Evaluation of proteinase-activated receptor-1 (PAR1) agonists and antagonists using a cultured cell receptor desensitization assay: activation of PAR2 by PAR1-targeted ligands

We developed a calcium signaling-based assay, using cultured human embryonic kidney cells (HEK), that evaluates simultaneously, the activation/desensitization or blockade of the proteinase-activated receptors, PAR1 and PAR2. Using this assay, we analyzed the actions of a number of previously described putative PAR1-targeted peptide agonists and antagonists. We found that most of the previously described PAR1-targeted agents can also activate/desensitize PAR2, and most of these peptides can also activate a calcium signaling pathway in a target cell that possesses PAR2 along with PAR1. Furthermore, we used this assay to develop a PAR1 receptor-activating probe [Ala-parafluoroPhe-Arg-Cha-Cit-Tyr-NH2 (Cit-NH2)], which displays a high degree of specificity for PAR1 over PAR2, and we used the assay to quantitate the ability of trypsin to disarm the activation of PAR1 by thrombin. The abilities of the PAR1-targeted agents to desensitize or block PAR1 in the HEK cell assay were compared with their activities in a human platelet aggregation assay. Our data illustrate the usefulness of the HEK cell assay for evaluating the PAR1/PAR2 selectivity of PAR-activating agonists. The PAR1-selective agonist that we developed using the assay should prove useful for studying the effects of selectively activating PAR1 in vivo.     

Lymphotoxin alpha/beta and tumor necrosis factor are required for stromal cell expression of homing chemokines in B and T cell areas of the spleen

Mice deficient in the cytokines tumor necrosis factor (TNF) or lymphotoxin (LT) alpha/beta lack polarized B cell follicles in the spleen. Deficiency in CXC chemokine receptor 5 (CXCR5), a receptor for B lymphocyte chemoattractant (BLC), also causes loss of splenic follicles. Here we report that BLC expression by follicular stromal cells is defective in TNF-, TNF receptor 1 (TNFR1)-, LTalpha- and LTbeta-deficient mice. Treatment of adult mice with antagonists of LTalpha1beta2 also leads to decreased BLC expression. These findings indicate that LTalpha1beta2 and TNF have a role upstream of BLC/CXCR5 in the process of follicle formation. In addition to disrupted follicles, LT-deficient animals have disorganized T zones. Expression of the T cell attractant, secondary lymphoid tissue chemokine (SLC), by T zone stromal cells is found to be markedly depressed in LTalpha-, and LTbeta-deficient mice. Expression of the SLC-related chemokine, Epstein Barr virus-induced molecule 1 ligand chemokine (ELC), is also reduced. Exploring the basis for the reduced SLC expression led to identification of further disruptions in T zone stromal cells. Together these findings indicate that LTalpha1beta2 and TNF are required for the development and function of B and T zone stromal cells that make chemokines necessary for lymphocyte compartmentalization in the spleen.     

Environmental upregulation of the atrial natriuretic peptide gene in the living fossil, Limulus polyphemus

Northern blot analysis revealed that atrial natriuretic peptide (ANP) gene expression occurs in heart, hematocytes and gills of the invertebrate Limulus polyphemus, the horseshoe crab. In low salinity and on land ANP prohormone messenger RNA in Limulus' heart was 32-fold less compared to that in a vertebrate heart (i.e., rat, Rattus norvegicus). ANP gene expression doubled (P < 0.05) in Limulus' heart and gills with change from land and low salinity to medium salinity and osmolality. ANP gene expression was 10-fold higher in Limulus' gills in seawater (i.e., high salinity). The products of this ANP gene expression (i.e., ANP, long acting natriuretic peptide, vessel dilator and kaliuretic peptide) were released and increased in the circulation, i.e., hemolymph, of Limulus proportional to the increase in salinity and osmolality (P = <0.01). These results suggest that modification of ANP gene expression enables animals to adapt to freshwater, seawater, and land.     

A trinucleotide deletion in the transthyretin gene (delta V 122) in a kindred with familial amyloidotic polyneuropathy

A 63-year-old white man of Ecuadorian origin had a subarachnoid hemorrhage at age 57 followed by numbness and paresthesia in his lower extremities. He subsequently developed sexual impotence, alternating constipation and diarrhea, urinary frequency, and difficulty in walking. Rectal biopsy revealed amyloid deposits immunohistochemically reactive with antitransthyretin antisera. Direct DNA sequencing of the transthyretin gene of the patient showed a trinucleotide deletion in exon 4. This deletion resulted in the loss of one of two valines at position 121 or 122. DNA analysis on 11 family members at risk revealed four mutant gene carriers. Plasma transthyretin levels in the mutant gene carriers measured by nephelometry were very low. Peptide sequence analysis revealed that most of plasma transthyretin was normal with only a small amount of variant protein. This is the first report of a DNA deletion in the transthyretin gene. We speculate that the loss of valine in the carboxyl terminal region of the transthyretin monomer alters stability of the tetrameric protein, which leads to rapid clearance from the plasma and amyloid deposition in the tissue.