Progressive Spreading of DNA Methylation in the GSTP1 Promoter CpG Island across Transitions from Precursors to Invasive Prostate Cancer.

Glutathione S-transferase pi 1 (GSTP1) is lowly expressed in normal prostate luminal cells and becomes induced in most proliferative inflammatory atrophy (PIA) lesions. GSTP1 becomes silenced in prostatic intraepithelial neoplasia (PIN) and prostate adenocarcinoma (CaP) via cytosine-phospho-guanine (CpG) island promoter hypermethylation. However, GSTP1 methylation patterns in PIA and PIN, and their relationship to patterns in CaP are poorly understood. We used bisulfite genomic sequencing to examine patterns of GSTP1 promoter CpG island methylation in laser capture microdissected benign, PIA, PIN, and CaP regions from 32 subjects that underwent radical prostatectomy. We analyzed 908 sequence clones across 24 normal epithelium, 37 PIA, 18 PIN, and 23 CaP regions, allowing assessment of 34,863 CpG sites with allelic phasing. Normal and PIA lesions were mostly unmethylated with 0.52 and 1.3% of total CpG sites methylated, respectively. PIN and CaP lesions had greater methylation with 24% and 51% of total CpG sites methylated, respectively. The degree of GSTP1 methylation showed progression from PIA << PIN < CaP. PIN lesions showed more partial methylation compared with CaP lesions. Partially methylated lesions were enriched for methylation changes at AP1 and SP1 transcription factor binding sites. These results demonstrate that methylation density in the GSTP1 CpG island in PIN was intermediate relative to that in normal prostate epithelium/PIA and CaP lesions. These results are consistent with gradual spreading of DNA methylation centered at the SP1/AP1 transcription factor binding sites in precursor lesions, with subsequent spreading of methylation across the entire CpG island in transition to CaP. PREVENTION RELEVANCE: DNA hypermethylation at the GSTP1 promoter progressively spreads from being unmethylated in normal prostate to intermediate levels in precursor lesions to extensive methylation in cancer. This molecular progression of GSTP1 promoter methylation patterns in early prostate carcinogenesis could be useful for identification and interception of prostate cancer precursors.

Identifying Phased Mutations and Complex Rearrangements in Human Prostate Cancer Cell Lines through Linked-Read Whole-Genome Sequencing.

A limited number of cell lines have fueled the majority of preclinical prostate cancer research, but their genomes remain incompletely characterized. Here, we utilized whole-genome linked-read sequencing for comprehensive characterization of phased mutations and rearrangements in the most commonly used cell lines in prostate cancer research including PC3, LNCaP, DU145, CWR22Rv1, VCaP, LAPC4, MDA-PCa-2b, RWPE-1, and four derivative castrate-resistant (CR) cell lines LNCaP_Abl, LNCaP_C42b, VCaP-CR, and LAPC4-CR. Phasing of mutations allowed determination of "gene-level haplotype" to assess whether genes harbored heterozygous mutations in one or both alleles. Phased structural variant analysis allowed identification of complex rearrangement chains consistent with chromothripsis and chromoplexy. In addition, comparison of parental and derivative CR lines revealed previously known and novel genomic alterations associated with the CR phenotype. IMPLICATIONS: This study therefore comprehensively characterized phased genomic alterations in the commonly used prostate cancer cell lines, providing a useful resource for future prostate cancer research.

Regional Gene Repression by DNA Double-Strand Breaks in G1 Phase Cells.

DNA damage responses (DDR) to double-strand breaks (DSBs) alter cellular transcription programs at the genome-wide level. Through processes that are less well understood, DSBs also alter transcriptional responses locally, which may be important for efficient DSB repair. Here, we developed an approach to elucidate the cis-acting responses to DSBs in G1 phase cells. We found that DSBs within a gene body silence its expression, as well as the transcription of local undamaged genes at a distance defined by the spread of γ-H2AX from the DSB. Importantly, DSBs not only repress ongoing transcription but also block the inducible expression of regional genes. DSB-mediated transcriptional repression depends on DDR signaling but does not require the generation of inaccessible chromatin. Our findings demonstrate that in G1 phase cells, DDR signaling establishes a robust and extensive region of transcriptional repression spreading from DSB sites and introduce an approach to study the mechanistic impact of targeted DNA breaks in nearly any chromatin environment.

A multiple myeloma-specific capture sequencing platform discovers novel translocations and frequent, risk-associated point mutations in IGLL5.

Multiple myeloma (MM) is a disease of copy number variants (CNVs), chromosomal translocations, and single-nucleotide variants (SNVs). To enable integrative studies across these diverse mutation types, we developed a capture-based sequencing platform to detect their occurrence in 465 genes altered in MM and used it to sequence 95 primary tumor-normal pairs to a mean depth of 104×. We detected cases of hyperdiploidy (23%), deletions of 1p (8%), 6q (21%), 8p (17%), 14q (16%), 16q (22%), and 17p (4%), and amplification of 1q (19%). We also detected IGH and MYC translocations near expected frequencies and non-silent SNVs in NRAS (24%), KRAS (21%), FAM46C (17%), TP53 (9%), DIS3 (9%), and BRAF (3%). We discovered frequent mutations in IGLL5 (18%) that were mutually exclusive of RAS mutations and associated with increased risk of disease progression (p = 0.03), suggesting that IGLL5 may be a stratifying biomarker. We identified novel IGLL5/IGH translocations in two samples. We subjected 15 of the pairs to ultra-deep sequencing (1259×) and found that although depth correlated with number of mutations detected (p = 0.001), depth past ~300× added little. The platform provides cost-effective genomic analysis for research and may be useful in individualizing treatment decisions in clinical settings.