Identification And Characterization Of Strica Homologs In Aedes Albopictus

Apoptosis is a physiological process of programmed cell death and is essential for the removal of unwanted and damaged cells to maintain the internal homeostasis. Apoptosis play important roles in many processes such as growth and development, organ shape and immune response. Disorder in apoptosis leads to autoimmune diseases, tumorigenesis, developmental malformation, and so on. The mechanism of apoptosis has been clarified in model species, especially in nematodes, fruit flies and mammals. The apoptosis network in nematodes is relative simple, while is the most complicated in mammals.Caspases are a family of cysteine-aspartic acid specific proteases playing essential roles during apoptosis. Caspase each contains a prodomain, a large subunit and a small subunit. Apoptotic caspases are divided into initiator caspases and effector caspases according to the time order functioning in the apoptotic cascade. Usually, initiator caspases contain a long prodomain, while effector caspases contain a short prodomain.In insects, apoptosis pathway has been well studied in the model species Drosophila melanogaster. Seven caspases have been identified in Drosophila:Dronc, Dredd, Strica, Dcp-1, Decay, Drice and Damm. Among them, Dronc, Dredd, and Strica are grouped to initiator caspases with a long prodomain. Strica is an insect-specific caspase containing a long serine- and threonine-rich prodomain. However, Strica is not well studied so far.Aedes albopictus, also called tiger mosquito, is an efficient epidemic viral vector for the transmission of arbovirus, which is a serious threat to public health due to its rapid adaption in overall world distribution, so it is of great significance to study the antiviral response in Aedes albopictus. Apoptosis serves as a kind of important antiviral response, but remains to be elucidated in Aedes albopictus.In this study, we identified three homologs of strica from Aedes albopictus, named as Aacasps15, Aacaspsl6 and Aacasps21. Sequence analyses indicated that they each encode a protein which contains a putative serine-and threonine-rich prodomain and a well conserved caspase catalytic domain. The expression profiles of Aacaspsl5, Aacaspsl6 and Aacasps21 during developmental and adult stages were analyzed:higher expression was observed in the 2nd instar larvae and female mosquito for Aacaspsl5 and Aacasps21, and in the female and male mosquitoes forAacaspsl6. Biochemical experiments in vitro indicated that these 3 caspases had the characteristics of initiator caspases:1) These caspases underwent autocatalytic cleavage when expressed from E. Coli, which was dependent of caspase activity; 2) Purified recombinant caspases exhibited the substrate specificities most similar with initiator caspase; 3) Recombinant caspases could cleave the potential effector caspase AaCASPS7. Furthermore, we identified these caspases as pro-apoptotic caspases in apoptosis pathway:1) AaCASPS15, AaCASPS16 and AaCASPS21 induced apoptosis when overexpressed both in HEK293T cells and C6/36 cells; 2) AaCASPS15, AaCASPS16 and AaCASPS21 were involved in apoptosis induced by actinomycin D and ultraviolet irradiation treatment. Taken together, our study provided the advantages for further researches on the role of Strica and Strica homologs in other insects, on the improvements in the incomplete apoptosis pathway in insects and on the relationship between virus and virus-borne vectors.