DNA sequence of the coding region of the HLA-B44 gene

An HLA-B44 cDNA clone was identified in a cDNA library constructed from an HLA-B44 homozygous cell line. The DNA sequence was determined and was found to contain the complete coding sequence but for (probably) the three N-terminal codons. Comparisons of the derived amino acid sequence with other HLA-A and -B locus amino acid sequences revealed four HLA-B44-specific substitutions including a new polymorphic site. Regions of strong sequence conservation for HLA-B-locus products were found at the nucleotide and amino acid levels.     

Methylation of transfer RNA during transformation of human lymphocytes by phytohemagglutinin

Methylation of transfer RNA during phytohemagglutinin induced transformation of human lymphocytes was studied by labeling the tRNA $\text{in}\text{vivo}$ with (methyl-H³)-methionine and measuring the distribution of tritium in the methylated nucleotides. An alteration in the pattern of methylation occurred within hours after PHA-stimulation and this change was maintained through several cell generations. There was a 50 to 94% increase in the relative amount of methylated N²-methyl-guanine (1 to 3 hr) and a 40 to 59% decrease in the relative amount of 1-methyladenine (1 to 12 hr). Treatment of the stimulated cells with Actinomycin D prevented the subsequent methylation not tRNA. However, inhibition of protein synthesis by puromycin did not effect the early changes observed in the methylation of tRNA.     

Light and electron microscopy of Rat kangaroo cells in mitosis

Rat kangaroo (PtK₂) cells were fixed and embedded in situ. Cells in mitosis were studied with the light microscope and thin sections examined with the electron microscope. Pericentriolar, osmiophilic material, rather than the centrioles, is probably involved in the formation of astral microtubules during prophase. Centriole migration occurs during prophase and early prometaphase. The nuclear envelope ruptures first in the vicinity of the asters. Nuclear pore complexes disintegrate as envelope fragments are dispersed to the periphery of the mitotic spindle. Microtubules invade the nucleus through gaps of the fragmented envelope. The number of microtubules and the degree of spindle organization increase during prometaphase and are maximal at metaphase. At this stage, chromosomes are aligned on the spindle equator, sister kinetochores facing opposite poles. Cytoplasmic organelles are excluded from the spindle. Prominent bundles of kinetochore microtubules converge towards the poles. Spindles in cold-treated cells consist almost exclusively of kinetochore tubules. Separating daughter chromosomes in early anaphase are connected by chromatin strands, possibly reflecting the rupturing of fibrous connections occasionally observed between sister chromatids in prometaphase. Breakdown of the spindle progresses from late anaphase to telophase, except for the stem bodies. Chromosomes decondense to form two masses. Nuclear envelope reconstruction, probably involving endoplasmic reticulum, begins on the lateral faces. Nuclear pores reappear on membrane segments in contact with chromatin. Microtubules are absent from reconstructed daughter nuclei.This report is to a large part based on a dissertation submitted by the author to the Graduate Council of the University of Florida in partial fulfillment of the requirements for the degree of Doctor of Philosophy.     

Dexamethasone stimulates thyrotropin-releasing hormone production in a C cell line

The hypothalamic peptide hormone TRH is also found in other tissues, including the thyroid. While TRH may be regulated by T3 in the hypothalamus, other regulators of TRH have not been identified and the regulation of TRH in nonhypothalamic tissues is unknown. We recently demonstrated the biosynthesis of TRH in the CA77 neoplastic thyroidal C cell line. We studied the regulation of TRH by dexamethasone in this cell line because glucocorticoids have been postulated to inhibit TSH secretion by decreasing TRH in the hypothalamus. Furthermore, TRH in the thyroid inhibits thyroid hormone release. Thus by regulating thyroidal TRH, glucocorticoids could also directly affect thyroid hormone secretion. Treatment of CA77 cells for 4 days with dexamethasone produced dose-dependent increases in both TRH mRNA and cellular and secreted TRH. Increases in TRH mRNA and peptide levels could be seen with 10(-9) M dexamethasone. A 4.8-fold increase in TRH mRNA and a 4-fold increase in secreted peptide were seen with 10(-7) M dexamethasone. Dexamethasone treatment did not increase beta-actin mRNA levels or cell growth. These results suggest that glucocorticoids may be physiological regulators of TRH in normal C cells. In addition to their inhibitory effects on TSH, glucocorticoids may decrease thyroid hormone levels by increasing thyroidal TRH. Since the glucocorticoid effects on C cell TRH are the converse of what is expected for hypothalamic TRH, glucocorticoid effects in these two tissues may be mediated by different regulators.     

Priming of the respiratory burst in human eosinophils is accompanied by changes in signal transduction

Addition of platelet-activating factor (PAF) to human eosinophils leads to the modulation of eosinophil responses. The respiratory burst, induced by opsonized particles, consists of an initiation and a propagation phase and is greatly enhanced ("primed") after pretreatment with PAF. This priming event induces the following changes in signal transduction between the opsonin receptors (in particular the CR3 receptor) and activation of the respiratory burst: 1) an enhanced activation of protein kinase C (PK-C): the initiation of the respiratory burst in untreated eosinophils is not sensitive to PK-C inhibition (via staurosporine) and is not accompanied by accumulation of diglycerides and changes in [Ca2+]i. After pretreatment with PAF, the initiation of the response is partly sensitive to inhibition of PK-C (via staurosporine) and is accompanied by accumulation of diglycerides and a fast and sustained increase in [Ca2+]i; and 2) an enhancement of a PK-C-independent initiation of the respiratory burst. The propagation phase in both primed and unprimed cells is sensitive for inhibition by staurosporine. Our results indicate that in eosinophils the phospholipase(s) responsible for the accumulation of the diglycerides and changes in [Ca2+]i during the initiation phase of the serum-treated zymosan response seem(s) to become associated with the signal transduction route only after priming with PAF. This results in the occurrence of two signal transduction routes that can act independently of each other.     

Dual mechanisms in priming of the chemoattractant-induced respiratory burst in human granulocytes. A Ca2+-dependent and a Ca2+-independent route

After interaction with so-called priming agents, the respiratory burst in human granulocytes does not become activated, but is enhanced upon subsequent stimulation with the chemoattractant FMLP. Investigating the mechanism of the priming reaction, we found that a transient rise in the cytosolic free calcium concentration [( Ca2+]i) suffices to irreversibly prime human granulocytes. Thus, platelet-activating factor (PAF) induced a transient increase in [Ca2+]i and primed the cells to an enhanced respiratory burst upon subsequent interaction with FMLP. Artificially, the transient rise in [Ca2+]i was mimicked by addition and subsequent removal of the Ca2+ ionophore ionomycin; this treatment too, primed the respiratory burst of the granulocytes. The priming induced by ionomycin was completely abolished when [Ca2+]i changes were buffered during exposure of the cells to the ionophore. The priming induced by PAF was only partially inhibited under [Ca2+]i-buffering conditions during priming, indicating that multiple pathways exist in the priming of granulocytes by PAF.     

Involvement of LFA-1 in lymphoma invasion and metastasis demonstrated with LFA-1-deficient mutants

Lymphocyte function-associated antigen-1 (LFA-1) is a leukocyte and lymphoma cell surface protein that promotes intercellular adhesion. We have previously shown that the invasion of hepatocyte cultures by lymphoma cells is inhibited by anti-LFA-1 antibodies (Roos, E., and F. F. Roossien. 1987. J. Cell Biol. 105:553-559). In addition, we now report that LFA-1 is also involved in invasion of lymphoma cells into fibroblast monolayers. To investigate the role of LFA-1 in metastasis of these lymphoma cells, we have generated mutants that are deficient in LFA-1 cell surface expression because of impaired synthesis of either the alpha or beta subunit precursor of LFA-1. We identified at least three distinct mutant clones. The invasive potential of the mutant cells in vitro, in both hepatocyte and fibroblast cultures, was considerably lower than that of parental cells. The metastatic potential of the mutants was much reduced, indicating that LFA-1 expression is required for efficient metastasis formation by certain lymphoma cells.