Search PubMed⌕ Search

Biomedical subjects

R Hofmeister

Publications and source records attributed to R Hofmeister.

At least 19 recordsLinked to original sources
PubMed2001

Generation of macrophages from early T progenitors in vitro.

Early T progenitors in the thymus have been reported to have the capacity to develop into B cells, thymic dendritic cells, and NK cells. Here we describe conditions that induce early T progenitors to develop into macrophages. Initially, we observed that early T progenitors could be induced to develop into macrophages by cytokines produced from a thymic stromal cell line, TFGD, and later we found that the cytokine mixture of M-CSF plus IL-6 plus IL-7 also induced macrophage differentiation from pro-T cells. M-CSF by itself was unable to induce macrophage differentiation from early T progenitors. To correlate this observation with the developmental potential of early T progenitors, mouse embryonic thymocytes were sorted into four populations, pro-T1 to pro-T4, based on the expression of CD44 and CD25, and then cultured with TFGD culture supernatant. We found that pro-T1 and pro-T2 cells, but not pro-T3 and pro-T4 cells, generate macrophages. Limiting dilution analysis of the differentiation capability of sorted pro-T2 cells also confirmed that pro-T2 cells could generate macrophages. These results suggest that T cells and thymic macrophages could originate from a common intrathymic precursor.

Animals↗
PubMed1999

Withdrawal of IL-7 induces Bax translocation from cytosol to mitochondria through a rise in intracellular pH.

IL-7 functions as a trophic factor during T lymphocyte development by a mechanism that is partly based on the induction of Bcl-2, which protects cells from apoptosis. Here we report a mechanism by which cytokine withdrawal activates the prodeath protein Bax. On loss of IL-7 in a dependent cell line, Bax protein translocated from the cytosol to the mitochondria, where it integrated into the mitochondrial membrane. This translocation was attributable to a conformational change in the Bax protein itself. We show that a rise in intracellular pH preceded mitochondrial translocation and triggered the change in Bax conformation. Intracellular pH in the IL-7-dependent cells rose steadily to peak over pH 7.8 by 6 hr after cytokine withdrawal, paralleling the time point of Bax translocation (a similar alkalinization and Bax translocation was also observed after IL-3 withdrawal from a dependent cell line). The conformation of Bax was directly altered by pH of 7.8 or higher and was demonstrated by increased protease sensitivity, exposure of N terminus epitopes, and exposure of a hydrophobic domain in the C terminus. Eliminating charged amino acids at the C or N termini of Bax induced a conformational change similar to that induced by raising pH, implicating these residues in the pH effect. Therefore, we have shown that by either cytokine withdrawal, experimental manipulation of pH, or site-directed mutagenesis, Bax protein changes conformation, exposing membrane-seeking domains, thereby inducing mitochondrial translocation and initiating the cascade of events leading to apoptotic death.

Animals↗
PubMed1999

Overexpression of CALNUC (nucleobindin) increases agonist and thapsigargin releasable Ca2+ storage in the Golgi.

We previously demonstrated that CALNUC, a Ca2+-binding protein with two EF-hands, is the major Ca2+-binding protein in the Golgi by 45Ca2+ overlay (Lin, P., H. Le-Niculescu, R. Hofmeister, J.M. McCaffery, M. Jin, H. Henneman, T. McQuistan, L. De Vries, and M. Farquhar. 1998. J. Cell Biol. 141:1515-1527). In this study we investigated CALNUC's properties and the Golgi Ca2+ storage pool in vivo. CALNUC was found to be a highly abundant Golgi protein (3.8 microg CALNUC/mg Golgi protein, 2.5 x 10(5) CALNUC molecules/NRK cell) and to have a single high affinity, low capacity Ca2+-binding site (Kd = 6.6 microM, binding capacity = 1.1 micromol Ca2+/micromol CALNUC). 45Ca2+ storage was increased by 2.5- and 3-fold, respectively, in HeLa cells transiently overexpressing CALNUC-GFP and in EcR-CHO cells stably overexpressing CALNUC. Deletion of the first EF-hand alpha helix from CALNUC completely abolished its Ca2+-binding capability. CALNUC was correctly targeted to the Golgi in transfected cells as it colocalized and cosedimented with the Golgi marker, alpha-mannosidase II (Man II). Approximately 70% of the 45Ca2+ taken up by HeLa and CHO cells overexpressing CALNUC was released by treatment with thapsigargin, a sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) (Ca2+ pump) blocker. Stimulation of transfected cells with the agonist ATP or IP3 alone (permeabilized cells) also resulted in a significant increase in Ca2+ release from Golgi stores. By immunofluorescence, the IP3 receptor type 1 (IP3R-1) was distributed over the endoplasmic reticulum and codistributed with CALNUC in the Golgi. These results provide direct evidence that CALNUC binds Ca2+ in vivo and together with SERCA and IP3R is involved in establishment of the agonist-mobilizable Golgi Ca2+ store.

Amino Acid Sequence↗
PubMed1999

Interleukin-7: physiological roles and mechanisms of action.

Interleukin-7 (IL-7), a product of stromal cells, provides critical signals to lymphoid cells at early stages in their development. Two types of cellular responses to IL-7 have been identified in lymphoid progenitors: (1) a trophic effect and (2) an effect supporting V(D)J recombination. The IL-7 receptor is comprised of two chains, IL-7R alpha and gamma(c). Following receptor crosslinking, rapid activation of several classes of kinases occurs, including members of the Janus and Src families and PI3-kinase. A number of transcription factors are subsequently activated including STATs, c-myc, NFAT and AP-1. However, it remains to be determined which, if any, previously identified pathway leads to the trophic or V(D)J endpoints. The trophic response to IL-7 involves protecting lymphoid progenitors from a death process that resembles apoptosis. This protection is partly mediated by IL-7 induction of Bcl-2, however other IL-7-induced events are probably also involved in the trophic response. The V(D)J response to IL-7 is partly mediated through increased production of Rag proteins (which cleave the target locus) and partly by increasing the accessibility of a target locus to cleavage through chromatin remodeling.

Animals↗
PubMed1998

The mammalian calcium-binding protein, nucleobindin (CALNUC), is a Golgi resident protein.

We have identified CALNUC, an EF-hand, Ca2+-binding protein, as a Golgi resident protein. CALNUC corresponds to a previously identified EF-hand/calcium-binding protein known as nucleobindin. CALNUC interacts with Galphai3 subunits in the yeast two-hybrid system and in GST-CALNUC pull-down assays. Analysis of deletion mutants demonstrated that the EF-hand and intervening acidic regions are the site of CALNUC's interaction with Galphai3. CALNUC is found in both cytosolic and membrane fractions. The membrane pool is tightly associated with the luminal surface of Golgi membranes. CALNUC is widely expressed, as it is detected by immunofluorescence in the Golgi region of all tissues and cell lines examined. By immunoelectron microscopy, CALNUC is localized to cis-Golgi cisternae and the cis-Golgi network (CGN). CALNUC is the major Ca2+-binding protein detected by 45Ca2+-binding assay on Golgi fractions. The properties of CALNUC and its high homology to calreticulin suggest that it may play a key role in calcium homeostasis in the CGN and cis-Golgi cisternae.

Amino Acid Sequence↗
PubMed1998

Preparation of Golgi subfractions with free-solution isotachophoresis: analysis of sphingomyelin synthesis in Golgi subfractions from rat liver.

A new displacement electrophoresis technique, termed free-solution isotachophoresis (FS-ITP) was used for the analysis of sphingolipid metabolism in Golgi subfractions. The discontinuous electrolyte system enables tissue-derived membrane vesicles to be separated and purified due to their polarity patterns in a mobility gradient. In this study total Golgi apparatus obtained from rat liver by discontinuous density gradient centrifugation was subfractionated by preparative FS-ITP, yielding enzymatically active cis-, medial-, and trans-Golgi subfractions. These membrane vesicles were assayed by the following established enzyme marker activities: NADH cytochrome c reductase (cis-Golgi), NADP phosphatase (medial-Golgi), and thiamine pyrophosphatase (trans-Golgi). The activity of phosphatidylcholine:ceramide phosphocholine transferase, a sphingomyelin synthesizing enzyme, is attributed to the cis- and medial-Golgi-derived subfractions. Analysis of Golgi lipids revealed a decline in membranous ceramide along the cis- to trans-Golgi polarity axis. Furthermore, significant amounts of newly synthesized sphingomyelin and diacylglycerol are transferred from the medial/cis- to the trans-Golgi compartment. The FS-ITP system is well suited for micropreparative experimental applications, as demonstrated by studies on phosphatidylcholine:ceramide phosphocholine transferase activity in Golgi membrane vesicles of rat liver obtained by FS-ITP.

Animals↗
PubMed1998

Nuclear factor kappaB is activated in macrophages and epithelial cells of inflamed intestinal mucosa.

BACKGROUND & AIMS: Transcription factors of the nuclear factor kappaB (NF-kappaB) family play an important role in the regulation of genes involved in inflammation. In inflammatory bowel diseases, proinflammatory cytokines known to be regulated by NF-kappaB are involved. The aim of this study was to investigate the role of NF-kappaB activation during mucosal inflammation in situ. METHODS: A monoclonal antibody, alpha-p65mAb, was applied for immunofluorescence and immunohistochemical analysis that recognizes activated NF-kappaB. Electrophoretic mobility shift assay was used to directly demonstrate the presence of active DNA-binding NF-kappaB. RESULTS: Using the alpha-p65mAb antibody, activated NF-kappaB could be found in biopsy specimens from inflamed mucosa but was almost absent in uninflamed mucosa. The number of cells showing NF-kappaB activation correlated with the degree of mucosal inflammation but was not significantly different between inflamed mucosa from patients with Crohn's disease, ulcerative colitis, and nonspecific colitis or diverticulitis. NF-kappaB activation was localized in macrophages and in epithelial cells as identified by double-labeling techniques. Electrophoretic mobility shift assay with isolated lamina propria mononuclear cells and epithelial cells confirmed these results. CONCLUSIONS: This study shows for the first time the activation of NF-kappaB during human mucosal inflammation in situ. In addition to macrophages, epithelial cells contained activated NF-kappaB, indicating an involvement in the inflammatory process.

Adult↗
PubMed1997

Activation of acid sphingomyelinase by interleukin-1 (IL-1) requires the IL-1 receptor accessory protein.

The cytokine interleukin-1 (IL-1) plays an important role in inflammation and regulation of immune responses, but the mechanisms of its signal transduction and cell activation processes are incompletely understood. Ceramide generated by sphingomyelinases (SMases) is known to function as an important second messenger molecule in the signaling pathway of IL-1 and tumor necrosis factor. To investigate the activation of SMases by IL-1, we used an IL-1 receptor type I (IL-1RI)-positive EL4 thymoma cell line, which is defective in IL-1R accessory protein (IL-1RAcP) expression. In this cell line (EL4D6/76), tumor necrosis factor induced ligand/receptor internalization, NFkappaB nuclear translocation, IL-2 production, and the activation of neutral (N)-SMase and acid (A)-SMase. In contrast, stimulation with IL-1 resulted only in the activation of N-SMase whereas ligand/receptor internalization, NFkappaB translocation, IL-2 production, and activation of A-SMase were not detected. Transfection of this functionally defective EL4D6/76 with IL-1RAcP cDNA restored these functions. These data suggest that A-SMase activity is strongly linked with the internalization of IL-1RI mediated by IL-1RAcP and that A-SMase and N-SMase are activated by different pathways.

Ceramides↗
PubMed1997

A critical role for interleukin-1 receptor accessory protein in interleukin-1 signaling.

Interleukin-1 (IL-1) is a central molecule in inflammation and immune responses whose pleiotropic activities are mediated by the type I IL-1 receptor (IL-1RI). The IL-1RI alone on the cell surface is silent after binding of the ligand. We show that the recently identified IL-1RI accessory protein (IL-1RAcP) converts the silent into a fully functional IL-1RI complex. Although transfection of IL-1RAcP into IL-1RAcP-deficient EL4D6/76 cells did not alter the binding kinetics or dissociation constants of the 125I-labeled IL-1alpha/IL-1RI complex, a very early event, internalization of the activated receptor complex, and a late event, IL-1-stimulated IL-2 production, were successfully restored. Therefore, recruitment of IL-1RAcP is a critical early step in the signaling cascade mediated by the IL-1RI activation complex.

Animals↗
PubMed1991

[The occurrence of tumors in large bears (Ursidae)--a literature review and six case descriptions].

Histological findings on two Malayan sun bears and four sloth bears show that malignant neoplasms play an important role in tropic bears. Further, most of the tumors originated from the hepatic and biliary tract. Our results were compared with other investigations on zoo animals during the last 70 years revealing that malignant neoplasms are the most common ones in bears of the family Ursidae. Accordingly to our results, sloth and Malayan sun bears seem to have a disposition to develop malignant neoplasms of the hepatic and biliary tract, but within other species only polar bears seem to suffer predominantly from such neoplasia. The reason for this phenomenon could be an alimentary intake of carcinogens. Furthermore, Malayan sun bears show very often neoplasms of the thyroid gland as it is also observed in other carnivora.

Animals↗
PubMed1990

The use of urinary N-acetyl-beta-D-glucosaminidase (NAG) for the detection of contrast-media-induced 'osmotic nephrosis' in rats.

Excretion of urinary N-acetyl-beta-glucosaminidase (NAG), lactate dehydrogenase (LDH), alkaline phosphatase (ALP) and gamma-glutamyltransferase (gamma-GT) was studied following single intravenous administrations of a non-ionic monomeric contrast medium (iohexol) at doses of 5.0, 7.5, 10.0 and 12.5 g iodine/kg body wt in rats. Measurements of urinary enzymes, serum urea nitrogen and serum creatinine were carried out on the 2nd, 3rd, 4th and 8th days after treatment. Histological examinations of kidneys were performed on days 3 and 8. From 5.0 g iodine/kg onwards urinary NAG showed a dose-dependent and significant (multiple comparison, alpha = 0.05) increase in the first 18-h urine samples after application. A significant increase in urinary LDH could be observed only at the highest dose of 12.5 g iodine/kg. All other biochemical parameters showed no differences when compared to the control group. The dose-dependent increase in lysosomal NAG correlated with the histological findings, i.e. there was dose-dependent vacuolization of proximal tubular cells, so-called 'osmotic nephrosis'.

Acetylglucosaminidase↗
PubMed1990

Effect of three non-ionic contrast media on rats and rabbits with regard to renal changes. Interspecies comparison.

The effect of three non-ionic contrast media (iosimide, iopamidol and iopromide) was investigated in rabbits and rats after single i.v. application up to high doses with regard to renal changes. Determinations of serum urea nitrogen and creatinine and urinary enzymes (lactate dehydrogenase, gamma-glutamyl-transpeptidase and N-acetyl-beta-D-glucosaminidase) as well as histological examinations of the kidneys were performed. The results obtained demonstrate that rabbit as an experimental animal was more sensitive than rat in exhibiting renal changes to contrast media. Furthermore, determinations of urinary enzymes demonstrated that gamma-GT in rabbits and LDH in rats were the most sensitive indicators for detection of early kidney damage. With regard to the high dose levels required, these kidney changes do not indicate any risk to humans at diagnostic dose levels.

Animals↗
PubMed1986

Value of enzyme determinations in urine for the diagnosis of nephrotoxicity in rats.

Excretion of urinary lactate dehydrogenase (LDH, EC 1.1.1.27), gamma-glutamyltransferase (gamma-GT, EC 2.3.2.2), alkaline phosphatase (ALP, EC 3.1.3.1), alanine aminopeptidase (AAP, EC 3.4.11.-), alanine aminotransferase (GPT, EC 2.6.1.2) and N-acetyl-beta-D-glucosaminidase (NAG, EC 3.2.1.30) was studied following a single i.v. application of 1 mg mercuric chloride/kg body weight or a radio contrast medium (SH H 340 AB) at a dose of 7.5 g iodine/kg body weight in rats. Measurements of urinary enzymes and serum urea nitrogen and creatinine were carried out on the second, third, fourth and ninth days after treatment. Histological examinations of kidneys were performed on day 9. A drastic increase in urinary LDH and moderate increase in gamma-GT, ALP and AAP and a very slight increase in GPT was observed in the first 18-h urine samples after mercuric chloride. This increase in enzymuria was associated with a drastic increase in serum urea nitrogen and creatinine, with a maximum on day 4. The radio contrast medium-treated animals showed a similar but less pronounced pattern of urinary enzymes excretion and only a slight increase of serum urea nitrogen on day 2. A good correlation was found between histological findings and enzymuria as well as serum urea nitrogen and creatinine. Thus, determination of only some urinary enzymes (LDH and gamma-GT) is valuable in predicting early nephrotoxicity and sufficient for the diagnosis of proximal tubule damage in rats.

Acetylglucosaminidase↗
PubMed1979

Toward a comprehensive geriatric educational experience.

A description of the goals and the accomplishments of a program in geriatric education and training is presented. Emphasis is laid on the potential role of departments of family and community medicine, even though vast resources may not be available. Such a program is of great importance, but it must be viewed as only the first step in the development of a comprehensive training model for either a school of medicine or a residency program in primary care. Upon graduation in Family Medicine, residents should not only be aware of the specific health needs of the elderly, but also be clinically competent to meet those needs.

Education, Medical, Graduate↗
PubMedDate not supplied

The internalized interleukin-1 activation complex in fibroblasts localizes to the Golgi apparatus.

In order to investigate binding and internalization of interleukin-1 (IL-1) by confocal laser scanning microscopy, we established a model system comprising an IL-1 receptor type I (IL-1R1) overexpressing transfectant of the murine fibrosarcoma cell line L929 (L929R1) and an N-terminal FLAG-tagged human recombinant IL-1 alpha (FLAG-IL-1 alpha). The function of the transfected receptors was shown by their IL-1-induced association with a kinase activity. The biological activity of the purified FLAG-IL-1 alpha was comparable to the unmodified molecule. L929RI cells were exposed to saturating concentrations of FLAG-IL-1 alpha. Two-color fluorescence analysis revealed increasing cell surface binding of FLAG-IL-1 alpha to the receptor over 30 min. This was followed by internalization and accumulation of the ligand/receptor complex at the Golgi apparatus. After 3 hr the receptor signal significantly decreased and patches of FLAG-epitopes reappeared on the cell surface, no longer colocalized with IL-1R1. Thus, in this model, the previously assumed nuclear accumulation of IL-1 was not detected but rather localization of the internalized IL-1/IL-1R1-complex to the Golgi apparatus was found. Direct effects of IL-1 on the nucleus or the nuclear membrane therefore are unlikely.

Animals↗