PubMed Health⌕ Search

Biomedical subjects

S S Martin

Publications and source records attributed to S S Martin.

At least 19 recordsLinked to original sources
PubMed2001

Quasi-equivalence in site-specific recombinase structure and function: crystal structure and activity of trimeric Cre recombinase bound to a three-way Lox DNA junction.

The crystal structure of a novel Cre-Lox synapse was solved using phases from multiple isomorphous replacement and anomalous scattering, and refined to 2.05 A resolution. In this complex, a symmetric protein trimer is bound to a Y-shaped three-way DNA junction, a marked departure from the pseudo-4-fold symmetrical tetramer associated with Cre-mediated LoxP recombination. The three-way DNA junction was accommodated by a simple kink without significant distortion of the adjoining DNA duplexes. Although the mean angle between DNA arms in the Y and X structures was similar, adjacent Cre trimer subunits rotated 29 degrees relative to those in the tetramers. This rotation was accommodated at the protein-protein and DNA-DNA interfaces by interactions that are "quasi-equivalent" to those in the tetramer, analogous to packing differences of chemically identical viral subunits at non-equivalent positions in icosahedral capsids. This structural quasi-equivalence extends to function as Cre can bind to, cleave and perform strand transfer with a three-way Lox substrate. The structure explains the dual recognition of three and four-way junctions by site-specific recombinases as being due to shared structural features between the differently branched substrates and plasticity of the protein-protein interfaces. To our knowledge, this is the first direct demonstration of quasi-equivalence in both the assembly and function of an oligomeric enzyme.

Attachment Sites, Microbiological↗
PubMed2001

Sensation seeking needs among 8th and 11th graders: characteristics associated with cigarette and marijuana use.

This cross-sectional school-based study explored the relationship between adolescent use of cigarettes and marijuana and the sensation seeking personality factors of (1) Disinhibition and (2) Thrill and Adventure Seeking. The study population included a representative sample of both male and female 8th and 11th graders in the state of Delaware. Analytic methods utilized included correlational analysis and multivariate logistic regression. In the multivariate logistic regression models, the Disinhibition personality factor accounted for cigarette and marijuana using behaviors with odds ratios ranging between 2 and 3. Thrill and Adventure Seeking was not a significant explanatory variable in any of the final multivariate models. Potential confounders (age, gender and race) were considered in all analyses. Of all the two-way interactions assessed, none was significant. The findings from this study utilizing a large general community sample indicate that sensation seeking needs are a potential risk factor for adolescent substance use.

Adolescent↗
PubMed2001

Human MCF10A mammary epithelial cells undergo apoptosis following actin depolymerization that is independent of attachment and rescued by Bcl-2.

Many tumor cells are impaired in adhesion-regulated apoptosis, which contributes to their metastatic potential. However, suppression of this apoptotic pathway in untransformed cells is not mediated only by adhesion to the extracellular matrix but also through the resulting ability to spread and adopt a distinct morphology. Since cell spreading is dependent on the integrity of the actin microfilament cytoskeleton, we sought to determine if actin depolymerization was sufficient to induce apoptosis, even in the presence of continuous attachment. For this study, we used a human mammary epithelial cell line (MCF10A), which is immortalized but remains adhesion dependent for survival. Treatment of MCF10A cells with latrunculin-A (LA), an inhibitor of actin polymerization, rapidly led to disruption of the actin cytoskeleton and caused cell rounding but preserved attachment. Initiation of apoptosis in LA-treated MCF10A cells was detected by mitochondrial localization of the Bax apoptotic protein, which was prevented by overexpression of Bcl-2. DNA fragmentation and poly(ADP-ribose) polymerase (PARP) cleavage in LA-treated MCF10A cells indicated progression to the execution phase of apoptosis. The MDA-MB-453 cell line, which was derived from a metastatic human mammary tumor, was resistant to PARP cleavage and loss of viability in response to actin depolymerization. Stable overexpression of Bcl-2 in the untransformed MCF10A cells was able to recapitulate the resistance to apoptosis found in the tumor cell line. We demonstrate that inhibition of actin polymerization is sufficient to stimulate apoptosis in attached MCF10A cells, and we present a novel role for Bcl-2 in cell death induced by direct disruption of the actin cytoskeleton.

Actins↗
PubMed2001

Internal poverty and teen pregnancy.

The subjects for the present study were drawn from the female students who participated in the National Education Longitudinal Study (NELS) initial eighth-grade data collection. Adolescent females who later became pregnant were matched on race, birth month, and birth year with adolescent females who did not report a pregnancy. The study examined selected predictor variables from the baseline 1988 wave of data in relation to the outcome variable of pregnancy status. Results indicated a statistically significant difference in locus of control between those females who later became pregnant and those who later did not experience a pregnancy during adolescence. Those who later became pregnant were much more likely to have an external locus of control (p = .0001). Females who later became pregnant were also more likely to have a poorer sense of personal efficacy (p = .0001). Finally, females who later experienced a teen pregnancy had more traditional occupational expectations (p = .006) and lower educational expectations (p = .001) than did those who did not later report a teen pregnancy.

Adolescent↗
PubMed2000

Use of radiographic atlases in a mass fatality.

In May and June of 1996, a forensic anthropology team from the C.A. Pound Human Identification Laboratory at the University of Florida identified 9 of 10 juveniles from the crash of ValuJet 592. The team relied primarily on a radiographic atlas developed and used by clinical practitioners to determine skeletal age. Postmortem radiographs of the juvenile victims were compared with radiographic standards to determine skeletal age. Skeletal age was then compared to a passenger list indicating the sex, weight, height, and chronological age of each individual. Tentative identifications based on the atlas method were organized into an exclusion matrix. Final identifications were based on this assessment in conjunction with other anthropological data such as appearance and fusion of ossification centers and estimation of stature.

Accidents, Aviation↗
PubMed1999

The functional role of CrkII in actin cytoskeleton organization and mitogenesis.

Crk is a member of a family of adapter proteins predominantly composed of Src homology 2 and 3 domains, whose role in signaling pathways is presently unclear. Using an in situ electroporation system which permits the introduction of glutathione S-transferase (GST) fusion proteins into cells, we found that c-CrkII bound to p130(cas), but not to paxillin in serum-starved rat-1 fibroblasts overexpressing the human insulin receptor (HIRc cells) in vivo. 17 nM insulin stimulation dissociated the binding of c-CrkII to p130(cas), whereas 13 nM insulin-like growth factor-I, 16 nM epidermal growth factor (EGF), and 10% serum each showed little or no effect. We found that stress fiber formation is consistent with a change in the p130(cas).c-CrkII interactions before and after growth factor stimulation. Microinjection of either GST-Crk-SH2 or -Crk-(N)SH3 domains, or anti-Crk antibody each inhibited stress fiber formation before and after insulin-like growth factor-I, EGF, and serum stimulation. Insulin stimulation by itself caused stress fiber breakdown and there was no additive effect of microinjection. Microinjection of anti-p130(cas) antibody also blocked stress fiber formation in quiescent cells. Microinjection of the Crk-inhibitory reagents also inhibited DNA synthesis after insulin-like growth factor-I, EGF, and serum stimulation, but not after insulin. These data suggest that the complex containing p130(cas).c-CrkII may play a crucial role in actin cytoskeleton organization and in anchorage-dependent DNA synthesis.

Actins↗
PubMed1999

In vivo selection of RNA-binding peptides from combinatorial libraries.

We have used a two step procedure to identify peptides that bind strongly to the Rev-response element (RRE) of HIV. In the first step, RRE-binding peptides were screened from a combinatorial peptide library generated by "randomization" using a small subset of the 20 amino acids. In the second step, one such RRE-binding peptide, RSG-1, was "evolved" into an even stronger RRE-binding peptide using a codon-based mutagenesis procedure. After 2 rounds of evolution, RSG-1.2 bound the RRE with 7-fold higher affinity than wild-type Rev peptide.

Amino Acid Sequence↗
PubMed1999

An SH2 domain-containing 5' inositolphosphatase inhibits insulin-induced GLUT4 translocation and growth factor-induced actin filament rearrangement.

Tyrosine kinase receptors lead to rapid activation of phosphatidylinositol 3-kinase (PI3 kinase) and the subsequent formation of phosphatidylinositides (PtdIns) 3,4-P2 and PtdIns 3,4, 5-P3, which are thought to be involved in signaling for glucose transporter GLUT4 translocation, cytoskeletal rearrangement, and DNA synthesis. However, the specific role of each of these PtdIns in insulin and growth factor signaling is still mainly unknown. Therefore, we assessed, in the current study, the effect of SH2-containing inositol phosphatase (SHIP) expression on these biological effects. SHIP is a 5' phosphatase that decreases the intracellular levels of PtdIns 3,4,5-P3. Expression of SHIP after nuclear microinjection in 3T3-L1 adipocytes inhibited insulin-induced GLUT4 translocation by 100 +/- 21% (mean +/- the standard error) at submaximal (3 ng/ml) and 64 +/- 5% at maximal (10 ng/ml) insulin concentrations (P < 0.05 and P < 0.001, respectively). A catalytically inactive mutant of SHIP had no effect on insulin-induced GLUT4 translocation. Furthermore, SHIP also abolished GLUT4 translocation induced by a membrane-targeted catalytic subunit of PI3 kinase. In addition, insulin-, insulin-like growth factor I (IGF-I)-, and platelet-derived growth factor-induced cytoskeletal rearrangement, i.e., membrane ruffling, was significantly inhibited (78 +/- 10, 64 +/- 3, and 62 +/- 5%, respectively; P < 0.05 for all) in 3T3-L1 adipocytes. In a rat fibroblast cell line overexpressing the human insulin receptor (HIRc-B), SHIP inhibited membrane ruffling induced by insulin and IGF-I by 76 +/- 3% (P < 0.001) and 68 +/- 5% (P < 0.005), respectively. However, growth factor-induced stress fiber breakdown was not affected by SHIP expression. Finally, SHIP decreased significantly growth factor-induced mitogen-activated protein kinase activation and DNA synthesis. Expression of the catalytically inactive mutant had no effect on these cellular responses. In summary, our results show that expression of SHIP inhibits insulin-induced GLUT4 translocation, growth factor-induced membrane ruffling, and DNA synthesis, indicating that PtdIns 3,4,5-P3 is the key phospholipid product mediating these biological actions.

3T3 Cells↗
PubMed1999

The terrible triad of the shoulder.

This case shows that the terrible triad of the shoulder-anterior dislocation, brachial plexus injury, and rotator cuff tear-can occur in younger populations than previously described. A high index of suspicion for this triad of injury should be maintained, particularly in those young individuals with grossly unstable shoulders. Once axillary nerve function has begun to return, simultaneous repair of all soft tissue injuries can lead to a stable, functional joint.

Accidents, Traffic↗
PubMed1998

Microsatellite instability in sarcomas.

BACKGROUND: Microsatellite instability (MIN) has been studied in a variety of carcinomas and gynecologic sarcomas, but never in musculoskeletal sarcomas. METHODS: We evaluated 16 skeletal and soft tissue sarcomas at nine genetic loci from chromosomal regions 1q, 5q, 7q, 12p, 13q, 17p, 19q, and two at 11p--all potential regions of interest regarding musculoskeletal sarcomas. RESULTS: MIN was identified at one or more loci in seven of the cancers studied (44%). Three tumors had more than one locus with MIN and one tumor, a high-grade osteogenic sarcoma, had five of nine loci positive for MIN. CONCLUSION: These results indicate that musculoskeletal sarcomas show instability in areas inside and outside the loci of known oncogenes. Areas of mismatch repair, as heralded by MIN, may contribute to the vast heterogeneity of these neoplasms.

Adolescent↗
PubMed1998

Spatial memory in young and older adults: environmental support and contextual influences at encoding and retrieval.

Previous studies have demonstrated the existence of an "unequal facilitation" effect in spatial memory. In those experiments, the provision of appropriate environmental support for recall was shown to enhance the recall performance of older adults more than that of young adults. In some cases, this process resulted in parity of performance between the two age groups. The present study evaluated the relative contribution of environmental support to the unequal facilitation effect at encoding and retrieval in a spatial memory task. Results, indicate that, although the provision of environmental support at both encoding and retrieval is necessary for optimal recall across the adult life span, the primary influence of such support for recall in the elderly derives from its presence at encoding.

Adult↗
PubMed1997

Molding a peptide into an RNA site by in vivo peptide evolution.

Short peptides corresponding to the arginine-rich domains of several RNA-binding proteins are able to bind to their specific RNA sites with high affinities and specificities. In the case of the HIV-1 Rev-Rev response element (RRE) complex, the peptide forms a single alpha-helix that binds deeply in a widened, distorted RNA major groove and makes a substantial set of base-specific and backbone contacts. Using a reporter system based on antitermination by the bacteriophage lambda N protein, it has been possible to identify novel arginine-rich peptides from combinatorial libraries that recognize the RRE with affinities and specificities similar to Rev but that appear to bind in nonhelical conformations. Here we have used codon-based mutagenesis to evolve one of these peptides, RSG-1, into an even tighter binder. After two rounds of evolution, RSG-1.2 bound the RRE with 7-fold higher affinity and 15-fold higher specificity than the wild-type Rev peptide, and in vitro competition experiments show that RSG-1.2 completely displaces the intact Rev protein from the RRE at low peptide concentrations. By fusing RRE-binding peptides to the activation domain of HIV-1 Tat, we show that the peptides can deliver Tat to the RRE site and activate transcription in mammalian cells, and more importantly, that the fusion proteins can inhibit the activity of Rev in chloramphenicol acetyltransferase reporter assays. The evolved peptides contain proline and glutamic acid mutations near the middle of their sequences and, despite the presence of a proline, show partial alpha-helix formation in the absence of RNA. These directed evolution experiments illustrate how readily complex peptide structures can be evolved within the context of an RNA framework, perhaps reflecting how early protein structures evolved in an "RNA world."

Amino Acid Sequence↗
PubMed1997

Localization of p21-activated kinase 1 (PAK1) to pinocytic vesicles and cortical actin structures in stimulated cells.

The mechanisms through which the small GTPases Rac1 and Cdc42 regulate the formation of membrane ruffles, lamellipodia, and filopodia are currently unknown. The p21-activated kinases (PAKs) are direct targets of active Rac and Cdc42 which can induce the assembly of polarized cytoskeletal structures when expressed in fibroblasts, suggesting that they may play a role in mediating the effects of these GTPases on cytoskeletal dynamics. We have examined the subcellular localization of endogenous PAK1 in fibroblast cell lines using specific PAK1 antibodies. PAK1 is detected in submembranous vesicles in both unstimulated and stimulated fibroblasts that colocalize with a marker for fluid-phase uptake. In cells stimulated with PDGF, in v-Src-transformed fibroblasts, and in wounded cells, PAK1 redistributed into dorsal and membrane ruffles and into the edges of lamellipodia, where it colocalizes with polymerized actin. PAK1 was also colocalized with F-actin in membrane ruffles extended as a response to constitutive activation of Rac1. PAK1 appears to precede F-actin in translocating to cytoskeletal structures formed at the cell periphery. The association of PAK1 with the actin cytoskeleton is prevented by the actin filament-disrupting agent cytochalasin D and by the phosphatidylinositol 3-kinase inhibitor wortmannin. Co-immunoprecipitation experiments demonstrate an in vivo interaction of PAK1 with filamentous (F)-actin in stimulated cells. Microinjection of a constitutively active PAK1 mutant into Rat-1 fibroblasts overexpressing the insulin receptor (HIRcB cells) induced the formation of F-actin- and PAK1-containing structures reminiscent of dorsal ruffles. These data indicate a close correlation between the subcellular distribution of endogenous PAK1 and the formation of Rac/Cdc42-dependent cytoskeletal structures and support an active role for PAK1 in regulating cortical actin rearrangements.

3T3 Cells↗
PubMed1997

The amino terminus of insulin-responsive aminopeptidase causes Glut4 translocation in 3T3-L1 adipocytes.

The insulin-responsive aminopeptidase (IRAP) is a constituent of the vesicles that contain the insulin-regulated glucose transporter (Glut4). Like Glut4, IRAP translocates to the cell surface in response to insulin. Microinjection into 3T3-L1 adipocytes of a glutathione S-transferase (GST) fusion protein containing the cytosolic portion of IRAP (GST-IRAP-(1-109)), resulted in translocation of Glut4 to the cell surface. Immunostaining of 3T3-L1 adipocytes for Glut4 showed that the percentage of cells with substantial cell surface Glut4 was 10% in unstimulated cells, 8% following injection of GST, and 27% following injection of GST-IRAP-(1-109). Increased cell surface Glut4 occurred within 5-10 min following injection and was maintained for at least 4 h. A fusion protein containing only 28 amino acids from IRAP (GST-IRAP-(55-82)) was as effective in increasing cell surface Glut4 as stimulation with 100 nM insulin (44% versus 43%, respectively). In contrast to insulin-stimulated Glut4 translocation, the redistribution of Glut4 following injection of GST-IRAP-(55-82) was not blocked by wortmannin or co-injection with a SH2 domain from the regulatory subunit of phosphatidylinositol 3-kinase. These data suggest that the amino terminus of IRAP interacts with a retention/sorting protein that also regulates the distribution of Glut4 in insulin-responsive cells.

3T3 Cells↗
PubMed1997

The proto-oncogene product p120(cbl) links c-Src and phosphatidylinositol 3'-kinase to the integrin signaling pathway.

Integrin-mediated cell adhesion triggers intracellular signaling cascades, including tyrosine phosphorylation of intracellular proteins. We show in this report that p120(cbl) (Cbl), the 120-kDa c-cbl proto-oncogene product, becomes tyrosine-phosphorylated during integrin-mediated macrophage cell adhesion to extracellular matrix substrata and anti-integrin antibodies. This tyrosine phosphorylation does not occur when cells attach to polylysine, to which cells adhere in a nonspecific fashion. It also does not take place when adhesion-induced reorganization of the cytoskeleton is inhibited with cytochalasin D. In contrast to the rapid and transient tyrosine phosphorylation of Cbl by CSF-1 stimulation, tyrosine phosphorylation of Cbl by cell attachment was gradual and persistent. Tyrosine-phosphorylated Cbl was found to form complexes with the SH2 domain-containing signaling proteins Src and phosphatidylinositol 3-kinase; in vitro kinase assays demonstrated that these kinases were active in the Cbl complexes following integrin ligand binding. Furthermore, Cbl was found to translocate to the plasma membrane in response to cell adhesion to fibronectin. These observations suggest that Cbl serves as a docking protein and may transduce signals to downstream signaling pathways following integrin-mediated cell adhesion in macrophages.

Animals↗
PubMed1997

Social factors predicting postpartum choice of Norplant among African-American and non-Hispanic white adolescents.

PURPOSE: This study was designed to determine the factors associated with Norplant choice for postpartum teens. METHODS: A total of 151 teenagers, ages 12-20 years, who delivered at the Medical Center of Delaware from July to December 1992, were offered insertion of Norplant within 48 h postpartum. A structured interview was conducted in the postpartum period after nondirective counseling sessions including a physical demonstration using anatomical models of various contraceptive methods. Student's t-tests, chi-square, and multivariate analyses were used. RESULTS: Eighty-six teenagers were African-American (mean age = 17.3 +/- 1.9 years) and 65 non-Hispanic white (NHW) (mean age = 18.3 +/- 1.5 years). The NHW teenagers were older (p < 0.001); the African-American teenagers were more likely to have Medicaid (49% vs. 14%; p < 0.001) and to have one or more friends who use Norplant (62% vs. 34%; p < 0.001). In multivariate analyses, NHW teenagers were more likely to choose Norplant if they had discussed their choice with a parent or guardian [adjusted odds ratio (AOR) = 14.6, 95% confidence interval (CI), 2.12-100.57]; had Medicaid funding (AOR = 12.1; 95% (CI), 10.6-91.34); and had any friends who used Norplant (AOR = 6.3; 95% (CI), 1.38-28.40). However, for African-American teenagers, the strongest predictor for choice of Norplant was number of prior children delivered. After two deliveries, there was a better than four-fold likelihood (AOR = 4.8; 95% (CI), 1.47-15.94) that African-American teenagers would choose Norplant. For the African-American teenagers, parental discussion, Medicaid status, and friends' use of Norplant were not as important as family size, but far greater percentages of the African-American teenagers had access to Medicaid funding and peers who used Norplant. CONCLUSIONS: NHW and African-American teenagers choose Norplant for different reasons. Lack of funding may have been a barrier to choosing Norplant. Discussions with parents and friends have a positive influence on choosing Norplant for NHW teenagers. African-American teenagers were more likely than NHW to have Medicaid coverage, and more frequently choose Norplant if the current birth was their third child.

Adolescent↗
PubMed1997

The small guanosine triphosphate-binding protein Rab4 is involved in insulin-induced GLUT4 translocation and actin filament rearrangement in 3T3-L1 cells.

Insulin's stimulation of glucose transport involves the translocation of vesicles containing the glucose transporter GLUT4 to the plasma membrane. Small GTP-binding proteins have been implicated in the regulation of vesicular traffic. We studied the effects of microinjection of wild-type Rab4 glutathione S-transferase fusion protein (WT Rab4), a GTP-binding defective mutant (Rab4 N121I), a guanosine triphosphatase-defective mutant (Rab4 Q67L), and a Rab4 antibody on insulin-induced GLUT4 translocation in 3T3-L1 adipocytes. Microinjection of Rab4 N121I and Rab4 antibodies had no effect on basal GLUT4 staining, but inhibited insulin-induced GLUT4 translocation by 50% compared with that in control IgG-injected cells. WT Rab4 and Rab4 Q67L microinjection had no effect on either basal or insulin-induced GLUT4 translocation. Premixing and coinjection of the Rab4 antibody with WT Rab4 almost completely abolished its inhibitory effect on insulin-induced GLUT4 translocation. In contrast, microinjection of an antibody directed against the highly conserved region of Rab3 proteins had no effect on insulin-induced GLUT4. These results point to a direct role of Rab4 in insulin-induced GLUT4 translocation, and that this effect is dependent on nucleotide binding to the protein. We also studied the effect of microinjection of the same proteins on insulin-induced actin filament rearrangement (membrane ruffling) in the same cell line. Microinjection of Rab4 N121I and Rab4 antibodies inhibited insulin-induced membrane ruffling by 40%, whereas WT Rab4 or a Rab3 antibody injection had no effect on cytoskeletal rearrangement. In summary, 1) Rab4 is a necessary component of the insulin/GLUT4 translocation signaling pathway; 2) the function of Rab4 in this pathway requires GTP binding; 3) Rab4 also participates in the process of insulin-induced membrane ruffling; and 4) Rab3 proteins do not seem to be involved in these processes.

3T3 Cells↗