Biomedical subjects

Alan R Saltiel

Publications and source records attributed to Alan R Saltiel.

41 records · Page 3Linked to original sources

PubMed2002

Insulin signaling pathways in time and space.

Despite remarkable progress in dissecting the signaling pathways that are crucial for the metabolic effects of insulin, the molecular basis for the specificity of its cellular actions is not fully understood. One clue might lie in the spatial and temporal aspects of signaling. Recent evidence suggests that signaling molecules and pathways are localized to discrete compartments in cells by specific protein interactions. Also, the rapid termination of tyrosine or lipid phosphorylation by phosphatases or serine kinases might tightly control the strength of a signaling pathway, thus determining its effect on growth, differentiation and metabolism.

Animals↗

PubMed2002

Small GTP-binding protein TC10 differentially regulates two distinct populations of filamentous actin in 3T3L1 adipocytes.

TC10 is a member of the Rho family of small GTP-binding proteins that has previously been implicated in the regulation of insulin-stimulated GLUT4 translocation in adipocytes. In a manner similar to Cdc42-stimulated actin-based motility, we have observed that constitutively active TC10 (TC10/Q75L) can induce actin comet tails in Xenopus oocyte extracts in vitro and extensive actin polymerization in the perinuclear region when expressed in 3T3L1 adipocytes. In contrast, expression of TC10/Q75L completely disrupted adipocyte cortical actin, which was specific for TC10, because expression of constitutively active Cdc42 was without effect. The effect of TC10/Q75L to disrupt cortical actin was abrogated after deletion of the amino terminal extension (DeltaN-TC10/Q75L), whereas this deletion retained the ability to induce perinuclear actin polymerization. In addition, alteration of perinuclear actin by expression of TC10/Q75L, a dominant-interfering TC10/T31N mutant or a mutant N-WASP protein (N-WASP/DeltaVCA) reduced the rate of VSV G protein trafficking to the plasma membrane. Furthermore, TC10 directly bound to Golgi COPI coat proteins through a dilysine motif in the carboxyl terminal domain consistent with a role for TC10 regulating actin polymerization on membrane transport vesicles. Together, these data demonstrate that TC10 can differentially regulate two types of filamentous actin in adipocytes dependent on distinct functional domains and its subcellular compartmentalization.

3T3 Cells↗

PubMed2002

APS facilitates c-Cbl tyrosine phosphorylation and GLUT4 translocation in response to insulin in 3T3-L1 adipocytes.

APS is a Cbl-binding protein that is tyrosine phosphorylated by the insulin receptor kinase. Insulin-stimulated phosphorylation of tyrosine 618 in APS is necessary for its association with c-Cbl and the subsequent tyrosine phosphorylation of Cbl by the insulin receptor in both 3T3-L1 adipocytes and CHO-IR cells. When overexpressed in these cells, wild-type APS but not an APS/Y(618)F mutant facilitated the tyrosine phosphorylation of coexpressed Cbl and its association with Crk upon insulin stimulation. APS-facilitated phosphorylation occurred on tyrosines 371, 700, and 774 in the Cbl protein. APS also interacted directly with the c-Cbl-associated protein (CAP) and colocalized with the protein in cells. The association was dependent on the SH3 domains of CAP and was independent of insulin treatment. Overexpression of the APS/Y(618)F mutant in 3T3-L1 adipocytes blocked the insulin-stimulated tyrosine phosphorylation of endogenous Cbl and binding to Crk. Moreover, the translocation of GLUT4 from intracellular vesicles to the plasma membrane was also inhibited by overexpression of the APS/Y(618)F mutant. These data suggest that APS serves as an adapter protein linking the CAP/Cbl pathway to the insulin receptor and, further, that APS-facilitated Cbl tyrosine phosphorylation catalyzed by the insulin receptor is a crucial event in the stimulation of glucose transport by insulin.

3T3 Cells↗

PubMedDate not supplied

Insulin signaling and the regulation of glucose transport.

Gaps remain in our understanding of the precise molecular mechanisms by which insulin regulates glucose uptake in fat and muscle cells. Recent evidence suggests that insulin action involves multiple pathways, each compartmentalized in discrete domains. Upon activation, the receptor catalyzes the tyrosine phosphorylation of a number of substrates. One family of these, the insulin receptor substrate (IRS) proteins, initiates activation of the phosphatidylinositol 3-kinase pathway, resulting in stimulation of protein kinases such as Akt and atypical protein kinase C. The receptor also phosphorylates the adapter protein APS, resulting in the activation of the G protein TC10, which resides in lipid rafts. TC10 can influence a number of cellular processes, including changes in the actin cytoskeleton, recruitment of effectors such as the adapter protein CIP4, and assembly of the exocyst complex. These pathways converge to control the recycling of the facilitative glucose transporter Glut4.

Animals↗

PubMedDate not supplied

Cloning and characterization of Cbl-associated protein splicing isoforms.

Cbl-associated protein (CAP) is an adaptor protein that plays important roles in both signal transduction and cytoskeleton rearrangement. Alternative splicing of the gene SORBS1 results in multiple isoforms of CAP protein. We report here the cloning of 3 new CAP isoforms, CAP2, CAP3, and CAP4, from mouse adipose tissue. RT-PCR analyses reveal that the isoform mRNAs are differentially expressed. CAP2, CAP3, and CAP4 contain a coiled-coil domain. In addition, CAP4 contains a proline-rich region, part of which exists in CAP3. Coimmunoprecipitation experiments show that CAP4 forms a homodimeric complex. While these new isoforms similarly interact with Cbl, they exhibit varied binding specificity toward vinculin. In contrast to CAP1 and CAP2, CAP4 does not interact with vinculin, and CAP3 binds with low affinity. Immunofluorescence analysis demonstrates differential subcellular localization of Myc-tagged CAP isoforms in 3T3-L1 adipocytes. These results suggest that these new isoforms of CAP might play different signaling roles.

3T3 Cells↗