LSP1 modulates the locomotion of monocyte-differentiated U937 cells

To examine the effect of lymphocyte specific protein 1 (LSP1) on phagocytic cell motility, stable transfection of LSP1-null U937 cell line with an episomal expression vector carrying the LSP1 complementary DNA created lines expressing varied LSP1 levels. Mock transfectants without LSP1 (U937(-)) and cell lines with LSP1 levels similar to those of monocytes (U937(+)) or 4-fold those of monocytes (U937(+)) express LSP1 as indicated and express other actin-binding proteins at normal levels before or after monocytic induction (MI) with dibutyryl cyclic adenosine monophosphate. The cell lines were compared for rate of growth and cell division and, after monocytic differentiation, were video-tracked to measure locomotion as distance moved in 2 hours and examined for morphologic changes. Rates of cell division and growth were similar for different U937 cell lines at all LSP1 levels. In contrast, mean rate of locomotion (micrometers moved in 2 hours) was slower in MI-U937( +) (7.78 + 1.11 microm, n = 3) and MI-U937(-) (23.89 + 2.78 microm, n = 3) than in MI-U937(+) cells (50.77 + 4.11 microm, n = 3). Compared with MI-U937(-), the locomotive histogram (n = 150 cells) of MI-U937(+) or MI-U937( +) cells shows all cells move respectively faster or slower as an entire cell population. In LSP1(+) U937 phagocytes, high LSP1 levels inhibit some (locomotion) but not all (cytokinesis) cell motile behaviors and cause the formation of surface projections. In contrast, normal LSP1 levels in U937 phagocytes enhance some (locomotion) but not all (cytokinesis) cellular motile behaviors and have no effect on cell morphology. Therefore, LSP1 level has a unique biphasic effect on cellular locomotion. The data suggest LSP1 is an important regulator of phagocyte locomotion.