Discovering high mobility group A molecular partners in tumour cells

Abstract

DNA-based activities rely on an extremely coordinated sequence of events performed by several chromatin-associated proteins which act in concert. High Mobility Group A (HMGA) proteins are non-histone architectural nuclear factors that participate in the regulation of specific genes but they are also believed to have a more general role in chromatin dynamics. The peculiarity of these proteins is their flexibility, both in terms of DNA-binding and in protein-protein interactions. Since these proteins act as core elements in the assembly of multiprotein complexes called enhanceosomes, and have already displayed the ability to interact with several different proteins, we started a proteomic approach for the systematic identification of their molecular partners. By a combination of affinity chromatography, two-dimensional gel electrophoresis and mass spectrometry we have identified about twenty putative HMGA interactors which could be roughly assigned to three different classes: mRNA processing proteins, chromatin remodelling related factors and structural proteins. Direct HMGA interaction with some of these proteins was confirmed by glutathione-S-transferase pull-down assays and the HMGA domain involved was mapped. Blot-overlay experiments reveal that members of the HMGA family share most of their molecular partners but, interestingly, it seems that there are some cell-type specific partners. Taken together, these experimental data indicate that HMGA proteins are highly connected nodes in the chromatin protein network. Since these proteins are strongly implicated with cancer development, the identification of molecules able to perturb the HMGA molecular network could be a possible tool to interfere with their oncogenic activity.

HMGA1 Inhibits the Function of p53 Family Members in Thyroid Cancer Cells

“…One microgram of each of the HMGA1 recombinant proteins was separated by SDS-PAGE and transferred to polyvinylidene difluoride membrane. Far Westerns were then carried out as previously described (36).…”

“…Because HMGA proteins have been shown to associate with and modulate the activity of several nuclear factors (1,2,36), here, we have explored whether HMGA may also influence the function of p53 family members. We found that HMGA1 associates in vivo with p53 family members, and that this interaction results in the inhibition of their tumor suppressor activity in thyroid cancer cells.…”

HMG chromosomal proteins in development and disease

“…It is likely that the ability of HMGA to participate in several type of processes is conferred by their interaction with a wide range of partners, including transcription factors, components of the splicing machinery, proteins involved in replication and chromatin assembly factors [26].…”

Epigenetic regulation of aging stem cells

“…Decreased NSC proliferation in the adult SVZ with age may thus be due, in part, to the observed decrease in the expression of Hmga2 in freshly isolated SVZ cells, which are enriched in neural stem and progenitors (Nishino et al, 2008). Although the role of HMGA2 in modulating chromatin structure in adult stem cells has not yet been addressed, studies in human fibroblasts suggest that HMGA2 alters chromatin compaction (Narita et al, 2006) or may complex with other structural chromatin-associated proteins (Sgarra et al, 2005(Sgarra et al, , 2008. Likely, decreasing levels of Hmga2 during aging (Nishino et al, 2008) results in altered chromatin compaction that either silences key stem cell proliferation genes or inappropriately activates genes, such p16 INK4a /p19 ARF , that limit stem cell function.…”