Abstract:
Apoptosis plays a key role in the physiology of multicellular organisms and is regulated by different promoting and inhibitory mechanisms. Cytokine-induced apoptotic inhibitor (CIAPI) was recently identified
as a key factor involved in apoptosis inhibition in higher vertebrate lineages. However, most of the CIAPIs
of lower vertebrate species are yet to be characterized. Herein, we molecularly characterized a teleostan
counterpart of CIAPI from rock bream (Oplegnathus fasciatus), designating as RbCIAPI. The complete coding
region of RbCIAPI was consisted of 942 nucleotides encoding a protein of 313 amino acids with a predicted molecular mass of ~33 kDa. RbCIAPI gene exhibited a multi-exonic architecture, consisting 9 exons
interrupted by 8 introns. Protein sequence analysis revealed that RbCIAPI shares significant homology
with known CIAPI counterparts, and phylogenetic reconstruction confirmed its closer evolutionary relationship with its fish counterparts. Ubiquitous spatial distribution of RbCIAPI was detected in our
quantitative real time polymerase chain reaction (qPCR) analysis, where more prominent expression levels
were observed in the blood and liver tissues. Moreover, the RbCIAPI basal transcription level was found
to be modulated by different bacterial and viral stimuli, which could be plausibly supported by our previous observations on the transcriptional modulation of the caspase 3 counterpart of rock bream (Rbcasp3)
in response to the same stimuli. In addition, our in vitro functional assay demonstrated that recombinant RbCIAPI could detectably inhibit the proteolysis activity of recombinant Rbcasp3. Collectively, our
preliminary results suggest that RbCIAPI may play an anti-apoptotic role in rock bream physiology, likely
by inhibiting the caspase-dependent apoptosis pathway. Therefore, RbCIAPI potentially plays an important role in host immunity by regulating the apoptosis process under pathogenic stress.
