Target validation of the inosine monophosphate dehydrogenase (IMPDH) gene in Cryptosporidium using Phylomer(®) peptides.

Cryptosporidiosis, a gastroenteric disease characterised mainly by diarrheal illnesses in humans and mammals is caused by infection with the protozoan parasite Cryptosporidium. Treatment options for cryptosporidiosis are limited, with the current therapeutic nitazoxanide, only partly efficacious in immunocompetent individuals. The parasite lacks de novo purine synthesis, and is exclusively dependant on purine salvage from its host. Inhibition of the inosine 5' monophosphate dehydrogenase (IMPDH), a purine salvage enzyme that is essential for DNA synthesis, thereby offers a potential drug target against this parasite. In the present study, a yeast-two-hybrid system was used to identify Phylomer peptides within a library constructed from the genomes of 25 phylogenetically diverse bacteria that targeted the IMPDH of Cryptosporidium parvum (IMPcp) and Cryptosporidium hominis (IMPch). We identified 38 unique interacting Phylomers, of which, 12 were synthesised and screened against C. parvum in vitro. Two Phylomers exhibited significant growth inhibition (81.2-83.8% inhibition; P < 0.05), one of which consistently exhibited positive interactions with IMPcp and IMPch during primary and recapitulation yeast two-hybrid screening and did not interact with either of the human IMPDH proteins. The present study highlightsthe potential of Phylomer peptides as target validation tools for Cryptosporidium and other organisms and diseases because of their ability to bind with high affinity to target proteins and disrupt function.

Novel alternative PBX3 isoforms in leukemia cells with distinct interaction specificities.

PBX3 is a member of the PBX family of TALE homeobox genes. The prototypic member, PBX1, was first identified in chromosomal translocations in B-lineage leukemia and is required for normal hematopoiesis. PBX2 and PBX3 were later identified as members of this highly conserved family by their strong homology to PBX1. While the expression pattern of PBX1 is restricted, PBX2 and PBX3 are ubiquitously expressed. Little is known about the functional role of PBX3. Our studies identified two PBX3 transcripts alternative to the canonical forms, PBX3A and PBX3B, resulting from a novel splice in PBX3. These new isoforms, named PBX3C and PBX3D, have been detected in all tissues and cell lines tested. Intriguingly, expression of PBX3D is favored in normal cells, whereas PBX3C expression is favored in leukemia cells. Functional studies showed that PBX3C and PBX3D proteins were unable to interact with the PBX-interacting factor PREP1 and weakly interacted with MEIS proteins. We propose that PBX3C and PBX3D may affect PBX3-mediated transcriptional regulation by acting in opposition to the known PBX proteins through alternative PBX3 complex formation. The identification and characterization of these novel PBX3 isoforms provide a foundation for a better understanding of the biological role of PBX3.

Transfection of the gene for B7-1 but not B7-2 can induce immunity to murine malignant mesothelioma.

Transfection of the genes encoding the co-stimulatory molecules B7-1 and B7-2 has enhanced the development of immunity to a variety of experimental tumors, although most of these were inherently immunogenic. We have determined the effect of expression of these genes on the induction of immunity to 2 non-immunogenic murine malignant mesothelioma (MM) cell lines (AC29 and AB1). We had previously shown that B7-1 transfection into AC29 delayed but did not prevent tumor development by certain of the transfectant clones. Here we demonstrate that over-expression of B7-1 can inhibit tumor development by certain AB1-B7-1 clones, that inhibition of transfectant growth is dependent on CD4+ and CD8+ T cells and that mice that reject some of these transfectant clones are capable of rejecting subsequent inocula of the parental cell line, AB1. The transfectant clones can generate tumor-specific cytotoxic T cells. By contrast, expression of B7-2 in several clones derived from either AB1 or AC29 had no significant effect on the development of tumors in vivo. Our data are consistent with data from other systems that show differences in the effect of modification by B7-1 or B7-2 on the modulation of anti-tumor immune responses. They demonstrate that such modifications can induce protective immunity against an MM cell line but confirm the intra- and inter-tumoral heterogeneity in the effect of genetic modification on the induction of immunity. Our observations are relevant to human MM because these cell lines have been derived from asbestos-induced tumors and share many properties with human cell lines of the same histological type.