183 Oral - Cell Stress and Cell Death
Saturday April 09, 11:15 AM - 11:30 AM

Authors:
Yujun Chen; Jocelyn McDonald

Affiliation: Kansas State University

Keywords:
h. other (The integrated stress response,ER stress); h. other (The integrated stress response,ER stress)

Collective cell migration is essential for many developmental and pathological processes. Drosophila border cells migrate as a cohesive cluster during oogenesis and provide an excellent genetic model to elucidate conserved mechanisms of collective cell movement. Previously, we discovered that Protein Phosphatase 1 (Pp1) catalytic subunits are critical molecular regulators of border cell collective versus single cell behaviors. We now show that the conserved Pp1 regulatory subunit dPPP1R15 (also known as GADD34) plays a crucial role in border cell migration. Overexpression of dPPP1R15 causes border cells to round up and completely dissociate from the cluster during migration. These defects are rescued by overexpression of Pp1 catalytic subunits (Pp1c). Moreover, overexpressing PPP1R15 mutants that cannot bind to Pp1c no longer show migration or cluster-dissociation phenotypes. These data together indicate that dPPP1R15 functions through Pp1c in border cells. In contrast, RNAi-mediated knockdown of dPPP1R15 prevents border cell delamination from the follicular epithelium. Live imaging reveals that, compared to control border cells, dPPP1R15-RNAi border cells also extend much smaller protrusions that are misdirected, thus contributing to the failure of border cells to migrate. The Pp1c/PPP1R15 complex is best known as a phosphatase complex that dephosphorylates eIF2alpha in the endoplasmic reticulum (ER) stress pathway. Indeed, loss of dPPP1R15 elevates phosphorylation and activation of eIF2alpha and increases expression of the known downstream transcription factor, ATF4, in border cells. In addition, upregulation of PERK, a major eIF2alpha kinase, blocks border cell delamination and migration. Interestingly, depleting PERK by RNAi also delays border cell migration. Overexpression of a non-phosphorylatable eIF2alpha mutant, or knockdown of ATF4, significantly rescues PPP1R15-RNAi induced migration defects. Overexpression of a phosphomimetic eIF2alpha mutant, or of ATF4, impairs migration. Together, our data support the idea that restraining the PERK-eIF2alpha-ATF4 ER stress pathway via the dPPP1R15 phosphatase is critical for proper border cell migration. Our studies identify a new role for dPPP1R15 as a key regulator of collective cell behaviors through modulation of the ER stress response.