-triphosphate [14], is particularly enriched at cell-surface microvilli, and associates in an ATP-releasable manner to the actin cytoskeleton [12,13]. In addition to its localization pattern, it has been proposed that this molecula...

Differential Effects of Environmental and Genetic Factors on T and B Cell Immune Traits

“…Given the comprehensive analysis of B cell subpopulations, we identified eQTL-effects on MYO1G expression and on the expression of a neighboring lncRNA. MYO1G has previously been implicated in B cell biology and blood cell numbers in a mouse model (Maravillas-Montero et al., 2014). Together, these results suggest the involvement of MYO1G in the active regulation of B cell levels in humans.…”

Class I myosins: Highly versatile proteins with specific functions in the immune system

“…). For example, the loss of MyoA in Dictyostelium brings a reduction in chemotaxis; a similar phenomenon has been described for Myo1g in B cells . Another example is MyoE from Dictyostelium discoideum that can bind to the same phospholipids (PIP 3 ) of the membrane than Myo1g and Myo1f from mice .…”

“…The analysis of lymphocyte proteomic profiles by mass spectrometry indicated that Myo1g is the most abundant class I myosin expressed by T lymphocytes. It localizes in the plasma membrane and is particularly enriched at the cell‐surface microvilli of T and B lymphocytes . Myo1g is also present in lipid rafts from B lymphocytes and neutrophils .…”

Myo1g is an active player in maintaining cell stiffness in B‐lymphocytes

“…In contrast, it is also known that this same alteration concurrently reduces the exocytosis of GPI‐anchored proteins in HeLa cells [Gauthier et al, ]. Additionally, we have previously reported an increase in the phagocytosis of S. aureus and a reduction in the secretion of tumor necrosis factor‐α by Myo1g −/− B‐cells [Maravillas‐Montero et al, ].…”

“…To eliminate the possibility that these changes were due to differences in CXCR5 expression, WT and Myo1g −/− B‐cells were stained and analyzed by FACS. The expression of CXCR5 is similar in the B‐lymphocytes from both types of mouse [Maravillas‐Montero et al, ].…”