Human thymic epithelial cells express an endogenous lectin, galectin-1, which binds to core 2 O-glycans on thymocytes and T lymphoblastoid cells.

Thymic epithelial cells play a crucial role in the selection of developing thymocytes. Thymocyte-epithelial cell interactions involve a number of adhesion molecules, including members of the integrin and immunoglobulin superfamilies. We found that human thymic epithelial cells synthesize an endogenous lectin, galectin-1, which binds to oligosaccharide ligands on the surface of thymocytes and T lymphoblastoid cells.

Cloning and characterization of human tissue inhibitor of metalloproteinases-3.

The tissue inhibitors of metalloproteinases (TIMPs) comprise a family of proteins, of which two members have so far been described in humans. We have cloned and sequenced a third human TIMP (hTIMP-3) from phorbol ester-differentiated THP-1 cells stimulated with bacterial lipopolysaccharide. The open reading frame encodes a 211-amino-acid precursor including a 23-residue secretion signal.

Tissue-specific enhancer of the human glycoprotein hormone alpha-subunit gene: dependence on cyclic AMP-inducible elements.

We identified and characterized elements which confer tissue specificity and cyclic AMP (cAMP) responsiveness to the human glycoprotein alpha-subunit gene. An enhancer containing an 18-base-pair repeat conferred cAMP responsiveness in a non-tissue-specific fashion. DNase I protection assays revealed DNA-binding factors that bound to this element in both placental and nonplacental cells.

A cloned chromogranin A (CgA) cDNA detects a 2.3Kb mRNA in diverse neuroendocrine tissues.

CgA is a 72Kd protein of unknown function that is present in many neuroendocrine tissues and co-secreted with their resident hormones. We prepared a cDNA library to the mRNA from CgA-producing human medullary thyroid carcinoma (MTC) cells in the expression vector lambda gt11. The library was screened with a panel of one polyclonal and two monoclonal antibodies to CgA.

Methylation analysis of a plasmid containing a mammalian cell cycle regulatory sequence after transient transfection into the host cell.

A hamster genomic sequence containing a cell cycle regulatory sequence derived from a histone H3.2 gene was transfected into K12 hamster fibroblasts in the form of plasmid DNA prepared from dam+ E. coli.

Use of a cell cycle mutant to delineate the critical period for the control of histone mRNA levels in the mammalian cell cycle.

Temporal analysis of DNA replication and histone mRNA accumulation in a hamster fibroblast cell cycle mutant (K12) showed that histone mRNA accumulates periodically during the cell cycle and reaches its highest level in the S phase. The direct correlation between the initiation of DNA synthesis and the accumulation of histone mRNA to high levels in S phase demonstrated the strict interdependence of these two events. Moreover, a critical period necessary for histone mRNA accumulation occurred late in G1 phase.

Transcriptional regulation of two genes specifically induced by glucose starvation in a hamster mutant fibroblast cell line.

This report concerns the characterization of the RNA transcripts encoded by two cDNA sequences p4A3 and p3C5, derived from a hamster temperature-sensitive mutant cell line K12. Using the two cDNA sequences as hybridization probes, we show that they occur as single copy genes in the hamster genome and encode for RNA transcripts which are highly inducible in K12 cells at 40.5 degrees C.

Characterization of a cell cycle mutant derived from hamster fibroblast: reversion analysis.

K12 is a temperature-sensitive (ts) mutant cell line derived from Chinese hamster fibroblasts. When incubated at the nonpermissive temperature, K12 cells exhibit the following properties: (a) the cells cannot initiate DNA synthesis;o (b) the synthesis of cytosol thymidine kinase is suppressed; and (c) the synthesis of three cellular proteins of molecular weights 94, 78, and 58 kdaltons is greatly enhanced. Here we characterize a spontaneous revertant clone, R12, derived from the K12 cells.

Coupling of histone and DNA synthesis in the somatic cell cycle.

The coupling of histone and DNA synthesis was examined in the temperature-sensitive hamster fibroblast cell line K12. By monitoring total cellular histone synthesis at various times after quiescent cells were stimulated to proliferate at permissive and nonpermissive temperatures, a direct correlation was found between the rates of DNA and histone synthesis. Furthermore, when DNA synthesis was blocked by the K12 mutation, histone synthesis was reduced to the basal rate.

Highly conserved glucose-regulated protein in hamster and chicken cells: preliminary characterization of its cDNA clone.

A temperature-sensitive mutant K12 derived from a Chinese hamster fibroblast has been shown to overproduce three specific proteins of Mr 94,000, 78,000, and 58,000 when incubated at the nonpermissive temperature (40.5 degrees C). We previously identified these proteins as glucose-regulated proteins similar to those observed in chicken embryo fibroblasts when the cells are starved of glucose.

Independent activation of the acetylcholine receptor from Torpedo californica at two sites.

Membrane vesicles enriched in acetylcholine receptor were prepared from the electroplax tissue of Torpedo californica. The receptor was reduced with dithiothreitol to expose a sulfhydryl group near the ligand binidng site and then treated in one of the following ways: (1) affinity alkylated treated in one of the following ways: (1) affinity alkylated with bromoacetylcholine, a receptor activator, (2) affinity alkylated with maleimidobenzyltrimethylammonium, a receptor inhibitor, or (3) reoxidized to the native state with dithiobis(2-nitrobenzoate). The affinity labels blocked half of the binding sites for alpha-bungarotoxin.