Ongoing research provides further understanding of the biology of RNase A ribonucleases that promote innate immunity (the eosinophil RNase 2 and RNase 3, tissue RNases 7 and 8, and leukocyte RNase A-2) with efforts focused toward understanding their mechanisms of action in health and disease. Our first report details the results of our study of the atypical human ribonuclease, RNase 8, discovered by our section several years ago upon release of the first draft of the human genome sequence (Zhang J et al. 2002. Nucleic Acids Res. 30:1169-1175.) RNase 8 is homolgous to, and is likely a recent duplication from the lysine-enriched, crucial antimicrobial RNase 7, but RNase 8 has no clear function nor had its gene product been characterized. In order to proceed with characterization, we isolated transcripts encoding RNase 8 via rapid amplification of cDNA ends (RACE) and RT-PCR and thereby elucidated the full open reading frame, which included an uncharacteristic distal start methionine and an additional 30 amino acids preceding what had been previously identified as a hydrophobic signal sequence. This newly-identified amino terminal sequence was hydrophilic, and was apparently conserved in the genomes of several higher primates. Given these observations, taken together with our study documenting the RNase A ribonuclease genes as scaffolds for evolutionary change (Nitto T, et al . 2006. J Biol Chem. 281:25622-25634), it was apparent that we needed to consider the possibility that RNase 8 might be something other than a standard secretory ribonuclease, perhaps only partially related to its original role. Toward this end, we determined that the distal translational start site was functional and promoted RNase 8 synthesis in transfected COS-7 cells. Overall, our results suggested that RNase 8 diverged considerably from typical RNase A family ribonucleases and may likewise exhibit unique function. This finding prompts a reconsideration of what we have previously termed functional pseudogenes (Zhang J et al. 2002 Nucleic Acids Res. 30:1169-1175), as RNase 8 may be responding to constraints that promote significant functional divergence from the canonical structure and enzymatic activity characteristic of the RNase A family. Reference: Chan CC et al., (2012) Genetic diversity of human RNase 8. BMC Genomics 13: 40. We also report a mouse model that includes the first successful deletion of a mouse eosinophil ribonuclease (relevant also for report AI000941). The characterization of this mouse will have profound impact on our understanding of the role of these enzymes in promoting homeostasis in vivo and at the cellular level.
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