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Ravi Iyengar

Publications and source records attributed to Ravi Iyengar.

12 recordsLinked to original sources
PubMed2002

Role of dynamic interactions in effective signal transfer for Gbeta stimulation of phospholipase C-beta 2.

Heterotrimeric G protein subunits regulate their effectors by protein-protein interactions. The regions involved in these direct interactions have either signal transfer or general binding functions (Buck, E., Li, J., Chen, Y., Weng, G., Scarlata, S., and Iyengar, R. (1999) Science 283, 1332-1335). Although key determinants of signal transfer regions for G protein subunits have been identified, the mechanisms of signal transfer are not fully understood. We have used a combinatorial peptide approach to analyze one Gbeta region, Gbeta86-105, involved in signal transfer to the effector phospholipase C (PLC)-beta2 to gain a more mechanistic understanding of Gbeta/PLC-beta2 signaling. Binding and functional studies with the combinatorial peptides on interaction with and stimulation/inhibition of phospholipase Cbeta2 indicate that binding affinity can be resolved from EC(50) for functional effects, such that peptides that have wild type binding affinities have 15- to 20-fold lower EC(50) values. Although more potent, these peptides display a much lower extent of maximal stimulation. These peptides synergize with Gbetagamma or peptides encoding the second Gbeta42-54 signal transfer region in maximally stimulating phospholipase C-beta2. Other combinatorial peptides from the Gbeta86-105 region that bind to PLC-beta2 by themselves submaximally stimulate and extensively inhibit Gbetagamma stimulation of PLC-beta2. The intrinsic stimulation function can be attributed to Arg-96 and Ser-97, the synergy function to Trp-99, and the binding affinity to Thr-87, Val-90, Pro-94, Arg-96, Ser-97, and Val-100. These results indicate that, even within signal transfer regions, residues involved in binding can be resolved from those involved in signal transfer and that signal transfer is likely to be achieved through dynamic rather than steady-state interactions.

Amino Acid Sequence↗
PubMed2002

Calpain as an effector of the Gq signaling pathway for inhibition of Wnt/beta -catenin-regulated cell proliferation.

Signaling pathways interact to integrate and regulate information flow in evoking complex cellular responses. We have studied the mechanisms and consequences of interactions between the Gq and Wnt/beta-catenin pathways. In human colon carcinoma SW480 cells, activation of the Gq pathway inhibits beta-catenin signaling as determined by transcriptional reporter and cell proliferation assays. Ca(2+) release from internal stores results in nuclear export and calpain-mediated degradation of beta-catenin in the cytoplasm. Galphaq does not inhibit the effects of constitutively activated DeltaN-XTCF3-VP16 chimera in SW480 cells. Similarly, in HEK293 cells the Gq pathway suppresses beta-catenin-T cell factor/lymphocyte enhancer factor-1 transcriptional activity induced by Wnt/Frizzled interaction or glycogen synthase kinase-3beta-resistant beta-catenin, but not DeltaN-XTCF3-VP16. We conclude that Gq signaling promotes nuclear export and calpain-mediated degradation of beta-catenin, which therefore contributes to the inhibition of Wnt/beta-catenin pathway.

Calcium↗
PubMed2002

MAP kinase phosphatase as a locus of flexibility in a mitogen-activated protein kinase signaling network.

Intracellular signaling networks receive and process information to control cellular machines. The mitogen-activated protein kinase (MAPK) 1,2/protein kinase C (PKC) system is one such network that regulates many cellular machines, including the cell cycle machinery and autocrine/paracrine factor synthesizing machinery. We used a combination of computational analysis and experiments in mouse NIH-3T3 fibroblasts to understand the design principles of this controller network. We find that the growth factor-stimulated signaling network containing MAPK 1, 2/PKC can operate with one (monostable) or two (bistable) stable states. At low concentrations of MAPK phosphatase, the system exhibits bistable behavior, such that brief stimulus results in sustained MAPK activation. The MAPK-induced increase in the amounts of MAPK phosphatase eliminates the prolonged response capability and moves the network to a monostable state, in which it behaves as a proportional response system responding acutely to stimulus. Thus, the MAPK 1, 2/PKC controller network is flexibly designed, and MAPK phosphatase may be critical for this flexible response.

3T3 Cells↗
PubMed2002

G protein pathways.

The heterotrimeric guanine nucleotide-binding proteins (G proteins) are signal transducers that communicate signals from many hormones, neurotransmitters, chemokines, and autocrine and paracrine factors. The extracellular signals are received by members of a large superfamily of receptors with seven membrane-spanning regions that activate the G proteins, which route the signals to several distinct intracellular signaling pathways. These pathways interact with one another to form a network that regulates metabolic enzymes, ion channels, transporters, and other components of the cellular machinery controlling a broad range of cellular processes, including transcription, motility, contractility, and secretion. These cellular processes in turn regulate systemic functions such as embryonic development, gonadal development, learning and memory, and organismal homeostasis.

Animals↗
PubMed2002

Adenovirus-directed expression of Q227L-G alpha(s) inhibits growth of established tumors of later-stage human breast cancer cells in athymic mice.

Elevation of cAMP inhibits proliferation and expression of the transformed phenotype in several cell types. We studied the effects of elevation of cAMP and expression of mutant (Q227L) activated G alpha(s) on the proliferation and tumorigenic capability of the later stage, metastatic estrogen-independent human breast cancer cell lines MDA-231 and MDA-435. Our studies show that 8Br-cAMP inhibits proliferation of these cells in culture and their ability to form colonies in soft agar. This inhibition may occur by different mechanisms in the two cell types. In MDA-231 cells, cAMP elevation results in sustained expression of the cell cycle inhibitor p27kip1 and inhibition of CDK2 activity, whereas in MDA-435 cells inhibition of mitogen-activated protein (MAP) kinase 1,2 activity is observed. We tested whether these effects in culture could be translated into inhibition of tumor growth in vivo. Tumors were developed in athymic (Nu/Nu) mice by injections of MDA-231 or MDA-435 cells. Injection of Q227L-G alpha(s) expressing adenoviral vector into these established tumors inhibited further tumor growth under conditions where tumors injected with either saline or adenoviral vector containing beta-galactosidase grew up to four to five times their original size. These results raise the possibility that sustained elevation of cAMP may have therapeutic value in the treatment of estrogen-resistant later stage breast cancers.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2002

Modeling of signaling networks.

Biochemical networks, including those containing signaling pathways, display a wide range of regulatory properties. These include the ability to propagate information across different time scales and to function as switches and oscillators. The mechanisms underlying these complex behaviors involve many interacting components and cannot be understood by experiments alone. The development of computational models and the integration of these models with experiments provide valuable insight into these complex systems-level behaviors. Here we review current approaches to the development of computational models of biochemical networks and describe the insights gained from models that integrate experimental data, using three examples that deal with ultrasensitivity, flexible bistability and oscillatory behavior. These types of complex behavior from relatively simple networks highlight the necessity of using theoretical approaches in understanding higher order biological functions.

Animals↗
PubMed2002

Computational analysis of isoform-specific signal regulation by CEACAM1-A cell adhesion molecule expressed in PC12 cells.

CEACAM1 is a signal-regulating, homophilic cell adhesion receptor system expressed in epithelia, vessel endothelia, and leukocytes. Here, we demonstrate that CEACAM1 is expressed also in PC12 cells, both as the common transmembrane isoforms, CEACAM1-L and CEACAM1-S, and as a novel, secreted, differentially spliced isoform. CEACAM1 can have both positive and negative effects on cell signaling. In an attempt to explain this dual behavior, we have initiated computational analysis of the signal-regulating effects of CEACAM1. This suggests that CEACAM1 can exert its signal-regulating activities by discriminating between binding of Src kinases and SHP phosphatases, respectively. Major factors that regulate this discrimination are the expression levels and expression ratios of transmembrane CEACAM1-L and CEACAM1-S, the concentration of secreted CEACAM1, and homophilic binding of CEACAM1 presented by neighboring cells.

Amino Acid Motifs↗
PubMed2001

Robustness of the bistable behavior of a biological signaling feedback loop.

Biological signaling networks comprised of cellular components including signaling proteins and small molecule messengers control the many cell function in responses to various extracellular and intracellular signals including hormone and neurotransmitter inputs, and genetic events. Many signaling pathways have motifs familiar to electronics and control theory design. Feedback loops are among the most common of these. Using experimentally derived parameters, we modeled a positive feedback loop in signaling pathways used by growth factors to trigger cell proliferation. This feedback loop is bistable under physiological conditions, although the system can move to a monostable state as well. We find that bistability persists under a wide range of regulatory conditions, even when core enzymes in the feedback loop deviate from physiological values. We did not observe any other phenomena in the core feedback loop, but the addition of a delayed inhibitory feedback was able to generate oscillations under rather extreme parameter conditions. Such oscillations may not be of physiological relevance. We propose that the kinetic properties of this feedback loop have evolved to support bistability and flexibility in going between bistable and monostable modes, while simultaneously being very refractory to oscillatory states. (c) 2001 American Institute of Physics.

Journal Article↗