Biomedical subjects

P M Hartl

Publications and source records attributed to P M Hartl.

4 recordsLinked to original sources

PubMed1996

Modulation of L-selectin ligand expression during an immune response accompanying tumorigenesis in transgenic mice.

Immune surveillance depends on lymphocyte access to tissue. Lymphocytes emigrate from blood when adhesion receptors such as L-selectin and the alpha 4 beta 7 integrin on these cells bind to ligands expressed on venular endothelium. Among transgenic mouse lines expressing an oncoprotein (Tag) in islet beta cells, some recognize Tag as nonself. In these mice, Tag expression elicits both beta cell hyperplasia with subsequent progression to tumors and lymphocytic infiltration. Endothelial ligands for L-selectin and alpha 4 beta 7 were upregulated in infiltrated islets in these transgenic mice. These ligands were not expressed in tumors, which were devoid of lymphocytic infiltration. In contrast, the adhesion molecules PECAM-1, ICAM-1, and VCAM-1 were expressed on endothelium in both noninfiltrated tumors and infiltrated islets. Thus, upregulation of expression of endothelial ligands for L-selectin and alpha 4 beta 7 may contribute to autoimmune infiltration. Repression of expression of these same ligands may be involved in the failure of tumor immunity.

Animals↗

PubMed1989

Nuclear transport in vitro.

In this paper, progress towards the goal of understanding communication between the nucleus and cytoplasm using an in vitro system is reviewed. To probe the mechanism of nuclear targeting, we developed an in vitro transport system and have begun to dissect the highly selective process of nuclear transport. The basic parameters of transport were defined using an easily isolated nuclear protein, nucleoplasmin. To study the interaction of nuclear targeting signals with the pore, an artificial nuclear transport substrate was constructed, which consists of human serum albumin coupled to the signal sequence of the SV40 T-antigen. A similar peptide-protein conjugate was made using a mutant signal sequence. These conjugates were fluorescently labeled and/or tagged with gold and tested for transport in the in vitro system. High levels of nuclear transport of the wild-type signal sequence-containing protein were observed, while no transport of the mutant signal sequence-containing protein was seen. Thus, the in vitro system correctly recognizes the single amino acid change between the wild-type and mutant signal sequences. We found that the observed nuclear transport was completely dependent on the presence of ATP. Using the in vitro system we identified a specific inhibitor of nuclear transport, the lectin wheat germ agglutinin (WGA), which we find binds directly to the nuclear pore. Probing blots of nuclear proteins with 125I-WGA identified a family of nuclear pore glycoproteins, including one major glycoprotein of 62K (K = 10(3)Mr) molecular weight. With the inhibitor and the in vitro assay, it has been possible to experimentally separate nuclear transport into two steps: (1) a step in which the signal sequence-bearing protein binds to the pore, followed by (2) a step in which the protein translocates through the pore. It is this second step which is the ATP-dependent step of transport, since pore binding but not translocation was seen to occur in the absence of ATP.

Acetylglucosamine↗

PubMed1986

Characterization of the endoplasmic reticulum-associated precursor of concanavalin A. Partial amino acid sequence and lectin activity.

Concanavalin A (ConA), which is not a glycoprotein, is synthesized as a glycoprotein precursor (pro-ConA) which is post-translationally processed. This processing results in the loss of a small glycopeptide with a high mannose oligosaccharide. Carrington et al. (Carrington, D.M., Auffret, A., and Hanke, D.E. (1985) Nature 313, 64-66) determined the nucleotide sequence of a cDNA for pro-ConA, and in the derived amino acid sequence the only glycosylation site is in the middle of the molecule. Furthermore, the derived amino acid sequence of the putative precursor of ConA was found not to be colinear with that of ConA. Here we show that pro-ConA is located primarily in an endoplasmic reticulum-rich organelle fraction. Pro-ConA was purified from this fraction and subjected to amino acid sequencing. The first 12 amino acids at the N-terminal end of pro-ConA correspond to amino acids 119-130 of mature ConA, and to amino acids 30-41 of the putative pre-pro-ConA, the sequence of which was derived from the nucleotide sequence of a cDNA. Amino acid sequencing of a tryptic glycopeptide with the high mannose side chain showed that the first 17 amino acids of this peptide correspond to amino acids 154-170 of pre-pro-ConA. The last six amino acids in this series correspond to the first six amino acids of mature ConA. These data fully support the hypothesis of Carrington et al. that the biosynthesis of ConA involves a post-translational peptide cleavage, transposition, and ligation within the original polypeptide. Pro-ConA from the organelle fraction does not bind to Sephadex G-50, indicating that it has no lectin activity. The processing of pro-ConA apparently imparts biological activity to this lectin.

Amino Acid Sequence↗

PubMed1985

Differential expression of kunitz and bowman-birk soybean proteinase inhibitors in plant and callus tissue.

Bowman-Birk soybean trypsin inhibitor (BBSTI) but not Kunitz soybean trypsin inhibitor (KSTI) was found in samples of undifferentiated and partially differentiated Amsoy 71 tissue culture callus. This suggests the differential metabolism of these two classes of proteinase inhibitors, whether the difference be in synthesis, in rates of degradation, or both. The differential metabolism of the proteinase inhibitors is also seen in the plant. Both BBSTI and KSTI were found in the hypocotyl, root, and epicotyl of the Amsoy 71 soybean seedling in addition to their expected presence in the cotyledons. Whereas the ratio of KSTI to BBSTI in the cotyledon was higher, the ratio of BBSTI to KSTI was higher in the extracotyledonary tissues of the seedling. The levels of both classes of proteinase inhibitors declined during seedling growth, except in the epicotyl and the proximal root. In both of these tissues, an increase in BBSTI, but not in KSTI content, expressed as milligrams inhibitor per plant part, occurred.

Journal Article↗