The serine protease homolog CLIPA14 modulates the intensity of the immune response in the mosquito Anopheles gambiae

Abstract

Clip domain serine protease homologs (SPHs) are positive and negative regulators of Anopheles gambiae immune responses mediated by the complement-like protein TEP1 against Plasmodium malaria parasites and other microbial infections. We have previously reported that the SPH CLIPA2 is a negative regulator of the TEP1-mediated response by showing that CLIPA2 knockdown (kd) enhances mosquito resistance to infections with fungi, bacteria, and Plasmodium parasites. Here, we identify another SPH, CLIPA14, as a novel regulator of mosquito immunity. We found that CLIPA14 is a hemolymph protein that is rapidly cleaved following a systemic infection. CLIPA14 kd mosquitoes elicited a potent melanization response against Plasmodium berghei ookinetes and exhibited significantly increased resistance to Plasmodium infections as well as to systemic and oral bacterial infections. The activity of the enzyme phenoloxidase, which initiates melanin biosynthesis, dramatically increased in the hemolymph of CLIPA14 kd mosquitoes in response to systemic bacterial infections. Ookinete melanization and hemolymph phenoloxidase activity were further increased after cosilencing CLIPA14 and CLIPA2, suggesting that these two SPHs act in concert to control the melanization response. Interestingly, CLIPA14 RNAi phenotypes and its infection-induced cleavage were abolished in a TEP1 loss-of-function background. Our results suggest that a complex network of SPHs functions downstream of TEP1 to regulate the melanization reaction.

Improved reference genome of the arboviral vectorAedes albopictus

“…aegypti, we only identified a single CEC gene in the new assembly. We found expansions in families involved in all immune phases of the melanization pathway (40). The most extreme expansion event regards the CLIP family of regulators with 118 members compared to 67 and 56 genes reported for Ae.…”

Mosquito Innate Immunity

“…These two SPs, CLIPB14 and CLIPB15, are synthesized by the hemocytes and are released into the hemolymph. These SPs appear to play an important role in enhancing the extent of melanization upon bacterial and Plasmodium infections [ 124 , 125 ]. Another class of molecules that regulate the activity of serine proteases and manipulate the immune system of mosquitoes are the serine protease inhibitors (serpins) [ 126 ].…”

The CLIP-domain serine protease CLIPC9 regulates melanization downstream of SPCLIP1, CLIPA8, and CLIPA28 in the malaria vector Anopheles gambiae

“…TEP1 circulates in the hemolymph as a full-length (TEP1-Full) and a cleaved (TEP1 cut ) form with a reactive thioester motif that binds microbial surfaces [44]. TEP1 cut opsonization drives a convertase mechanism that amplifies TEP1 cut accumulation from circulating TEP1-Full and ultimately promotes microbial melanization [4,[45][46][47][48][49][50]. SPCLIP1 (also called CLIPA30) localizes to microbial surfaces in a TEP1-dependent manner and positively regulates melanization by promoting TEP1 convertase activity [46,51].…”