Poster abstracts

Poster number 69 submitted by Rajbir Singh

Histone isoforms: A new level of histone complexity involved in cell proliferation and tumorigenesis

Rajbir Singh (Molecular and Cellular Biochemistry), Sean Harshman (Biomedical Science Graduate Program), David Lucas (Hematology and Oncology), Michael A Freitas (Molec Vir, Imm & Med Gen), John C Byrd (Hematology and Oncology), Mark R Parthun (Molecular and Cellular Biochemistry)

Abstract:
Epigenetic regulation comprises the changes in gene expression that are not mediated at the DNA sequence level. Molecular mechanisms that mediate epigenetic regulation mainly include DNA methylation and chromatin modifications. Emerging evidence indicates that both mechanisms act in concert to provide stable and heritable gene expression patterns in higher eukaryotic genomes. Since epigenetic alterations are recognized to occur in various developmental disorders and cancer, understanding this intrinsic complexity of chromatin structure is critical in understanding and treating these diseases. In our study, we have uncovered a new level of complexity in human chromatin due to the presence of functionally distinct isoforms of the replication-dependent core histones that can influence cell proliferation and tumorigenicity. In our effort to understand the epigenetic changes associated with the leukemic state, the histone pool from B cells of Chronic Lymphocytic Leukemia (CLL) patients was isolated and the mass spectrometry analysis was carried out to map up the entire spectrum of changes involved in the metastatic state. The most significant change associated with CLL was the relative decrease in abundance of specific histone H2A isoforms. These variants differ by 1-2 residues from their canonical counterparts. Followed by this we analyzed the blood samples from 129 CLL patients using real time PCR to correlate the respective downregulation of protein levels with mRNA expression and reveal its possible role as a marker of cancer progression. Statistical analysis confirmed that downregulation of these isoforms corresponds to an increased time to treatment of CLL from diagnosis. We extended our study to bladder and breast cancers and found a unique pattern of histone related changed in cancer. Furthermore, knockdown studies revealed the distinct role of some of these isoforms in cell proliferation and tumorigenesis as evident by various growth kinetic and proliferation assays. The outcomes of this study will not only provide the clinicians with novel insights into the cancer biology, but will also bring to light the mechanisms for maintenance and transmission of epigenetic integrity and the disorders during which such integrity is compromised.

Keywords: Histone , cancer