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Heat shock transcription factors demonstrate a distinct mode of interaction with mitotic chromosomes

ABSTRACT: A large number of transcription factors have been shown to bind and interact with mitotic chromosomes, which may promote the efficient reactivation of transcriptional programs following cell division. Although the DNA-binding domain (DBD) contributes strongly to TF behavior, the mitotic behaviors of TFs from the same DBD family may vary. To define the mechanisms governing TF behavior during mitosis in mouse embryonic stem cells, we examined two related TFs: Heat Shock Factor 1 and 2 (HSF1 and HSF2). We found that HSF2 maintains site-specific binding genome-wide during mitosis, whereas HSF1 binding is somewhat decreased. Surprisingly, live-cell imaging shows that both factors appear excluded from mitotic chromosomes to the same degree, and are similarly more dynamic in mitosis than in interphase. Exclusion from mitotic DNA is not due to extrinsic factors like nuclear import and export mechanisms. Rather, we found that the HSF DBDs can coat mitotic chromosomes, and that HSF2 DBD is able to establish site-specific binding. These data further confirm that site-specific binding and chromosome coating are independent properties, and that for some TFs, mitotic behavior is largely determined by the non-DBD regions.

ORGANISM(S): Mus musculus

PROVIDER: GSE214219 | GEO | 2023/04/28

REPOSITORIES: GEO

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Project description:Prostate cancer (PrCa) is one of the most common malignancies in Western countries. However, the pathways that promote invasion, especially in late-stage castration-resistant PrCa (CRPC), are poorly understood. Heat shock factors (HSFs) are transcriptional regulators essential for cell survival upon proteotoxic stress, and HSF1 is also identified as a driver of oncogenesis. Here, our aim was to elucidate the molecular mechanisms that contribute to CRPC and invasion. In silico analyses showed that high HSF1 expression levels correlate with poor survival and high Gleason score in PrCa. In the same data set, HSF2, which has not previously been linked to cancer, displayed decreased expression. Using 3-dimensional (3D) organotypic PrCa cultures that spontaneously undergo an invasive conversion, opposite effects of HSF1 and HSF2 were observed; tumor spheroids lacking HSF1 grew slowly, were polarized and devoid of invasive structures, and depletion of HSF2 potentiated invasiveness. In the in vivo xenograft chorioallantoic membrane model, HSF1 silencing caused tumor regression and fibrosis, and knockdown of HSF2 generated large invasive tumors, verifying the results from the 3D-cultures. Gene expression profiling revealed enrichment of genes connected to translational control when either HSF1 or HSF2 was silenced. HSF1-specific targets were associated with progression of tumorigenesis, whereas HSF2 targets were involved in focal adhesion, critical for invasion. This study provides the first evidence for HSF2 functioning in cancer, i.e. as a tumor suppressor. Moreover, human PrCa tissue microarrays demonstrated increased nuclear HSF1 expression, which significantly correlated with high-grade Gleason score. Cytoplasmic HSF1 was detected in a subset of tumors and intriguingly, correlated with decreased disease-specific survival. This was most pronounced in intermediate Gleason score 7 tumors and in metastases. We propose the use of HSF1 as a biomarker to predict PrCa outcome, thus facilitating clinical decision-making and supporting individualized treatment choices. HSF1 and HSF2 siRNA transfection was performed in triplicates (biological replicates), for 5 and 8 days prior to harvesting total RNA; and compared to PC-3 cells transfected with scrambled control siRNAs for 5 and 8 days, respectively.

Project description:During mitosis, RNA polymerase and most transcription factors are excluded from the chromosomes and transcription ceases. The transcriptional re-activation of the genome, following mitosis, requires the re-setting of cell-type specific programs that were initially established during development. However, only about one-fifth of transcription factors are retained on chromosomes throughout mitosis and a subset of these have been shown to facilitate target gene reactivation during mitotic exit. How such “bookmarking” factors bind to chromatin in mitosis and re-activate transcription is central to the stability of transcriptional programs across multiple cell cycles. We compared a diverse set of transcription factors involved in liver differentiation and found different modes of mitotic chromosome binding. The pioneer transcription factor FoxA1, which is among the first to bind liver genes in development, exhibits virtually complete mitotic chromosome binding, whereas other liver factors bind with a range of efficiencies. Yet genome-wide analysis shows that only about 15% of the FoxA1 interphase target sites are bound in mitosis; the latter include sites at genes for maintaining cell differentiation. FoxA1 mutants that perturb specific and nonspecific DNA binding reveal a significant contribution of nonspecific binding events in mitotic chromatin. Such nonspecific binding appears to spread from interphase FoxA1 targets and may serve as storage sites. The hierarchy of specific binding, nonspecific binding, partial chromatin binding, and failure to bind mitotic chromosomes reflects the temporal sequence of the factors’ developmental roles in gene activation. Gene expression was assessed in asynchronously cycling cells in order to determine whether FoxA1 is disposed to bind to high- or low-expressed genes during mitosis. Heatmap analysis shows that FoxA1's mitotic targets are among the highest-expressed genes in asynchronous cells. Total RNA was collected from three different plates with asynchronous HUH7 cells using the RNeasy mini kit (Qiagen Valencia CA). Expression microarrays were performed with a Human Gene 1.OST array (Affymetrix) at the UPenn Microarray Core Facility and assessed using Partek.

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Heat shock transcription factors demonstrate a distinct mode of interaction with mitotic chromosomes

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