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Z Songyang

Publications and source records attributed to Z Songyang.

At least 19 recordsLinked to original sources
PubMed1998

SRPK2: a differentially expressed SR protein-specific kinase involved in mediating the interaction and localization of pre-mRNA splicing factors in mammalian cells.

Reversible phosphorylation plays an important role in pre-mRNA splicing in mammalian cells. Two kinases, SR protein-specific kinase (SRPK1) and Clk/Sty, have been shown to phosphorylate the SR family of splicing factors. We report here the cloning and characterization of SRPK2, which is highly related to SRPK1 in sequence, kinase activity, and substrate specificity. Random peptide selection for preferred phosphorylation sites revealed a stringent preference of SRPK2 for SR dipeptides, and the consensus derived may be used to predict potential phosphorylation sites in candidate arginine and serine-rich (RS) domain-containing proteins. Phosphorylation of an SR protein (ASF/SF2) by either SRPK1 or 2 enhanced its interaction with another RS domain-containing protein (U1 70K), and overexpression of either kinase induced specific redistribution of splicing factors in the nucleus. These observations likely reflect the function of the SRPK family of kinases in spliceosome assembly and in mediating the trafficking of splicing factors in mammalian cells. The biochemical and functional similarities between SRPK1 and 2, however, are in contrast to their differences in expression. SRPK1 is highly expressed in pancreas, whereas SRPK2 is highly expressed in brain, although both are coexpressed in other human tissues and in many experimental cell lines. Interestingly, SRPK2 also contains a proline-rich sequence at its NH2 terminus, and a recent study showed that this NH2-terminal sequence has the capacity to interact with a WW domain protein in vitro. Together, our studies suggest that different SRPK family members may be uniquely regulated and targeted, thereby contributing to splicing regulation in different tissues, during development, or in response to signaling.

Amino Acid Sequence↗
PubMed1998

Stimulation through the T cell receptor leads to interactions between SHB and several signaling proteins.

Shb is a recently described Src homology 2 (SH2) domain-containing adaptor protein. Here we show that Shb is expressed in lymphoid tissues, and is recruited into signaling complexes upon activation of Jurkat T cells. Grb2 binds proline-rich motifs in Shb via its SH3 domains. As a result, a number of proteins detected in anti-Shb and anti-Grb2 immunoprecipitates are shared, including phosphoproteins of 22, 36/38, 55/57 and 70 kDa. Shb-association with p22, which represents the T cell receptor associated zeta chain, occurs through the Shb SH2 domain. The central region of Shb binds p36/38. Since this interaction was inhibited by phosphotyrosine, this region of Shb is likely to contain a non-SH2 PTB (phosphotyrosine binding) domain. The Shb PTB domain was found to preferentially bind the sequence Asp-Asp-X-pTyr when incubated with a phosphopeptide library. A peptide corresponding to a phosphorylation site in 34 kDa Lnk inhibited association between Shb and p36/38. Overexpression of Shb in Jurkat cells led to increased basal phosphorylation of Shb-associated p36/38 and p70 proteins. Inactivation of the Shb SH2 domain by an R522K mutation resulted in a reduced stimulation of tyrosine phosphorylation of several proteins in response to CD3 crosslinking when expressed in Jurkat cells. Together, our results show three distinct domains of Shb all participate in the formulation of multimeric signaling complexes in activated T cells. These results indicate that the Shb protein functions in T cell receptor signaling.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Peptide and protein phosphorylation by protein tyrosine kinase Csk: insights into specificity and mechanism.

Csk (C-terminal Src kinase) is a protein tyrosine kinase that phosphorylates Src family member C-terminal tails, resulting in down-regulation of Src family members. The molecular basis of Csk's substrate specificity and catalytic mechanism with a protein substrate was investigated. Using a peptide library approach, preferential amino acids which are unrelated to the conserved Src C-terminal sequence were identified. The validity of these preferences was confirmed by synthesizing a short consensus peptide and demonstrating its high catalytic efficiency with Csk. These results underscore the difficulties of relying on amino acids neighboring tyrosine in protein sequences as predictors of protein kinase substrate specificity for in vivo analysis. In addition, a catalytically inactive version of the Src family member, Lck (lymphoid cell kinase), was expressed, purified, and evaluated as a Csk substrate. It was proven to be the most catalytically efficient substrate yet identified for Csk. The high efficiency of purified Csk phosphorylating a pure, unphosphorylated Src family member argues against the importance of an SH2-phosphotyrosine docking interaction or the involvement of extra recruitment proteins in facilitating Csk phosphorylation of Src family members. Kinetic studies revealed that the chemical step is at least partially rate-determining in Csk-mediated phosphoryl transfer to the Lck protein. Other properties including preferences for Mn over Mg, thio effects, and Km's for ATP also correlate fairly well between protein and peptide phosphorylation. The lack of a significant impact of increased salt on the Km for Lck phosphorylation differs from Csk-mediated poly(Glu,Tyr) phosphorylation, and argues against the importance of electrostatic effects in the Csk-Lck binding interaction. The failure of the Lck phosphorylation product (phosphotyrosine-505) to significantly inhibit Csk phosphorylation of Lck is consistent with a catalytic model involving multidomain structural interactions between substrate and enzyme.

Adenosine Triphosphate↗
PubMed1997

The Cbl phosphotyrosine-binding domain selects a D(N/D)XpY motif and binds to the Tyr292 negative regulatory phosphorylation site of ZAP-70.

The Cbl protooncogene product has emerged as a novel negative regulator of receptor and non-receptor tyrosine kinases through currently undefined mechanisms. Therefore, determining how Cbl physically interacts with tyrosine kinases is of substantial interest. We recently identified a phosphotyrosine binding (PTB) domain residing within the N-terminal transforming region of Cbl (Cbl-N), which mediated direct binding to ZAP-70 tyrosine kinase. Here, we have screened a degenerate phosphopeptide library and show that the Cbl-PTB domain selects a D(N/D)XpY motif, reminiscent of but distinct from the NPXpY motif recognized by the PTB domains of Shc and IRS-1/2. A phosphopeptide predicted by this motif and corresponding to the in vivo negative regulatory phosphorylation site of ZAP-70 (Tyr(P)292) specifically inhibited binding of ZAP-70 to Cbl-N. A ZAP-70/Y292F mutant failed to bind to Cbl-N, whereas a D290A mutant resulted in a 64% decrease in binding, confirming the importance of the Tyr(P) and Y-2 residues in Cbl-PTB domain recognition. Finally the ZAP-70/Y292F mutant also failed to associate with Cbl-N or full-length Cbl in vivo. These results identify a potential Cbl-PTB domain-dependent role for Cbl in the negative regulation of ZAP-70 and predict potential Cbl-PTB domain binding sites on other protein tyrosine kinases known to interact with Cbl.

3T3 Cells↗
PubMed1997

Interleukin 3-dependent survival by the Akt protein kinase.

Interleukin 3 (IL-3)-dependent survival of hematopoietic cells is known to rely on the activity of multiple signaling pathways, including a pathway leading to activation of phosphoinositide 3-kinase (PI 3-kinase), and protein kinase Akt is a direct target of PI 3-kinase. We find that Akt kinase activity is rapidly induced by the cytokine IL-3, suggesting a role for Akt in PI 3-kinase-dependent signaling in hematopoetic cells. Dominant-negative mutants of Akt specifically block Akt activation by IL-3 and interfere with IL-3-dependent proliferation. Overexpression of Akt or oncogenic v-akt protects 32D cells from apoptosis induced by IL-3 withdrawal. Apoptosis after IL-3 withdrawal is accelerated by expression of dominant-negative mutants of Akt, indicating that a functional Akt signaling pathway is necessary for cell survival mediated by the cytokine IL-3. Thus Akt appears to be an important mediator of anti-apoptotic signaling in this system.

Animals↗
PubMed1997

High-affinity binding of the Drosophila Numb phosphotyrosine-binding domain to peptides containing a Gly-Pro-(p)Tyr motif.

The phosphotyrosine-binding (PTB) domain is a recently identified protein module that has been characterized as binding to phosphopeptides containing an NPXpY motif (X = any amino acid). We describe here a novel peptide sequence recognized by the PTB domain from Drosophila Numb (dNumb), a protein involved in cell fate determination and asymmetric cell division during the development of the Drosophila nervous system. Using a Tyr-oriented peptide library to screen for ligands, the dNumb PTB domain was found to bind selectively to peptides containing a YIGPYphi motif (phi represents a hydrophobic residue). A synthetic peptide containing this sequence bound specifically to the isolated dNumb PTB domain in solution with a dissociation constant (Kd) of 5.78 +/- 0.74 microM. Interestingly, the affinity of this peptide for the dNumb PTB domain was increased (Kd = 1.41 +/- 0.10 microM) when the second tyrosine in the sequence was phosphorylated. Amino acid substitution studies of the phosphopeptide demonstrated that a core motif of sequence GP(p)Y is required for high-affinity binding to the dNumb PTB domain. Nuclear magnetic resonance experiments performed on isotopically labeled protein complexed with either Tyr- or pTyr-containing peptides suggest that the same set of amino acids in the dNumb PTB domain is involved in binding both phosphorylated and nonphosphorylated forms of the peptide. The in vitro selectivity of the dNumb PTB domain is therefore markedly different from those of the Shc and IRS-1 PTB domains, in that it interacts preferentially with a GP(p)Y motif, rather than NPXpY, and does not absolutely require ligand phosphorylation for binding. Our results suggest that the PTB domain is a versatile protein module, capable of exhibiting varied binding specificities.

Animals↗
PubMed1997

Juxtamembrane tyrosine residues couple the Eph family receptor EphB2/Nuk to specific SH2 domain proteins in neuronal cells.

Eph-related receptor tyrosine kinases have been implicated in the control of axonal navigation and fasciculation. To investigate the biochemical mechanisms underlying such functions, we have expressed the EphB2 receptor (formerly Nuk/Cek5/Sek3) in neuronal NG108-15 cells, and have observed the tyrosine phosphorylation of multiple cellular proteins upon activation of EphB2 by its ligand, ephrin-B1 (formerly Elk-L/Lerk2). The activated EphB2 receptor induced the tyrosine phosphorylation of a 62-64 kDa protein (p62[dok]), which in turn formed a complex with the Ras GTPase-activating protein (RasGAP) and SH2/SH3 domain adaptor protein Nck. RasGAP also bound through its SH2 domains to tyrosine-phosphorylated EphB2 in vitro, and complexed with activated EphB2 in vivo. We have localized an in vitro RasGAP-binding site to conserved tyrosine residues Y604 and Y610 in the juxtamembrane region of EphB2, and demonstrated that substitution of these amino acids abolishes ephrin-B1-induced signalling events in EphB2-expressing NG108-15 cells. These tyrosine residues are followed by proline at the + 3 position, consistent with the binding specificity of RasGAP SH2 domains determined using a degenerate phosphopeptide library. These results identify an EphB2-activated signalling cascade involving proteins that potentially play a role in axonal guidance and control of cytoskeletal architecture.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Sequence specificity of C-terminal Src kinase (CSK)--a comparison with Src-related kinases c-Fgr and Lyn.

An eicosapeptide encompassing the C-terminal tail of c-Src (Tyr527) which is conserved in most Src-related protein kinases, is phosphorylated by C-terminal Src kinase (CSK) and by the two Src-related protein kinases c-Fgr and Lyn, with similar kinetic constants. Two related peptides reproducing the C-terminal segments of c-Src mutants defective in CSK phosphorylation [MacAuley, A., Okada, M., Nada, S., Nakagawa, H. & Cooper, J. A. (1993) Oncogene 8, 117-124] AFLEDSCTGTEPLYQRGENL (mutant number 28) and AFLEDNFTGTKPQYHPGENL (mutant number 29), proved a better and a much worse substrates, respectively than the wild-type peptide, with either CSK or the two Src kinases. By changing individual residues in the best peptide substrate, it was shown that the main element responsible for its improved phosphorylation is leucine at position -1 (instead of glutamine), while lysine at position -3 (instead of glutamate) has a detrimental effect, possibly accounting for the negligible phosphorylation of peptide derived from mutant number 29. By contrast to most peptide substrates, including the Src C-terminal peptides, which exhibit relatively high K(m) values, a polyoma-virus-middle-T-antigen-(mT)-derived peptide with tyrosine embedded in a highly hydrophobic sequence (EEEPQFEEIPIYLELLP) exhibits with CSK a quite low K(m) value (63 microM). Consistent with this, the optimal sequence selected by CSK in an oriented peptide library is XXXIYMFFF. This is different from sequences selected by Lyn (DEEIYEELX) and c-Fgr (XEEIYGIFF), although they all share a high selection for a hydrophobic residue at n-1. In sharp contrast, TPKIIB/p38syk, related to the catalytic domain of p72syk, selects acidic residues at nearly all positions, n-1 included. These data support the notion that the features determining the specific phosphorylation of the C-terminal tyrosine residue of Src do not reside in the primary structure surrounding the target tyrosine. They also show that this site does not entirely fulfil the optimal consensus sequence recognized by CSK, disclosing the possibility that as yet unrecognized CSK targets structurally unrelated to the C-terminal tyrosine residue of Src kinases may exist.

Amino Acid Sequence↗
PubMed1997

The SH3 domain of amphiphysin binds the proline-rich domain of dynamin at a single site that defines a new SH3 binding consensus sequence.

Amphiphysin is an SH3 domain-containing neuronal protein that is highly concentrated in nerve terminals where it interacts via its SH3 domain with dynamin I, a GTPase implicated in synaptic vesicle endocytosis. We show here that the SH3 domain of amphiphysin, but not a mutant SH3 domain, bound with high affinity to a single site in the long proline-rich region of human dynamin I, that this site was distinct from the binding sites for other SH3 domains, and that the mutation of two adjacent amino acids in dynamin I was sufficient to abolish binding. The dynamin I sequence critically required for amphiphysin binding (PSRPNR) fits in the novel SH3 binding consensus identified for the SH3 domain of amphiphysin via a combinatorial peptide library approach: PXRPXR(H)R(H). Our data demonstrate that the long proline-rich stretch present in dynamin I contained multiple SH3 domain binding sites that recognize interacting proteins with high specificity.

Amino Acid Sequence↗
PubMed1997

Determination of the specific substrate sequence motifs of protein kinase C isozymes.

Protein kinase C (PKC) family members play significant roles in a variety of intracellular signal transduction processes, but information about the substrate specificities of each PKC family member is quite limited. In this study, we have determined the optimal peptide substrate sequence for each of nine human PKC isozymes (alpha, betaI, betaII, gamma, delta, epsilon, eta, mu, and zeta) by using an oriented peptide library. All PKC isozymes preferentially phosphorylated peptides with hydrophobic amino acids at position +1 carboxyl-terminal of the phosphorylated Ser and basic residues at position -3. All isozymes, except PKC mu, selected peptides with basic amino acids at positions -6, -4, and -2. PKC alpha, -betaI, -betaII, -gamma, and -eta selected peptides with basic amino acid at positions +2, +3, and +4, but PKC delta, -epsilon, -zeta, and -mu preferred peptides with hydrophobic amino acid at these positions. At position -5, the selectivity was quite different among the various isozymes; PKC alpha, -gamma, and -delta selected peptides with Arg at this position while other PKC isozymes selected hydrophobic amino acids such as Phe, Leu, or Val. Interestingly, PKC mu showed extreme selectivity for peptides with Leu at this position. The predicted optimal sequences from position -3 to +2 for PKC alpha, -betaI, -betaII, -gamma, -delta, and -eta were very similar to the endogenous pseudosubstrate sequences of these PKC isozymes, indicating that these core regions may be important to the binding of corresponding substrate peptides. Synthetic peptides based on the predicted optimal sequences for PKC alpha, -betaI,-delta, -zeta, and -mu were prepared and used for the determination of Km and Vmax for these isozymes. As judged by Vmax/Km values, these peptides were in general better substrates of the corresponding isozymes than those of the other PKC isozymes, supporting the idea that individual PKC isozymes have distinct optimal substrates. The structural basis for the selectivity of PKC isozymes is discussed based on residues predicted to form the catalytic cleft.

Amino Acid Sequence↗
PubMed1997

Recognition of unique carboxyl-terminal motifs by distinct PDZ domains.

The oriented peptide library technique was used to investigate the peptide-binding specificities of nine PDZ domains. Each PDZ domain selected peptides with hydrophobic residues at the carboxyl terminus. Individual PDZ domains selected unique optimal motifs defined primarily by the carboxyl terminal three to seven residues of the peptides. One family of PDZ domains, including those of the Discs Large protein, selected peptides with the consensus motif Glu-(Ser/Thr)-Xxx-(Val/Ile) (where Xxx represents any amino acid) at the carboxyl terminus. In contrast, another family of PDZ domains, including those of LIN-2, p55, and Tiam-1, selected peptides with hydrophobic or aromatic side chains at the carboxyl terminal three residues. On the basis of crystal structures of the PSD-95-3 PDZ domain, the specificities observed with the peptide library can be rationalized.

Amino Acid Sequence↗
PubMed1996

The inositol 5'-phosphatase SHIP binds to immunoreceptor signaling motifs and responds to high affinity IgE receptor aggregation.

Immunoreceptors such as the high affinity IgE receptor, FcepsilonRI, and T-cell receptor-associated proteins share a common motif, the immunoreceptor tyrosine-based activation motif (ITAM). We used the yeast tribrid system to identify downstream effectors of the phosphorylated FcepsilonRI ITAM-containing subunits beta and gamma. One novel cDNA was isolated that encodes a protein that is phosphorylated on tyrosine, contains a Src-homology 2 (SH2) domain, inositolpolyphosphate 5-phosphatase activity, three NXXY motifs, several proline-rich regions, and is called SHIP. Mutation of the conserved tyrosine or leucine residues within the FcepsilonRI beta or gamma ITAMs eliminates SHIP binding and indicates that the SHIP-ITAM interaction is specific. SHIP also binds to ITAMs from the CD3 complex and T cell receptor zeta chain in vitro. SHIP protein possesses both phosphatidylinositol-3,4,5-trisphosphate 5'-phosphatase and inositol-1,3,4,5-tetrakisphosphate 5'-phosphatase activity. Phosphorylation of SHIP by a protein-tyrosine kinase, Lck, results in a reduction in enzyme activity. FcepsilonRI activation induces the association of several tyrosine phosphoproteins with SHIP. SHIP is constitutively tyrosine-phosphorylated and associated with Shc and Grb2. These data suggest that SHIP may serve as a multifunctional linker protein in receptor activation.

Animals↗
PubMed1996

Sequence requirements for the recognition of tyrosine-based endocytic signals by clathrin AP-2 complexes.

We recently determined that fusion proteins containing tyrosine-based endocytic signals bind to the mu 2 subunit of AP-2, the complex that drives clathrin coat formation and mediates endocytosis from the plasma membrane. Here we analyze the selectivity of peptide recognition by mu 2 and by AP-2 using combinatorial selection methods and surface plasmon resonance. Both mu 2 and AP-2 are shown to interact with various sequences of the form tyrosine-polar-polar-hydrophobic (Yppø) found on receptors that follow the clathrin pathway. The optimal sequence for interaction with mu 2 and with AP-2 has tyrosine as an anchor and prefers arginine at position Y + 2 and leucine at position Y + 3. In contrast, no preferred sequence is detected surrounding the Yppø signal, indicating that recognition of the Yppø endocytic signal does not require a prefolded structure. We conclude that sorting into the endocytic pathway is governed by a surprisingly simple interaction between the mu 2 chain and a tyrosine-containing tetrapeptide sequence.

Amino Acid Sequence↗
PubMed1996

Regulation of the Lck SH2 domain by tyrosine phosphorylation.

Src homology 2 (SH2) domains bind to phosphotyrosine (Tyr(P)) residues in specific sequence contexts in other proteins and thereby mediate tyrosine phosphorylationdependent protein-protein interactions. The SH2 domain of the Src family kinase Lck is phosphorylated at tyrosine 192 in T cells upon T cell antigen receptor triggering. We have studied the consequences of this phosphorylation on the properties of the SH2 domain and on the function of Lck in T cell activation. We report that phosphorylation at Tyr192 reduced the capacity of the isolated SH2 domain to bind a high affinity peptide ligand and Tyr(P)-containing cellular proteins. This effect was mimicked by mutation of Tyr192 to an acidic residue. In intact T cells, where Lck participates in T cell antigen receptor signal transduction in an SH2 domain-dependent manner, phosphorylation of Tyr192 correlated with reduced downstream signaling. Our results indicate that tyrosine phosphorylation of the SH2 domain of Lck terminates its high affinity binding to ligands, thereby negatively regulating its participation in T cell antigen receptor signaling. This represents a novel mechanism for the regulation of the function of SH2 domains.

Amino Acid Sequence↗
PubMed1996

Platelet-derived growth factor-induced formation of tensin and phosphoinositide 3-kinase complexes.

Tensin is an SH2 domain-containing cytoskeletal protein that binds to and caps actin filaments. Investigation of signal transduction mechanisms associated with tensin revealed the presence of phosphoinositide 3-kinase (PI 3-kinase) activity in tensin immunoprecipitates from platelet-derived growth factor-treated cells. Association of PI 3-kinase activity with tensin was transitory, and the amount of activity was approximately 1% of the total PI 3-kinase activity found in anti-phosphotyrosine (anti-pY) immunoprecipitates. In vitro, PI 3-kinase activity associated with the SH2 domain of tensin in a platelet-derived growth factor-dependent manner. The optimal phosphopeptide binding specificity of the SH2 domain of tensin was determined to be phospho-Y (E or D), N, (I, V, or F). Synthetic phosphopeptides containing the sequence YENI could specifically block the association of PI 3-kinase activity with tensin in a dose-dependent manner. These results suggest that PI 3-kinase interacts with the cytoskeleton via the SH2 domain of tensin and may play an important role in platelet-derived growth factor-induced cytoskeletal reorganization that is concomitant with cell migration and proliferation.

Amino Acid Sequence↗
PubMed1996

Specificity of LIM domain interactions with receptor tyrosine kinases.

LIM domains, Cys-rich motifs containing approximately 50 amino acids found in a variety of proteins, are proposed to direct protein*protein interactions. To identify structural targets recognized by LIM domains, we have utilized random peptide library selection, the yeast two-hybrid system, and glutathione S-transferase fusions. Enigma contains three LIM domains within its carboxyl terminus and LIM3 of Enigma specifically recognizes active but not mutant endocytic codes of the insulin receptor (InsR) (Wu, R. Y., and Gill, G. N. (1994) J. Biol. Chem. 269, 25085-25090). Interaction of two random peptide libraries with glutathione S-transferase-LIM3 of Enigma indicated specific binding to Gly-Pro-Hyd-Gly-Pro-Hyd-Tyr-Ala corresponding to the major endocytic code of InsR. Peptide competition demonstrated that both Pro and Tyr residues were required for specific interaction of InsR with Enigma. In contrast to LIM3 of Enigma binding to InsR, LIM2 of Enigma associated specifically with the receptor tyrosine kinase, Ret. Ret was specific for LIM2 of Enigma and did not bind other LIM domains tested. Mutational analysis indicated that the residues responsible for binding to Enigma were localized to the carboxyl-terminal 61 amino acids of Ret. A peptide corresponding to the carboxyl-terminal 20 amino acids of Ret dissociated Enigma and Ret complexes, while a mutant that changed Asn-Lys-Leu-Tyr in the peptide to Ala-Lys-Leu-Ala or a peptide corresponding to exon16 of InsR failed to disrupt the complexes, indicating the Asn-Lys-Leu-Tyr sequence of Ret is essential to the recognition motif for LIM2 of Enigma. We conclude that LIM domains of Enigma recognize tyrosine-containing motifs with specificity residing in both the LIM domains and in the target structures.

3T3 Cells↗