Lasp-1 is a regulated phosphoprotein within the cAMP signaling pathway in the gastric parietal cell

Abstract

Activation of the cAMP signaling pathway is correlated with increased secretory-related events in a wide variety of cell types including the gastric parietal cell. Within this pathway, as well as in other intracellular signaling pathways, protein phosphorylation serves as a major downstream regulatory mechanism. However, although agonist and cAMP-dependent activation of cAMP-dependent protein kinase (PKA) has been demonstrated, little is currently known about the downstream in vivo phosphoprotein substrates of this enzyme. Here we report the isolation, microsequencing, and cloning of a LIM and SH3 domain-containing, cAMP-responsive, 40-kDa phosphoprotein (pp40) from rabbit gastric parietal cells. The deduced amino acid sequence for pp40 is 93.5%, homologous with the putative protein product of the human gene lasp-1, which was recently identified based on its overexpression in some breast carcinomas. In addition to LIM and SH3 domains, the rabbit homolog contains two highly conserved PKA consensus sequences as well as two conserved SH2 binding motifs and several other putative protein kinase phosphorylation sites, including two for tyrosine kinase(s). Combined Northern and Western blot analyses indicate that pp40/lasp-1 is widely expressed (through a single 3.3-kb message) not only in epithelial tissues but also in muscle and brain. Furthermore, stimulation of isolated parietal cells, distal colonic crypts, and pancreatic cells with the adenylyl cyclase activator forskolin leads to the appearance of a higher molecular weight form of pp40/lasp-1, a finding which is consistent with an increase in protein phosphorylation. Thus pp40/lasp-1 appears to be regulated within the cAMP signaling pathway in a wide range of epithelial cell types. Because the cAMP-dependent increase in pp40 phosphorylation is correlated with secretory responses in the parietal cell and because pp40 appears to be widely distributed among various secretory tissues, this newly defined signaling protein may play an important role in modulating ionic transport or other secretory-related activities in many different cell types.

Overexpression of LASP-1 mediates migration and proliferation of human ovarian cancer cells and influences zyxin localisation

“…To date, more than 50 different adhesion proteins that regulate the LASP-1 in human ovarian cancer TGP Grunewald et al rate and organisation of actin polymerisation and focal adhesion turnover in protrusion have been identified. In earlier publications, overexpression of LASP-1 mRNA in metastatic lymph nodes derived from breast cancer patients, as well as the co-amplification of the gene together with HER-2/neu (c-erbB2) were demonstrated (Chew et al, 1998;Legge et al, 2005). Two additional observations underscore the importance of LASP-1 in cancer.…”

“…The actin-binding domains in the core of the LASP-1 protein mediate an interaction between LASP-1 and actin at cell membrane extensions, but not along the actin stress fibres (Schreiber et al, 1998;Chew et al, 2002;Butt et al, 2003;Keicher et al 2004;Nakagawa et al, 2006). The exact cellular function of LASP-1 is still not known, but the protein has previously been reported to localise within multiple sites of dynamic actin assembly such as focal contacts, focal adhesions, lamellipodia, membrane ruffles and pseudopodia (Tomasetto et al, 1995a;Chew et al, 1998Chew et al, , 2000Chew et al, , 2002Lin et al, 2004).…”

“…In rabbit parietal cells, elevation of intracellular cAMP by forskolin induced a partial translocation of LASP-1 to the apically directed F-actin-rich intracellular canaliculus, which is the site of active HCl secretion (Chew et al, 1998(Chew et al, , 2000. Beyond this, phosphorylation on serine 146 resulted in translocation of the protein from the membrane to the cytosol and was followed by reduced cell migration (Butt et al, 2003).…”

Isolation, Cloning, and Characterization of a New Mammalian Coronin Family Member, Coroninse, Which Is Regulated within the Protein Kinase C Signaling Pathway

“…The 66-kDa phosphoprotein was identified by autoradiographic comparisons with unstimulated controls. Changes in phosphorylation were quantitated using Bio Image two-dimensional gel analyzer software (19,20) or a Molecular Dynamics PhosphorImager.…”

The human LASP1 gene is fused to MLL in an acute myeloid leukemia with t(11;17)(q23;q21)

“…Consistent with the actin-binding capacity of LASP1, immunohistochemical analysis displayed a diffuse cytoplasmic staining (Schreiber et al, 1998b). In addition, in vitro studies revealed that rabbit pp40/lasp1 is one of the few unequivocally determined downstream phosphoprotein substrates of the cAMP-dependent serine/threonine protein kinase, PKC (Chew et al, 1998(Chew et al, , 2000.…”