Genomic and supragenomic structure of the nucleotide-like G-protein-coupled receptor GPR34

Abstract

Directed cloning approaches and large-scale sequencing of several vertebrate genomes unveiled many new members of the G-protein-coupled receptor (GPCR) superfamily, among them GPR34. Initial studies showed that GPR34 is an evolutionarily old GPCR structurally related to a group of ADP-like receptors. To gain insight into the genomic organization, regulation of expression, and supragenomic diversification of GPR34 several vertebrate species were analyzed. In contrast to the obviously intronless coding region GPR34 displays an evolutionary preserved 5' noncoding intron-exon structure. Further, an alternatively used cryptic intron was identified within the coding region, which shortens the N terminus by 47 amino acids. Ubiquitous expression of GPR34 is driven by genomic sequences upstream of at least two transcriptional start regions in mouse and rat but only one region in human. In rodents, both promoters are active in all tissues investigated, but the level of activity is tissue-specific. At the translational level, several conserved in-frame AUGs within the first 150 bp of the coding region may serve as start points for translation in human and other mammals. Combinatory mutagenesis and expression of reporter constructs confirmed these multiple translational start points and revealed a preference for the second in-frame AUG in human GPR34. Our data show that multiple translation initiation starts and alternative splicing contribute to the supragenomic diversification of GPR34.

Altered Immune Response in Mice Deficient for the G Protein-coupled Receptor GPR34

“…Increased DTH Reaction in GPR34-deficient Mice-Because GPR34 is highly expressed in immune cells (10,16,40), we challenged the immune system in a DTH test to screen for differences between WT and KO mice. The DTH test investigates the reaction of the organism toward an antigen after prior immunization.…”

“…More detailed analyses showed GPR34 expression in the myeloid progenitor cell line HL-60 in K562 cells, and WEHI-3B cells, the macrophage cell line RAW 264.1 (10), and in the murine mast cell line P815. These findings suggest a granulocytic/monocytic expression pattern that is consistent with the ubiquitous expression pattern seen in tissues.…”

“…Phylogenetic studies revealed that GPR34 has been highly conserved over the past 450 million years of vertebrate evolution, and no GPR34-deficient vertebrate has been identified yet (9). To date, there is no report of GPR34 deficiency in humans, and sequencing of more than 100 worldwide samples of human genomic DNA revealed no functionally relevant alleles indicating the physiological importance of the gene (10). GPR34 was, however, included in a microdeletion and breakpoints at the Xp11.4 locus in a Turner syndrome patient (11) and mucosa-associated lymphoid tissue lymphoma (12,13).…”

Dendritic Cells Regulate GPR34 through Mitogenic Signals and Undergo Apoptosis in Its Absence

“…GPR34 is highly expressed in immune cells (macrophages and microglia) (6,9) and immune system-derived cell lines (HL-60, K562, WEHI-3B, RAW 264.7, P815) (10). Immune systemchallenging conditions on mice showed that GPR34 deficiency results in an improper immune response, with higher susceptibility to systemic infections (6).…”

t(X;14)(p11.4;q32.33) is recurrent in marginal zone lymphoma and up-regulates GPR34

“…11,12 The receptor mRNA is ubiquitously expressed in all human tissues, particularly in placenta, brain and spleen. 13 Recent studies suggest that GPR34, found to be abundantly expressed in mast cells, is the functional mast cell receptor for lysophosphatidyl-L-serine (lysoPS).…”