Alterations In DNA Synthesis Research Articles

The urinary bladder carcinogen propoxur does not produce genotoxic effects in the urinary bladder of Wistar male rats

Propoxur (PPX) is a carbamate insecticide which induced urinary bladder cancer in Wistar rats when fed at 5000ppm in Altromin 1321 diet (1321). In the present investigation, PPX was studied for induction of several key events related to modes of action (MOA) of carcinogenicity in urinary bladders (UBs). Wistar rats were administered the compound for 28 days at 8000ppm in Provini Liba SA 3883 diet, which is similar to the 1321 diet. o-Anisidine HCl (AH) was used as a genotoxic UB carcinogenic comparator, and trisodium nitrilotriacetate (NTA) as an epigenetic UB carcinogen comparator. Along with the non-dosed control and three test substance groups (PPX, AH, NTA), four more groups were additionally fed 2% ammonium chloride (AC) in the diet to acidify the urine, since 1321 was reported to increase urinary pH. AC did acidify the urine, as expected, although the 3883 diet itself did not increase pH values above 8. In the alkaline comet assay, AH produced DNA single strand breaks (SSBs) in the UB urothelium (UBU) irrespective of AC administration, whereas PPX and NTA did not. In the nucleotide 32P-postlabeling assay (NPL), AH produced DNA adducts irrespective of AC administration, whereas PPX and NTA did not. Routine (H&E) histopathology evaluation of the UBU did not reveal any hyperplasia or evidence of luminal microprecipitates or calculi in any of the groups. Assessment of UBU proliferation as measured by immunohistochemistry of proliferating cell nuclear antigen, revealed that NTA and NTA plus AC increased the replicating fraction (RF). Also AH plus AC, but not AH alone, increased the RF of UBU, whereas PPX groups were not significantly different from controls. Thus, the results reveal no evidence for DNA SSBs, binding, or alteration of DNA synthesis in the UBU by PPX, while demonstrating UBU DNA damage by AH and showing that NTA does not damage DNA, but causes increased UBU proliferation. The findings are in accord with a genotoxic MOA for AH, and an epigenetic MOA for NTA. The MOA of PPX does not involve genotoxicity and may be specific to the 1321 diet.

Mcm10 deficiency causes defective-replisome-induced mutagenesis and a dependency on error-free postreplicative repair

Mcm10 is a multifunctional replication factor with reported roles in origin activation, polymerase loading, and replication fork progression. The literature supporting these variable roles is controversial, and it has been debated whether Mcm10 has an active role in elongation. Here, we provide evidence that the mcm10–1 allele confers alterations in DNA synthesis that lead to defective-replisome-induced mutagenesis (DRIM). Specifically, we observed that mcm10–1 cells exhibited elevated levels of PCNA ubiquitination and activation of the translesion polymerase, pol-ζ. Whereas translesion synthesis had no measurable impact on viability, mcm10–1 mutants also engaged in error-free postreplicative repair (PRR), and this pathway promoted survival at semi-permissive conditions. Replication gaps in mcm10–1 were likely caused by elongation defects, as dbf4–1 mutants, which are compromised for origin activation did not display any hallmarks of replication stress. Furthermore, we demonstrate that deficiencies in priming, induced by a pol1–1 mutation, also resulted in DRIM, but not in error-free PRR. Similar to mcm10–1 mutants, DRIM did not rescue the replication defect in pol1–1 cells. Thus, it appears that DRIM is not proficient to fill replication gaps in pol1–1 and mcm10–1 mutants. Moreover, the ability to correctly prime nascent DNA may be a crucial prerequisite to initiate error-free PRR.

Effects of combined radiofrequency radiation exposure on the cell cycle and its regulatory proteins

The aim of this study was to investigate whether single or combined radio frequency (RF) radiation exposure has effects on the cell cycle and its regulatory proteins. Exposure of MCF7 cells to either single (837 MHz) or combined (837 and 1950 MHz) RF radiation was conducted at specific absorption rate values of 4 W/kg for 1 h. During the exposure period, the chamber was made isothermal by circulating water through the cavity. After RF radiation exposure, DNA synthesis rate and cell cycle distribution were assessed. The levels of cell cycle regulatory proteins, p53, p21, cyclins, and cyclin-dependent kinases were also examined. The positive control group was exposed to 0.5 and 4 Gy doses of ionizing radiation (IR) and showed changes in DNA synthesis and cell cycle distribution. The levels of p53, p21, cyclin A, cyclin B1, and cyclin D1 were also affected by IR exposure. In contrast to the IR-exposed group, neither the single RF radiation- nor the combined RF radiation-exposed group elicited alterations in DNA synthesis, cell cycle distribution, and levels of cell cycle regulatory proteins. These results indicate that neither single nor combined RF radiation affect cell cycle progression.

Aberrant nuclear factor-κB activity and its participation in the growth of human malignant astrocytoma

It has been suggested that nuclear factor (NF)-kappaB, a pleiotropic transcription factor, controls cell proliferation. The authors examined NF-kappaB activity and its participation in the growth of human malignant astrocytoma. The authors examined NF-kappaB activity in human malignant astrocytoma cell lines and high-grade astrocytoma tissues by using electrophoretic mobility shift assays and immunohistochemical studies, respectively. In addition, messenger (m)RNA expression of p50 and RelA, which are representative subunits of NF-kappaB, and IkappaBalpha, which is a representative inhibitory protein of NF-KB, were analyzed using Northern blot hybridization in the astrocytoma cell lines. Furthermore, alterations in DNA synthesis and cell growth in the astrocytoma cell lines were examined after inhibition of NF-kappaB activity by RelA antisense oligodeoxynucleotide. The authors found NF-kappaB activity in all astrocytoma cell lines and high-grade astrocytoma tissues that were examined, but not in the fetal astrocyte strain or in normal cerebral tissue. Expression of p50, RelA, and IkappaBalpha mRNA was found in the fetal astrocyte strain and normal adult brain tissue, in addition to the astrocytoma cell lines. The relative levels of expression of these mRNAs were similar among these cell lines, the cell strain, and normal tissue. The RelA antisense oligodeoxynucleotide specifically reduced the levels of RelA mRNA expression and NF-kappaB activity in the astrocytoma cell lines, thus significantly inhibiting their DNA synthesis and cell growth. Human malignant astrocytoma cells have aberrant NF-KB activity, which promotes their growth. This activity is not associated with aberrant expression of p50 and RelA.

Anticancer drug targets: growth factors and growth factor signaling.

Signaling mechanisms that drive cell proliferation are closely associated with tumor malignancy. Components of these pathways, encoded by some of the very first oncogenes identified, include the PDGF-like ligand Sis, the tyrosine kinases Src and HER-2/c-Neu (HER-2), and the GTP-binding switch Ras. The study of communication by these oncoproteins has identified a complex array of intracellular circuits. In some cancers, mutations in key components lead to constitutive activation of these pathways; this activation is associated with the proliferative properties of the tumor cells. In this Perspective, I provide a broad overview of a growth factor signal transduction system, with a focus on those points that have been translated to drugs or clinical candidates. Due to editorial restrictions limiting the number of reference citations, much of the clinical data gleaned from abstracts is not listed in the references. Instead, the reader is directed to the 1999 Proceedings of the American Society of Clinical Oncology and the 1999 Proceedings of the AACR-NCI-EORTC International Conference. Signaling pathways are initiated with the binding of a ligand, such as PDGF, EGF, EGF-like ligands (e.g., TGF-α and amphiregulin), or IGF, to its cognate transmembrane receptor (1). Ligand binding induces the dimerization of receptor subunits, promoting autophosphorylation of the receptor and recruiting a variety of intracellular docking proteins (such as Grb2, Shc, and Nck) to the plasma membrane. These docking proteins create a molecular scaffold from which subsequent signals emanate. For example, the guanine nucleotide exchange factor Sos binds to Grb2, which in turn interacts with the Ras protein. Ras serves as a molecular switch in the plasma membrane that alternates between an inactive GDP-bound state and an active GTP-bound state. Normally, Ras is bound to GDP because of the abundance of GTPase-activating protein and neurofibromin, which both suppress Ras function. However, upon recruitment of Sos to the membrane, Sos binds Ras-GDP and facilitates release of GDP. In cells, the nucleotide GTP is about 10-fold more abundant than GDP; GTP binds to Ras by mass action. Ras-GTP adopts a conformation that permits interaction with downstream targets called effector molecules. These effectors include the protein kinase Raf, which activates the MAP kinase cascade; GTPase-activating protein, which links Ras to the Rho/Rac pathway; and phosphoinositide (PI) 3′-kinase and Ral–guanine nucleotide dissociation stimulator (Ral-GDS), which activate lipid pathways (2). The dysregulation of these signals in tumor cells leads to multiple cellular changes, including alterations in DNA synthesis, lipid metabolism, cellular morphology, cell adhesion properties, and gene expression. In the broadest sense, the study of signaling mechanisms has already yielded therapeutic agents in the treatment of cancer, as evidenced by antiestrogens, antiandrogens, agonists of gonadotropin-releasing hormone, and stem cell growth factors, for example. However, research into oncoproteins that function within the signal transduction system is only beginning to be applied in the clinic. Therapeutic approaches of interest include tools such as mAbs against the extracellular domain of receptors, oligonucleotides that are antisense to key target proteins, and small molecule inhibitors of enzymes (Table ​(Table11). Table 1 Examples of inhibitors of growth factor signaling for cancer treatment

Ventromedial hypothalamic lesion-induced vagal hyperactivity stimulates rat pancreatic cell proliferation

BACKGROUND & AIMS: Ventromedial hypothalamic (VMH) lesions cause an increase in DNA content in the rat pancreas. This study examined the role of cell proliferation in the mitotic response of the rat pancreas after VMH lesion formation. METHODS: Alterations in rat pancreatic DNA content, DNA synthesis, and labeling indices using antiproliferation cell nuclear antigen molecular antibody were measured 0,1,3, and 7 days after VMH lesion formation. Additionally, the effects of vagotomy, atropine, or anti-insulin antibody on VMH lesion-induced alterations in DNA synthesis were examined. Pancreatic samples were also treated with double immunostaining: first for PCNA and then for insulin, glucagon, and somatostatin. RESULTS: Pancreatic weight, DNA content, and DNA synthesis increased in animals receiving VMH lesions. Proliferation was primarily observed in islet B and acinar cells beginning 1 day after VMH lesion formation, reaching a maximum rate after 3 days. VMH lesion- induced stimulation of DNA synthesis was completely inhibited by vagotomy or atropine administration but not by anti-insulin antibody. CONCLUSIONS: Vagal hyperactivity produced by VMH lesions stimulated cell proliferation of rat pancreatic islet B and acinar cells primarily through a cholinergic receptor mechanism. (Gastroenterology 1996 Mar;110(3):885-93)

Reactive oxygen species inducible by low-intensity laser irradiation alter DNA synthesis in the haemopoietic cell line U937.

The purpose of this study was to evaluate the possible role of reactive oxygen species (ROS) in mediating previously recorded alterations in DNA synthesis, inducible by low-intensity laser irradiation (LILI), in the haemopoietic cell line U937. The ability of LILI (660 nm, 12 mW, 5 kHz) to induce ROS from U937 cells was assessed spectrophotometrically at energy densities (E.D.) from 1.0 to 11.5 J/cm2. In order to assess whether laser-induced ROS could alter cellular proliferation DNA synthesis was measured post-irradiation, by the incorporation of tritiated thymidine (3H-TdR) into the cells in both the presence and absence of the antioxidant catalase (CAT). Detectable ROS were produced post-irradiation only from the differentiated form of the cell line. Analysis by Student's t-test for unrelated groups showed a significant difference, at E.D.s 2.9 and 8.6 J/cm2, in the extent of DNA synthesis occurring in cells irradiated in the presence of CAT or in its absence. These findings demonstrate that laser-inducible ROS can mediate laser's effects on this cell line.

Reactive oxygen species inducible by low‐intensity laser irradiation alter DNA synthesis in the haemopoietic cell line U937

Background and Objective The purpose of this study was to evaluate the possible role of reactive oxygen species (ROS) in mediating previously recorded alterations in DNA synthesis, inducible by low-intensity laser irradiation (LILI), in the haemopoietic cell line U937. Study Design/Materials and Methods The ability of LILI (660 nm, 12 mW, 5 kHz) to induce ROS from U937 cells was assessed spectrophotometrically at energy densities (E.D.) from 1.0 to 11.5 J/cm2. In order to assess whether laser-induced ROS could alter cellular proliferation DNA synthesis was measured post-irradiation, by the incorporation of tritiated thymidine (3H-TdR) into the cells in both the presence and absence of the antioxidant catalase (CAT). Results Detectable ROS were produced posy-irradiation only from the differentiated form of the cell line. Analysts by Student's t-test for unrelated groups showed a significant difference, at E.D.s 2.9 and 8.6 J/cm2, in the extent of DNA synthesis occurring in cells irradiated in the presence of CAT or in its absence. Conclusion These findings demonstrate that laser-inducible ROS can mediate laser's effects on this cell line. © 1996 Wiley-Liss, Inc.

Alterations in DNA synthesis and cellular constituents in mouse lung following bleomycin injections.

Changes in the DNA synthesis and cellular constituents of mouse lung following repeated bleomycin (BLM) injections were studied. ICR mice were administered BLM subdermally for 10 days. Wet lung weight was increased 1.36 times on day 5 after the final administration compared with control mice receiving an identical volume of saline only for 10 days. The total number of cells in the bronchoalveolar lavage fluid of the BLM group reached a maximum on day 14, and histologic investigation of the lungs revealed marked cellular infiltrations. The labeling index obtained by the antibromodeoxyuridine monoclonal antibody method for cells was increased from days 5 to 14 in the BLM group. By day 28, these inflammatory changes had subsided and fibrotic remodeling had occurred. DNA polymerase activity in the lung tissue reached its maximal level on day 5 and remained unchanged until day 14. This phenomenon occurred in parallel with increases in DNA content and synthesis. During this period, an increase in DNA polymerase-beta activity and new induction of DNA polymerase-alpha activity were observed by phosphocellulose column chromatography. From these observations, it is concluded that: (1) repeated injections of BLM cause DNA injury in lung cells; (2) there is a subsequent increase in the DNA repair function as supported by the finding of an increase in DNA polymerase-beta activity; and (3) these lead further to cell proliferation as supported by the increase in both DNA polymerase-alpha activity and DNA content. Thus, a close relationship between morphologic changes and altered DNA synthesis was observed in the lungs of mice after BLM injections.

Alteration of DNA synthesis in human brain tumor cells by gallium nitrate in vitro

We measured 3H-thymidine incorporation by human brain tumor cell lines treated with varying doses of gallium nitrate. These DNA synthesis data indicate that the effects of gallium documented for brain tumor cell viability parallel those for alterations in DNA synthesis. The primitive, poorly-differentiated, small, round-cell tumors (medulloblastoma and rhabdomyosarcoma) appear to be more sensitive than glially differentiated neoplasms (glioblastoma) to DNA synthesis inhibition by gallium nitrate.

Transferrin Receptor Expression in Rat Liver: Immunohistochemical and Biochemical Analysis of the Effect of Age and Iron Storage

Hepatic transferrin receptors were studied in normal male rats at 1 to 59 wk after weaning, using immunohistochemical and biochemical techniques. The number of transferrin receptors measured and the intensity of the staining in situ decreased rapidly during the first 10 wk of life and more slowly thereafter. Immunohistochemistry further demonstrated changes in the topographical and (sub)cellular localization of the transferrin receptor. In the young rat livers, staining was almost exclusively present on hepatocytes in acinar zone 2 + 3 in a honeycomb to sinusoidal pattern. With aging, a panacinar heterogeneous and mainly sinusoidal staining of hepatocytes was more frequent. Kupffer cell positivity was more obvious as compared with the young rat livers. The observed changes in transferrin receptor expression may partly be explained by age-dependent alterations in DNA synthesis and proliferative potential of the liver cells. A series of rats were iron loaded with carbonyl iron up to 39 wk and "unloaded" by administration of a normal diet during 20 wk. In these animals, serial histochemical studies showed predominantly parenchymal (7 to 14 wk), mixed parenchymal and reticuloendothelial (39 wk) and almost exclusive reticuloendothelial siderosis (59 wk). In the siderotic livers transferrin receptor numbers tended to be lower than in the controls with significant differences after 14 and 39 wk. Immunohistochemistry showed decreased parenchymal but increased reticuloendothelial transferrin receptor expression with iron load. After the period of unloading, parenchymal transferrin receptors were virtually absent despite the negligible siderosis of these cells. In contrast, siderotic reticuloendothelial cells were intensely positive. These findings support down-regulation of parenchymal transferrin receptor resulting from iron storage. However, the positivity of siderotic reticuloendothelial cells and the absence of re-emergence of parenchymal receptors in conditions of minimal parenchymal and prominent reticuloendothelial siderosis need further elucidation.

Nuclear DNA synthesis is blocked by UV irradiation in dictyostelium discoideum

We have used a thymidine auxotroph of the simple eukaryote, Dictyostelium discoideum and alkaline sucrose gradients of isolated nuclei to study alterations in DNA synthesis following irradiation of replicating haploid cells with 254 nm UV light. Three responses were charcterized using pulse-chase protocols: (1) Lags in DNA synthesis as measured by the amount of label incorporated were 4, 9, and 20 h after 10, 50, and 200 J/m2. (2) The DNA synthesized during a 15-min pulse immediately after irradiation was of lower single strand molecular weight: 7, 3.5, and 3 × 106 dalton after 0, 50, and 200 J/m2. (3) The time required for maturation of the nascent DNA to full-sized strands of 2 × 108 dalton was 45−50 min for unirradiated cells, 3 h after 10 J/m2. The DNA of the irrafiated cells did not mature uniformly during these delays; instead, a period of no increase in size was followed by a rapid, nearly control rate of maturation. We conclude: (a) at least some UV lesions block elongation of relicons; (b) the elongation of the replicons and their subsequent joining to yield mature high molecular weight DNA occurs after most of the lesions are repaired; (c) the timing of the different aspects of recovery suggest that initiation of replication is also inhibited.

Ovine uterine morphogenesis: effects of age and progestin administration and withdrawal on neonatal endometrial development and DNA synthesis.

To determine effects of age and administration and withdrawal of a synthetic progestin (P) on endometrial development and DNA synthesis, ewe lambs were ovariectomized on d 0 (birth) and assigned to one of four groups (n = three/group) that provided (by means of hemihysterectomy) the following uterine tissue types: 1) d 0 control, 2) d 13 control, 3) d 26 control, 4) d 13 after 13 d exposure to P (13P) and 5) d 26 after P exposure from d 0 to 13 (26P). Uterine tissues were processed for histology or explanted with [methyl-3 H] thymidine for autoradiography. Labeling index (LI) was determined for stroma and epithelium in caruncular and intercaruncular endometrial areas and for lumenal and glandular epithelium in uteri with glands. Endometrial glands were absent on d 0, evident at d 13 and well developed by d 26. Day 0 LI was greater (P less than .05) in caruncular than in intercaruncular areas, and greater in stromal than in epithelial tissues. Relationships were reversed in d 13 endometrium (day X endometrial area, P less than .07). Caruncular stromal LI was greater on d 0 than later (P less than .02), whereas intercaruncular epithelial LI was greater after d 0 (P less than .05), but decreased from d 13 to 26 (P less than .05). Glandular epithelial LI was higher on d 13 than on d 26 (P less than .03). Administration of P inhibited endometrial gland development and suppressed d 13P intercaruncular LI (P less than .05). Withdrawal of P was followed by endometrial gland development and increased (P less than .01) intercaruncular epithelial LI in d 26P uteri. Ovary-independent initiation of endometrial gland development involves age- and region-specific alterations in DNA synthesis and could involve negative control.

Cell kinetic effects of low doses of the skin carcinogen 7,12-dimethylbenz[a]anthracene on hairless mouse epidermis.

Groups of hairless (hr/hr) mice were given a single, topical skin application of either 50, 5 or 0.5 micrograms 7,12-dimethylbenz[a]anthracene (DMBA). At different times up to 3 days after treatment epidermal DNA distribution patterns were determined by flow cytometry, and sp. act. of DNA and labeling indices were obtained based on incorporation of [3H]thymidine. Mitotic rates were determined by the Colcemid method, and the number of basal and suprabasal cells were scored in histological sections. All three doses of DMBA led to an early depression in the uptake of [3H] thymidine, associated with an accumulation of cells with S phase DNA content peaking at 16 h. By combining the methods for studying DNA synthesis, it can be concluded that the alterations observed probably were due to a slow rate of DNA synthesis in the S phase cells, rather than to a block at the entrance of cells into the S phase. Three days after the application, DMBA still maintained an effect on the cell cycle progression, at least in the S phase. There was an obvious dose-response relationship in the inhibition of epidermal DNA synthesis. Six hours after application of the two highest doses of DMBA an early increase in the mitotic rate was observed. This short-lasting high mitotic rate was followed by a transient, very brief increase in the number of suprabasal cells. Thereafter a decrease in both the mitotic rate and the number of suprabasal cells occurred, probably caused by the alterations in DNA synthesis. After the lowest dose there was no such early increase in the mitotic rate and no initial, short-lasting increase in the number of suprabasal cells. Hence, this study shows that decreasing doses of DMBA provoke decreasing degrees of the same type of cell kinetic perturbations in the epidermal cell cycle.

The activity of tissue enzymes in iron-deficient rat and man: an overview.

The effects of iron deficiency in rat and/or man on iron-containing enzymes of different tissues is reviewed. Iron deficiency results in a decrease of skeletal muscle iron containing proteins e.g. myoglobin, cytochromes c, a + a3, and alpha-glycerophosphate oxidase. Iron deficiency produces a reduction in the activity of several respiratory enzymes in the mitochondrial fraction of cardiac muscle, particularly: NADH cytochrome c reductase, succinic cytochrome c reductase, succinic dehydrogenase and NADH ferricyanide oxidoreductase. The effects of iron deficiency on brain tissue is emphasized with respect to cytochromes, monoaminoxidase and amino acids metabolism. Host defence to infection (controversial data), decrease in body temperature, alteration of DNA synthesis, collagen and lipid metabolism, liver and gastrointestinal mucous cytochromes activity perturbations are discussed.

Hyperthermia and the Cell Nucleus

Recent reviews document that hyperthermic shock inhibits the major nuclear activities, including semiconservative DNA replication (1, 2). These inhibitions may result either from a direct effect of heat on the cell nucleus or as a consequence of changes in other cell compartments [e.g., cell membrane damage (3)]. Here we review recent results concerning heat-induced changes in mammalian cell nuclear structure and function, principally DNA replication. These data are discussed in terms of a current model of nuclear organization in order to relate these heat-induced alterations in the nucleus to known cellular effects of heat, such as cytotoxicity and alterations in DNA synthesis.

Manipulation of brain DNA synthesis is achieved by using a systemic immunological disease.

Previously, we showed that as early as postnatal day 11 an immunological disease, graft-versus-host disease, induced by grafting allogeneic lymph node cells into an immunoincompetent neonatal rat significantly decreases cerebellar histogenesis--i.e., DNA synthesis and the number of newly formed neurons. Here, we report that, subsequent to successful immunotherapy, there was a reversal of the deleterious graft-versus-host disease-induced alterations in DNA synthesis in individual cerebellar germinal cells. Immunotherapy involved treating the diseased rats on postnatal days 11, 12, and 13 with alloantiserum specifically directed against the grafted lymph node cells injected on the day of birth. On postnatal day 14, diseased, serum-treated, and control littermates were injected with [3H]thymidine and, 15 min later, the cerebella were excised and autoradiographed. A 0.72-mm segment of the external granular layer in the cerebellar fissure between lobules VIB and C was searched for labeled cells. The control group had the greatest number of labeled cells, defined by the presence of six or more autoradiographic grains. (43 +/- 4, mean +/- SEM) and the greatest number of grains per cell (9.5 +/- 0.2). Rats with the disease had few labeled cells (4 +/- 2) and the number of grains per cell was low (6.6 +/- 0.6); however, serum treatment increased both the number of labeled cells (26 +/- 8) and the number of grains per cell (7.4 +/- 0.2). These results show that without mononuclear infiltrates or inflammation in the cerebellum, a systemic immunological disease can dramatically decrease DNA synthesis per germinal cell and, moreover, that halting the disease by alloantiserum therapy can reverse this effect. These findings emphasize the sensitive plastic nature of neuronal cell acquisition in the normally developing brain.

Photoaugmentation in the Hairless Mouse: A Study Using Ornithine Decarboxylase Activity and Alteration of DNA Synthesis as Markers of Epidermal Response

Photoaugmentation is the potentiation of UVB-induced cutaneous erythema by UV irradiation. We have examined other cutaneous responses to UVB irradiation-the 4 hr depression of DNA synthesis, the 48 hr stimulation of DNA synthesis, and the induction of ornithine decarboxylase (ODC), to determine whether these were also susceptible to augmentation by UVA, which does not cause these responses when administered alone. No photoaugmentation of DNA synthesis, stimulation or ODC induction occurred. The early depression of DNA synthesis was slightly augmented for this did not consistently reach significance.

A simple method for measuring DNA synthesis in epidermis and sebaceous glands and its application in chalone assays.

Liquid scintillation counting and autoradiography were used to measure DNA synthesis (3H-TdR uptake and incorporation) by the epidermis and the sebaceous glands in mouse pinna skin. Using this approach it has been possible to show that a chalone-like inhibitor of DNA synthesis acts rapidly to restrict the flow of epidermal G1 cells into S-phase. The point of action within the cell cycle is probably at the G1-S phase 'boundary'. The technique described is sufficiently sensitive to be used for measuring small alterations in DNA synthesis in short-term experiments and for long-term experiments in which the size of the progenitor cell population is altered by systemic or topical administration of compounds influencing DNA synthesis.

Biological effects of alkali-treated protein and lysinoalanine: an overview.

The renal alterations induced by alkali-treated protein and lysinoalanine are reviewed and their biological implications discussed. Alkali-treated proteins and lysinoalanine, an unusual amino acid formed in proteins during alkali treatment, have been shown to produce a renal alteration characterized by nuclear and cytoplasmic enlargement, with alterations in DNA synthesis, mitotsis and nucleoprotein. These changes are localized in the straight portion of the proximal renal tubule and have been observed in rats but not in several other species. The nephrotoxic effect of synthetic lysinoalanine has been consistently demonstrated, but the ability of alkali-treated protein to induce renal alterations is apparently modified by factors other than lysinoalanine content. Factors which may influence the development of the kidney lesions in animals fed alkali-treatment protein are discussed, including nutritional factors, the chemical form of lysinoalanine in the protein, species differences, and metabolic fate. Other clinical and experimental conditions that result in similar renal alterations are presented for comparison with the lysinoalanine induced lesion, and possible functional consequences are considred.