Dendritic Cell Adenosylhomocysteine Hydrolase-Like Protein 1 (AHCYL1) and Inositol Phospholipid Signaling Are Potential Targets for Modulating Their Function.

Abstract

Recipient and donor dendritic cells (DC) initiate acute graft versus host disease after allogeneic hematopoietic stem cell transplantation and activated DC predict for severe disease. Using a differential display technique, we isolated the cDNA for an adenosylhomocysteine hydrolase-like protein 1 (AHCYL1), a novel intracellular protein with ~50% protein identity to adenosylhomocysteine hydrolase (AHCY) and showed that it was upregulated in activated human DC (Dekker et al. Immunogenetics. 2002; 53:993). AHCYL1 binds to the inositol 1,4,5-trisphosphate receptor (IP3R), suggesting that AHCYL1 is involved in intracellular calcium release (Ando et al. J Biol Chem. 2003; 278:10602). Given that intracellular calcium levels control DC function, we reasoned that AHCYL1 was a potential target for modulating DC function. Therefore, we sought functional data using the zebrafish model. We identified two zebrafish AHCYL1 orthologs (zAHCYL1A and B) by bioinformatics and reverse transcriptase-polymerase chain reaction (RT-PCR). Unlike the ubiquitously present AHCY genes, AHCYL1 genes were only detected in segmented animals and AHCYL1 proteins were highly conserved among species. Phylogenic analysis suggested that the AHCYL1 gene diverged early from AHCY and evolved independently. Quantitative RT-PCR showed that zAHCYL1A and B mRNA expression was regulated differently to the other AHCY-like protein zAHCYL2 and zAHCY during zebrafish embryogenesis. Injection of morpholino antisense oligos against zAHCYL1A and B into zebrafish embryos inhibited zAHCYL1A and B mRNA translation specifically and induced ventralized morphologies. Conversely, human and zebrafish AHCYL1A mRNA injection into zebrafish embryos induced dorsalized morphologies, that were similar to those obtained by depleting intracellular calcium with thapsigargin. The injection of hAHCY had little effect on the embryos. These data suggest that AHCYL1 has a different function from AHCY and plays an important role in zebrafish embryogenesis by modulating IP3R function and consequent intracellular calcium release. It also suggests that blocking AHCYL1 in DC may have a significant effect on DC function, which might, ultimately, be exploited therapeutically. We have generated AHCYL1 gene deleted mice and these will be used to explore these questions further.