SUMMARYGenerating and maintaining proper lumen size and shape in tubular organs is essential for organ function. Here, we demonstrate a novel role for p21-activated kinase 1 (Pak1) in defining the size and shape of the Drosophila embryonic salivary gland lumen by regulating the size and elongation of the apical domain of individual cells. Pak1 mediates these effects by decreasing and increasing E-cadherin levels at the adherens junctions and basolateral membrane, respectively, through Rab5-and Dynamindependent endocytosis. We also demonstrate that Cdc42 and Merlin act together with Pak1 to control lumen size. A role for Pak1 in E-cadherin endocytosis is supported by our studies of constitutively active Pak1, which induces the formation of multiple intercellular lumens in the salivary gland in a manner dependent on Rab5, Dynamin and Merlin. These studies demonstrate a novel and crucial role for Pak1 and E-cadherin endocytosis in determining lumen size and shape, and also identify a mechanism for multiple lumen formation, a poorly understood process that occurs in normal embryonic development and pathological conditions.
During collective migration of the Drosophila embryonic salivary gland, the distal gland cells mediate integrin-based contacts with surrounding tissues while proximal gland cells change shape and rearrange. Here, we show that αPS1βPS integrin controls salivary gland migration through Rac1 GTPase which downregulates E-cadherin in proximal and distal gland cells, and promotes extension of actin-rich basal membrane protrusions in the distal cells. In embryos mutant for multiple edematous wings(mew), which encodes the αPS1 subunit of the αPS1βPS integrin heterodimer, or rac1 and rac2 GTPases, salivary gland cells failed to migrate, to downregulate E-cadherin and to extend basal membrane protrusions. Selective inhibition of Rac1 in just the proximal or distal gland cells demonstrate that proximal gland cells play an active role in the collective migration of the whole gland and that continued migration of the distal cells depends on the proximal cells. Loss of rac1rac2 also affected gland lumen length and width whereas, loss of mew affected lumen length only. Activation of rac1 in mew mutant embryos significantly rescued the gland migration, lumen length and basal membrane protrusion defects and partially rescued the E-cadherin defects. Independent of mew, Rac regulates cell shape change and rearrangement in the proximal gland, which is important for migration and lumen width. Our studies shed novel insight into a Rac1-mediated link between integrin and cadherin adhesion proteins in vivo, control of lumen length and width and how activities of proximal and distal gland cells are coordinated to result in the collective migration of the entire salivary gland.
The intracellular Src homology 2 (SH2) domain-containing protein-tyrosine phosphatase (SHP-1) has been characterized as a negative regulator of T cell function, contributing to the definition of T cell receptor signaling thresholds in developing and peripheral mouse T lymphocytes. The activation of SHP-1 is achieved through the engagement of its tandem SH2 domains by tyrosine-phosphorylated proteins; however, the identity of the activating ligand(s) for SHP-1, within mouse primary T cells, is presently unresolved. The identification of SHP-1 ligand(s) in primary T cells would provide crucial insight into the molecular mechanisms by which SHP-1 contributes to in vivo thresholds for T cell activation. Here we present a combination of biochemical and yeast genetic analyses indicating CD22 to be a T cell ligand for the SHP-1 SH2 domains. Based on these observations we have confirmed that CD22 is indeed expressed on mouse primary T cells and capable of associating with SHP-1. Significantly, CD22-deficient T cells demonstrate enhanced proliferation in response to anti-CD3 or allogeneic stimulation. Furthermore, the co-engagement of CD3 and CD22 results in a raising of TCR signaling thresholds hence demonstrating a previously unsuspected functional role for CD22 in primary T cells. SHP-1,1 an intracellular protein-tyrosine phosphatase, has been demonstrated to be a negative regulator of TCR signaling thresholds (1). SHP-1 is normally maintained in a catalytically inactive state whereby activation minimally requires the engagement of the amino-terminal SH2 domain of SHP-1 by phosphotyrosine (PY)-containing ligand (2, 3). It is predicted that SHP-1-activating ligand(s) exists on mouse naïve T cells based on substantial functional evidence indicating SHP-1 to be catalytically active in naïve T cells (1, 4 -8). It is currently assumed that SHP-1 is activated by one or more components of the TCR signaling pathway. Indeed, the intracellular proteintyrosine kinase, ZAP-70, has been proposed to bind SHP-1 (9).However, the best evidence of SHP-1-associating molecules in other hemopoietic cells relates to the family of immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptors (10). In particular, ITIM receptors Ly49 and CD66a associate with SHP-1 in subpopulations of primary T cells, but to date there has been no definition of the ITIM receptors that activate SHP-1 in the majority of mouse primary T cells (11).In the first instance, we have exploited SHP-1-deficient moth-eaten T cells to assist in the definition of genuine associations between SHP-1 and TCR signaling components in CD3/TCR-stimulated mouse primary T cells. Our results reveal no binding of the CD3 invariant chains or ZAP-70 to SHP-1 in mouse primary T cells following TCR/CD3 ligation. However, by employing pervanadate (PV) to induce a robust tyrosine phosphorylation of cellular proteins in primary T cells, we demonstrated that a glycosylated tyrosyl phosphoprotein of 150 kDa, (pp150) associates with SHP-1 in mouse peripheral T cells. We have ident...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.