Broad expression analysis of human ANTXR1/TEM8 transcripts reveals differential expression and novel splizce variants.
Tumor endothelial marker 8 (TEM8; ANTXR1) is one of two anthrax toxin receptors; the other is capillary morphogenesis gene 2 protein (CMG2; ANTXR2). TEM8 shows enhanced expression in certain tumor endothelia, and is thought to be a player in tumor vasculature formation. However, a comprehensive expression profile of individual TEM8 variants in normal or cancerous tissues is lacking. In this work we carried out an extensive analysis of all splice variants of human TEM8 in 12 digestive tissues, and 8 each fetal and adult tissues, 6 of them cognate pairs. Using variant-specific primers, we first ascertained the status of full-length transcripts by nested PCR. We then carried out quantitative analysis of each transcript by real-time PCR. Three splice variants of TEM8 were reported before, two single-pass integral membrane forms (V1 and V2) and one secreted (V3). Our analysis has revealed two new variants, one encoding a membrane-bound form of the receptor and the other secreted, which we have designated V4 and V5, respectively. All tissues had V1, V2, V3, and V4, but only prostate had V5. Real-time PCR revealed that all variants are present at different levels in various tissues. V3 appeared the most abundant of all. To ascertain its functionality for anthrax toxin, we expressed the newly identified form V4 in a receptor-negative host cell, and included V1 and V2 for comparison. Cytotoxicity, toxin binding, and internalization assays showed V4 to be as efficient a receptor as V1 and V2.
Cell and Molecular Biology Program, Department of Biology, The University of Texas at San Antonio, San Antonio, Texas, United States of America.
Micaela
M
Vargas
Raghavendra
R
Karamsetty
Stephen H
SH
Leppla
G Jilani
GJ
Chaudry
D000328:Adult; D001483:Base Sequence; D001921:Brain / Q000378:metabolism; D019295:Computational Biology; D017931:DNA Primers / Q000235:genetics; D004586:Electrophoresis; D005333:Fetus / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008297:Male; D008840:Microfilament Proteins; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000378:metabolism*; D011467:Prostate / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D011956:Receptors, Cell Surface / Q000378:metabolism*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D059467:Transcriptome / Q000235:genetics*
C473287:ANTXR1 protein, human; D017931:DNA Primers; D008840:Microfilament Proteins; D009363:Neoplasm Proteins; D020033:Protein Isoforms; D011956:Receptors, Cell Surface