PML nuclear bodies are highly organised DNA-protein structures with a function in heterochromatin remodelling at the G2 phase

Abstract

We have recently demonstrated that heterochromatin HP1 proteins are aberrantly distributed in lymphocytes of patients with immunodeficiency, centromeric instability and facial dysmorphy (ICF) syndrome. The three HP1 proteins accumulate in one giant body over the 1qh and 16qh juxtacentromeric heterochromatins, which are hypomethylated in ICF. The presence of PML (promyelocytic leukaemia) protein within this body suggests it to be a giant PML nuclear body (PML-NB). The structural integrity of PML-NBs is of major importance for normal cell functioning. Nevertheless, the structural organisation and the functions of these nuclear bodies remain unclear. Here, we take advantage of the large size of the giant body to demonstrate that it contains a core of satellite DNA with proteins being organised in ordered concentric layers forming a sphere around it. We extend these results to normal PML-NBs and propose a model for the general organisation of these structures at the G2 phase. Moreover, based on the presence of satellite DNA and the proteins HP1, BRCA1, ATRX and DAXX within the PML-NBs, we propose that these structures have a specific function: the re-establishment of the condensed heterochromatic state on late-replicated satellite DNA. Our findings that chromatin-remodelling proteins fail to accumulate around satellite DNA in PML-deficient NB4 cells support a central role for PML protein in this cellular function.

Probing PML body function in ALT cells reveals spatiotemporal requirements for telomere recombination

“…Our observations suggest a structural model according to which APBs are organized, similarly to PML bodies (14), into concentric layers of proteins, PML constituting the outermost layer with which chromosome ends interact (Fig. 3C).…”

“…Nonetheless, these interactions display morphological characteristics that strongly resemble depicted associations of PML with foreign viral DNA (1,30) or with hypomethylated heterochromatic DNA sequences (14). In these cases, and in contrast to telomeres clusters in APBs, the PML protein engulfs the DNA rather than the latter being associated with the surface of the PML body.…”

“…Strikingly, 3D imaging followed by deconvolution analysis revealed that the shelterin protein TRF2, a telomeric marker, no longer forms a unique focus with the PML signal. Instead, multiple TRF2 foci are detected in association with the outermost layer of these APBs, whereas other components of PML bodies, for instance the BLM protein (14), are preferentially associated with the inner layers (Fig. 1A).…”

PML nuclear bodies: Assembly and oxidative stress-sensitive sumoylation

“…7,[25][26][27] Immunoelectron or high resolution confocal analyses indicate that the PML protein forms the outer shell, whereas partner proteins are concentrated in the inner core. 26,[28][29][30] The outer PML shell is associated with the nuclear matrix, a loosely defined, insoluble nuclear scaffold that is resistant to nuclease and high salt extraction and thought to support nuclear organization and compartmentalization. 31,32 Over the course of many years, a growing number of functionally distinct proteins and enzymes were shown to be recruited into PML NBs, notably p53 and many of its regulatory enzymes.…”

Patient mutations alter ATRX targeting to PML nuclear bodies

“…Indeed, it has been postulated that the association of satellite DNA with ATRX, Daxx and HP1 within PML-NBs at the G 2 phase may facilitate reestablishment of condensed heterochromatin at satellite DNA. 35 Certainly, one could speculate that proper targeting of ATRX to PML-NBs is essential for ATRX-directed chromatin remodeling of specific target genes tagged for silencing during neural development. Mutations located within the SNF2 domain may attenuate (but not abolish) the chromatin-remodeling activity and/or the localization to the PML-NB such that the ATRX-specific target genes are derepressed.…”