Histone gene switching in murine erythroleukemia cells is differentiation specific and occurs without loss of cell cycle regulation

We investigated the expression characteristics of the fully replication-dependent (FRD) and the partially replication-dependent (PRD) histone gene variants by measuring changes in steady-state mRNA levels during hexamethylene bisacetamide (HMBA)-induced differentiation of murine erythroleukemia (MEL) cells. Between 24 and 60 h after induction, there was a dramatic switch in histone gene expression, such that the ratio of PRD to FRD transcripts increased severalfold over that found in uninduced MEL cells. We demonstrated that this gene switching was not simply a partial or complete uncoupling of PRD gene expression from DNA synthesis. PRD and FRD transcript levels were regulated coordinately upon treatment of uninduced or induced MEL cells with inhibitors of DNA synthesis, protein synthesis, or both. Using several criteria, we were unable to detect any difference in PRD and FRD gene expression under any conditions except in cells undergoing differentiation. MEL cells were arrested at a precommitment stage of differentiation by induction with HMBA in the presence of dexamethasone (DEX). If DEX was subsequently removed, DNA synthesis resumed, the cells underwent commitment, and histone gene switching was observed. In contrast, if both DEX and HMBA were removed, DNA synthesis still resumed, but commitment did not occur and no gene switching was observed. These results imply that histone gene switching is intimately related to the differentiation process.

Isolation and characterization of a mouse fully replication-dependent H1 gene within a genomic cluster of core histone genes

We have used an oligonucleotide complementary to a sequence coding for the conserved central globular domain of H1s to screen a mouse genomic library for H1 genes. We then used a series of universal histone oligonucleotides to identify five different H1 genes which were linked to core histone genes. We characterized one of the H1 genes which was linked to an H2a, an H2b, an H3, and an H4 histone gene. This characterization involved: 1) sequencing of the coding region of the gene and several hundred base pairs of flanking region. 2) Comparison of this sequence to other H1 sequences from other organisms. This sequence analysis clearly showed that the gene coded for an H1 and identified H1 consensus sequences in the 5'- and 3'-flanking region. 3) Mapping of the 5'- and 3'-ends of the mRNA complementary to this gene by S1 nuclease analysis. 4) Identifying this gene and an adjacent H3 gene as being of the fully replication-dependent expression class, by measuring changes in the steady state levels of their mRNAs in the presence of hydroxyurea and during differentiation of murine erythroleukemia cells.

Dihydrolipoyl transacetylase of Escherichia coli. Formation of 8-S-acetyldihydrolipoamide

The dihydrolipoyl transacetylase component (E2) of the pyruvate dehydrogenase complex catalyzes the reaction of acetyl coenzyme A (acetyl-CoA) with dihydrolipoamide, producing coenzyme A and S-acetyldihydrolipoamide. The acetyl group is shown by experiments reported herein to be bonded to S8 in the enzymatic product. 1H NMR analysis of synthetic samples of both structural isomers of S-acetyl-S-(phenylmercurio)dihydrolipoamide enabled structural assignments to be made. Reaction of 8-S-acetyl-6-S-(phenylmercurio)dihydrolipoamide with 3-mercaptopropionic acid in chloroform produced 8-S-acetyldihydrolipoamide which contained a small amount (5%) of the 6-S isomer. Reaction of 6,8-di-S-acetyldihydrolipoamide with NH2OH produced a 4:1 mixture of 6-S-acetyldihydrolipoamide and the 8-S isomer. These compounds did not isomerize at significant rates in chloroform but rapidly isomerized to the equilibrium mixture in aqueous solution (Keq = 3.4). The second-order rate constants for the hydroxide-catalyzed isomerization were found to be kf = (1.15 +/- 0.07) X 10(6) M-1 X s-1 and kr = (3.36 +/- 0.20) X 10(5) M-1 X s-1 in the direction of the formation of the 8-S isomer. The enzymatic product was trapped by addition of phenylmercuric hydroxide within 15 s-30 min after starting the reaction. 1H NMR analysis of the products obtained at various times showed that the enzymatic product was 8-S-acetyldihydrolipoamide, which underwent progressive isomerization to the mixture of isomers within a few minutes. In the reaction of acetyl-CoA with dihydrolipoamide, the latter substrate reacts in place of enzyme-bound dihydrolipoyl moieties. Therefore, acetylation occurs at the 8-S position of bound lipoyl groups.

Alterations in the transferrin receptor of human erythroleukemic cells after induction of hemoglobin synthesis

When K562 human erythroleukemic cells are induced to differentiate by addition of hemin to their medium, the number of binding sites for transferrin on the cell surface is substantially reduced. This reflects an internalization of receptors since no such reduction is observed when the total binding sites in soluble extracts of uninduced and differentiating cells are compared. The internalization of transferrin receptors has also been shown using lactoperoxidase-mediated radioiodination of cell surfaces and by immune precipitation of total and surface labeled receptors using an anti-receptor monoclonal antibody. Transferrin receptors from uninduced and differentiating cells were partially purified by affinity chromatography on transferrin-Sepharose and shown to be disulfide-bridged homodimers of a polypeptide with an apparent molecular weight of approximately 90,000. This protein is a phosphoprotein that can be resolved by isoelectric focusing into three major and two minor forms. By digestion with bacterial alkaline phosphatase, it was shown that at least four of these forms are probably phosphorylation variants of a single polypeptide. As differentiation proceeds, the proportions of the individual forms of the receptor change with a shift to the more phosphorylated polypeptides.

Secretion of human chorionic gonadotropin and alpha-fetoprotein by an ovarian germ cell tumor of apparent yolk sac origin

alpha-Fetoprotein (alpha FP) and four placental proteins, human chorionic gonadotropin (hCG), human placental lactogen (hpL), pregnancy specific beta 1-glycoprotein (SP1), and placental protein 5 (PP5), were measured in a 17-year-old patient with endodermal sinus tumor of the ovary. The circulating levels of alpha FP were consistently high (more than 14 mg/ml), and alpha FP was localized in tissue sections using immunohistochemical techniques. None of the four placental proteins was detectable in serum samples, but hCG was detected in urinary concentrates in an episodic manner. This ectopic hCG resembled placental hCG in its physicochemical and immunological characteristics. Unlike alpha FP, hCG was not detected in the tumor by immunohistochemical methods. This study indicates that the neoplasm elaborated both hCG and alpha FP. Whether pure endodermal sinus tumor of the ovary is capable of secreting hCG cannot be answered by this study because of limited histologic sampling. The likelihood that this represents a mixed germ cell tumor in which only the endodermal sinus tumor element was sampled remains a possibility. This study also indicates that the 24-hr urinary concentrate is far more sensitive than serum samples for hCG detection.

Reactivation of Chlamydia trachomatis lung infection in mice by cortisone

To study the latency, chronicity, and recurrent nature of chlamydial infection, we attempted to reactivate Chlamydia trachomatis lung infection in mice by immunosuppressive therapy with cortisone. Mice were treated with subcutaneous injections of cortisone acetate (125 mg/kg) every other day, starting on day 14 after intranasal inoculation of C. trachomatis serotype B (TW-5). C. trachomatis was recovered from the lungs beginning day 6 after the start of cortisone treatment until the end of the observation period on day 12 of treatment. Overall, the reactivation was successful in 8 of 55 mice treated with cortisone, in contrast to 0 of 41 inoculated, untreated mice (P = 0.009) and 0 of 35 uninoculated, treated mice. Cortisone treatment affected the ability of peritoneal exudate cells to respond to migratory inhibition after exposure to purified whole organisms of C. trachomatis serotype B (TW-5) but had little effect on serum antibody titers, indicating a possible role for cellular immunity in resistance against C. trachomatis infection in the lung.