Dynamic interaction of HMGA1a proteins with chromatin

Abstract

High-mobility-group proteins A1 (HMGA1; previously named HMGI/Y) function as architectural chromatin-binding proteins and are involved in the transcriptional regulation of several genes. We have used cells expressing proteins fused to green fluorescent protein (GFP) and fluorescence recovery after photobleaching (FRAP) to analyze the distribution and dynamics of HMGA1a in vivo. HMGA1-GFP proteins localize preferentially to heterochromatin and remain bound to chromosomes during mitosis. FRAP experiments showed that they are highly mobile components of euchromatin, heterochromatin and of mitotic chromosomes, although with different resident times. For a more-detailed investigation on the interaction of HMGA1a with chromatin, the contribution of the AT-hook DNA-binding motifs was analyzed using point-mutated HMGA1a-GFP proteins. Furthermore, by inhibiting kinase or histone deacetylase activities, and with the help of fusion proteins lacking specific phosphorylation sites, we analyzed the effect of reversible modifications of HMGA1a on chromatin binding. Collectively our data show that the kinetic properties of HMGA1a proteins are governed by the number of functional AT-hooks and are regulated by specific phosphorylation patterns. The higher residence time in heterochromatin and chromosomes, compared with euchromatic regions, correlates with an increased phosphorylation level of HMGA1a. The regulated dynamic properties of HMGA1a fusion proteins indicate that HMGA1 proteins are mechanistically involved in local and global changes in chromatin structure.

LHP1, the Arabidopsis homologue of HETEROCHROMATIN PROTEIN1, is required for epigenetic silencing of FLC

“…However, the continued association of VRN1 with chromosomes all the way through mitosis was unexpected. Most Polycomb, Polycomb-associated proteins, and transcription factors have been found to be displaced from their recognition sequences during mitosis (43-47); however, some do remain, including Drosophila GAGA factor and Pipsqueak, which function as sequence-specific binding proteins and are involved in recruitment of Polycomb complexes to the Polycomb response element and high-mobility-group proteins, which bind DNA non-sequence-specifically (48)(49)(50)(51)(52). Knowledge of VRN1 interactors may help elucidate why it remains associated during mitosis and the significance of this finding for epigenetic stability of FLC silencing.…”

Chinese hamster ORC subunits dynamically associate with chromatin throughout the cell-cycle

“…The rapid in vivo exchange rates appear to be a result of several factors, including: the active displacement of proteins by another copy of the same protein, the presence of chromatin remodeling complexes that actively displace proteins, ATP levels and post-translation modifications [60][61][62][63][64][65][66][67][68][69]. In addition, decreasing the temperature at which the cells are photobleached results in reduced protein mobility [60,66,70].…”

Upregulation of HMGA2 in thyroid carcinomas: A novel molecular marker to distinguish between benign and malignant follicular neoplasias

“…The high mobility group A (HMGA) proteins are small chromatin associated nonhistone proteins that act as architectural transcription factors (Wolffe, 1994;Bustin and Reeves, 1996). HMGA proteins have three DNA-binding domains designated as AT-hooks, enabling their binding to the minor groove of AT-rich DNA, and an acidic C-tail responsible for protein-protein interactions (Reeves and Nissen, 1990;Chau et al, 1995;Harrer et al, 2004;Reeves and Beckerbauer, 2005). The interaction of HMGA with DNA leads to changes in chromatin structure involving HMGA proteins in the regulation of the expression of a high number of target genes.…”