ERG and CHD1 heterogeneity in prostate cancer: Use of confocal microscopy in assessment of microscopic foci

Abstract

Background Biomarkers predicting tumor response are important to emerging targeted therapeutics. Complimentary methods to assess and understand genetic changes and heterogeneity within only few cancer cells in tissue will be a valuable addition for assessment of tumors such as prostate cancer that often have insufficient tumor for next generation sequencing in a single biopsy core. Methods Using confocal microscopy to identify cell-to-cell relationships in situ, we studied the most common gene rearrangement in prostate cancer (TMPRSS2 and ERG) and the tumor suppressor CHD1 in 56 patients who underwent radical prostatectomy. Contingency tables and the chi-square test were used to determine associations between mutation status of the genes and tumor phenotype. Results Wild type ERG was found in 22 of 56 patients; ERG copy number was increased in 10/56, and ERG rearrangements confirmed in 24/56 patients. In 24 patients with ERG rearrangements, the mechanisms of rearrangement were heterogeneous, with deletion in 14/24, a split event in 7/24, and both deletions and split events in the same tumor focus in 3/24 patients. Overall, 14/45 (31.1%) of patients had CHD1 deletion, with the majority of patients with CHD1 deletions (13/14) correlating with ERG-rearrangement negative status (p< 0.01). Conclusions These results demonstrate the ability of confocal microscopy and FISH to identify the cell-to-cell differences in common gene fusions such as TMPRSS2–ERG that may arise independently within the same tumor focus. These data support the need to study complimentary approaches to assess genetic changes that may stratify therapy based on predicted sensitivities.

ERG-Mediated Cell Invasion: A Link between Development and Tumorigenesis

“…Similarly for ERG , a chromosomal translocation will result in fusion of TMPRSS2 and ERG . Because these two genes are located on the same arm of chromosome 21, a deletion of the region between TMPRSS2 (21q22.2) and ERG (21q22.3) can also result in fusion [50]. Previous studies suggest a role for chromodomain helicase DNA-binding protein 1 (CHD1) in the formation of the rearrangement.…”

“…CHD1 binds to H3K4-trimethylated histones and remodels chromatin with high levels of this transcriptionally active histone mark. In prostate cancer, CHD1 is often deleted or mutated, and, intriguingly, the CHD1 loss is only detected in ERG-negative prostate cancers [50,51]. Mechanistic studies suggest that chromatin remodeling mediated by CHD1 allows the activation of androgen receptor target genes such as TMPRSS2 , and that consistently open chromatin at these loci increases the likelihood of chromosomal breaks and induces rearrangements that could produce aberrant gene fusions [51].…”

Precision Medicine: Implications for Science and Practice

“…Although there are many published examples, an assessment of tumor heterogeneity that we performed in over 50 patients with prostate cancer found genomic differences in ERG and CHD1 genes by fluorescence in situ hybridization (FISH) and confocal microscopy, suggesting significant heterogeneity even within a single tumor focus (24). As a potential clinical example supporting the hypothesis that more multi-targeted approaches to therapy can improve outcomes, a phase III trial was designed through the Eastern Cooperative Oncology Group (including one of the authors-RSD) to evaluate the combination of up-front docetaxel chemotherapy combined with androgen ablation compared with standard "single-target" androgen ablation in patients with advanced prostate cancer (25).…”

The Chromodomain Helicase DNA-Binding Chromatin Remodelers: Family Traits that Protect from and Promote Cancer

“…But the most striking evidence for CHD1 inactivation is in prostate cancer, where it is deleted or mutated (Grasso et al 2012; Huang et al 2012; Liu et al 2012; Burkhardt et al 2013; Martin et al 2013; Blattner et al 2014; Gao et al 2014; Scott et al 2014; Tereshchenko et al 2014; Attard et al 2015; Fisher et al 2015; Sowalsky et al 2015). Indeed, homozygous deletion of CHD1 is the second most common genetic event in prostate cancer after PTEN deletion (Liu et al 2012).…”

“…Chromosome rearrangements that cause overexpression of ETS family members, most commonly translocations between the androgen-regulated gene TMPRSS2 and the ERG gene, are frequent in some types of prostate cancer (Clark and Cooper 2009). CHD1 lesions occur in ETS fusion-negative prostate cancer (Grasso et al 2012; Martin et al 2013; Tereshchenko et al 2014), indicating that the CHD1 status defines a unique prostate cancer subtype (Attard et al 2015; Fisher et al 2015). Whereas CHD1 mutation and ETS fusions are mutually exclusive, CHD1 inactivation co-occurs with speckle type PTB/POZ protein (SPOP) mutations (Blattner et al 2014) and MAP3K7 deletion (Rodrigues et al 2015), suggesting that these lesions cooperate with CHD1 loss to drive tumorigenesis in the prostate.…”