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Biomedical subjects

V M Rivera

Publications and source records attributed to V M Rivera.

At least 55 records · Page 3Linked to original sources
PubMed1996

A humanized system for pharmacologic control of gene expression.

Gene therapy was originally conceived as a medical intervention to replace or correct defective genes in patients with inherited disorders. However, it may have much broader potential as an alternative delivery platform for protein therapeutics, such as cytokines, hormones, antibodies and novel engineered proteins. One key technical barrier to the widespread implementation of this form of therapy is the need for precise control over the level of protein production. A suitable system for pharmacologic control of therapeutic gene expression would permit precise titration of gene product dosage, intermittent or pulsatile treatment, and ready termination of therapy by withdrawal of the activating drug. We set out to design such a system with the following properties: (1) low baseline expression and high induction ratio; (2) positive control by an orally bioavailable small-molecule drug; (3) reduced potential for immune recognition through the exclusive use of human proteins; and (4) modularity to allow the independent optimization of each component using the tools of protein engineering. We report here the properties of this system and demonstrate its use to control circulating levels of human growth hormone in mice implanted with engineered human cells.

Animals↗
PubMed1995

Neurologic manifestations of AIDS: a comparative study of two populations from Mexico and the United States.

Neurologic complications associated with human immunodeficiency virus type 1 (HIV-1) infection vary geographically. To understand the pattern of HIV-associated neurologic complications in Mexico, 120 AIDS patients from Mexico City, Mexico, and 500 AIDS patients from Houston, Texas, were studied cross-sectionally and retrospectively. Neurologic, laboratory, imaging, and pathologic examinations identified 40 Mexican patients and 130 U.S. patients with neurologic complications. Whereas AIDS dementia complex was the most common neurologic manifestation in both groups, intracranial tuberculoma was present only in the Mexican population (10%). Primary brain lymphoma was more prevalent in the U.S. population (8.4%). The different findings in the Mexican population likely reflect afflictions common to developing countries--a high prevalence of tuberculosis and a high mortality rate. These conditions preclude complications such as lymphoma, which develop later in the natural course of HIV infection.

AIDS Dementia Complex↗
PubMed1995

Clustering of Syk is sufficient to induce tyrosine phosphorylation and release of allergic mediators from rat basophilic leukemia cells.

In mast cells, antigen-mediated aggregation of the high-affinity receptor for immunoglobulin E, Fc epsilon RI, stimulates tyrosine phosphorylation and activation of multiple signaling pathways leading to the release of several classes of mediators of the allergic response. Early events induced upon cross-linking of Fc epsilon RI include tyrosine phosphorylation of Fc epsilon RI subunits and activation of the tyrosine kinase p72syk (Syk), which binds to tyrosine-phosphorylated Fc epsilon RI. Clustering of Syk, as a result of its interaction with aggregated Fc epsilon RI, may play a role in activating one or more of the signaling pathways leading to mediator release. To test this possibility, Syk was introduced into a model mast cell line (rat basophilic leukemia cells) as part of a chimeric transmembrane protein containing the extracellular and transmembrane domains of CD16 and CD7, respectively. Clustering of the Syk chimera, using antibodies against CD16, was found to be sufficient to stimulate early and late events normally induced by clustering of Fc epsilon RI. Specifically, aggregation of Syk induced degranulation, leukotriene synthesis, and expression of cytokine genes. Induction of mediator release was dependent on the kinase activity of Syk. Consistent with this finding, clustering of Syk also induced the tyrosine phosphorylation of a profile of proteins, including phospholipase C-gamma 1 and mitogen-activated protein kinase, similar to that induced upon clustering of Fc epsilon RI. These results strongly suggest that Syk is an early and critical mediator of multiple signaling pathways that emanate from the Fc epsilon RI receptor and give rise to the allergic response.

Animals↗
PubMed1994

L-type voltage-sensitive calcium channel activation stimulates gene expression by a serum response factor-dependent pathway.

A mechanism by which calcium-induced signals are transduced to the nucleus to activate transcription of the c-fos proto-oncogene has been characterized. The serum response element (SRE), a region of the c-fos gene which controls growth factor-induced transcription, is now shown to mediate c-fos transcription in response to activation of L-type voltage-sensitive calcium channels. Calcium-dependent transcriptional activation through the SRE is mediated by the serum response factor (SRF). Membrane depolarization induces phosphorylation of SRF at Ser-103, an event shown to enhance the ability of SRF to bind the SRE. Ca(2+)-induced SRF phosphorylation occurs via a pathway that may involve Ca2+/calmodulin-dependent kinases.

Animals↗
PubMed1994

Neurologic deficit in patients at high risk with thoracoabdominal aortic aneurysms: the role of cerebral spinal fluid drainage and distal aortic perfusion.

PURPOSE: This prospective study evaluated the possible prevention of postoperative neurologic deficit in patients at high risk with thoracoabdominal aortic aneurysms (TAAA), types I and II, by use of perioperative cerebrospinal fluid drainage and distal aortic perfusion. METHODS: Between September 18, 1992, and August 8, 1993, 45 consecutive patients underwent TAAA repair (14 type I, 31 type II). Thirty-six were men and nine were women. The median age was 63 years (range 28 to 88). Twenty-four of 45 patients (53%) had dissection and 17 of 45 (38%) had prior proximal aortic replacement. All patients underwent perioperative cerebrospinal fluid drainage and distal aortic perfusion. Median aortic clamping time was 42 minutes. Thirty-five of 45 patients (78%) underwent intercostal artery reattachment. RESULTS: The 30-day survival rate was 96% (43 of 45 patients). Early neurologic deficit occurred in two of 45 patients (4%), and late neurologic deficit also occurred in two of 45 patients (4%). We compared the neurologic deficit of our current group of 45 patients with the data of a previously unpublished study of 112 patients also from this center. Total neurologic deficit for the current group was four of 45 (9%) versus the previous group of 35 of 112 (31%) with a p value of 0.0034 (Pearson chi-square test). Neurologic deficit for patients with type I TAAA was 0 of 14 (0%) versus 15 of 73 (21%) (p = 0.062); for patients with type II TAAA 4 of 31 (13%) versus 20 of 39 (51%) (p = 0.0008). In patients with aortic dissection, neurologic deficit was 3 of 24 (12%) versus 9 of 32 (28%) (p = 0.0304); no dissection was 1 of 21 (5%) versus 26 of 80 (32%) (p = 0.011). For aortic clamp times less than 45 minutes, neurologic deficit was 1 of 24 (4%) versus 14 of 68 (21%) (p = 0.061); for aortic clamp times equal to or greater than 45 minutes, neurologic deficit was 3 of 21 (14%) versus 21 of 44 (48%) (p = 0.0090). CONCLUSION: Neurologic deficit in patients treated for types I and II TAAA was reduced significantly by perioperative cerebral spinal fluid drainage and distal aortic perfusion.

Adult↗
PubMed1993

A growth factor-induced kinase phosphorylates the serum response factor at a site that regulates its DNA-binding activity.

A signaling pathway by which growth factors may induce transcription of the c-fos proto-oncogene has been characterized. Growth factor stimulation of quiescent fibroblasts activates a protein kinase cascade that leads to the rapid and transient phosphorylation of the serum response factor (SRF), a regulator of c-fos transcription. The in vivo kinetics of SRF phosphorylation and dephosphorylation parallel the activation and subsequent repression of c-fos transcription, suggesting that this phosphorylation event plays a critical role in the control of c-fos expression. The ribosomal S6 kinase pp90rsk, a growth factor-inducible kinase, phosphorylates SRF in vitro at serine 103, the site that becomes newly phosphorylated upon growth factor stimulation in vivo. Phosphorylation of serine 103 significantly enhances the affinity and rate with which SRF associates with its binding site, the serum response element, within the c-fos promoter. These results suggest a model in which the growth factor-induced phosphorylation of SRF at serine 103 contributes to the activation of c-fos transcription by facilitating the formation of an active transcription complex at the serum response element.

3T3 Cells↗
PubMed1991

The serum response factor is extensively modified by phosphorylation following its synthesis in serum-stimulated fibroblasts.

Growth factor regulation of c-fos proto-oncogene transcription is mediated by a 20-bp region of dyad symmetry, termed the serum response element. The inner core of this element binds a 67-kDa phosphoprotein, the serum response factor (SRF), that is thought to play a pivotal role in the c-fos transcriptional response. To investigate the mechanism by which SRF regulates c-fos expression, we generated polyclonal anti-SRF antibodies and used these antibodies to analyze the biochemical properties of SRF. These studies indicate that the synthesis of SRF is transient, occurring within 30 min to 4 h after serum stimulation of quiescent fibroblasts. Newly synthesized SRF is transported to the nucleus, where it is increasingly modified by phosphorylation during progression through the cell cycle. Within 2 h of serum stimulation, differentially modified forms of SRF can be distinguished on the basis of the ability to bind a synthetic serum response element. SRF protein exhibits a half-life of greater than 12 h and is predominantly nuclear, with no change occurring in its localization upon serum stimulation. We find that the induction of SRF synthesis is regulated at the transcriptional level and that cytoplasmic SRF mRNA is transiently expressed with somewhat delayed kinetics compared with c-fos mRNA expression. These features of SRF expression suggest a model whereby newly synthesized SRF functions in the shutoff of c-fos transcription.

Animals↗
PubMed1990

The inner core of the serum response element mediates both the rapid induction and subsequent repression of c-fos transcription following serum stimulation.

Serum stimulation of quiescent fibroblasts results in a dramatic increase in c-fos transcription that peaks by 15 min and is then rapidly repressed to basal levels within 60 min. Using a nuclear run-on assay to follow directly the kinetics of transcription of mutant c-fos constructs, we demonstrate that the serum response element (SRE) is the site of regulation of both the induction and repression events. This is indicated by the ability of the SRE to mediate c-fos kinetics of induced transcription when fused to a heterologous gene and in the absence of a recognizable TATA element. Functions of the inner core and the outer palindromic arms of the SRE have been determined by mutagenesis. The 14-bp inner core binds the serum response factor (SRF) and is, itself, sufficient to mediate both the induction and shutoff of serum-stimulated transcription. Therefore, SRF and any other factors that regulate the transient kinetics of c-fos transcription require no more than these 14 nucleotides to function. The palindromic outer arms of the SRE stabilize the binding of SRF and thereby enhance the transcriptional response to serum. Autoregulation by the c-fos gene product is not affected by the direct interaction of Fos/Jun complexes with the c-fos promoter and is likely to be mediated by either a novel function of the Fos protein or by an effect of Fos on the expression of another gene.

Animals↗
PubMed1990

Growth factor-induced gene expression: the ups and downs of c-fos regulation.

Many growth factor-inducible immediate-early genes, including c-fos, encode transcription factors that are believed to propagate the mitogenic signal by activating a program of gene expression critical for cell proliferation. This review summarizes work aimed at elucidating the molecular mechanisms by which a growth factor-induced signal effects a change in gene expression. In the case of c-fos, both the activation and repression of transcription are mediated by the serum response element, a dyad symmetrical sequence found upstream of the c-fos gene. This element binds a complex of proteins, a component(s) of which may be the target of the growth factor-induced signal. Recent progress made towards understanding the roles of these factors in the regulation of c-fos transcription will be described.

Animals↗
PubMed1989

Analysis of the sequence-specific interactions between Cro repressor and operator DNA by systematic base substitution experiments.

We measured quantitatively the binding affinities of purified Cro repressor to the chemically synthesized wild-type and mutant OR1 operators, consisting of all three possible base-pair substitutions and of thymine to uracil substitutions at each base-pair position of the 17-base-pair operator sequence. The sequence-specific interactions between Cro repressor and the operator DNA occur at the symmetrically disposed outer 7-base-pair positions of each half operator and at the central base-pair position. The binding of Cro is almost symmetrical with respect to the pseudo-twofold symmetry of the binding site. The binding free energy changes calculated from the affinity changes are mostly additive for specific Cro binding. Also the binding affinities of Cro to the operators or any other DNA sequences can be predicted by simple addition of free energy changes of single base substitutions. We isolated cro mutants by site-directed mutagenesis and studied their DNA binding to the wild-type and base-substituted mutant operators. The sequence-specific contacts derived from such studies are significantly different from the models proposed by Ohlendorf et al. [Ohlendorf, D. H., Anderson, W. F., Takeda, Y. & Matthews, B. W. (1982) Nature (London) 298, 719-723] and by Hochschild et al. [Hochschild, A., Douhan, J., III, & Ptashne, M. (1986) Cell 47, 807-816].

Amino Acid Sequence↗
PubMed1988

Comparative sequence analysis of the 5' noncoding region of the enteroviruses and rhinoviruses.

A comparative sequence analysis of the 5' noncoding region of a subgroup of the picornaviruses, including the polioviruses, coxsackie B3, and the human rhinoviruses, reveals the conservation of certain features despite the divergence of sequence. In this subgroup, for which nine complete sequences are available, two long stretches of sequence, two pyrimidine-rich regions, and 22 hairpins are conserved. Based on these results, similar secondary structures encompassing the entire 5' noncoding regions of these viruses are predicted. The fact that sequence divergence occurred only in a manner that allowed conservation of these structures implicates a biologically functional role for this region. The possible roles it may have in the picornavirus life cycle are discussed.

Base Sequence↗
PubMed1986

Narcolepsy following cerebral hypoxic ischemia.

A 51-year-old man with non-HLA-DR2 histocompatibility developed classic signs and symptoms of the narcoleptic tetrad soon after recovering from an episode of cardiopulmonary insufficiency, which occurred during induction of surgical anesthesia. Symptoms included excessive daytime sleepiness, hypnagogic hallucinations, sleep paralysis, and cataplexy. The diagnosis was confirmed by repeated polysomnographic examinations in the sleep laboratory. Cerebral hemodynamic changes during the onset of sleep showed remarkable increases of cerebral blood flow during the onset of rapid-eye-movement sleep similar to those reported previously in patients with narcolepsy. Magnetic resonance imaging showed focal regions of abnormal spin-echo signals in the ventral pons.

Anesthesia, Intravenous↗
PubMed1986

Patterns of auditory abnormality in multiple sclerosis.

This paper stresses the relatively high prevalence of auditory abnormality in multiple sclerosis. An auditory test battery consisting of the acoustic reflex (AR), the auditory brainstem response (ABR), the masking level difference (MLD) and speech audiometry (SA) was administered to 62 patients with diagnosed 'definite' multiple sclerosis. The AR showed the highest identification rate (71%). SA was next (55%), followed by the ABR (52%) and the MLD (45%). The combination of an abnormality on either AR, ABR or SA yielded a 90% identification rate. Interestingly, the combination of AR or SA or MLD yielded an 87% identification rate without any contribution from ABR.

Adult↗
PubMed1983

Relationships among auditory brain stem responses, masking level differences and the acoustic reflex in multiple sclerosis.

We report the results of a study in which we compared auditory brain stem responses (ABR), the binaural masking level difference (MLD) for a 500-Hz pure tone and acoustic reflexes in 20 patients with confirmed multiple sclerosis. Our intent was to determine whether abnormalities in the three measures were related or whether they varied independently. The results indicated that the size of the MLD varied with the integrity of wave III of the ABR. When the ABR was abnormal to the extent of lacking wave III on one or both ears, there was no release from masking and the crossed acoustic reflex was abnormal, as well. The sensitivity of the MLD to retrocochlear disorder was comparable to that of ABR, and was greater than that provided by speech audiometry or acoustic reflexes.

Adult↗