ORP3 Splice Variants and Their Expression in Human Tissues and Hematopoietic Cells

Abstract

ORP3 is a member of the newly described family of oxysterol-binding protein (OSBP)-related proteins (ORPs). We previously demonstrated that this gene is highly expressed in CD34(+) hematopoietic progenitor cells, and deduced that the "full-length" ORP3 gene comprises 23 exons and encodes a predicted protein of 887 amino acids with a C-terminal OSBP domain and an N-terminal pleckstrin homology domain. To further characterize the gene, we cloned ORP3 cDNA from PCR products and identified multiple splice variants. A total of eight isoforms were demonstrated with alternative splicing of exons 9, 12, and 15. Isoforms with an extension to exon 15 truncate the OSBP domain of the predicted protein sequence. In human tissues there was specific isoform distribution, with most tissues expressing varied levels of isoforms with the complete OSBP domain; while only whole brain, kidney, spleen, thymus, and thyroid expressed high levels of the isoforms associated with the truncated OSBP domain. Interestingly, the expression in cerebellum, heart, and liver of most isoforms was negligible. These data suggest that differential mRNA splicing may have resulted in functionally distinct forms of the ORP3 gene.

Subfamily III of mammalian oxysterol-binding protein (OSBP) homologues: the expression and intracellular localization of ORP3, ORP6, and ORP7

“…AB014604). This ORP3 cDNA encodes a protein which corresponds to ORP3 isoform 1a (AAM27386) (Collier et al 2003). Human ORP6 (AF323728) and ORP7 (AF323729) cDNAs were also cloned from HuH7 cell line as described earlier (Lehto et al 2001).…”

“…1). The ORP3-N cDNA encodes a protein (445 aa), which is 197 amino acids shorter than ORP3 isoform 2a (AAM27390) (Collier et al 2003). All constructs were verified by cycle sequencing (BIGDYE) and an automated ABI377 sequencer (Applied Biosystems).…”

“…Antibodies were affinity purified using CnBr-activated Sepharose 4B (Amersham Pharmacia Biotech) with covalently coupled peptides. The ORP3 peptide antibody should recognize all eight known human isoforms (Collier et al 2003). The NCBI sequence database contains two alternatively spliced human ORP6 variants, of which isoform a (NP_115912) is recognized by our peptide antibody, whereas isoform b (NP_665682) is not detected by this antibody.…”

“…It is also evident that several ORPs have multiple splice variants, which seem to be expressed in a tissuespecific manner (Laitinen et al 1999;Lehto et al 2001;Jaworski et al 2001;Johansson et al 2003;Collier et al 2003). Although very little is known about the promoters and the transcriptional regulation of ORP genes, there is some evidence that their expression is regulated during the cell cycle (BesØme et al 1986;Whitfield et al 2002) and cell differentiation (Grecorio-King et al 2001;Lapteva et al 2001;Ross et al 2002;Anniss et al 2002;Tanaka et al 2002;Johansson et al 2003).…”

Functions of OSBP/ORP Family Proteins and Their Relation to Dyslipidemia

“…Epidemiological study: Epidemiological studies of ORP1S or ORP2 are not reported yet. (Collier, Gregorio-King et al 2003). In human tissues there was specific isoform distribution, with most tissues expressing varied levels of isoforms with the complete ORD; while only whole brain, kidney, spleen, thymus, and thyroid expressed high levels of the isoforms associated with the truncated ORD.…”