Abstract
The Ras GTPase superfamily, including more than 100 members, plays a vital role in a number of cellular processes, such as cytoskeleton recombination, gene expression, and signaling pathway regulation. Some members of the superfamily participate in innate immunity in animals. However, there have been few studies of RhoA on this aspect. In the present study, we identified a RhoA GTPase in the shrimp Marsupenaeus japonicus and named it MjRhoA. Expression of MjRhoA was significantly upregulated in hemocytes and heart of shrimp challenged with Vibrio anguillarum. Overexpression of MjRhoA in shrimp caused the total bacterial number to decrease significantly and knockdown of MjRhoA increased the bacterial number obviously, with a consequent decline in shrimp survival. These results confirmed the antibacterial function of MjRhoA in shrimp. Further study showed that rate of phagocytosis of hemocytes was decreased in MjRhoA-knockdown shrimp. Interestingly, we observed that MjRhoA was translocated onto the hemocyte membrane at 1 h post V. anguillarum challenge. The expression levels of the β-integrin-mediated phagocytosis markers ROCK2 and Arp2/3 declined significantly after knockdown of MjRhoA. These results suggested that the antibacterial function of MjRhoA was related to β-integrin-mediated phagocytosis in shrimp. Our previous study identified that a C-type lectin, hFcLec4, initiated β-integrin mediated phagocytosis after bacterial infection. Thus, knockdown of hFcLec4 and β-integrin was performed. The results showed that the translocation of MjRhoA from the cytoplasm to membrane was inhibited and the expression level of MjRhoA was decreased, suggesting that MjRhoA participated in hFcLec4-integrin mediated phagocytosis. Therefore, our study identified a new hFcLec4-integrin-RhoA dependent phagocytosis against bacterial infection in shrimp.
Highlights
Small GTPases play a crucial role in the biological functions of organisms
The present study found that a member of the Rho GTPases, MjRhoA, participates in hFcLec4-β-integrin-mediated hemocyte phagocytosis to protect the host from infection by V. anguillarum. β-Integrin has been identified to play a role in anti-microbial immunity in Drosophila [24]
An ortholog of the integrin (BINT2) that has been identified in the mosquito Anopheles gambia is related to phagocytosis because its gene knockout resulted in reduced phagocytosis of E. coli by 70% [25]
Summary
Many small GTPase members have been identified and all the members belong to the Ras GTPase superfamily [1]. The Ras superfamily is divided into five groups: Ras, Ran, Rho, Rab, and Arf/Sar families [2]. Except for the Arf family, the other four groups exhibit GTPase activity. All members of these families have two states, the active state (GTP-binding state) and the inactive state (GDP-binding state). The two states can be reversed by guanine nucleotide exchange factors (GEF) and GTPase-activating proteins (GAP). Through this transformation between the active and inactive states, the small GTPases successfully regulate their downstream effectors [3]
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