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Biomedical subjects

David A Williams

Publications and source records attributed to David A Williams.

At least 19 recordsLinked to original sources
PubMed2007

Chemotherapy for myeloid malignancy in children with Fanconi anemia.

BACKGROUND: Children with Fanconi anemia (FA) have a markedly increased risk of developing myeloid malignancies. Historically, patients with FA and myeloid malignancy have extremely poor outcomes. There are currently no clinical trials or case series addressing the use of chemotherapy for children with FA, except in the context of preparative regimens for stem cell transplantation (SCT). In this report we describe the toxicity of a chemotherapy approach for patients with FA and myeloid malignancy to achieve cytoreduction prior to SCT. PATIENTS AND METHODS: Four patients with FA and myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) were treated with chemotherapy (fludarabine 30 mg/m(2) and cytosine arabinoside 300 mg/m(2) each on days 2-4 and granulocyte-colony stimulating factor (G-CSF) 5 microg/kg on days 1-5), termed reduced intensity FLAG prior to SCT. RESULTS: The chemotherapy was well tolerated with expected hematologic toxicity and no measurable toxicity in other organs. Two of the three patients with AML cleared blasts from their bone marrow. Reduction in marrow cellularity was also achieved in one patient with hypercellular MDS. CONCLUSION: These data indicate that children with FA and myeloid malignancy can tolerate chemotherapy and achieve clearance of disease. It remains unclear whether pre-SCT chemotherapy improves currently poor survival rates for SCT in FA patients with myeloid malignancies and further studies are needed to determine if there is a clinical role for this strategy.

Acute Disease↗
PubMed2007

Assessor status influences pain recall.

UNLABELLED: Anecdotal clinical reports suggest that patients report differing levels of pain, depending on the status within the medical hierarchy of the individual gathering the pain rating. This observation has clinical relevance, given the practice of delegating the assessment of pain to lower status clinic staff members. In this study, both pain and mood were assessed in 70 patients diagnosed with low back pain at pretreatment, immediately after epidural lumbar injection, and again 2 weeks later by phone. At the 2-week follow-up, patients were also asked to recall the postprocedural rating that they had given immediately after the injection. This rating was obtained by either the treating physician or by a research assistant who was present at the time of injection, on a randomly determined basis. Current ratings of pain and mood did not differ for either group before the epidural injection, after the epidural injection, or at the 2-week follow-up. Two-week recall of postprocedural pain did, however, differ depending on assessor status. Those called by the physician provided recalled pain ratings that closely matched the ratings provided immediately after the procedure. Those called by the research assistant provided ratings that were 86% higher (that is, worse) than their original ratings. This status-driven bias in recalled postprocedural pain reporting is discussed in the context of social demands inherent in the physician-patient relationship, with implications for assessing treatment effectiveness in clinical practice and research. PERSPECTIVE: Accurate assessment of patients' pain is critical to effective pain management and treatment planning. This study found evidence of a status-based bias in which physicians elicited lower ratings of previously experienced pain associated with treatment procedures than did staff members of lower status.

Affect↗
PubMed2007

Stem cell collection and gene transfer in Fanconi anemia.

Fanconi anemia (FA) is a rare genetic syndrome characterized by progressive bone marrow failure (BMF), congenital anomalies, and a predisposition to malignancy. Successful gene transfer into hematopoietic stem cells (HSCs) could reverse BMF in this disease. We developed clinical trials to determine whether a sufficient number of CD34(+) stem cells could be collected for gene modification and to evaluate the safety and efficacy of HSC-corrective gene transfer in FA genotype A (FANCA) patients. Here, we report that FA patients have significant depletion of their BM CD34(+) cell compartment even before severe pancytopenia is present. However, oncoretroviral-mediated ex vivo gene transfer was efficient in clinical scale in FA-A cells, leading to reversal of the cellular phenotype in a significant percentage of CD34(+) cells. Re-infusion of gene-corrected products in two patients was safe and well tolerated and accompanied by transient improvements in hemoglobin and platelet counts. Gene correction was transient, likely owing to the low dose of gene-corrected cells infused. Our early experience shows that stem cell collection is well tolerated in FA patients and suggests that collection be considered as early as possible in patients who are potential candidates for future gene transfer trials.

Adolescent↗
PubMed2006

Rac1 and a GTPase-activating protein, MgcRacGAP, are required for nuclear translocation of STAT transcription factors.

STAT transcription factors are tyrosine phosphorylated upon cytokine stimulation and enter the nucleus to activate target genes. We show that Rac1 and a GTPase-activating protein, MgcRacGAP, bind directly to p-STAT5A and are required to promote its nuclear translocation. Using permeabilized cells, we find that nuclear translocation of purified p-STAT5A is dependent on the addition of GTP-bound Rac1, MgcRacGAP, importin alpha, and importin beta. p-STAT3 also enters the nucleus via this transport machinery, and mutant STATs lacking the MgcRacGAP binding site do not enter the nucleus even after phosphorylation. We conclude that GTP-bound Rac1 and MgcRacGAP function as a nuclear transport chaperone for activated STATs.

Animals↗
PubMed2006

Rac1 GTPase regulates cell genomic stability and senescence.

The Rho family small GTPase Rac1 has been shown to play multiple roles in cell regulation, including actin cytoskeleton organization, transcriptional activation, microtubule dynamics, and endocytosis. Here, we report a novel role of Rac1 in regulating genomic stability and cell senescence. We observed in primary mouse embryonic fibroblasts that deletion of rac1 by gene targeting, as well as expression of the constitutively active Rac1 mutant L61Rac1, led to decreased cell growth that was associated with altered cell cycle progression at both G(1)/S and G(2)/M phases, increased apoptosis, and premature senescence. The senescence induction by either loss or gain of Rac1 activity was due at least in part to an increase in cellular reactive oxygen species (ROS). rac1 gene deletion caused a compensatory up-regulation of a closely related family member, Rac3, in mouse embryonic fibroblasts, the activity of which induced ROS production independently of Rac1. Furthermore, the Rac1-regulated ROS production and senescence correlated with the extent of DNA damage in the Rac1(-/-) and L61Rac1 cells. Treatment of these cells with a ROS inhibitor inhibited phospho-H2AX-positive nuclear focus formation. Finally, phospho-Ser(15) p53 was significantly increased in L61Rac1 and Rac1(-/-) cells, and genetic deletion of p53 from these cells readily reversed the senescence phenotype, indicating that Rac1 is functionally dependent on p53 in regulating cell senescence. Taken together, our results show that Rac1 activity serves as a regulator of cell senescence through modulation of cellular ROS, genomic stability, and p53 activity.

Animals↗
PubMed2006

RhoH GTPase recruits and activates Zap70 required for T cell receptor signaling and thymocyte development.

RhoH is a hematopoietic-specific, GTPase-deficient member of the Rho GTPase family with unknown physiological function. Here we demonstrate that Rhoh-/- mice have impaired T cell receptor (TCR)-mediated thymocyte selection and maturation, resulting in T cell deficiency. RhoH deficiency resulted in defective CD3zeta phosphorylation, impaired translocation of the signaling molecule Zap70 to the immunological synapse and reduced activation of Zap70-mediated signaling in thymic and peripheral T cells. Proteomic analyses demonstrated that RhoH is a component of TCR signaling and is required for recruitment of Zap70 to the TCR through interaction with RhoH noncanonical immunoreceptor tyrosine-based activation motifs (ITAMs). In vivo reconstitution studies also demonstrated that RhoH function depends on phosphorylation of the RhoH ITAMs. These findings suggest that RhoH is a critical regulator of thymocyte development and TCR signaling by mediating recruitment and activation of Zap70.

Animals↗
PubMed2006

Cerebrospinal fluid corticotropin-releasing factor concentration is associated with pain but not fatigue symptoms in patients with fibromyalgia.

Previous studies have identified stress system dysregulation in fibromyalgia (FM) patients; such dysregulation may be involved in the generation and/or maintenance of pain and other symptoms. Corticotropin-releasing factor (CRF) is the principal known central nervous system mediator of the stress response; however, to date no studies have examined cerebrospinal fluid (CSF) CRF levels in patients with FM. The relationship between CSF CRF level, heart rate variability (HRV), and pain, fatigue, and depressive symptoms was examined in patients with FM. Among participants (n=26), CSF CRF levels were associated with sensory pain symptoms (r=0.574, p=0.003) and affective pain symptoms (r=0.497, p=0.011), but not fatigue symptoms. Increased HRV was also strongly associated with increased CSF CRF and FM pain. In multivariate analyses adjusting for age, sex, and depressive symptoms, the association between CSF CRF and sensory pain symptoms (t=2.54, p=0.027) persisted. Women with FM who reported a history of physical or sexual abuse had lower CSF CRF levels than women who did not report such a history. CSF CRF levels are associated with both pain symptoms and variation in autonomic function in FM. Differences in CSF CRF levels among women with and without a self-reported history of physical or sexual abuse suggest that subgroups of FM patients may exist with different neurobiological characteristics. Further studies are needed to better understand the nature of the association between CSF CRF and pain symptoms in FM.

Adrenal Cortex Hormones↗
PubMed2006

Rac GTPases regulate the morphology and deformability of the erythrocyte cytoskeleton.

Actin oligomers are a significant structural component of the erythrocyte cytoskeleton. Rac1 and Rac2 GTPases regulate actin structures and have multiple overlapping as well as distinct roles in hematopoietic cells; therefore, we studied their role in red blood cells (RBCs). Conditional gene targeting with a loxP-flanked Rac1 gene allowed Crerecombinase-induced deletion of Rac1 on a Rac2 null genetic background. The Rac1(-/-);Rac2(-/-) mice developed microcytic anemia with a hemoglobin drop of about 20% and significant anisocytosis and poikilocytosis. Reticulocytes increased more than 2-fold. Rac1(-/-);Rac2(-/-) RBCs stained with rhodamine-phalloidin demonstrated F-actin meshwork gaps and aggregates under confocal microscopy. Transmission electron microscopy of the cytoskeleton demonstrated junctional aggregates and pronounced irregularity of the hexagonal spectrin scaffold. Ektacytometry confirmed that these cytoskeletal changes in Rac1(-/-);Rac2(-/-) erythrocytes were associated with significantly decreased cellular deformability. The composition of the cytoskeletal proteins was altered with an increased actin-to-spectrin ratio and increased phosphorylation (Ser724) of adducin, an F-actin capping protein. Actin and phosphorylated adducin of Rac1(-/-);Rac2(-/-) erythrocytes were more easily extractable by Triton X-100, indicating weaker association to the cytoskeleton. Thus, deficiency of Rac1 and Rac2 GTPases in mice alters actin assembly in RBCs and causes microcytic anemia with reticulocytosis, implicating Rac GTPases as dynamic regulators of the erythrocyte cytoskeleton organization.

Actin Cytoskeleton↗
PubMed2006

Inhibition of RhoA GTPase activity enhances hematopoietic stem and progenitor cell proliferation and engraftment.

Ras-related Rho GTPases regulate actin cytoskeletal organization, adhesion, gene transcription, and cell-cycle progression. The Rac subfamily of Rho GTPases and Cdc42 has been shown to play essential roles in hematopoietic stem cell (HSC) engraftment and mobilization. Here, we study the role of RhoA, a related Rho GTPase, in HSC functions. Using retrovirus-mediated gene transfer of a dominant-negative (DN) mutant of RhoA (RhoAN19), we demonstrate that down-regulation of RhoA activity resulted in increased HSC engraftment and self-renewal as measured by competitive repopulation and serial transplantation assays. However, overexpression of RhoAN19 resulted in decreased migration toward SDF-1alpha and alpha(4)beta(1)- and alpha(5)beta(2)-integrin-mediated adhesion of hematopoietic progenitor cells in vitro. Low RhoA activity was associated with higher proliferation rate of hematopoietic progenitor cells and increased cells in active phases of cell cycle, most likely via decreasing p21Cip/Waf expression and increasing cyclin D1 levels. Thus, reducing RhoA activity by optimizing the balance between adhesion/migration and proliferation/self-renewal results in a net increase in HSC engraftment. This mechanism could provide a novel therapeutic target to enhance HSC therapies.

Animals↗
PubMed2006

Genetic deletion of Rac1 GTPase reveals its critical role in actin stress fiber formation and focal adhesion complex assembly.

Rac1 is an intracellular signal transducer regulating a variety of cell functions. Previous studies by overexpression of dominant-negative or constitutively active mutants of Rac1 in clonal cell lines have established that Rac1 plays a key role in actin lamellipodia induction, cell-matrix adhesion, and cell anoikis. In the present studies, we have examined the cellular behaviors of Rac1 gene-targeted primary mouse embryonic fibroblasts (MEFs) after Cre recombinase-mediated deletion of Rac1 gene. Rac1-null MEFs became contracted and elongated in morphology and were defective in lamellipodia formation, cell spreading, cell-fibronectin adhesion, and focal contact formation in response to platelet-derived growth factor or serum. Unexpectedly, deletion of Rac1 also abolished actin stress fibers in the cells without detectable alteration of endogenous RhoA activity. Although the expression and/or activation status of focal adhesion complex components such as Src, FAK, and vinculin were not affected by Rac1 deletion, the number and size of adhesion plaques were significantly reduced, and the molecular complex between Src, FAK, and vinculin was dissembled in Rac1-null cells. Overexpression of an active RhoA mutant or ROK failed to rescue the stress fiber and adhesion plaque defects of the Rac1-null cells. Although Rac1 deletion caused a significant reduction in phospho-PAK1, -AKT, and -ERK under serum stimulation, reconstitution of active PAK1, but not AKT or MEK1, was able to rescue the actin cytoskeleton and adhesion phenotypes of the Rac1-deficient cells. Furthermore, Rac1 deletion led to a marked increase in spontaneous apoptosis that could be rescued by active PAK1, AKT, or MEK1 expression. Our results obtained from gene-targeted primary MEFs indicate that Rac1 is essential not only for lamellipodia induction but also for the RhoA-regulated actin stress fiber and focal adhesion complex formation and that Rac1 is involved in cell survival regulation through anoikis-dependent as well as -independent mechanisms.

Actins↗
PubMed2006

The association between experimental and clinical pain measures among persons with fibromyalgia and chronic fatigue syndrome.

Evoked or experimental pain is often used as a model for the study of clinical pain, yet there are little data regarding the relationship between the two. In addition, there are few data regarding the types of stimuli and stimulus intensities that are most closely related to clinical pain. In this study, 36 subjects with fibromyalgia (FM), chronic fatigue syndrome (CFS), or both syndromes were administered measures of clinical pain and underwent a dolorimetry evaluation. Subjects also underwent experimental pain testing utilizing heat and pressure stimulation. Stimulation levels evoking low, moderate and high sensory intensity, and comparable levels of unpleasantness, were determined for both types of stimuli using random staircase methods. Clinical pain was assessed using visual analogue ratings and the short form of the McGill Pain Questionnaire (MPQ). Ratings of heat pain sensation were not significantly associated with clinical pain ratings, with the exception of unpleasantness ratings at high stimulus intensities. Pain threshold and tolerance as assessed by dolorimetry were significantly associated with average measures of clinical pain. Both intensity and unpleasantness ratings of pressure delivered using random staircase methods were significantly associated with clinical pain at low, moderate and high levels, and the strength of the association was greater at increasingly noxious stimulus intensities. These findings suggest that random pressure stimulation as an experimental pain model in these populations more closely reflects the clinical pain for these conditions. These findings merit consideration when designing experimental studies of clinical pain associated with FM and CFS.

Adult↗