Influence of chlorambucil, a bifunctional alkylating agent, on the histone variant biosynthesis of HEp-2 cells

Age-dependent response of lymphocytes in the induction of the linker histone variant, H1 degrees and histone H4 acetylation after treatment with the histone deacetylase inhibitor, trichostatin A

In the present study we investigated the age-related response of Phytohemaglutinin (PHA)-activated S phase human lymphocytes isolated from peripheral blood from donors of four different age groups, namely young (25-30 years), mid-aged (40-45 years), senior (60-65 years) and elderly (80-95 years) on the induction of the linker histone variant, H1 degrees and histone H4 acetylation after treatment with the very specific histone deacetylase (HDAC) inhibitor, trichostatin A (TSA). The cell system of peripheral blood lymphocytes is ideal for the study of H1 degrees induction since they do not synthesize this particular linker histone variant. Lymphocytes isolated from peripheral blood were activated with PHA (5 microg/10(6) cells/ml medium) and placed in culture for a duration of 72 h at which time cells are in the S phase. Forty-eight hours after inoculation, TSA (250 ng/10(6) cells/ml medium) was added to the cell cultures for a period of 24 h. Assays were performed 72 h after initiation of cultures. The results showed that the induction of H1 degrees after TSA treatment increased to a statistically significant degree in the elderly age group with respect to both the young and the mid-aged age groups. Moreover histone H4 acetylation was found to increase as a function of increasing donor age. A hyperacetylation pattern was observed even in the youngest age group analyzed. Specifically, the tetra-acetylated (H4.4) H4 form increased to a statistically significant degree with the concomitant decrease in the non-acetylated H4 for (H4.0) as a function of donor age. The other acetylated H4 forms (H4.1, H4.2, and H4.3) remained more or less constant, irrespective of donor age. These results show that the sensitivity of lymphocytes to TSA is enhanced with increasing donor age. Since to date, 11 class I and II HDACs have been isolated that have been found by other investigators to have differential responses to HDAC inhibitors, these findings may indicate that there is also a differential age-related response of certain HDACs or perhaps a senescent-specific HDAC. This line of research warrants further study.

Lymphocytes from bipolar and schizophrenic patients share common biochemical markers related to histone synthesis and histone cell membrane localization characteristic of an activated state

In a previous communication, based on the total histone and histone variants' synthesis rates, biochemical parameters used for the characterization of the activation state of lymphocytes, we showed that a portion of the lymphocyte population obtained from peripheral blood of patients with bipolar disorder in the manic and/or depressed phases of the illness were in an activated state as opposed to normothymic patients and control subjects whose lymphocytes are in a resting, Go, state. In light of these previous findings, in the present investigation, we have analyzed total histone synthesis rates and the H2A and H3 histone variants' synthesis pattern of acid-extracted histones from the lymphocytes' nuclear fraction obtained from control subjects, patients with bipolar disorder in all phases of the illness, and patients with schizophrenia. Additional biochemical parameters, such as total cellular protein and DNA synthesis rates, were also studied. Moreover, recent findings from other investigators showed the association of histones on the plasma membrane fraction of PHA-activated, but not Go resting lymphocytes. Based on these results, acid-extracted proteins from the plasma membrane fraction obtained from control, bipolar patients in all phases of the illness, and schizophrenic patients were analyzed by immunoblotting using a polyclonal histone antibody, anti-H2B. All biochemical parameters tested show that a portion of the lymphocyte population from bipolar, i.e. manic and depressive, as well as schizophrenic patients are in an activated state and clearly indicate that the unusual for lymphocytes cell cycle-related histone biochemical properties are common to both disorders.

The effect of the histone deacetylase inhibitor, trichostatin A, on total histone synthesis, H1(0) synthesis and histone H4 acetylation in peripheral blood lymphocytes increases as a function of increasing age: a model study

A pilot study was initiated in order to ascertain whether the age of the donor might affect either the induction of the expression of H1(0) or histone H4 acetylation by the very specific histone deacetylase inhibitor, trichostatin A. This was investigated in a cell system which normally does not express this linker histone variant, i.e. peripheral blood lymphocytes (PBL), which were obtained from donors of different ages (25-95 years). Forty-eight hours after activation by the mitogen phytohemaglutinin (PHA), 250 ng of trichostatin A per 10(6) cells per ml culture medium was added and cultured for an additional 24h. Assays were performed 72 h after initiation of cultures, i.e. during the S phase. It was found that in PBL, trichostatin A induced the expression of the linker histone variant, H1(0) as well as histone H4 acetylation, and, more importantly, that these effects were enhanced with increasing age of the donor. More specifically, under the influence of trichostatin A, PBL showed increasing H1(0) synthesis rates and increasing levels of histone H4 acetylation as a function of increasing age of the donor. Moreover, although trichostatin A induced an increasing expression of H1(0) with increasing age, it also concomitantly partially inhibited S phase total histone synthesis. This inhibition also increased as a function of increasing age of the donor.

A morphological study of the effect of chlorambucil during the S and G2 phases of the cell cycle of synchronized HEp-2 cancer cell populations using computerized morphometry

Chlorambucil, a bisalkylating agent, used extensively in the treatment of autoimmune and neoplastic diseases, is known to affect DNA synthesis. However recent studies have revealed that it also affects the synthesis of other nuclear protein constituents, especially histones. Since histones play a major role in both the structural and functional integrity of chromatin, we have analyzed the morphological effects of this agent, using low dose conditions and synchronized populations of HEp-2 cancer cells in the S and G2 phases of the cell cycle. Analyses at the light and electron microscopy levels were undertaken using synchronous image analysis techniques. Computerized morphometry was used so as to evaluate various nuclear and cytological morphological parameters. It was found that chlorambucil affects the organization of chromatin, as well as other cellular parameters in a manner characteristic of decreased tumor aggressiveness. A finding of significance in this study was that chlorambucil exerted its influence on all these morphological parameters only when treatment was initiated at the beginning of the S phase and not during the second half of the S phase or the G2 phase.

T-lymphocyte long-term cultures have a constant histone variant pattern during aging

Human peripheral long-term T-lymphocyte cell cultures show some characteristics similar to those of fibroblast cell lines, the latter of which have been used as in vitro systems for cellular aging studies for many years. Both show a limited in vitro life span, as well as a progressive prolongation of their cell cycle with increasing age. However, whereas T-cell cultures die from apoptosis at the end of their proliferative capacity, fibroblasts can be maintained for long periods of time in stationary cultures as postmitotic senescent cells. Previous studies analyzing the histone variant pattern of a human lung embryonic fibroblast cell line have shown that this pattern changes as a function of cumulative population doublings in a manner not unlike that found in terminally differentiating systems. In the present study the histone variant composition of long-term T-cell cultures was analyzed as a function of population doublings and compared to a human diploid fibroblast system. The results from this study provide a distinction at the molecular level among these two in vitro aging model systems, because it was found that long-term T-cell cultures show a constant histone variant constitution throughout their in vitro life, dissimilar to previous findings using the fibroblast cell system.

Peripheral blood lymphocytes of bipolar affective patients have a histone synthetic profile indicative of an active cell state

1. Although abnormalities of the immune system have been described in depression, no information exists regarding the biochemical parameters which could characterize the physiological state of lymphocytes from patients with bipolar affective disorder. 2. Lymphocytes of normal control subjects are known to be in the Go resting phase of the cell cycle. Histone synthesis is characteristically different during the Go, G1/G2 and the S phases of the cell cycle. As such, it can be used as a biochemical marker with which to distinguish between cycling and noncycling cells. 3. In order to investigate the possibility of whether or not the lymphocytes of patients with bipolar affective disorder are in an activated state, typical of cycling cells, total histone and histone variant synthesis were analysed in peripheral blood lymphocytes of a group of 12 patients with bipolar affective disorder and 7 normal controls. 4. According to the histone variant synthesis pattern, lymphocytes of patients in normothymia have values similar to those of controls, i.e., of noncycling cells, while patients in either the depressed or the manic phase have values intermediate to those of resting and cycling cells. 5. This study shows that histone synthesis can perhaps be used as a biochemical parameter of possible significance in differentiating amongst the three phases of the illness.

Influence of DNA replication inhibition on expression of cell growth and tissue-specific genes in osteoblasts and osteosarcoma cells

Interrelationships between proliferation and expression of cell growth as well as bone cell-related genes were examined from two standpoints. First, the consequence of downregulating proliferation by DNA synthesis inhibition on expression of a cell cycle-regulated histone gene and genes associated with development of the bone cell phenotype (type I collagen, alkaline phosphatase, osteopontin, and osteocalcin) was investigated. Second, the requirement for stringent growth control to support functional relationships between expression of proliferation and differentiation-related genes was explored. Parameters of cell growth and osteoblast-related gene expression in primary cultures of normal diploid osteoblasts, that initially express proliferation-dependent genes and subsequently postproliferative genes associated with mature bone cell phenotypic properties, were compared to those operative in ROS 17/2.8 osteosarcoma cells that concomitantly express cell growth and mature osteoblast phenotypic genes. Our findings indicate that in both normal diploid osteoblasts and osteosarcoma cells, expression of the cell cycle regulated histone genes is tightly coupled with DNA synthesis and controlled predominantly at a posttranscriptional level. Inhibition of proliferation by blocking DNA synthesis with hydroxyurea upregulates a subset of developmentally expressed genes that postproliferatively support progressive establishment of mature osteoblast phenotypic properties (e.g., alkaline phosphatase, type 1 collagen, and osteopontin). However, the osteocalcin gene, which is expressed during the final stage of osteoblast differentiation when extracellular matrix mineralization occurs, is not upregulated. Variations in the extent to which inhibition of proliferation in normal diploid osteoblasts and in ROS 17/2.8 osteosarcoma cells selectively affects transcription and cellular levels of mRNA transcripts from bone cell-related genes (e.g., osteocalcin) may reflect modifications in proliferation/differentiation interrelationships when stringent growth control is abrogated.