S100A6 and Its Brain Ligands in Neurodegenerative Disorders

The S100A6 protein is present in different mammalian cells and tissues including the brain. It binds Ca2+ and Zn2+ and interacts with many target proteins/ligands. The best characterized ligands of S100A6, expressed at high level in the brain, include CacyBP/SIP and Sgt1. Research concerning the functional role of S100A6 and these two ligands indicates that they are involved in various signaling pathways that regulate cell proliferation, differentiation, cytoskeletal organization, and others. In this review, we focused on the expression/localization of these proteins in the brain and on their possible role in neurodegenerative diseases. Published results demonstrate that S100A6, CacyBP/SIP, and Sgt1 are expressed in various brain structures and in the spinal cord and can be found in different cell types including neurons and astrocytes. When it comes to their possible involvement in nervous system pathology, it is evident that their expression/level and/or subcellular localization is changed when compared to normal conditions. Among diseases in which such changes have been observed are Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), epileptogenesis, Parkinson’s disease (PD), Huntington’s disease (HD), and others.

S100A6 promotes proliferation and migration of HepG2 cells via increased ubiquitin-dependent degradation of p53

PurposeS100A6 protein (calcyclin), a small calcium-binding protein of the S100 family, is often upregulated in various types of cancers, including hepatocellular carcinoma (HCC). The aim of this study was to illustrate the molecular mechanism of S100A6 in regulating the proliferation and migration of HCC cells.MethodsThe expressions of S100A6 in human HCC and adjacent non-tumor liver specimens were detected using immunoblotting and quantitative PCR (qPCR). The recombinant glutathione S-transferase (GST)-tagged human S100A6 protein was purified and identified. After treatment with S100A6, the proliferation of HepG2 cells was detected by the MTT and colony formation assay, and the migration of HepG2 cells was investigated by the transwell migration assay; the protein levels of cyclin D1 (CCND1), E-cadherin, and vimentin were also tested by immunoblotting. The effect of S100A6 on p21 and nuclear factor-κB pathway was verified by performing the dual luciferase assay. Then, the expression of p21 and its transcription activator, p53, was examined using immunoblotting and qPCR, the ubiquitination of which was investigated through co-immunoprecipitation.ResultsIt was found that the level of S100A6 was higher in the HCC tissues than in the adjacent non-tumor liver specimens. Exogenous overexpression of S100A6 promoted the proliferation and migration of HepG2 cells. S100A6 was observed to regulate p21 mRNA and protein expression levels and decrease p53 protein expression level, not mRNA level, by promoting the ubiquitination of p53 via the proteasome-dependent degradation pathway.ConclusionOur study indicated that S100A6 overexpression could promote the proliferation and migration of HCC cells by enhancing p53 ubiquitin-dependent proteasome degradation, ultimately regulating the p21 expression level.