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Stress-induced transcription of satellite III repeats.

Jolly C, Metz A, Govin J, Vigneron M, Turner BM, Khochbin S, Vourc'h C - J. Cell Biol. (2003)

Bottom Line: These stress-induced structures, which form primarily on the 9q12 region in humans through direct binding of HSF1 to satellite III repeats, do not colocalize with transcription sites of known hsp genes.In this paper, we show that nuclear stress granules correspond to RNA polymerase II transcription factories where satellite III repeats are transcribed into large and stable RNAs that remain associated with the 9q12 region, even throughout mitosis.This work not only reveals the existence of a new major heat-induced transcript in human cells that may play a role in chromatin structure, but also provides evidence for a transcriptional activity within a locus considered so far as heterochromatic and silent.

View Article: PubMed Central - PubMed

Affiliation: INSERM U309, Institut A. Bonniot, 38706 La Tronche cedex, France. caroline.jolly@ujf-grenoble.fr

ABSTRACT
Exposure of mammalian cells to stress induces the activation of heat shock transcription factor 1 (HSF1) and the subsequent transcription of heat shock genes. Activation of the heat shock response also correlates with a rapid relocalization of HSF1 within a few nuclear structures termed nuclear stress granules. These stress-induced structures, which form primarily on the 9q12 region in humans through direct binding of HSF1 to satellite III repeats, do not colocalize with transcription sites of known hsp genes. In this paper, we show that nuclear stress granules correspond to RNA polymerase II transcription factories where satellite III repeats are transcribed into large and stable RNAs that remain associated with the 9q12 region, even throughout mitosis. This work not only reveals the existence of a new major heat-induced transcript in human cells that may play a role in chromatin structure, but also provides evidence for a transcriptional activity within a locus considered so far as heterochromatic and silent.

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Stress-induced HSF1 granules contain acetylated core histones. HSF1 (green) and acetylated forms of each core histone (red) were codetected by immunofluorescence in HeLa cells submitted or not to a 1-h heat shock at 42°C. At 37°C, HSF1 is diffusely distributed in the nucleus and cytoplasm, and acetylated histones exhibit a punctate distribution throughout the nucleus. After heat shock, acetylated forms of the four core histones are present to various extents within stress granules. Bar, 5 μm.
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fig2: Stress-induced HSF1 granules contain acetylated core histones. HSF1 (green) and acetylated forms of each core histone (red) were codetected by immunofluorescence in HeLa cells submitted or not to a 1-h heat shock at 42°C. At 37°C, HSF1 is diffusely distributed in the nucleus and cytoplasm, and acetylated histones exhibit a punctate distribution throughout the nucleus. After heat shock, acetylated forms of the four core histones are present to various extents within stress granules. Bar, 5 μm.

Mentions: As this local concentration of RNA polymerase II does not necessarily reveal a transcriptional activity of the locus, we next looked for the presence of another marker of transcription within the granules, i.e., hyperacetylated histones. Indeed, transcription activation correlates with an increase in core histone acetylation of the transcribed region (for reviews see Turner, 2002; Fischle et al., 2003). We thus performed immunofluorescence on non–heat-shocked and heat-shocked cells with a panel of specific antibodies (Turner and Fellows, 1989; White et al., 1999): H2A acetylated on K5 (H2Aac), H2B acetylated on K12 and K15 (H2Bac), H3 acetylated on K9 and K18 (H3ac), and H4 acetylated on K5, K8, K12, and/or K16 (H4ac). Results are shown in Fig. 2. At 37°C, a punctate nuclear distribution was observed with all four antibodies. In heat-shocked cells, a diffuse labeling of the nucleoplasm was still observed. In addition, most of the cells displayed nuclear accumulation sites of acetylated histones that colocalize with nuclear stress granules as shown by the codetection of HSF1 in these cells. Immunofluorescence with an antibody to the unmodified form of H2B confirmed that our observations were not merely due to a higher density of histones within stress granules (unpublished data). Interestingly, we did not find accumulation of H3 phosphorylated on serine 10 as described for transcribing heat-shock puffs on Drosophila polytene chromosomes (Nowak and Corces, 2000; Labrador and Corces, 2003), perhaps because human chromosome 9 sat III repeats are not structured as a canonical heat-shock promoter (unpublished data). Thus, nuclear stress granules contain acetylated core histones.


Stress-induced transcription of satellite III repeats.

Jolly C, Metz A, Govin J, Vigneron M, Turner BM, Khochbin S, Vourc'h C - J. Cell Biol. (2003)

Stress-induced HSF1 granules contain acetylated core histones. HSF1 (green) and acetylated forms of each core histone (red) were codetected by immunofluorescence in HeLa cells submitted or not to a 1-h heat shock at 42°C. At 37°C, HSF1 is diffusely distributed in the nucleus and cytoplasm, and acetylated histones exhibit a punctate distribution throughout the nucleus. After heat shock, acetylated forms of the four core histones are present to various extents within stress granules. Bar, 5 μm.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171959&req=5

fig2: Stress-induced HSF1 granules contain acetylated core histones. HSF1 (green) and acetylated forms of each core histone (red) were codetected by immunofluorescence in HeLa cells submitted or not to a 1-h heat shock at 42°C. At 37°C, HSF1 is diffusely distributed in the nucleus and cytoplasm, and acetylated histones exhibit a punctate distribution throughout the nucleus. After heat shock, acetylated forms of the four core histones are present to various extents within stress granules. Bar, 5 μm.
Mentions: As this local concentration of RNA polymerase II does not necessarily reveal a transcriptional activity of the locus, we next looked for the presence of another marker of transcription within the granules, i.e., hyperacetylated histones. Indeed, transcription activation correlates with an increase in core histone acetylation of the transcribed region (for reviews see Turner, 2002; Fischle et al., 2003). We thus performed immunofluorescence on non–heat-shocked and heat-shocked cells with a panel of specific antibodies (Turner and Fellows, 1989; White et al., 1999): H2A acetylated on K5 (H2Aac), H2B acetylated on K12 and K15 (H2Bac), H3 acetylated on K9 and K18 (H3ac), and H4 acetylated on K5, K8, K12, and/or K16 (H4ac). Results are shown in Fig. 2. At 37°C, a punctate nuclear distribution was observed with all four antibodies. In heat-shocked cells, a diffuse labeling of the nucleoplasm was still observed. In addition, most of the cells displayed nuclear accumulation sites of acetylated histones that colocalize with nuclear stress granules as shown by the codetection of HSF1 in these cells. Immunofluorescence with an antibody to the unmodified form of H2B confirmed that our observations were not merely due to a higher density of histones within stress granules (unpublished data). Interestingly, we did not find accumulation of H3 phosphorylated on serine 10 as described for transcribing heat-shock puffs on Drosophila polytene chromosomes (Nowak and Corces, 2000; Labrador and Corces, 2003), perhaps because human chromosome 9 sat III repeats are not structured as a canonical heat-shock promoter (unpublished data). Thus, nuclear stress granules contain acetylated core histones.

Bottom Line: These stress-induced structures, which form primarily on the 9q12 region in humans through direct binding of HSF1 to satellite III repeats, do not colocalize with transcription sites of known hsp genes.In this paper, we show that nuclear stress granules correspond to RNA polymerase II transcription factories where satellite III repeats are transcribed into large and stable RNAs that remain associated with the 9q12 region, even throughout mitosis.This work not only reveals the existence of a new major heat-induced transcript in human cells that may play a role in chromatin structure, but also provides evidence for a transcriptional activity within a locus considered so far as heterochromatic and silent.

View Article: PubMed Central - PubMed

Affiliation: INSERM U309, Institut A. Bonniot, 38706 La Tronche cedex, France. caroline.jolly@ujf-grenoble.fr

ABSTRACT
Exposure of mammalian cells to stress induces the activation of heat shock transcription factor 1 (HSF1) and the subsequent transcription of heat shock genes. Activation of the heat shock response also correlates with a rapid relocalization of HSF1 within a few nuclear structures termed nuclear stress granules. These stress-induced structures, which form primarily on the 9q12 region in humans through direct binding of HSF1 to satellite III repeats, do not colocalize with transcription sites of known hsp genes. In this paper, we show that nuclear stress granules correspond to RNA polymerase II transcription factories where satellite III repeats are transcribed into large and stable RNAs that remain associated with the 9q12 region, even throughout mitosis. This work not only reveals the existence of a new major heat-induced transcript in human cells that may play a role in chromatin structure, but also provides evidence for a transcriptional activity within a locus considered so far as heterochromatic and silent.

Show MeSH
Related in: MedlinePlus