Identification and Biochemical Characterization of High Mobility Group Protein 20A as a Novel Ca2+/S100A6 Target

The H2A.Z and NuRD associated protein HMG20A controls early head and heart developmental transcription programs

Specialized chromatin-binding proteins are required for DNA-based processes during development. We recently established PWWP2A as a direct histone variant H2A.Z interactor involved in mitosis and craniofacial development. Here, we identify the H2A.Z/PWWP2A-associated protein HMG20A as part of several chromatin-modifying complexes, including NuRD, and show that it localizes to distinct genomic regulatory regions. Hmg20a depletion causes severe head and heart developmental defects in Xenopus laevis. Our data indicate that craniofacial malformations are caused by defects in neural crest cell (NCC) migration and cartilage formation. These developmental failures are phenocopied in Hmg20a-depleted mESCs, which show inefficient differentiation into NCCs and cardiomyocytes (CM). Consequently, loss of HMG20A, which marks open promoters and enhancers, results in chromatin accessibility changes and a striking deregulation of transcription programs involved in epithelial-mesenchymal transition (EMT) and differentiation processes. Collectively, our findings implicate HMG20A as part of the H2A.Z/PWWP2A/NuRD-axis and reveal it as a key modulator of intricate developmental transcription programs that guide the differentiation of NCCs and CMs.

S100A6 Protein-Expression and Function in Norm and Pathology

S100A6, also known as calcyclin, is a calcium-binding protein belonging to the S100 protein family. It was first identified and purified more than 30 years ago. Initial structural studies, focused mostly on the mode and affinity of Ca²⁺ binding and resolution of the resultant conformational changes, were soon complemented by research on its expression, localization and identification of binding partners. With time, the use of biophysical methods helped to resolve the structure and versatility of S100A6 complexes with some of its ligands. Meanwhile, it became clear that S100A6 expression was altered in various pathological states and correlated with the stage/progression of many diseases, including cancers, indicative of its important, and possibly causative, role in some of these diseases. This, in turn, prompted researchers to look for the mechanism of S100A6 action and to identify the intermediary signaling pathways and effectors. After all these years, our knowledge on various aspects of S100A6 biology is robust but still incomplete. The list of S100A6 ligands is growing all the time, as is our understanding of the physiological importance of these interactions. The present review summarizes available data concerning S100A6 expression/localization, interaction with intracellular and extracellular targets, involvement in Ca²⁺-dependent cellular processes and association with various pathologies.