Quantification of histone H1 subtypes using targeted proteomics

Abstract

AbstractHistone H1 is involved in the regulation of chromatin structure. Human somatic cells express up to seven subtypes: H1.0, H1.1-H15, and H1X. The variability in the proportions of somatic H1s (H1 complement) is one evidence supporting their functional specificity. Alterations in the protein levels of different H1 subtypes have been observed in cancer, suggesting their potential as biomarkers and that they might play a role in disease development. These reasons led us to develop a mass spectrometry based (MS) parallel reaction monitoring (PRM) assay suitable for the quantification of H1 subtypes. Our PRM method is based on the quantification of unique peptides for each subtype, providing high specificity. Evaluation of the PRM performance on three human cell lines showed high reproducibility and sensitivity. Quantification values agreed with the electrophoretic and Western blot, indicating the accuracy of the results. We used PRM to characterize the H1 complement in peripheral blood samples of healthy individuals, finding that the more abundant subtypes were H1.4 and H1.5. Analysis by PRM of samples from chronic myeloid leukemia patients showed that higher levels of H1 were associated with imatinib resistance, suggesting its potential as a predictive biomarker. Non-responder patients had lower proportions of H1.0, H1.1, and H1X than responders, hinting that their alteration could be involved in the acquisition of resistance.