Targeted Proteomic Analyses of Histone H4 Acetylation Changes Associated with Homologous-Recombination-Deficient High-Grade Serous Ovarian Carcinomas

Approximately
20% of high-grade serous ovarian cancers are homologous-recombination
(HR)-deficient due to genetic and epigenetic mutations of HR pathway
genes including the tumor suppressor genes BRCA1 and
2. HR deficiency (HRD) compromises cells’ ability to efficiently
repair DNA damage, but it also increases sensitivity to chemotherapeutic
treatment strategies; however, not all ovarian cancer patients with
HRD tumors exhibit positive responses to chemotherapy. Our previous
iTRAQ-based comprehensive proteomic characterization of high-grade
serous ovarian carcinomas found that lower levels of histone H4 acetylation
at Lys12 and Lys16 (H4-K12acK16ac) were associated with HRD tumors
compared with non-HRD tumors. In the current study, we developed and
validated an H4-K12acK16ac parallel-reaction-monitoring (PRM)-targeted
mass-spectrometry-based assay to analyze acetylation changes of histone
H4 and to determine the association of these changes with total H4,
histone acetyltransferase, and histone deacetylase (HDAC) levels.
Whereas the levels of H4 and histone acetyltransferases were stable
irrespective of HRD status, the levels of histone H4 acetylation and
one HDAC, HDAC6, were elevated in the HRD tumors. Relative H4 acetylation
levels were also analyzed by an antibody-based approach in additional
ovarian tumors. It is possible that specific H4 acetylation at Lys12
and Lys16 associated with HRD could inform chemotherapeutic treatment
modalities to improve ovarian cancer patients’ treatment response.