Dictyostelium Erk2 is an atypical MAPK required for chemotaxis

Abstract

The Dictyostelium genome encodes only two MAPKs, Erk1 and Erk2, and both are expressed during growth and development. Reduced levels of Erk2 expression have been shown previously to restrict cAMP production during development but still allow for chemotactic movement. In this study the erk2 gene was disrupted to eliminate Erk2 function. The absence of Erk2 resulted in a complete loss of folate and cAMP chemotaxis suggesting that this MAPK plays an integral role in the signaling mechanisms involved with this cellular response. However, folate stimulation of early chemotactic responses, such as Ras and PI3K activation and rapid actin filament formation, were not affected by the loss of Erk2 function. The erk2 cells had a severe defect in growth on bacterial lawns but assays of bacterial cell engulfment displayed only subtle changes in the rate of bacterial engulfment. Only cells with no MAPK function, erk1erk2 double mutants, displayed a severe proliferation defect in axenic medium. Loss of Erk2 impaired the phosphorylation of Erk1 in secondary responses to folate stimulation indicating that Erk2 has a role in the regulation of Erk1 activation during chemotaxis. Loss of the only known Dictyostelium MAPK kinase, MekA, prevented the phosphorylation of Erk1 but not Erk2 in response to folate and cAMP confirming that Erk2 is not regulated by a conventional MAP2K. This lack of MAP2K phosphorylation of Erk2 and the sequence similarity of Erk2 to mammalian MAPK15 (Erk8) suggest that the Dictyostelium Erk2 belongs to a group of atypical MAPKs. MAPK activation has been observed in chemotactic responses in a wide range of organisms but this study demonstrates an essential role for MAPK function in chemotactic movement. This study also confirms that MAPKs provide critical contributions to cell proliferation.

A G-protein-coupled chemoattractant receptor recognizes lipopolysaccharide for bacterial phagocytosis

“…Using live cell imaging, we observed that cAMP-coated beads—but not uncoated beads—induced localized signaling responses, such as accumulation of PH CRAC -GFP and ΔlimE-GFP, followed by bead engulfment ( Fig 2E and 2F ). Previous studies indicated that cAMP receptor 1 (cAR1) works mainly with Gα2Gβγ subunits [ 38 – 40 ], while fAR1 may couple with Gα4Gβγ subunits [ 41 – 43 ]. We found that cAMP-coated beads induced these localized responses with subsequent phagocytic cup formation in WT , gα4 − , and far1 − cells ( S3B Fig ) but not in car1 − , gβ − , or gα2 − cells, in which cAMP sensing is abolished ( S3C Fig ).…”

“…Bacteria engulfment by Dictyostelium was conducted in both suspension and adhesion cultures as previously described [ 23 , 41 ]. Overnight cultured K .…”

The Atypical MAP Kinase ErkB Transmits Distinct Chemotactic Signals through a Core Signaling Module

“…ErkB null cells are defective in both speed of movement and chemotactic orientation in a variety of folate gradients ( Schwebs et al., 2018 ), presumably reflecting cumulative effects of mis-regulation of target proteins. Null mutants in these targets present diverse movement phenotypes.…”

The Life Cycle of <b><i>Dictyostelium discoideum</i></b> Is Accelerated via MAP Kinase Cascade by a Culture Extract Produced by a Synthetic Microbial Consortium

“…The proliferative stimulation and preferred formation of fruiting bodies by EMXG could both be ascribed to the elevated cellular cAMP level as evident from Table 1. Close correlation between cell proliferation and cAMP has been reported [Schwebs et al, 2018]. Still, questions remain, for example, as to the exact action site of EMXG during D. discoideum cell cycle, its mode of action other than chemoattractant, or how EMXG facilitates the enhanced formation of aggregating foci.…”