Reelin is a platelet protein and functions as a positive regulator of platelet spreading on fibrinogen

Abnormalities of platelet functions have been linked to reelin-impaired neuronal disorders. However, little attention has been given to understanding the interplay between reelin and platelet. In this study, reelin was found to present in the human platelets and megakaryocyte-like leukemic cells. Reelin-binding assays revealed that extracellular reelin can interact with platelets through the receptor belonging to the low density lipoprotein receptor gene family. The reelin-to-platelet interactions enhance platelet spreading on fibrinogen concomitant with the augmentation of lamellipodia formation and F-actin bundling. In contrast, reelin has no effect on integrin αIIbβ3 activation and agonist-induced platelet aggregation. Molecular analysis revealed that the up-regulation of Rac1 activity and the inhibition of protein kinase C δ-Thr505 phosphorylation are important for reelin-mediated enhancement of platelet spreading on fibrinogen. These findings demonstrate for the first time that reelin is present in platelets and the reelin-to-platelet interactions play a novel role in platelet signaling and functions.     

Caveolin regulation of neuronal intracellular signaling

Caveolin proteins physically interact with and compartmentalize membrane-localized signaling proteins to facilitate high-fidelity intracellular signaling. Though primarily studied outside the nervous system, recent investigations have revealed that caveolin proteins are key modulators of a variety of neuronal intracellular signaling pathways. Through both protein aggregation and segregation, caveolin proteins can exert positive and negative influences on intracellular signaling. This review will detail recent findings regarding caveolin function in the brain.     

The effect of pinealectomy on serum progesterone and oestradiol levels during the last stage of pregnancy in rats

Summary Pinealectomy leads to significantly higher levels of progesterone (on days 19 and 20 of gestation) and oestradiol (on days 21 and 22) in the serum of pregnant rats. These results indicate that during the last phase of pregnancy the pineal gland may be modifying the levels of gonadal hormones, although not affecting the sequence of the physiological events.Acknowledgment. The authors wish to thank Miss Ute Schmidt for her invaluable technical assistance.     

Monoclonal antibodies identify a cell-surface antigen associated with an activated cellular oncogene

A variety of antigens have been identified on the surface of the malignant cell. However, identical antigens are often found on non-malignant cells of the same or different histological origin, or of a different stage of embryonic development. Many of these tumour-associated antigens appear to be only incidentally expressed on neoplastic cells. Clearly, it would be of great interest to identify cell-surface antigens whose expression is associated specifically with the transformed state and linked directly with the mechanisms responsible for transformation. The detection of activated cellular oncogenes in human and animal cancer cells by the technique of DNA transfection has allowed the isolation of genetic elements which are thought to have a critical role in malignancy. Here, in an effort to identify cell-surface antigens associated with the neoplastic process, we have generated hybridomas which secrete monoclonal antibodies that react specifically with cell-surface determinants found on NIH 3T3 cells transformed by transfection with a group of rat neuroblastoma oncogenes. These antibodies bind to and immunoprecipitate a phosphoprotein of relative molecular mass 185,000 (185 K) from a DNA donor rat neuroblastoma and 13 independent rat neuroblastoma DNA transfectants. There was no antibody reactivity with normal NIH 3T3 cells or with NIH 3T3 cells transformed by various other agents.     

Effect of acute administration of Δ1-tetrahydrocannabinol on β-endorphin levels in plasma and brain tissue of the rat

Summary Acute treatment with ¹-tetrahydrocannabinol (¹-THC) elevated the concentration of -endorphin-like immunoreactivity (-ELIR) in plasma and in the hypothalamus, but not in the hippocampus of rats habituated to the injection procedure. These effects were not obtained with the psychotropically inert analog of (¹-THC), cannabidiol. In animals that had not been habituated to the injection procedure, placebo treatment induced a decrease in hippocampal -ELIR.The authors acknowledge the skillful technical assistance of Mrs Willeke Logtenberg.     

Predominant naturally processed peptides bound to HLA-DR1 are derived from MHC-related molecules and are heterogeneous in size.

Peptides bound to class I molecules are 8-10 amino acids long, and possess a binding motif representative of peptides that bind to a given class I allele. In the only published study of naturally processed peptides bound to class II molecules (mouse I-Ab and I-Eb), these peptides were longer (13-17 amino acids) and had heterogenous carboxy terminals but precise amino-terminal truncations. Here we report the characterization of acid-eluted peptides bound to HLA-DR1 by high-performance liquid chromatography, mass spectrometry and microsequencing analyses. The relative molecular masses of the peptides varied between 1,602 and 2,996 (13-25 residues), the most abundant individual M(r) values being between 1,700 and 1,800, corresponding to an average peptide length of 15 residues. Complete sequence data were obtained for twenty peptides derived from five epitopes, of which all but one were from self proteins. These peptides represented sets nested at both the N- and C-terminal ends. Binding experiments confirmed that all of the isolated peptides had high affinity for the groove of DR1. Alignment of the peptides bound to HLA-DR1 and the sequences of 35 known HLA-DR1-binding peptides revealed a putative motif. Although peptides bound to class II molecules may have some related features (due to the nonpolymorphic HLA-DR alpha-chain), accounting for degenerate binding to different alleles, particular amino acids in the HLA-DR beta-chains presumably define allelic specificity of peptide binding.