Distinct Properties of Human HMGN5 Reveal a Rapidly Evolving but Functionally Conserved Nucleosome Binding Protein

Abstract

The HMGN family is a family of nucleosome-binding architectural proteins that affect the structure and function of chromatin in vertebrates. We report that the HMGN5 variant, encoded by a gene located on chromosome X, is a rapidly evolving protein with an acidic C-terminal domain that differs among vertebrate species. We found that the intranuclear organization and nucleosome interactions of human HMGN5 are distinct from those of mouse HMGN5 and that the C-terminal region of the protein is the main determinant of the chromatin interaction properties. Despite their apparent differences, both mouse and human HMGN5 proteins interact with histone H1, reduce its chromatin residence time, and can induce large-scale chromatin decompaction in living cells. Analysis of HMGN5 mutants suggests that distinct domains in HMGN5 affect specific steps in the interaction of H1 with chromatin. Elevated levels of either human or mouse HMGN5 affect the transcription of numerous genes, most in a variant-specific manner. Our study identifies HMGN5 as a rapidly evolving vertebrate nuclear protein with species-specific properties. HMGN5 has a highly disordered structure, binds dynamically to nucleosome core particles, modulates the binding of H1 to chromatin, reduces the compaction of the chromatin fiber, and affects transcription.

Growth Cone Localization of the mRNA Encoding the Chromatin Regulator HMGN5 Modulates Neurite Outgrowth

“…Indeed, in line with previous observations in different cell types (22,42), we show that HMGN5 overexpression affects chromatin structure in both neuroblastoma cells as well as hippocampal neurons (Fig. 5 and 9).…”

“…supporting the physiological relevance of the magnitude of the effect we observe in N1E-115 cells (22). These results suggest that growth cone mRNA localization and translation influence HMGN5 phosphorylation and chromatin binding properties to regulate neurite outgrowth in N1E-115 cells.…”

“…5C and E), indicating a rearrangement of heterochromatin. Fluorescence recovery after photobleaching (FRAP) and cross-linking experiments have previously revealed that HMGN5 interacts with linker histone H1 and reduces its binding to chromatin (22,42). To test whether this was also the case in N1E-115 cells, we performed FRAP experiments on cells expressing both histone H1-GFP and HMGN5 ( Fig.…”

“…For generating FISH probes, the 3=-UTR sequence of Hmgn5 and the coding sequence of EGFP were cloned into pBluescript II KS(ϩ/Ϫ) (Agilent Technologies). The EGFP-H1 construct was described previously (22), while the HMGN5-mRuby2 expression constructs were obtained by cloning the mRuby2 coding sequence in the place of EGFP in the HMGN5-GFP expression constructs. All primers used for cloning are listed in Table S1 in the supplemental material.…”

High Mobility Group Protein N5 (HMGN5) and Lamina-associated Polypeptide 2α (LAP2α) Interact and Reciprocally Affect Their Genome-wide Chromatin Organization

“…These associations could conceivably affect the chromatin interactions and function of HMGNs. Here we report that the human HMGN5 variant (10) interacts with the lamina-associated polypeptide 2␣ (LAP2␣). LAP2␣ is a LEM domain protein that interacts with A-type lamins (11).…”