A secreted protein is an endogenous chemorepellant in Dictyostelium discoideum

Abstract

Chemorepellants may play multiple roles in physiological and pathological processes. However, few endogenous chemorepellants have been identified, and how they function is unclear. We found that the autocrine signal AprA, which is produced by growing Dictyostelium discoideum cells and inhibits their proliferation, also functions as a chemorepellant. Wild-type cells at the edge of a colony show directed movement outward from the colony, whereas cells lacking AprA do not. Cells show directed movement away from a source of recombinant AprA and dialyzed conditioned media from wild-type cells, but not dialyzed conditioned media from aprA − cells. The secreted protein CfaD, the G protein Gα8, and the kinase QkgA are necessary for the chemorepellant activity of AprA as well as its proliferation-inhibiting activity, whereas the putative transcription factor BzpN is dispensable for the chemorepellant activity of AprA but necessary for inhibition of proliferation. Phospholipase C and PI3 kinases 1 and 2, which are necessary for the activity of at least one other chemorepellant in Dictyostelium , are not necessary for recombinant AprA chemorepellant activity. Starved cells are not repelled by recombinant AprA, suggesting that aggregation-phase cells are not sensitive to the chemorepellant effect. Cell tracking indicates that AprA affects the directional bias of cell movement, but not cell velocity or the persistence of cell movement. Together, our data indicate that the endogenous signal AprA acts as an autocrine chemorepellant for Dictyostelium cells.

A Retinoblastoma Orthologue Is Required for the Sensing of a Chalone in Dictyostelium discoideum

“…7). Cell speeds were similar to what we have previously observed (17), and there were no significant differences in the speeds of wild-type or rblA Ϫ cells in the presence or absence of a rAprA gradient. Together, these results suggest that RblA does not affect the ability of cells to move on a glass surface and that RblA is required for proper AprAinduced chemorepulsion.…”

“…This is supported by the observations that aprA Ϫ and cfaD Ϫ cells die more rapidly than wild-type cells after reaching stationary density and that starved aprA Ϫ and cfaD Ϫ cells produce fewer viable spores than do wildtype cells (14,15). AprA also acts as a chemorepellent, which helps to disperse cells at the edge of a colony (17). Retinoblastoma (RB) is a key regulatory protein of the cell cycle, and mutations in retinoblastoma can increase the chance of developing a specific hereditary ocular tumor also called retinoblastoma (18).…”

“…AprA acts as an autocrine chemorepellent that facilitates the spreading of groups of cells (17). We found that rblA Ϫ cells are able to sense and respond to an AprA gradient but less efficiently than wild-type cells.…”

“…Colony edge imaging was done as described previously (28). Chemotaxis of cells in response to rAprA was measured by using an Insall chamber (30) and a 0-to 2,000-ng/ml AprA gradient, as described previously (17). Cell speeds in the Insall chambers were measured according to methods described previously (31).…”

“…rblA ؊ cells have reduced sensitivity to the chemorepellent effect of AprA. High levels of extracellular AprA in the vicinity of a colony of cells, and lower levels far away from the colony, cause an AprA gradient that directs the chemotaxis of cells away from the colony (17). Since RblA is required for the effect of AprA on cell proliferation (Fig.…”