Aggregation behavior of proteins on the surface of gold nanoparticles (AuNPs) has been extensively studied for its promising applications in biosensing, bioimaging, photodynamic therapy, drug delivery, etc. In this work, we studied adsorption kinetics of an antimicrobial protein, regenerating islet-derived protein 3-alpha (REG3A), on the surface of as-synthesized citrate-capped AuNPs under the influence of lipopolysaccharides (LPSs), with a combined method of UV–vis spectroscopy, multivariate analysis, and molecular dockings. In the AuNPs–REG3A binary system, a component with an “up-and-down” signal was detected by the in-depth data analysis on time-resolved spectroscopic data, corresponding to the protein agglomeration and exfoliation observed in transmission electron microscopy and atomic force microscopy experiments. Intriguingly, LPSs can rescue the spectral oddity—the adsorption pattern in the AuNPs–REG3A–LPS ternary system becomes normal and similar to a typical single-layer mode as in our previous study of the serum albumin–AuNP system (Ren, X.; et al., Spectrosc. Lett., 2016, 49, 434−443). The following molecular modeling suggests that LPS molecules mainly interact with three segments of REG3A amino acid sequences, i.e., P109–T110–Q111–G112, P115–N116, and P137–S138–T139. The latter two protein–ligand interactions impair the REG3A–REG3A protein–protein interaction between the two subunits (E114–P115–N116–G117–E118 and N136–P137–S138–T139–I140). Thus, our results elucidate the LPS inhibitory effect on fibrous protein self-aggregation at the AuNP surface, and molecular dockings give a plausible mechanism to rationalize the competition among protein–protein and protein–ligand interactions.
Gemcitabine is a widely employed first-line chemotherapeutic drug for pancreatic cancer (PCa). However, the rapid emergence of gemcitabine resistance poses a major clinical hurdle. Here, we identified REG3A as a crucial determinant of poor prognosis in PCa. Notably, REG3A was upregulated in tumor tissues from clinical gemcitabine-resistant PCa patients. Through comprehensive in vitro cellular assays and in vivo studies using Reg3g (the murine homolog of REG3A) knockout mice, we demonstrated that REG3A deficiency sensitized PCa to gemcitabine treatment. Mechanistically, RNA sequencing (RNA-Seq) combined with Protein-Protein Interaction (PPI) analysis revealed that REG3A functioned as an exocytosis protein binds to the novel membrane receptor GPR54. The interaction increased membrane localization of GPR54, which subsequently engaged ARRB2 as a scaffolding molecule, leading to activation of the ERK1/2 pathway and suppression of gemcitabine-induced apoptosis. Moreover, the GPR54 agonist KP10 synergistically enhanced gemcitabine resistance in conjunction with REG3A, while interference with GPR54 or its antagonist KP234 attenuated REG3A-induced gemcitabine resistance. Targeting REG3A or pharmacologically inhibiting its downstream signaling molecules may represent a promising strategy to overcome gemcitabine resistance. Overall, REG3A could serve as a potential biomarker for gemcitabine resistance in PCa, offering a new avenue for therapeutic intervention and patient stratification.
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