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J Samuelson

Publications and source records attributed to J Samuelson.

At least 37 records · Page 2Linked to original sources
PubMed1996

Heterogeneity of Entamoeba histolytica rac genes encoding p21rac homologues.

Entamoeba histolytica (Eh), the parasite that causes amebic dysentery, is the only protozoan that phagocytoses bacteria, epithelial cells and red blood cells. Numerous low-molecular weight GTP-binding proteins, called p21rac, are implicated in signal transduction and actin polymerization during phagocytosis by macrophages and Dictyostelium discoideum (Dd). Here, molecular cloning techniques were used to obtain four Eh rac genes that encoded putative p21rac, as well as segments of two Eh rac pseudogenes. The predicted Eh p21rac, which share 55-81% amino acid (aa) identities with each other, include one that closely resembles the p21rac1 of man, Dd, Drosophila melanogaster and Caenorhabditis elegans; two that resemble the p21racC of Dd; and one that is unique. An alignment of the Eh rac ORF with other rac family proteins reveals multiple aa that distinguish p21rac1, p21racC and p21cdc42. We conclude that the Eh genes encoding amebic p21rac, which are the first identified from a protozoan parasite, are numerous and heterogeneous.

Amino Acid Sequence↗
PubMed1996

Hepatitis C virus reinfection in orthotopic liver transplant patients with or without concomitant hepatitis B infection.

Although recurrence of hepatitis C virus (HCV) in orthotopic liver transplant (OLT) patients is frequent, the relationship between HCV recurrence and graft pathology, particularly in patients who also have a history of hepatitis B virus (HBV), is unclear. The recurrence of HCV after OLT was determined by reverse transcriptase-nested polymerase chain reaction (RT-PCR) in the sera and livers of 41 patients with OLT, 32 of whom underwent transplants for HCV or HBV-related disease. Results were compared with liver function tests, liver histology (including HBV immunohistochemistry), and antibody status. HCV PCR was more frequently positive in OLT patients with a history of HCV only (59%) than in those with a history of both HCV and HBV (41%) or no history of viral infection (2%). Recurrent HCV (60% overall) was associated with mild elevation of liver function tests and mild to moderate hepatitis. In patients who underwent transplants for both HCV and HBV disease, hepatitis on biopsy was more frequently associated with recurrent HBV than with recurrent HCV. We conclude that graft reinfection with HCV, which is frequent in OLT patients with or without HBV recurrence, is usually associated with only mild to moderate hepatitic changes compatible with graft survival.

Base Sequence↗
PubMed1996

Physiology and molecular biology of multidrug resistance in Entamoeba histolytica.

In this paper, we present the most relevant facts on multidrug resistance (MDR) in the protozoan parasite Entamoeba histolytica. MDR in E. histolytica presents characteristics similar to transformed mammalian cells. E. histolytica drug resistant mutants show cross-resistance to several drugs, and as in mammalian cells the resistance is reverted by verapamil. Six P-glycoprotein-like genes (EhPgp) have been cloned and characterized. Apparently, four of these genes are transcribed in drug-resistant mutants (EhPgp1, EhPgp2, EhPgp5 and EhPgp6), although only EhPgp1, EhPgp5 and EhPgp6 transcripts were clearly detected. The open reading frame (ORF) of the four completely full length genes is about 1300 amino acids long. EhPgp1, EhPgp2 and EhPgp5 have between 64 and 67% of positional identity among them, while EhPgp6 shows 38 to 46% positional identity to the other ameba genes. Interestingly, the phylogenetic tree suggested that Entamoeba P-glycoproteins are more related to the human and mouse P-glycoproteins than to the Plasmodium and Leishmania P-glycoproteins. Differential gene expression in drug-resistant mutants was detected when specific probes for each Ehpgp gene were used. To understand the differential expression of EhPgp genes we initiated the characterization of the upstream flanking regions of EhPgp1 and EhPgp5 genes. Upstream sequences showed between 53 and 66% of positional identity to Dictyostelium discoideum promoters.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Increase in mRNA of multiple Eh pgp genes encoding P-glycoprotein homologues in emetine-resistant Entamoeba histolytica parasites.

With the goal of understanding possible mechanisms of drug resistance by the protozoan parasite Entamoeba histolytica (Eh), two novel Eh P-glycoprotein (Pgp) genes (Eh pgp5 and Eh pgp6) were sequenced, and the expression of four Eh pgp genes determined in wild-type (wt) clone A and emetine-resistant (EmR) clone C2 amebae. The Eh pgp5 gene encodes a 1301-amino acid (aa) protein that is similar to those of Eh pgp1 (64% aa identity), Eh pgp2 (61%), Eh pgp6 (39%) and Homo sapiens MDR (multidrug-resistance-encoding)(Hs MDR1; 38%) genes. The 1282-aa Eh pgp6 open reading frame (ORF), which is 19-28 aa shorter than those encoded by other Eh pgp, is also similar to those of Eh pgp1 (46% aa identity), Eh pgp2 (38%), and Hs MDR1 (39%). Both Eh pgp5 and Eh pgp6 ORF predict two ATP-binding cassettes and twelve hydrophobic alpha-helices, which form the putative transmembrane channel. EmR clone C2 amebae, growing at all concentrations of drug, show increased amounts of Eh pgp1 and Eh pgp6 mRNA when compared to wt clone A amebae. In contrast, only clone C2 amebae selected for growth at the highest concentrations of emetine (100-200 micrograms/ml) show increased Eh pgp5 mRNA, while mRNA of both clone C2 and clone A Eh amebae fail to bind an Eh pgp2-specific probe. It appears then that multiple Pgp may contribute to amebic Em resistance in vitro.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

Molecular cloning of ras and rap genes from Entamoeba histolytica.

To better understand growth regulation in the protozoan parasite Entamoeba histolytica, ameba genes homologous to the ras oncogene and rap (Krev-1) anti-oncogene were cloned. Two putative ameba ras genes (Ehras1 and Ehras2) were identified, which contain 205 and 203 amino acid (aa) open reading frames (ORFs), respectively. The Ehras1 ORF shows an 91% positional identity with that of Ehras2, a 55% identity with Dictyostelium discoideum (Dd) ras, and a 47% identity with human (Hs) ras. Two ameba rap genes (Ehrap1 and Ehrap2) were identified, both of which contain 184-aa ORFs. The Ehrap1 ORF shows a 93% positional identity with that of Ehrap2, a 60% identity with Dd rap, a 61% identity with Hs Krev-1, and a 45% identity with that of Ehras1. Conserved aa in each ameba ras and rap ORF include GTP-binding sites, effector site, site of ADP-ribosylation by Pseudomonas exoenzyme S, and COOH-terminus CAAX. As all Xs = Leu or Phe, ameba ras and rap proteins may be gerenylgerenylated and not farnesylated. Both ras and rap genes are transcribed by trophozoites. A single 21-kDa ameba ras protein reacts with the rat Y13-259 anti-ras monoclonal antibody, which is located on the cytosolic side of the plasma membrane. These are the first ras and rap genes identified from a protozoan parasite.

Amino Acid Sequence↗
PubMed1994

Cloning of Entamoeba genes encoding proteolipids of putative vacuolar proton-translocating ATPases.

Molecular cloning techniques were used to identify genes encoding the proteolipids of putative vacuolar proton-transporting ATPases (V-ATPases; EC 3.6.1.35) of Entamoeba histolytica (Ehvma3) and Entamoeba dispar. The Ehvma3 gene encoded a 177-amino-acid peptide, with an M(r) of 18,110, which showed extensive positional identities with peptides of E. dispar (92%), Schizosaccharomyces pombe (58%), and humans (56%).

Amino Acid Sequence↗
PubMed1993

Cloning of the Eh cdc2 gene from Entamoeba histolytica encoding a protein kinase p34cdc2 homologue.

To understand better growth regulation in the protozoan parasite, Entamoeba histolytica (Eh), a homologue of the cdc2 gene encoding the yeast cyclin-dependent protein kinase, p34cdc2, has been cloned and sequenced. This gene, called Eh cdc2, contains a 79-bp intron located in the same place as the second of four introns in the Schizosaccharomyces pombe cdc2 gene. The sequence of an Eh cdc2 cDNA confirms the conserved eukaryotic splice donor (GT) and acceptor (AG) sites and shows that Eh is able to splice mRNAs. The spliced Eh cdc2 open reading frame is 291 amino acids (aa) long, encoding an M(r) 33,806 protein. The primary sequence of Eh cdc2 is most like those of cdc2 homologues Eg1 of Xenopus laevis and CDK2 of man (52% aa identity with each) and codes for (i) the serine (Ser), threonine (Thr), and tyrosine residues phosphorylated in p34cdc2 proteins, (ii) 32 of 33 aa conserved in other Ser/Thr protein kinases, and (iii) the sequence PVTSVRE instead of PSTAIRE found in most p34cdc2 proteins. This is the first cell-division-cycle regulatory protein homologue, as well as the first intron identified from Eh.

Amino Acid Sequence↗
PubMed1993

Molecular cloning of a rho family gene of Entamoeba histolytica.

An Entamoeba histolytica gene (Eh rho1) was cloned that encodes a putative low-molecular-mass GTP-binding protein, most similar to the ras homologue rho. The Eh rho1 open reading frame was 208 amino acids long and encoded a 23-kDa protein similar to Saccharomyces cerevisiae RHO1-RHO4 and CDC42 and human rhoA, rac1, and G25K gene products. This similarity was greatest at the NH2 terminus of Eh rho1 where two GTP-binding sites and a possible effector site were conserved. A cysteine residue at the COOH terminus of Eh rho1 was followed by eight hydrophobic amino acids rather than the three hydrophobic amino acids present in other ras family proteins.

Amino Acid Sequence↗