Actin cytoskeletal deregulation, caused by RhoGEF2 overexpression, induces cell competition dependent on Ptp10D, Crumbs, and the Hippo signaling pathway

In Drosophila larval epithelial tissues, cells containing mutations in the apico-basal polarity proteins, Scrib, Dlg or Lgl, are eliminated by cell competition when surrounded by wild-type cells. In these polarity-impaired cells, signaling mediated by the receptor-type tyrosine phosphatase Ptp10D upon engagement with its ligand Sas in the surrounding wild-type cells triggers cell competition via EGFR pathway inhibition and JNK pathway activation, which induces apoptosis of the mutant cells. Here, we investigate whether directly triggering cytoskeletal deregulation (which usually occurs downstream of cell polarity disruptions) is sufficient to trigger their elimination by cell competition via the Sas-Ptp10D signaling system. We show that actin cytoskeleton deregulated cells (as induced by RhoGEF2 overexpression ( RhoGEF2 ^OE )) are eliminated when surrounded by wild-type cells, and that Ptp10D knockdown increases RhoGEF2 ^OE clone growth, revealing the importance of Ptp10D in the elimination of RhoGEF2 ^OE cells. Mechanistically, in clones that are moderately overexpressing RhoGEF2 ^OE , Ptp10D knockdown rescued cell elimination by reducing Hippo signaling. In this setting, JNK and EGFR-Ras signaling were not affected (in contrast to what occurs in apico-basal mutant cells), suggesting that Sas-Ptp10D may regulate the Hippo pathway directly in RhoGEF2 ^OE cells. We also found that mutations in the apical cell polarity protein, Crb, partially rescued the elimination of RhoGEF2 ^OE clones, showing that Crb normally plays a role in RhoGEF2 ^OE clone elimination. In this setting, in which RhoGEF2 ^OE is highly overexpressed, JNK and Hippo signaling were elevated while EGFR-Ras signaling was reduced, and crb loss normalized these pathways. crb mutant cells also showed reduced abundance of and apical membrane localization of Ptp10D, suggesting that Crb may play an important role in Sas-Ptp10D mediated cell competition. Thus, actin cytoskeleton deregulation, caused by RhoGEF2 ^OE , results in clone elimination dependent on Crb, Ptp10D, and Hippo signaling. Altogether, our results reveal that Ptp10D is acting more broadly in cell competition to trigger the elimination of actin cytoskeleton deregulated loser cells, as well as polarity-impaired cells.