Protein-DNA interactions at the H4-site III upstream transcriptional element of a cell cycle regulated histone H4 gene: differences in normal versus tumor cells

Upstream sequences of the H4 histone gene FO108 located between nt -418 to -213 are stimulatory for in vivo transcription. This domain contains one protein/DNA interaction site (H4-Site III) that binds factor H4UA-1. Based on methylation interference, copper-phenanthroline protection, and competition assays, we show that H4UA-1 interacts with sequences between nt -345 to -332 containing an element displaying sequence-similarity with the thyroid hormone response element (TRE). Using gel retardation assays, we also demonstrate that H4UA-1 binding activity is abolished at low concentrations of Zn2+ (0.75 mM), a characteristic shared with the thyroid hormone (TH) receptor DNA binding protein. Interestingly, phosphatase-treatment of nuclear proteins inhibits formation of the H4UA-1 protein/DNA complex, although a complex with higher mobility (H4UA-1b) can be detected; both complexes share identical protein-DNA contacts and competition behaviors. These findings suggest that phosphorylation may be involved in the regulation of H4-Site III protein/DNA interactions by directly altering protein/protein associations. H4-Site III interactions were examined in several cell culture systems during cell growth and differentiation. We find that H4UA-1 binding activity is present during the cell cycle of both normal diploid and transformed cells. However, during differentiation of normal diploid rat calvarial osteoblasts, we observe a selective loss of the H4UA-1/H4-Site III interaction, concomitant with an increase of the H4UA-1b/H4-Site III complex, indicating modifications in the heteromeric nature of protein/DNA interactions during downregulation of transcription at the cessation of proliferation. Transformed cells have elevated levels of H4UA-1, whereas H4UA-1b is predominantly present in normal diploid cells; this alteration in the ratio of H4UA-1 and H4UA-1b binding activities may reflect deregulation of H4-Site III interactions in transformed cells. We propose that H4-Site III interactions may contribute, together with protein/DNA interactions at proximal regulatory sequences, in determining the level of H4-FO108 histone gene transcription.

Regulation of histone gene expression

Histone genes are expressed during the S phase of the cell cycle. Control is at multiple levels and is mediated by the integration of regulatory signals in response to cell-cycle progression and the onset of differentiation. Much work has been carried out on the H4 gene promoter, which appears to be organized into a series of distinct regulatory elements. The three-dimensional organization of the promoter and, in particular, its spatial relationship with the nuclear matrix scaffold, may be important factors of transcription regulation.

Multiple mechanisms regulate the proliferation-specific histone gene transcription factor HiNF-D in normal human diploid fibroblasts

The proliferation-specific transcription factor complex HiNF-D interacts with sequence specificity in a proximal promoter element of the human H4 histone gene FO108, designated Site II. The occupancy of Site II by HiNF-D has been implicated in proper transcription initiation and as a component of the cell cycle regulation of this gene. In the present study we have investigated the role of the HiNF-D/Site II interaction in controlling the level of H4 histone gene transcription during modifications of normal cellular growth. HiNF-D binding activity is present at high levels in rapidly proliferating cultures of human diploid fibroblasts and is reduced to less than 2% upon the cessation of proliferation induced by serum deprivation of sparsely population fibroblast cultures. Density-dependent quiescence also abolishes HiNF-D binding activity. Downregulation of transcription from the H4 gene occurs concomitant with the loss of the HiNF-D/Site II interaction, further suggesting a functional relationship between Site II occupancy and the capacity for transcription. Serum stimulation of quiescent preconfluent cells results in an increase in HiNF-D binding activity as the cells are resuming DNA synthesis and H4 histone gene transcription. Density-inhibited quiescent cells respond to serum stimulation with only a minimal increase in the HiNF-D binding activity, 30% of maximal levels. However, H4 histone gene transcription is stimulated to a level equal to that detected in extracts of the sparsely populated serum-stimulated cultures. These results suggest that there is a threshold level of HiNF-D binding activity necessary for the activation of H4 histone gene transcription.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of heat shock genes during differentiation of mammalian osteoblasts and promyelocytic leukemia cells

The progressive differentiation of both normal rat osteoblasts and HL-60 promyelocytic leukemia cells involves the sequential expression of specific genes encoding proteins that are characteristic of their respective developing cellular phenotypes. In addition to the selective expression of various phenotype marker genes, several members of the heat shock gene family exhibit differential expression throughout the developmental sequence of these two cell types. As determined by steady state mRNA levels, in both osteoblasts and HL-60 cells expression of hsp27, hsp60, hsp70, hsp89 alpha, and hsp89 beta may be associated with the modifications in gene expression and cellular architecture that occur during differentiation. In both differentiation systems, the expression of hsp27 mRNA shows a 2.5-fold increase with the down-regulation of proliferation while hsp60 mRNA levels are maximal during active proliferation and subsequently decline post-proliferatively. mRNA expression of two members of the hsp90 family decreases with the shutdown of proliferation, with a parallel relationship between hsp89 alpha mRNA levels and proliferation in osteoblasts and a delay in down-regulation of hsp89 alpha mRNA levels in HL-60 cells and of hsp89 beta mRNA in both systems. Hsp70 mRNA rapidly increases, almost twofold, as proliferation decreases in HL-60 cells but during osteoblast growth and differentiation was only minimally detectable and showed no significant changes. Although the presence of the various hsp mRNA species is maintained at some level throughout the developmental sequence of both osteoblasts and HL-60 cells, changes in the extent to which the heat shock genes are expressed occur primarily in association with the decline of proliferative activity. The observed differences in patterns of expression for the various heat shock genes are consistent with involvement in mediating a series of regulatory events functionally related to the control of both cell growth and differentiation.

Stairway assays: rapid localization of multiple protein/DNA interaction sites in gene-regulatory 5' regions

We describe a rapid method for initial localization of protein/DNA-binding sites in large DNA segments, even when biological information is limited. The procedure combines the gel retardation assay with bidirectional deletion analysis using restriction enzymes. Electrophoresis of binding reactions with a bidirectional set of progressively shortened probes results in a stairway pattern of both uncomplexed DNA and specific protein/DNA complexes. The loss of binding upon deletion of specific DNA segments localizes the boundaries of protein/DNA interaction sites. Stairway assays are illustrated using cloned DNA fragments spanning three histone gene promoters, but it is possible to adapt this method for any segment of genomic DNA that can be amplified using PCR methods. Multiple binding sites were established for transcription factors, chromatin-associated proteins and sequence specific nuclear matrix proteins, thereby validating this approach for at least three classes of DNA-binding proteins.

Protein/DNA interactions involving ATF/AP1-, CCAAT-, and HiNF-D-related factors in the human H3-ST519 histone promoter: cross-competition with transcription regulatory sites in cell cycle controlled H4 and H1 histone genes

Protein/DNA interactions of the H3-ST519 histone gene promoter were analyzed in vitro. Using several assays for sequence specificity, we established binding sites for ATF/AP1-, CCAAT-, and HiNF-D related DNA binding proteins. These binding sites correlate with two genomic protein/DNA interaction domains previously established for this gene. We show that each of these protein/DNA interactions has a counterpart in other histone genes: H3-ST519 and H4-F0108 histone genes interact with ATF- and HiNF-D related binding activities, whereas H3-ST519 and H1-FNC16 histone genes interact with the same CCAAT-box binding activity. These factors may function in regulatory coupling of the expression of different histone gene classes. We discuss these results within the context of established and putative protein/DNA interaction sites in mammalian histone genes. This model suggests that heterogeneous permutations of protein/DNA interaction elements, which involve both general and cell cycle regulated DNA binding proteins, may govern the cellular competency to express and coordinately control multiple distinct histone genes.

Coordination of protein-DNA interactions in the promoters of human H4, H3, and H1 histone genes during the cell cycle, tumorigenesis, and development

Coordinate transcriptional control of replication-dependent human H4, H3, and H1 histone genes was studied by comparing levels of H3 and H1 histone promoter binding activities with those of H4 histone promoter factor HiNF-D during the cell cycle of both normal diploid and tumor-derived cells, as well as in fetal and adult mammalian tissues. Both H3 and H1 histone promoters interact with binding activities that, as with HiNF-D, are maximal during S-phase but at low levels in the G1-phase of normal diploid cells. However, these analogous DNA binding activities are constitutively maintained at high levels throughout the cell cycle in four different transformed and tumor-derived cells. Downregulation of the H3 and H1 histone promoter factors in conjunction with HiNF-D is observed in vivo at the onset of quiescence and differentiation during hepatic development. Hence, our results indicate a tight temporal coupling of three separate protein-DNA interactions in different histone promoters during the cell cycle, development, and tumorigenesis. This suggests that a key oscillatory, cell-growth-control mechanism modulates three analogous histone gene promoter protein-DNA interactions in concert. The derangement of this mechanism in four distinct tumor cells implies that concerted deregulation of these histone promoter factors is a common event resulting from heterogeneous aberrations in normal cell growth mechanisms during tumorigenesis. We postulate that this mechanism may be involved in the coordinate regulation of the human H4, H3, and H1 histone multigene families.

Single-copy flanking sequences in human histone gene clusters map to chromosomes 1 and 6

Two single-copy sequences flanking two different human histone gene clusters were used as probes to map these clusters by in situ hybridization. pFF435B, a unique sequence subclone derived from a lambda genomic clone (lambda HHG55) containing H2A, H2B, H3, and H4 genes, mapped to chromosome 1q21 (chi 2 = 120.99, P less than 0.001). pST519E, a single-copy sequence derived from a lambda genomic clone (lambda HHG17) containing only H3 and H4 genes, mapped to chromosome 6p21 (chi 2 = 112.62, P less than 0.001). These findings agree with previous assignments of human histone genes to chromosomes 1 and 6 and demonstrate that the single-copy flanking sequences in different human histone gene clusters are unique for different chromosomes.

Transcriptional element H4-site II of cell cycle regulated human H4 histone genes is a multipartite protein/DNA interaction site for factors HiNF-D, HiNF-M, and HiNF-P: involvement of phosphorylation

Cell cycle regulated gene expression was studied by analyzing protein/DNA interactions occurring at the H4-Site II transcriptional element of H4 histone genes using several approaches. We show that this key proximal promoter element interacts with at least three distinct sequence-specific DNA binding activities, designated HiNF-D, HiNF-M, and HiNF-P. HiNF-D binds to an extended series of nucleotides, whereas HiNF-M and HiNF-P recognize sequences internal to the HiNF-D binding domain. Gel retardation assays show that HiNF-D and HiNF-M each are represented by two distinct protein/DNA complexes involving the same DNA binding activity. These results suggest that these factors are subject to post-translational modifications. Dephosphorylation experiments in vitro suggest that both electrophoretic mobility and DNA binding activities of HiNF-D and HiNF-M are sensitive to phosphatase activity. We deduce that these factors may require a basal level of phosphorylation for sequence specific binding to H4-Site II and may represent phosphoproteins occurring in putative hyper- and hypo-phosphorylated forms. Based on dramatic fluctuations in the ratio of the two distinct HiNF-D species both during hepatic development and the cell cycle in normal diploid cells, we postulate that this modification of HiNF-D is related to the cell cycle. However, in several tumor-derived and transformed cell types the putative hyperphosphorylated form of HiNF-D is constitutively present. These data suggest that deregulation of a phosphatase-sensitive post-translational modification required for HiNF-D binding is a molecular event that reflects abrogation of a mechanism controlling cell proliferation. Thus, phosphorylation and dephosphorylation of histone promoter factors may provide a basis for modulation of protein/DNA interactions and H4 histone gene transcription during the cell cycle and at the onset of quiescence and differentiation.

Involvement of the cell cycle-regulated nuclear factor HiNF-D in cell growth control of a human H4 histone gene during hepatic development in transgenic mice

Regulation of the cell cycle-controlled histone gene promoter factor HiNF-D was examined in vivo. Proliferative activity was measured by DNA replication-dependent histone mRNA levels, and HiNF-D binding activity was found to correlate with cell proliferation in most tissues. Furthermore, HiNF-D is down-regulated during hepatic development, reflecting the onset of differentiation and quiescence. The contribution of transcription to histone gene expression was directly addressed in transgenic mice by using a set of fusion constructs containing a human H4 histone gene promoter linked to three different genes. Transgene expression in both fetal and adult mice paralleled endogenous mouse histone mRNA levels in most tissues, consistent with this promoter conferring developmental, cell growth-related transcriptional regulation. Our results suggest that HiNF-D is stringently regulated in vivo in relation to cell growth and support a primary role for HiNF-D in the proliferation-specific expression of H4 histone genes in the intact animal. Further, the data presented here provide an example in which apparent tissue specificity of gene expression reflects the proliferative state of various tissues and demonstrate that multiple levels of histone gene regulation are operative in vivo.

Nucleotide sequence and expression of a deep-sea ribulose-1,5-bisphosphate carboxylase gene cloned from a chemoautotrophic bacterial endosymbiont

The gene coding for ribulose-1,5-bisphosphate carboxylase [RuBisCO; 3-phospho-D-glycerate carboxy-lyase (dimerizing), EC 4.1.1.39] was cloned from a sulfur-oxidizing chemoautotrophic bacterium that resides as an endosymbiont within the gill tissues of Alvinoconcha hessleri, a gastropod inhabiting deep-sea hydrothermal vents. Nucleotide sequence analysis of the cloned fragment demonstrated that the genes encoding the large (RbcL) and small (RbcS) subunits of the symbiont RuBisCO were organized similarly to the RuBisCO operons of free-living photo- and chemoautotrophic prokaryotes. The symbiont rbcL gene shared the highest degree of nucleotide sequence identity with the cyanobacterium Anabaena (69%) while the rbcS nucleotide sequence shared 61% identity with that of the green alga Chlamydomonas reinhardtii. Comparison with a 153-nucleotide partial rbcL sequence from a symbiont of the bivalve Solemya reidi indicated that the two symbiont sequences shared 85% sequence identity at the nucleotide level and 93% at the amino acid level, suggesting a relatively recent common origin. Escherichia coli transformed with a plasmid carrying the RuBisCO operon of the gastropod symbiont in the proper orientation for transcription from the plasmid lac promoter expressed catalytically active RuBisCO. The presence of enzyme activity suggests the proper assembly of the subunits of this deep-sea RuBisCO into the holoenzyme.

Structural and functional analysis of the rat testis-specific histone H1t gene

A 6.86 kb rat genomic DNA fragment containing the testis-specific histone H1t gene and the histone H4t gene has been sequenced. S1-nuclease protection analyses of total cellular RNA from rat liver and testis showed that histone H1t mRNA was present only in testis. Examination of various highly enriched populations of rat testis cell types revealed that H1t mRNA was found exclusively in a fraction enriched in pachytene spermatocytes. When protein, DNA interactions within the proximal promoter region of the histone H1t gene were examined by electrophoretic mobility shift assays, only minor differences were found in mobility shift patterns of the H1t promoter in assays comparing binding of nuclear proteins from pachytene spermatocytes and early spermatids. However, major differences in binding were observed upon comparing nuclear proteins from rat pachytene spermatocytes to liver. Comparison of binding patterns of rat testis, rat hepatoma H4 cells, HeLa cells, and COS-1 cells also revealed dramatic differences. Transcriptional activity of the histone H1t promoter was examined by measuring H1t promoted chloramphenicol acetyltransferase (CAT) mRNA levels in transient expression assays in transfected rat hepatoma H4 cells, HeLa cells, and COS-1 cells. These assays revealed that the histone H1t promoted CAT gene functioned poorly in HeLa cells and COS-1 cells compared to expression with the parent SV40 promoted vector pSV2CAT. The H1t promoted CAT gene apparently did not work at all in transfected rat hepatoma H4 cells, which is consistent with testis germinal cell specific expression of the histone H1t gene.

Nipple stimulation for labor augmentation

A randomized, prospective study was undertaken to evaluate the efficacy of nipple stimulation with a breast pump as compared to oxytocin for augmentation of labor. The average and maximal uterine activity achieved was significantly higher in the oxytocin-stimulated group, without significant differences in the length of labor stages, cesarean section rate, Apgar scores or umbilical artery pH. Fifty percent of the patients failed to respond to nipple stimulation after 30 minutes and were switched to oxytocin. These patients experienced a more rapid rate of cervical dilation in the active phase and reached higher maximal uterine activity with oxytocin stimulation; however, the cesarean section rate was highest in this group. Nipple stimulation with a breast pump appears to be a safe and effective alternative to oxytocin for the augmentation of labor.

Progressive changes in the protein composition of the nuclear matrix during rat osteoblast differentiation

Primary cultures of fetal rat calvarial osteoblasts undergo a developmental sequence with respect to the temporal expression of genes encoding osteoblast phenotypic markers. Based on previous suggestions that gene-nuclear matrix associations are involved in regulating cell- and tissue-specific gene expression, we investigated the protein composition of the nuclear matrix during this developmental sequence by using high-resolution two-dimensional gel electrophoresis. The nuclear matrix was isolated at times during a 4-week culture period that represent the three principal osteoblast phenotypic stages: proliferation, extracellular matrix (ECM) maturation, and mineralization. The most dramatic changes in the nuclear matrix protein patterns occurred during transitions from the proliferation to the ECM maturation stage and from ECM maturation to the mineralization period, with only minor variations in the profiles within each period. These stage-specific changes, corresponding to the major transition points in gene expression, indicate that the nuclear matrix proteins reflect the progressive differentiation of the bone cell phenotype. Subcultivation of primary cells delays mineralization, and a corresponding delay was observed for the nuclear matrix protein patterns. Thus, the sequential changes in protein composition of the nuclear matrix that occur during osteoblast differentiation represent distinct stage-specific markers for maturation of the osteoblast to an osteocytic cell in a bone-like mineralized ECM. These changes are consistent with a functional involvement of the nuclear matrix in mediating modifications of developmental gene expression.

Vitamin D-mediated modifications in protein-DNA interactions at two promoter elements of the osteocalcin gene

By the combined use of DNase I footprinting, electrophoretic mobility-shift assay, and methylation interference analysis, we have identified a series of sequence-specific protein-DNA interactions in the 5' flanking region of the rat osteocalcin gene. Stimulation of osteocalcin gene expression by 1,25-dihydroxyvitamin D3, a physiologic mediator of this bone-specific gene in vitro and in vivo, is associated with modifications in the binding of ROS 17/2.8 cell nuclear factors to two promoter segments that up-regulate transcription. One segment located between -462 and -437 exhibits a vitamin D-dependent increase in sequence-specific binding of nuclear factors. This element (CTGGGTGAATGAGGACATTACTGACC), identified at single nucleotide resolution, contains a region of hyphenated dyad symmetry and shares sequence homology with consensus steroid-responsive elements and with the sequence that has been identified as the vitamin D receptor binding site in the human osteocalcin gene. We have also observed that vitamin D stimulation of osteocalcin gene expression results in a 5-fold increase in protein binding to the region of the osteocalcin box, a 24-nucleotide segment in the proximal promoter with a CCAAT motif as the central core. Our results demonstrate protein-DNA interactions in a vitamin D-responsive element and in a second sequence, the osteocalcin box, both of which are involved in the physiologic regulation of the osteocalcin gene in response to 1,25-dihydroxyvitamin D3.

Modifications in molecular mechanisms associated with control of cell cycle regulated human histone gene expression during differentiation

Histone proteins are preferentially synthesized during the S-phase of the cell cycle, and the temporal and functional coupling of histone gene expression with DNA replication is mediated at both the transcriptional and posttranscriptional levels. The genes are transcribed throughout the cell cycle, and a 3-5-fold enhancement in the rate of transcription occurs during the first 2 h following initiation of DNA synthesis. Control of histone mRNA stability also accounts for some of the 20-100fold increase in cellular histone mRNA levels during S-phase and for the rapid and selective degradation of the mRNAs at the natural completion of DNA replication or when DNA synthesis is inhibited. Two segments of the proximal promoter, designated Sites I and II, influence the specificity and rate of histone gene transcription. Occupancy of Sites I and II during all periods of the cell cycle by three transacting factors (HiNF-A, HiNF-C, and HiNF-D) suggests that these protein-DNA interactions are responsible for the constitutive transcription of histone genes. Binding of HiNF-D in Site II is selectively lost, whereas occupancy of Site I by HiNF-A and -C persists when histone gene transcription is down regulated when cells terminally differentiate. These results are consistent with a primary role for interactions of HiNF-D with a proximal promoter element in rendering cell growth regulated human histone genes transcribable in proliferating cells.

Human H4 histone gene transcription requires the proliferation-specific nuclear factor HiNF-D. Auxiliary roles for HiNF-C (Sp1-like) and HiNF-A (high mobility group-like)

The proximal promoter of the human H4 histone gene F0108 contains two in vivo protein binding domains, sites I and II. In this report we show that these sequences interact with three nuclear factors: HiNF-D, HiNF-C, and HiNF-A. HiNF-C is a metal ion-requiring protein that binds to an Sp1 consensus binding site. HiNF-C and HiNF-A bind independently to the distally located site I, possibly in conjunction with other proteins, and deletion of site I reduces transcription rates 4- to 6-fold in vitro. Factor HiNF-D binds to an H4 histone-specific element (5'-dGGTPyPyTCAATCNG-GTCCG, where Py indicates pyrimidine) present in site II that has previously been shown to be essential for in vivo expression of this H4 histone gene. All three binding activities are present in human HeLa S3 cells throughout the cell cycle and in exponentially growing mouse C127 and human HL60 cells. This result is consistent with the transcription of H4 histone genes throughout the cell cycle. However, unlike HiNF-A and HiNF-C, HiNF-D is not present in terminally differentiated HL60 cells, in which histone gene transcription is down-regulated. These findings suggest a crucial role for HiNF-D, with an auxiliary role for HiNF-C and possibly HiNF-A, in the regulation of H4 histone gene transcription. Furthermore, the conservation of potential HiNF-D binding sites in mammalian H4 histone gene promoters suggests that HiNF-D has an essential role in the coordinate transcriptional down-regulation of the H4 histone multigene subfamily during the shutdown of proliferation.

The human H1 histone gene FNC16 is functionally expressed in proliferating HeLa S3 cells and is down-regulated during terminal differentiation in HL60 cells

The human H1 histone gene FNC16 resides in a 2.7-kb EcoRI fragment present in a histone gene cluster that also contains one copy of each of the core (H2A, H2B, H3, and H4) histone genes. The cap site for FNC16 H1 mRNA is located 58 nucleotides upstream of the ATG translational start codon, and S1 nuclease protection analysis clearly distinguishes between correctly initiated FNC16 transcripts and transcripts from other nonidentical H1 histone genes. We have observed, using S1 analysis, that the FNC16 H1 histone gene is expressed in a replication-dependent manner in HeLa cells and is expressed in proliferating, but down-regulated in differentiated, HL60 cells. Similar results were found in HeLa S3 and HL60 cells for the cell cycle-dependent human H4 histone gene FO108. Nuclear extracts derived from HeLa S3 cells are capable of directing FNC16 H1 histone gene transcription in vitro. This finding is consistent with previous work that established at least two sites for protein-DNA interaction in vitro in the proximal promoter region of this gene. We have observed a difference in the extent to which the FNC16 H1 histone gene is expressed in HeLa S3 and proliferating HL60 cells, which suggests that this H1 gene is differentially regulated in various cell types. Although results reported for a potentially identical human H1 histone gene designated Hh8C (LaBella, F., Zhong, R., and Heintz, N. (1988) J. Biol. Chem. 263, 2115-2118) support differential regulation of human H1 genes in various cell types, their observations that the Hh8C gene is not expressed in HeLa cells and that the restriction patterns differ indicate that FNC16 and Hh8C are different H1 genes.

Human H1 histone gene promoter CCAAT box binding protein HiNF-B is a mosaic factor

Vertebrate histone gene promoters in many cases contain an upstream element, 5'dCCAAT, that has been implicated in modulating the efficiency of transcription of a broad spectrum of genes. We have previously isolated a nuclear factor (HiNF-B) that binds specifically to the CCAAT element of a cell cycle regulated human H1 histone gene. This factor shows similarities with other CCAAT box binding proteins in that it recognizes the same sequence but shows a distinct chromatographic behavior. In the present study, we have employed the gel retardation assay to demonstrate that HiNF-B is a cell cycle independent DNA binding protein that is conserved in both human and mouse cells. Using a series of reconstitution experiments with partially purified HiNF-B fractions, we show that this factor requires association of at least two components for site-specific binding. The composite structure of HiNF-B suggests that binding of at least some CCAAT elements in vertebrates may require cooperative interaction of CCAAT box binding proteins with other factors.

Persistence of a micrococcal nuclease sensitive region spanning the promoter-coding region junction of a cell cycle regulated human H4 histone gene throughout the cell cycle

We have examined the chromatin structure of the cell cycle regulated human H4 histone gene FO108A at various times during the cell cycle, by treating nuclei isolated from synchronized HeLa S3 cells with micrococcal nuclease. Purified DNA was fractionated electrophoretically, transferred to nitrocellulose, and hybridized to small (150-250 nucleotides) radiolabeled probes from various portions of the promoter and coding regions of the gene. Our results indicate the existence of a micrococcal nuclease sensitive region located between positions -60 and +90 base pairs (bp) from the start codon of the gene, which includes the TATA box. This nuclease-sensitive region persists at all the cell cycle times analyzed. Hybridization with a 250-bp probe containing only coding region sequences reveals a disrupted nucleosomal ladder during early S phase, when this H4 histone gene replicates and exhibits an enhanced level of transcription. By mid-S phase, the regular nucleosomal structure of the coding region is restored and persists during subsequent phases of the cell cycle. The disruption of a normal nucleosomal organization in the promoter and mRNA coding regions of this H4 histone gene is also supported by the sensitivity of these sequences to S1 nuclease.

Two target sites for protein binding in the promoter region of a cell cycle regulated human H1 histone gene

The 5' region of a cell cycle regulated human H1 histone gene appears to contain at least six promoter DNA elements that are shared with some, but not all human core (H2A, H2B, H3 and H4) histone genes. We show that two of these elements represent separate binding sites for two distinct, partially purified factors. The first promoter domain contains A/T rich repeats and is involved in the binding of HiNF-A, a nuclear factor previously found to bind to A/T rich direct repeats in the promoters of human H4 and H3 histone genes. The second domain, containing the general promoter element 5' dACCAAT, acts as a binding site for a two component mosaic factor we have designated HiNF-B. These data suggest that coordinate transcriptional regulation of human H1 and core histone genes may involve two classes of trans-acting factors: those specific for histone gene promoters and those that act on a broad spectrum of human gene promoters.

Intracellular distribution of histone mRNAs in human fibroblasts studied by in situ hybridization

We have used in situ hybridization to study the intracellular distribution of mRNAs for cell cycle-dependent core and H1 histone proteins in human WI-38 fibroblasts. Because histones are abundant nuclear proteins and histone mRNA expression is tightly coupled to DNA synthesis, it was of interest to determine whether histone mRNAs are localized near the nucleus. Cells were hybridized with tritiated DNA probes specific for either histone H1, histone H4, actin, or poly(A)+ mRNA and were processed for autoradiography. In exponentially growing cultures, the fraction of histone mRNA-positive cells correlated well with the fraction of cells in S phase and was eliminated by hydroxyurea inhibition of DNA synthesis. Within individual cells the label for histone mRNA was widely distributed throughout the cytoplasm and did not appear to be more heavily concentrated near the nucleus. However, histone mRNA appeared to exhibit patchy, nonhomogeneous localization, and a quantitative evaluation confirmed that grain distributions were not as uniform as they were after hybridizations to poly(A)+ mRNA. Actin mRNA in WI-38 cells was also widely distributed throughout the cytoplasm but differed from histone mRNA in that label for actin mRNA was frequently most dense at the outermost region of narrow cell extensions. The localization of actin mRNA was less pronounced but qualitatively very similar to that previously described for chicken embryonic myoblasts and fibroblasts. We conclude that localization of histones in WI-38 cells is not facilitated by localization of histone protein synthesis near the nucleus and that there are subtle but discrete and potentially functional differences in the distributions of histone, actin, and poly(A)+ mRNAs.

Regulation of human histone gene expression: transcriptional and posttranscriptional control in the coupling of histone messenger RNA stability with DNA replication

The extent to which transcriptional and posttranscriptional regulation contributes to the coupling of histone gene expression and DNA replication was examined during the cell cycle in synchronized HeLa S3 cells. Rates of transcription were determined in vitro in isolated nuclei. A 3-5-fold increase in cell cycle dependent histone gene transcription was observed in early S phase, prior to the peak of DNA synthesis. This result is consistent with a previous determination of histone mRNA synthesis in intact cells [Plumb, M., Stein, J., & Stein, G. (1983) Nucleic Acids Res. 11, 2391]. The transcription of these genes did not change appreciably after inhibition of DNA replication by hydroxyurea treatment, although Northern blot analysis indicated that cellular levels of histone mRNA decreased rapidly in the presence of the drug. Total cellular levels of histone mRNA closely parallel the rate of DNA synthesis as a function of cell cycle progression, reaching a maximal 20-fold increase as compared with non S phase levels. This DNA synthesis dependent accumulation of histone mRNA occurs predominantly in the cytoplasm and appears to be mediated primarily by control of histone mRNA stability. Changes in nuclear histone mRNA levels were less pronounced. These combined observations suggest that both transcriptional regulation and posttranscriptional regulation contribute toward control of the cell cycle dependent accumulation of histone mRNA during S phase, while the stability of histone mRNA throughout S phase and the selective turnover of histone mRNAs, either at the natural termination of S phase or following inhibition of DNA synthesis, are posttranscriptionally regulated.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of an enhancer-like element upstream from a cell cycle dependent human H4 histone gene

We have identified a segment of DNA in the region 6,500 nucleotides upstream from a cell-cycle-dependent human H4 histone gene (pF0108A) which exhibits properties of an enhancer element. This distal element is not required for cap site initiation from the F0108A H4 histone gene. When the enhancer element is present in the genome as a stable integrated sequence, either in its natural upstream location or in a construct where the element is moved just upstream from the proximal promoter sequences, a 25-fold increase in the level of human H4 histone RNAs is observed. This increased level of mRNA reflects an increase in the rate of transcription. The enhancer effect is also observed when the distal element is inserted in inverse orientation with respect to this gene. In addition, the far upstream element can increase expression of a prokaryotic chloramphenicol acetyl transferase (CAT) gene under control of the simian virus 40 (SV40) early promotor, indicating that the ability to influence transcription is not confined to the gene with which it is normally associated. The ability of the histone gene distal enhancer element to function in both mouse and human cells indicates that transacting regulatory factors encoded by either the human or murine genome are capable of mediating the functional properties of this element, further supporting the cross-species compatibility of regulatory sequences and molecules that influence transcription of human histone genes.

Nucleosomal organization of a BPV minichromosome containing a human H4 histone gene

To address the relationship between chromatin structure and histone gene expression, the nucleosomal organization of a cell cycle-dependent human H4 histone gene in a bovine papilloma virus (BPV) minichromosome was examined. The nucleosome repeat length of the human H4 histone gene, maintained as a stable episome in a C127 mouse cell line designated I-8, was compared with that of the chromosomal copy of the H4 gene in human (HeLa) cells. In both cell lines, the H4 histone gene is predominantly expressed during the S phase of the cell cycle. The nucleosome repeat length of total HeLa cell and C127 mouse cell chromatin was similarly examined. Nuclei were digested with micrococcal nuclease and the DNA was fractionated electrophoretically, transferred to nitrocellulose filters and hybridized with radiolabelled (32P) cloned DNA probes. The nucleosome repeat length of the H4 gene, as an episome in the C127 mouse cell (153 +/- 8) and as an integrated copy in a HeLa cell (163 +/- 10) was considerably shorter than total genomic host cell (C127) (190 +/- 5) or HeLa cell chromatin (183 +/- 7). Our results indicate that the episomal H4 histone gene is packaged as chromatin. Moreover, the shortened nucleosome repeat length of the H4 gene, both as an episome or integrated chromosome sequence, suggests that the repeat length is characteristic of the gene and may be functionally related to its cell cycle regulated expression.

A nuclear protein with affinity for the 5' flanking region of a cell cycle dependent human H4 histone gene in vitro

A nuclear protein with affinity for the 5' flanking region of a cell cycle dependent human H4 histone gene has been partially purified from nuclear extracts of human HeLa S3 cells. The region involved in the binding of the protein has been localized to an upstream DNA segment using an electrophoretic mobility shift assay. This DNA segment is devoid of RNA polymerase II consensus sequences and contains both homopurinic and A/T rich tracts. Analogous experiments have identified a similar, and perhaps identical, factor that has affinity for a cell cycle dependent human H3 histone gene promoter. This protein appears to bind to a DNA segment containing A/T rich sequences that bear homology with the binding region of the H4 histone promoter. Cell synchronization experiments have shown that the overall affinity of the protein(s) for the H3 and H4 histone 5' flanking regions in vitro is not dramatically altered during the cell cycle. Although the rate of histone gene transcription is modulated during early S phase, transcription occurs throughout the cell cycle. Hence, the protein(s) we have detected here may play a role in the basal expression of these genes.

Coupling of histone mRNA levels to radioresistant DNA synthesis in ataxia-telangiectasia cells

Cloned genomic DNA for human histone H1, H3 and H4 genes has been used to determine the effects of gamma-radiation on histone mRNA levels and synthesis in ataxia-telangiectasia cells. Synthesis of histone mRNA was determined in cells synchronized with aphidicolin. Effects of irradiation on DNA synthesis and passage through S phase were also monitored. Irradiation was found to slow the passage of control cells through the cell cycle but had no effect on progression of ataxia-telangiectasia cells. H1 and core histone mRNA synthesis was inhibited by radiation in two control cell lines after release from aphidicolin block. No inhibition was observed in one ataxia-telangiectasia cell line and a small degree of inhibition in a second. An increased level of mRNA was observed in both irradiated control and ataxia-telangiectasia cells at 5-7 h post-irradiation compared to unirradiated cells. Similar results were obtained in log phase cells. These results demonstrate that histone mRNA synthesis is radioresistant in ataxia-telangiectasia cells and is coupled to radioresistant DNA synthesis in these cells.

Stance phase control of above-knee prostheses: knee control versus SACH foot design

The mobility of above-knee amputees (A/K) is limited, in part, due to the performance of A/K prostheses during the stance phase. Currently stance phase control of most conventional A/K prostheses can only be achieved through leg alignment and choice of the SACH (Solid Ankle Cushioned Heel) foot. This paper examines the role of the knee controller in relation to a SACH foot during the stance phase of level walking. The three-dimensional gait mechanics were measured under two stance phase conditions. In the first set of trials, the amputee used a prosthesis with a conventional knee controller that allowed the amputee to maintain the knee joint in full extension during the stance phase. In the second set of trials, the prosthetic knee, during stance, echoed the modified kinematics of the amputee's sound (intact) knee that had been recorded during the previous sound stance phase. Analysis and interpretation of the data indicate the following: (1) SACH foot design can strongly influence the walking mechanics independent of the knee controller; (2) knee controller design and SACH foot design are mutually interdependent; and (3) normal kinematics imposed on the prosthetic knee does not necessarily produce normal hip kinematics (e.g. reduce the abnormal rise in the prosthetic side hip trajectory). Future research is necessary to explore and exploit the interdependency of prosthetic knee control and foot design.

Synthesis and aldose reductase inhibitory activity of substituted 2-oxoquinoline-1-acetic acid derivatives

A number of 2-oxoquinoline-1-alkanoic acids that contain the N-acylglycine fragment found in several known inhibitors of aldose reductase were synthesized and tested in the rat lens assay. All of the target compounds were prepared by alkylation of the appropriate 2-oxoquinoline intermediates with a halo ester, followed by hydrolysis of the intermediate esters. In the rat lens assay, the 1-acetic acid derivatives 9a-e display the highest level of aldose reductase inhibitor activity with IC50 values of 0.45-6.0 microM. Modification of the 1-acetic acid moiety by esterification, substitution of an alpha-methyl group, or insertion of an additional methylene unit results in reduced inhibitory potency. Structure-activity data also suggests that both the benzene and 2-oxopyridine rings of 9a-e contribute substantially toward activity and that inhibitory potency is influenced by aromatic ring substituents.

Reversible changes in the nucleosomal organization of a human H4 histone gene during the cell cycle

The organization of nucleosomes associated with a cell cycle regulated human H4 histone gene was examined in synchronized HeLa S3 cells. At various times during the cell cycle, nuclei were digested with micrococcal nuclease, and the nucleosomal pattern of the gene was obtained by Southern blot analysis using radiolabeled human histone H4 gene probes. We have detected reversible changes during the cell cycle in the chromatin structure of this gene, as reflected by the shortening of the nucleosomal spacing after replication and the peak of transcription. This variation is also observed when DNA and protein syntheses are inhibited. By using a probe that comprises 250 base pairs (bp) of the coding region and 240 bp of the 5' end of the gene, containing the promoter and DNase I sensitive sequences, we also have observed a general disruption of the nucleosomal organization, which is reflected by a degeneration of the characteristic nucleosomal ladder produced by micrococcal nuclease digestion. This modification coincides with the replication and active transcription of the gene (early S phase), which recovers its regular nucleosomal appearance when both processes have been completed, although the nucleosome linker length is shortened. When the probe utilized comprises the distal 3' end of the gene, there is no disruption of the nucleosomal pattern, but the linker region also exhibits a shortened length. A non-cell cycle regulated gene (beta-globin) does not exhibit such modifications in any of the situations analyzed.(ABSTRACT TRUNCATED AT 250 WORDS)

Human histone genes map to multiple chromosomes

Histone genes were mapped to at least three human chromosomes by Southern blot analysis of DNAs from a series of mouse-human somatic cell hybrids (using 32P-labeled cloned human histone DNA as probes). Chromosome assignment was confirmed by in situ hybridization of radiolabeled histone gene probes (3H-labeled) to metaphase chromosomes. One human histone gene cluster (lambda HHG41) containing an H3 and H4 gene resides only on chromosome 1, whereas other clusters containing core (H3, H4, H2A, and H2B) alone (lambda HHG17) or core together with H1 histone genes (lambda HHG415) have been assigned to chromosomes 1, 6, and 12. These results suggest that the multigene family of histone coding sequences that reside in a series of clusters may be derived from a single cluster containing one each of the genes for the five principal classes of histone proteins. During the course of evolution, a set of events, probably involving reduplication, sequence modification, and recombination, resulted in the present pattern of human histone gene distribution among several chromosomes.

Selective expression of histone genes in mouse-human hybrid cells

Mouse-human hybrid cells preferentially segregating mouse chromosomes contain predominantly human histone mRNAs and synthesize human histone proteins. In contrast, hybrids segregating human chromosomes contain both human and murine histone mRNAs, yet synthesize only mouse histone proteins. These results suggest transcriptional control of histone gene expression in hybrids segregating mouse chromosomes and post-transcriptional regulation in hybrids segregating human chromosomes.

A series of repetitive DNA sequences are associated with human core and H1 histone genes

Repetitive DNA sequences, derived from the human beta-globin gene cluster, were mapped within a series of human genomic DNA segments containing core (H2A, H2B, H3 and H4) and H1 histone genes. Cloned recombinant lambda CH4A phage with human histone gene inserts were analyzed by Southern blot analysis using the following 32P-labeled (nick translated) repetitive sequences as probes: Alu I, Kpn I and LTR-like. A cloned DNA designated RS002-5'C6 containing (i) a (TG)16 simple repeat, (ii) an (ATTTT)n repeat and (iii) a 52 base pair alternating purine and pyrimidine sequence was also used as a radiolabelled hybridization probe. Analysis of 12 recombinant phage, containing 6 arrangements of core histone genes, indicated the presence of Alu I, Kpn and RS002-5'C6 repetitive sequences. In contrast, analysis of 4 human genomic DNA segments, containing both core and H1 histone genes, indicated the presence of only Alu I family sequences. LTR-like sequences were not detected in association with any of the core or H1 histone genes examined. These results suggest that human histone and beta-globin genes share certain aspects of sequence organization in flanking regions despite marked differences in their overall structure and pattern of expression.

Nuclear antigens in the HeLa cell cycle

Antisera to 0.35 M NaCl extracts and residues of S phase HeLa nuclei were reacted with electrophoretically separated proteins from the nuclei or nuclear material of HeLa cells synchronized in G1, S, G2 or M phases of the cell cycle. Quantitative evaluation of the peroxidase-antiperoxidase stained nitrocellulose transfers (Western blots) revealed significant changes in the quantities of nuclear non-histone proteins during the cell cycle. Immunochemical staining of electrophoretically separated nuclear antigens permits their selective detection in minute quantities and in the presence of many additional proteins.

cis-Diamminedichloroplatinum-mediated crosslinking of nuclear proteins to DNA is cell cycle specific

Immunochemical analysis was employed to investigate the cell cycle-dependent protein-DNA crosslinking by cis-diamminedichloroplatinum II (cis-DDP), in HeLa-S3 cells. Cells synchronized by double thymidine block or hydroxyurea were released into S phase and incubated at 2-h intervals with cis-DDP as they progressed through S1, G2, M, and then into G1 and S phases of the subsequent cycle. Immunoblots of the DNA-crosslinked antigens reacted with antisera to 0.35 M NaCl extract or residue of HeLa S-phase nuclei revealed that several antigens changed their DNA-crosslinking pattern during the progression of HeLa cells through their reproductive cycle.

Variations in the organization of human genomic DNA segments containing H1 histone genes

We have isolated from a lambda Ch4A library four human genomic DNA segments containing H1 histone genes. Analysis of the representation and organization of histone coding sequences indicates that three of these cloned DNA segments contain both core and H1 histone genes. One of the cloned human H1 histone genes has no core histone genes in close proximity.

Is human histone gene expression autogenously regulated?

It has been well documented that core and H1 histone mRNAs accumulate in a manner which closely parallels the initiation of DNA synthesis and histone protein synthesis, suggesting that the onset of histone gene expression early during S phase is at least in part transcriptionally mediated. In fact, it appears that throughout S phase the synthesis of histone proteins is modulated by the availability of histone mRNAs. On the other hand, the stability of histone mRNAs and the destabilization of histone mRNAs when DNA replication is completed or inhibited are highly selective, tightly coupled and largely post-transcriptionally controlled. We present a model to account for histone mRNA turnover whereby the natural or inhibitor-induced termination of DNA replication results in an immediate loss of high affinity binding sites for newly synthesized histone proteins which in turn brings about a transient accumulation of unbound histones. These unbound histones could modify the histone translation complex, via interactions with polysomal histone mRNAs, in such a manner as to render histone mRNAs accessible to cellular ribonucleases. This type of mechanism would be operative solely at the post-transcriptional level and would be compatible with the rapid, RNA synthesis-independent destabilization of histone mRNAs which occurs following inhibition of DNA replication, as well as with the requirement for protein synthesis for histone mRNA destabilization to be initiated.

Effect of adenovirus infection on expression of human histone genes

The influence of adenovirus type 2 infection of HeLa cells upon expression of human histone genes was examined as a function of the period of infection. Histone RNA synthesis was assayed after run-off transcription in nuclei isolated from mock-infected cells and after various periods of adenovirus infection. Histone protein synthesis was measured by [3H]leucine labeling of intact cells and fluorography of electrophoretically fractionated nuclear and cytoplasmic proteins. The cellular representation of RNA species complementary to more than 13 different human histone genes was determined by RNA blot analysis of total cellular, nuclear or cytoplasmic RNA by using a series of 32P-labeled cloned human histone genes as hybridization probes and also by analysis of 3H-labeled histone mRNA species synthesized in intact cells. By 18 h after infection, HeLa cell DNA synthesis and all parameters of histone gene expression, including transcription and the nuclear and cytoplasmic concentrations of core and H1 mRNA species, were reduced to less than 5 to 10% of the control values. By contrast, transcription and processing of other cellular mRNA sequences have been shown to continue throughout this period of infection. The early period of adenovirus infection was marked by an inhibition of transcription of histone genes that accompanied the reduction in rate of HeLa cell DNA synthesis. These results suggest that the adenovirus-induced inhibition of histone gene expression is mediated in part at the transcriptional level. However, the persistence of histone mRNA species at concentrations comparable to those of mock-infected control cells during the early phase of the infection, despite a reduction in histone gene transcription and histone protein synthesis, implies that histone gene expression is also regulated post-transcriptionally in adenovirus-infected cells. These results suggest that the tight coupling between histone mRNA concentrations and the rate of cellular DNA synthesis, observed when DNA replication is inhibited by a variety of drugs, is not maintained after adenovirus infection.

Influence of delta 9-tetrahydrocannabinol on expression of histone and ribosomal genes in normal and transformed human cells

The influence of delta 9-tetrahydrocannabinol (delta 9-THC) on the cellular levels of histone mRNAs and ribosomal RNAs was examined in several normal and transformed human cell lines--HeLa S3 cells, WI-38 human diploid fibroblasts, SV40-transformed WI-38 cells, and A549 lung carcinoma cells. RNA sequences were quantitatively assayed by electrophoretic fractionation, transfer to nitrocellulose, and hybridization with cloned genomic human histone or ribosomal DNA sequences. Treatment with delta 9-THC (10-40 microM) for 10 hr resulted in a concentration-dependent decrease in the representation of H2A, H2B, H3 and H4 histone mRNAs without a significant inhibitory effect on the levels of ribosomal RNAs. The cannabinoid-mediated inhibitory effect on histone gene expression was less evident in cells with active drug-metabolizing systems.

Variations in the organization and expression of human histone genes in normal diploid and tumor cell lines

The organization and expression of human histone genes were examined in W138 normal human diploid fibroblasts, SV40 transformed W138 cells, A549 epithelial lung carcinoma cells, two adeno-carcinoma cell lines (LOVO and HT29) and three leukemia cell lines (HL60, KG1 and K562). Analysis of the restriction enzyme digests of total genomic DNAs by hybridization with a series of cloned human histone sequences indicated polymorphic organization of at least a subset of the moderately reiterated human histone genes in these cells. Quantitative and qualitative differences were also observed in the representation of histone mRNAs by Northern blot analysis using cloned human histone genes as hybridization probes. However, there was no apparent correlation between variations in the representation of transcripts from various copies of the histone genes, variations in histone gene organization, and the extent of tumor progression.

A decreased influence of cannabinoids on macromolecular biosynthesis and cell proliferation in human cells which metabolize polycyclic hydrocarbon carcinogens

The influence of psychoactive and nonpsychoactive cannabinoids on macromolecular biosynthesis and cell proliferation was compared in normal and transformed human cells which differ with respect to their abilities to metabolize polycyclic hydrocarbon-containing carcinogens. delta 9-THC, delta 8-THC, 11-OH-delta 9-THC, cannabinol and cannabidiol cause a dose-dependent inhibition of [3H]thymidine, [3H]uridine and [3H]leucine incorporation and a dose-dependent inhibition of cell growth in both normal and transformed human cells. The effectiveness of cannabinoids in modifying nucleic acid biosynthesis, protein biosynthesis, and cell growth does not appear to be related to expression of the transformed phenotype; however, cells with enhanced drug metabolizing capacities, including abilities to metabolize polycyclic hydrocarbon-containing carcinogens, are significantly less sensitive to cannabinoid-induced effects on macromolecular biosynthesis and cell growth.

A nuclear matrix antigen HeLa and other human malignant cells

Antisera were obtained in rabbits to preparations of dehistonized chromatin from HeLa cells. By complement fixation assays, the antisera reacted with HeLa cell chromatin but only marginally with human placenta chromatin. The complement-fixing reactivity of the antisera was inversely related to the amount of dehistonized chromatin used for immunization. Immunochemical staining of electrophoretically separated chromosomal proteins transferred to nitrocellulose sheets revealed numerous antigens in chromatin preparations from several human tumors, placenta, and normal kidney. While immunoabsorption of the antisera with placenta chromatin removed some of the immunochemical staining, many of the electrophoretically separated antigens resisted repeated immunoabsorptions. However, further comparisons revealed that only one major protein antigen (band at an approximate molecular weight of 81,000) was represented in all the assayed human tumors while being absent from human placenta or kidney. Fractionation of HeLa cells into three cytoplasmic and several nuclear fractions showed that almost all the antigens recognized by antisera to dehistonized chromatin were nuclear. The antigenic protein with an approximately molecular weight of 81,000 was found associated with the nuclear matrix fraction.

Histone proteins in HeLa S3 cells are synthesized in a cell cycle stage specific manner

The synthesis of histone proteins in G1 and S phase HeLa S3 cells was examined by two-dimensional electrophoretic fractionation of nuclear and total cellular proteins. Newly synthesized histones were detected only in S phase cells. Histone messenger RNA sequences, as detected by hybridization with cloned human histone genes, were present in the cytoplasm of S phase but not G1 cells.