Modifying effects of carboxyl group on the interaction of recombinant S100A8/A9 complex with tyrosinase

Toward an understanding of the conformational plasticity of S100A8 and S100A9 Ca2+-binding proteins

S100A8 and S100A9 are small, human, Ca²⁺-binding proteins with multiple intracellular and extracellular functions in signaling, regulation, and defense. The two proteins are not detected as monomers but form various noncovalent homo- or hetero-oligomers related to specific activities in human physiology. Because of their significant roles in numerous medical conditions, there has been intense research on the conformational properties of various S100A8 and S100A9 proteoforms as essential targets of drug discovery. NMR or crystal structures are currently available only for mutated or truncated protein complexes, mainly with bound metal ions, that may well reflect the proteins' properties outside cells but not in other biological contexts in which they perform. Here, we used structural mass spectrometry methods combined with molecular dynamics simulations to compare the conformations of wild-type full-length S100A8 and S100A9 subunits in biologically relevant homo- and hetero-dimers and in higher oligomers formed in the presence of calcium or zinc ions. We provide, first, rationales for their functional response to changing environmental conditions, by elucidating differences between proteoforms in flexible protein regions that may provide the plasticity of the binding sites for the multiple targets, and second, the key factors contributing to the variable stability of the oligomers. The described methods and a systematic view of the conformational properties of S100A8 and S100A9 complexes provide a basis for further research to characterize and modulate their functions for basic science and therapies.

Calprotectin (S100A8/S100A9): a key protein between inflammation and cancer

BACKGROUND

Calprotectin (S100A8/S100A9), a heterodimeric EF-hand Ca²⁺ binding protein, are abundant in cytosol of neutrophils and are involved in inflammatory processes and several cancerous pathogens.

OBJECTIVE

The purpose of the present systematic review is to evaluate the pro- and anti-tumorigenic functions of calprotectin and its relation to inflammation.

MATERIALS AND METHODS

We conducted a review of studies published in the Medline (1966-2018), Scopus (2004-2018), ClinicalTrials.gov (2008-2018) and Google Scholar (2004-2018) databases, combined with studies found in the reference lists of the included studies.

RESULTS

Elevated levels of S100A8/S100A9 were detected in inflammation, neoplastic tumor cells and various human cancers. Recent data have explained that many cancers arise from sites of infection, chronic irritation, and inflammation. The inflammatory microenvironment which largely includes calprotectin, has an essential role on high producing of inflammatory factors and then on neoplastic process and metastasis.

CONCLUSION

Scientists have shown different outcomes in inflammation, malignancy and apoptosis whether the source of the aforementioned protein is extracellular or intracellular. These findings are offering new insights that anti-inflammatory therapeutic agents and anti-tumorigenic functions of calprotectin can lead to control cancer development.

Effect of calprotectin subunit S100A9 on the expression and methylation of OCLN in human melanoma cell line A-375

Increased levels of calprotectin subunits S100A8 and S100A9 have been detected in human cancers. Melanoma is the most aggressive type of skin cancer, and its treatment is challenging because of its brain metastasis. OCLN encodes occluding, which plays a major role in the formation and regulation of tight junctions. The aim of this study was to evaluate the methylation status of the OCLN promoter and its expression in A-375 melanoma cells treated with or without various concentrations of S100A9 for 24, 48, and 72 h. Total RNA was extracted, and synthesized cDNA was assessed by performing real-time PCR. MSP-PCR was performed after treatment with bisultfie. Recombinant S100A9 inhibited the proliferation of the A-375 cell line and the expression of the OCLN gene was downregulated in a time- and concentration-dependent manner. Results of MSP-PCR showed that the OCLN gene promoter in a human melanoma cell line (A-375) was semimethylated.