Myosin reorganization in activated RBL cells correlates temporally with stimulated secretion

Abstract

Rat basophilic leukemia cells secrete histamine and serotonin in response to cross-linking of the IgE receptor by multivalent antigen [Metzger et al., 1986: Ann. Rev. Immunol. 4:419-470]. Receptor crosslinking also induces phosphorylation of the light and heavy chains of myosin II with kinetics similar to that of secretion [Ludowyke et al., 1989: J. Biol. Chem. 264:12492-12501]. Here we show that myosin II localization changes after activation with similar kinetics. Furthermore, these changes are coincident with changes in cell shape and increase in motile activity induced by activation. Within 2 min, activated cells begin to flatten, spread on their substratum, and extend lamellipodia which show active ruffling. Quantitation of the extent of cell spreading from video micrographs shows that 48% of the cells increase significantly in surface area by 5 min and 71% by 15 min. Myosin II is uniformly distributed in unactivated cells but is deficient in newly formed lamellipodia that start to appear at 2 min after activation. In contrast these lamellipodia show strong staining for actin. Further changes in myosin organization are detected by 15 min after activation when myosin reappears in the cell periphery, is concentrated in the perinuclear area, and is also organized in punctate linear arrays that extend from the nucleus to the cell periphery. The kinetics of the early cell shape changes and formation of the myosin-deficient lamellipodia correlate well with, and may relate to, the increase in the level of myosin II phosphorylation reported by Ludowyke et al. [1989: J. Biol. Chem. 264:12492-12501]. Changes in the distribution of cell surface-bound IgE also occur upon antigen activation, and they correlate with the myosin distribution in a manner that suggests that they may be driven by myosin II.

Tissue-specific subcellular immunolocalization of a myosin-like protein in maize root apices

“…reported to induce movements of latex beads on Chara actin bundles (Shimmen and Yano 1984) and rotations of Nitella chloroplasts (Kuroda and Kamiya 1975). Moreover, similarly as we report it here for plant cells, myosin II is known to be localized in a spotlike manner throughout the cytoplasm in a wide range of eukaryotic cell types (Yonemura and Pollard 1992, Maupin et al 1994, Spudich 1994, Yumura 1996, Ikonen et al 1997.…”

Lysophosphatidic acid stimulates actomyosin contraction in astrocytes

“…Myosin II contraction is thought to serve a number of functions in nonmuscle cells including, involvement in formation of the cleavage furrow during cytokinesis (Schroeder, 1973;Fujiwara and Pollard, 1976;Rappaport, 1986), secretion (Kumakura et al, 1994;Spudich, 1994), cell motility (reviewed by Wilson et al,1992;Maciver, 1996), and cell contraction during wound healing (Martin and Lewis, 1992;Bement et al, 1993;Brock et al, 1996). Actin and myosin II have been localized to the edges of small injured areas both in monolayers of epithelial cells (Bement et al, 1993) and embryonic chicken wing bud (Martin and Lewis, 1992) where they may play a role in wound closure.…”

Rac regulates phosphorylation of the myosin-II heavy chain, actinomyosin disassembly and cell spreading

“…Phosphorylation of the myosin-II heavy chain occurs in several mammalian cell types 22 , but the biochemical or physiological consequences of this phosphorylation in vertebrate cells are largely unknown. Several studies have suggested a role for MHC phosphorylation in regulated secretion [23][24][25] . In lower eukaryotes such as Dictyostelium and Acanthamoeba, heavy-chain phosphorylation inhibits either the assembly or the activity of myosin II (ref.…”