GTPase stimulation in shrimp Ras(Q(61)K) with geranylgeranyl pyrophosphate but not mammalian GAP

Extracellular vesicles and post-translational protein deimination signatures in haemolymph of the American lobster (Homarus americanus)

The American lobster (Homarus americanus) is a commercially important crustacean with an unusual long life span up to 100 years and a comparative animal model of longevity. Therefore, research into its immune system and physiology is of considerable importance both for industry and comparative immunology studies. Peptidylarginine deiminases (PADs) are a phylogenetically conserved enzyme family that catalyses post-translational protein deimination via the conversion of arginine to citrulline. This can lead to structural and functional protein changes, sometimes contributing to protein moonlighting, in health and disease. PADs also regulate the cellular release of extracellular vesicles (EVs), which is an important part of cellular communication, both in normal physiology and in immune responses. Hitherto, studies on EVs in Crustacea are limited and neither PADs nor associated protein deimination have been studied in a Crustacean species. The current study assessed EV and deimination signatures in haemolymph of the American lobster. Lobster EVs were found to be a poly-dispersed population in the 10-500 nm size range, with the majority of smaller EVs, which fell within 22-115 nm. In lobster haemolymph, 9 key immune and metabolic proteins were identified to be post-translationally deiminated, while further 41 deiminated protein hits were identified when searching against a Crustacean database. KEGG (Kyoto encyclopedia of genes and genomes) and GO (gene ontology) enrichment analysis of these deiminated proteins revealed KEGG and GO pathways relating to a number of immune, including anti-pathogenic (viral, bacterial, fungal) and host-pathogen interactions, as well as metabolic pathways, regulation of vesicle and exosome release, mitochondrial function, ATP generation, gene regulation, telomerase homeostasis and developmental processes. The characterisation of EVs, and post-translational deimination signatures, reported in lobster in the current study, and the first time in Crustacea, provides insights into protein moonlighting functions of both species-specific and phylogenetically conserved proteins and EV-mediated communication in this long-lived crustacean. The current study furthermore lays foundation for novel biomarker discovery for lobster aquaculture.

Trap RACK1 with Ras to mobilize Src signaling at syndecan-2/p120-GAP upon transformation with oncogenic ras

HiTrap-syndecan-2/p120-GAP and HiTrap-syndecan-2/RACK1 affinity columns were applied to reveal that Src tyrosine kinase was highly expressed in BALB/3T3 cells transfected with plasmids pcDNA3.1-[S-ras(Q(61)K)] of shrimp Penaeus japonicus. Both columns were effective to isolate Src tyrosine kinase. The selective molecular affinity for Src was found to be stronger with HiTrap-syndecan-2/RACK1, as revealed with competitive RACK1 to dislodge Src from HiTrap-syndecan-2/p120-GAP. We thus challenged the syndecan-2/p120-GAP and syndecan-2/RACK1 with GTP-K(B)-Ras(Q(61)K). The reaction between RACK1 and syndecan-2 was sustained in the presence of mutant Ras proteins, but not the reaction between p120-GAP and syndecan-2. In the presence of syndecan-2, GTP-K(B)-Ras(Q(61)K) exhibited sufficient reactivity with p120-GAP to discontinue the reaction between p120-GAP and syndecan-2. But the interference of mutant Ras disappeared when Src tyrosine kinase was introduced to stabilize the syndecan-2/p120-GAP complex. On the other hand, in the absence of syndecan-2, GTP-K(B)-Ras(Q(61)K) was found to react with RACK1. The reaction between GTP-K(B)-Ras(Q(61)K) and RACK1 could provide a mechanism to deprive RACK1 for the organization of syndecan-2/RACK1 complex and to facilitate the formation of syndecan-2/p120-GAP complex, as well as to provide docking sites for Src signaling upon transformation with oncogenic ras.

P120-GAP associated with syndecan-2 to function as an active switch signal for Src upon transformation with oncogenic ras

BALB/3T3 cells transfected with plasmids pcDNA3.1-[S-ras(Q(61)K)] of shrimp Penaeus japonicus were applied to reveal a complex of p120-GAP/syndecan-2 being highly expressed upon transformation. Of interest, most of the p120-GAP/syndecan-2 complex was localized at caveolae, a membrane microdomain enriched with caveolin-1. To confirm the molecular interaction between syndecan-2 and p120-GAP, we further purified p120-GAP protein from mouse brains by using an affinity column of HiTrap-RACK1 and expressed mouse RACK1-encoded fusion protein and mouse syndecan-2-encoded fusion protein in bacteria. We report molecular affinities exist between p120-GAP and RACK1, syndecan-2 and RACK1 as well as p120-GAP and syndecan-2. The selective affinity between p120-GAP and syndecan-2 was found to be sufficient to detach RACK1. The p120-GAP/syndecan-2 complex was demonstrated to keep Src tyrosine kinase in an activated form. On the other hand, the syndecan-2/RACK1 complex was found to have Src in an inactivated form. These data indicate that the p120-GAP/syndecan-2 complex at caveolae could provide a docking site for Src to transmit tyrosine signaling, implying that syndecan-2/p120-GAP functions as a tumor promoter upon transformation with oncogenic ras of shrimp P. japonicus.

Effects of prenyl pyrophosphates on the binding of S-Ras proteins with KSR

BALB/3T3 cells were transformed by transfection with DNA encoding the mutated ras(Q(61)K) from shrimp Penaeus japonicus (Huang et al., 2001. J. Exp. Zool. 289:441-448). On a Western blot, the kinase suppressor of Ras (KSR) in the membrane fraction was expressed at slightly reduced level as compared to that of the untransformed cells. To understand this in more detail, the interaction of the bacterially expressed shrimp Ras (S-Ras) with KSR was investigated using KSR purified from mice brains. SDS-polyacrylamide gel electrophoresis and Western blot analysis revealed that the monomers of the purified KSR have a relative molecular mass of 60,000. Purified KSR was found to bind with digoxigenylated S-ras-encoding fusion protein (Dig-S-Ras) with high affinity in the absence of ATP, and the binding activity of KSR was sustained upon phosphorylation of Dig-S-Ras with mitogen-activated protein kinase (MAPK). The association of purified KSR with S-Ras was confirmed. Differences between the effects of farnesyl pyrophosphate and geranylgeranyl pyrophosphate on the binding of S-Ras with the purified KSR were assessed. Densitometer analysis revealed that at nanogram concentration, farnesyl pyrophosphate inhibited the binding of S-Ras with KSR competently, but geranylgeranyl pyrophosphate did not. The present study provides the evidence that decrease of the concentration of farnesyl pyrophosphate to sub-microgram levels lower the affinity of Ras proteins with KSR in the signaling pathway.

Role of steroidogenic factor 1 and aromatase in temperature-dependent sex determination in the red-eared slider turtle

Red-eared slider turtles are genetically bipotential for sex determination. In this species, as in many other reptiles, incubation temperature of the egg determines gonadal sex. At higher incubation temperatures females are produced and increasing temperature appears to increase estrogen production in the embryonic brain. Treatment of eggs incubating at a male-producing temperature with exogenous estrogen causes ovaries to form. At a female-biased incubation temperature, prevention of estrogen biosynthesis or administration of nonaromatizable androgens results in the development of testes. In mammals, steroidogenic factor 1 (SF-1) regulates most genes required for estrogen biosynthesis, including aromatase. In both mammals and red-eared sliders, SF-1 is differentially expressed in males and females during gonadogenesis. We have examined both SF-1 gene expression and aromatase activity in embryos incubating at different temperatures and after manipulation to change the course of gonadal development. Our findings indicate a central role for SF-1 in enacting the effect of estrogen. Estrogen treatment directly or indirectly downregulates SF-1 and, ultimately, causes development of females. The inhibition of estrogen results in upregulation of SF-1 and male hatchlings. Thus, SF-1 may lie at the center of one molecular crossroad in male versus female differentiation of the red-eared slider.