Pancreatic Cancer Derived 3-D Organoids as Clinical Tool to Predict Response to Radiation and Chemo-Radiation Therapy

PURPOSE/OBJECTIVE(S)

Pancreatic cancer (PC) is the fourth leading cause of cancer death in both men and women. The standard of care for patients with locally advanced PC of chemotherapy, stereotactic radiotherapy (RT) or chemo-radiation-therapy has shown highly variable and limited success rates. However, three-dimensional (3D) Pancreatic tumor organoids (PTOs) have shown promise to study tumor response to drugs, and emerging treatments under in vitro conditions. We investigated the potential for using 3D organoids to evaluate the precise radiation and drug dose responses of in vivo PC tumors.

MATERIALS/METHODS

PTOs were created from mouse pancreatic tumor tissues, and their microenvironment was compared to that of in vivo tumors using immunohistochemical staining. The organoids and in vivo PC tumors were treated with fractionated X-ray RT, 3-bromopyruvate (3BP) anti-tumor drug, and with a combination of 3BP + fractionated RT. We quantified treatment response by metabolic imaging and immunofluorescence of αSMA and vimentin markers.

RESULTS

Pancreatic tumor organoids (PTOs) exhibited a similar fibrotic microenvironment and molecular response (as seen by apoptosis biomarker expression) as in vivo tumors. Untreated tumor organoids and in vivo tumor both exhibited proliferative growth of 6 folds the original size after 10 days, whereas no growth was seen for organoids and in vivo tumors treated with 8 (Gray) Gy of fractionated RT. Tumor organoids showed reduced growth rates of 3.2x and 1.8x when treated with 4 and 6 Gy fractionated RT, respectively. Interestingly, combination of 100 µM of 3BP + 4 Gy of RT showed pronounced growth inhibition as compared to 3-BP alone or 4 Gy of radiation alone. Further, we observed overexpression of OCT-4, SOX2, Nanog cancer stem cell markers (CSC) indicated presence of cancer stem cells in tumor organoids which might have some role in resistance to therapies and recurrence in pancreatic cancer.

CONCLUSION

PTOs produced a similar microenvironment and exhibited similar growth characteristics as in vivo tumors following treatment, indicating their potential for predicting in vivo tumor sensitivity and response to RT and combined chemo-RT treatments. Cancer stem cells in pancreatic cancer could be playing a role in resistance to therapies and recurrence in pancreatic cancer.

Determination of the vertical distribution of radioelements (K, U, Th, Cs) in soils from portable HP-Ge spectrometer measurements: A tool for soil erosion studies

Soil erosion studies, based on the 137Cs technique, require a lot of time-consuming cores to determine soil loss or gain. We show that portable HP-Ge spectrometer can be used to determine the content and the distribution in the soil of natural and artificial radionuclides. Simulations of gamma-rays transport throughout the soil profile used a Monte Carlo code. The methodology requires a unique undisturbed coring site to build the models, calibrate the spectrometer readings and derive soil denudation or accumulation thickness.

Charon's size and an upper limit on its atmosphere from a stellar occultation

Pluto and its satellite, Charon (discovered in 1978; ref. 1), appear to form a double planet, rather than a hierarchical planet/satellite couple. Charon is about half Pluto's size and about one-eighth its mass. The precise radii of Pluto and Charon have remained uncertain, leading to large uncertainties on their densities. Although stellar occultations by Charon are in principle a powerful way of measuring its size, they are rare, as the satellite subtends less than 0.3 microradians (0.06 arcsec) on the sky. One occultation (in 1980) yielded a lower limit of 600 km for the satellite's radius, which was later refined to 601.5 km (ref. 4). Here we report observations from a multi-station stellar occultation by Charon, which we use to derive a radius, R(C) = 603.6 +/- 1.4 km (1sigma), and a density of rho = 1.71 +/- 0.08 g cm(-3). This occultation also provides upper limits of 110 and 15 (3sigma) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere.

The UV-inducible RNA-binding protein A18 (A18 hnRNP) plays a protective role in the genotoxic stress response

We have previously shown that specific RNA-binding proteins (RBP) are activated by genotoxic stress. The role and function of these stress-activated RBP are, however, poorly understood. The data presented here indicate that the RBP A18 heterogeneous ribonucleoprotein (hnRNP) is induced and translocated from the nuclei to the cytoplasm after exposure to UV radiation. Using a new in vitro system we identified potential cellular targets for A18 hnRNP. Forty-six mRNA transcripts were identified, most of which are stress- or UV-responsive genes. Two important stress-responsive transcripts, the replication protein A (RPA2) and thioredoxin, were studied in more detail. Northwestern analyses indicate that A18 hnRNP binds specifically to the 3'-untranslated region of RPA2 transcript independently of its poly(A) tail, whereas the poly(A) tail of thioredoxin mRNA reinforces binding. Overexpression of A18 hnRNP increases the mRNAs stability and consequently enhances translation in a dose-dependent manner. Moreover, cell lines expressing reduced levels of A18 hnRNP are more sensitive to UV radiation. These data suggest that A18 hnRNP plays a protective role against genotoxic stresses by translocating to the cytosol and stabilizing specific transcripts involved in cell survival.

Inhibition of p53 transcriptional activity by the S100B calcium-binding protein

The levels of S100 Ca(2+)-binding proteins correlate with the progression of certain tumors, but their role, if any, in carcinogenesis is still poorly understood. S100B protein associates with both the p53 oligomerization domain (residues 325-355) and the extreme C terminus of the tumor suppressor p53 (residues 367-392). Consequently, S100B inhibits p53 tetramer formation and p53 phosphorylation mediated by protein kinase C, on p53 C-terminal end. In this report, we show that the S100B protein decreases p53 DNA binding and transcriptional activity. The effect of S100B is reflected in vivo by a reduced accumulation of p53, p21, and MDM2 protein levels in co-transfection assays and in response to bleomycin. The S100B can still interact with p53 in the absence of p53 extreme C-terminal end and reduce the expression of p53 downstream effector genes. These data indicate that S100B does not require p53 extreme C-terminal end to inhibit p53 activity. Collectively, these findings imply that elevated levels of S100B in tumors such as astrocytomas and gliomas could inhibit p53 functions and contribute to cancer progression.

Insecticide resistance status, esterase activity, and electromorphs from mosquito populations of Culex quinquefasciatus Say (Diptera: Culicidae), in Houston (Harris County), Texas

Culex quinquefasciatus Say is a vector of St. Louis encephalitis (SLE) in Texas. This disease is endemic and prevalent in the Houston area. Disease prevention through mosquito control is mainly targeted against adults by application of a resmethrin-piperonyl butoxide formulation (Scourge). Immature mosquitoes were collected from eight areas in Harris County during 1998. The susceptibility status of these populations to Scourge, malathion, and resmethrin, the latter alone or with an esterase inhibitor as a synergist, was determined using a bottle assay with females. The population structure was investigated by electrophoretic analysis of esterases and their activity. Individual females were also analyzed for esterase activity by plate assay and for isoenzyme pattern by native PAGE. Bioassays indicated high levels of resistance to malathion in all areas. In addition, the effectiveness of Scourge in mosquitoes from area 51 deteriorated throughout the season. A localized, distinctive esterase pattern and activity level was observed in mosquitoes from different areas. Overall, the frequency of esterases Est alpha 2 (A2)/Est beta 2 (B2) was higher than that of Est beta 1 (B1). Altogether, these results indicate the onset of a fragile situation for mosquito control that should be further analyzed to effectively maintain the SLE prevention program for Harris County.

Association with Cdc2 and inhibition of Cdc2/Cyclin B1 kinase activity by the p53-regulated protein Gadd45

Recently Gadd45, a p53-regulated stress protein, has been implicated in the activation of a G2/M checkpoint after damage by UV radiation and alkylating agents. While inhibitory phosphorylation of Cdc2 and suppression of cyclin B1 levels are known to be involved in G2 delays after genotoxic stress, Gadd45 has now been found to directly inhibit the activity of Cdc2/Cyclin B1 complex, while it had no appreciable effect on Cdk2/ Cyclin E activity even at very high levels of Gadd45. In contrast, p21CiP1/Waf1 is an universal cdk/cyclin inhibitor and inhibited both of the cyclin complexes tested here. Gadd45 was also able to physically interact with Cdc2, but not Cyclin B1. Addition of Gadd45 to immunoprecipitated Cdc2/Cyclin B1 in vitro led to a dissociation of this complex, and thus may represent a new checkpoint mechanism whereby Cdc2/Cyclin B1 can be inhibited. With the use of an antisense approach, reduced Gadd45 expression attenuated the suppression of Cdc2/Cyclin B1 activity in UV-irradiated human cells. Taken together, these results implicate Gadd45 in the control of G2/M cell cycle progression after certain stresses.

Gadd45, a p53-responsive stress protein, modifies DNA accessibility on damaged chromatin

This report demonstrates that Gadd45, a p53-responsive stress protein, can facilitate topoisomerase relaxing and cleavage activity in the presence of core histones. A correlation between reduced expression of Gadd45 and increased resistance to topoisomerase I and topoisomerase II inhibitors in a variety of human cell lines was also found. Gadd45 could potentially mediate this effect by destabilizing histone-DNA interactions since it was found to interact directly with the four core histones. To evaluate this possibility, we investigated the effect of Gadd45 on preassembled mononucleosomes. Our data indicate that Gadd45 directly associates with mononucleosomes that have been altered by histone acetylation or UV radiation. This interaction resulted in increased DNase I accessibility on hyperacetylated mononucleosomes and substantial reduction of T4 endonuclease V accessibility to cyclobutane pyrimidine dimers on UV-irradiated mononucleosomes but not on naked DNA. Both histone acetylation and UV radiation are thought to destabilize the nucleosomal structure. Hence, these results imply that Gadd45 can recognize an altered chromatin state and modulate DNA accessibility to cellular proteins.

Evidence for distinct kinase-mediated pathways in gadd gene responses

We have evaluated the role of various protein kinases on the induction of the gadd (growth arrest and DNA damage inducible) genes, using a panel of protein kinase inhibitors. Our data indicate that three different stress response pathways mediating gadd gene induction are most likely regulated by different protein kinases or combinations of protein kinases. The protein kinase inhibitor staurosporine and the temperature sensitive (ts) p34cdc2 mutant reduced induction by the alkylating agent methylmethane sulfonate (MMS) of the rodent gadd45 and gadd153 genes. However, staurosporine had no effect of the ionizing radiation (IR) induction of the human GADD45. Caffeine and 2-aminopurine, on the other hand, completely blocked this IR induction. Suramin, an antitumor drug that interferes with the interaction of growth factors with their receptors, inhibited the UV radiation induction of GADD45 and GADD153 but had no effect on the MMS and IR pathways. Elevated expression of gadd45 by medium depletion (starvation) was partially reduced by the addition of either genistein or tyrphostin, two protein tyrosine kinase inhibitors, while gadd153 was affected by tyrphostin only. Two inhibitors acting preferentially on cAMP-dependent protein kinase (PKA), N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide, HCl (H8) and protein kinase inhibitor (PKI), also had a moderate effect on the medium depletion-induced levels of both gadd genes. Thus, these varied effects of inhibitors on gadd gene responses point to important differences in the pathways controlling these responses.

Identification of several human homologs of hamster DNA damage-inducible transcripts. Cloning and characterization of a novel UV-inducible cDNA that codes for a putative RNA-binding protein

Low ratio hybridization subtraction technique was previously used in this laboratory to enrich and isolate a number of low abundance UV-inducible hamster transcripts (Fornace, A. J., Jr., Alamo, I. J., and Hollander, M. C. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 8800-8804) that led to the identification and cloning of five important hamster and human GADD genes (Fornace, A. J., Jr., Nebert, D. W., Hollander, M. C., Luethy, J. D., Papathanasiou, M., Fargnoli, J., and Holbrook, N. J. (1989) Mol. Cell. Biol. 9, 4196-4203). In this study we have characterized the remaining DNA damage-inducible (DDI) transcripts. Of the 24 DDI clones, 3 clones (A13, A20, and A113) representing different regions of the same hamster cDNA exhibited near perfect homology to human p21(WAF1/CIP1) cDNA. The DDI clones A26, A88, and A99 displayed very high sequence homologies with the human proliferating nuclear antigen, rat translation initiation factor-5 (eIF-5), and human thrombomodulin, respectively, whereas clones A29 and A121 matched with express sequence tagged sequences of unknown identity. The DDI clones A18, 106, and A107 were different isolates of the same hamster cDNA (hereafter referred to as A18) and displayed high sequence homology with the members in the heterogeneous ribonucleoprotein (hnRNP) family. Using the hamster A18 partial-length cDNA as a probe, we screened human fibroblast cDNA library and isolated the corresponding full-length human cDNA. The deduced amino acid sequence revealed that the putative protein contains all the canonical features of a novel glycine-rich hnRNP. The A18 mRNA levels were specifically increased in response to DNA damage induced by UV irradiation or UV mimetic agents. Thus the putative A18 hnRNP is the first hnRNP whose mRNA is specifically regulated in response to UV-induced DNA damage; accordingly, it may play some role in repair of UV-type DNA damage.

Identification of an additional p53-responsive site in the human epidermal growth factor receptor gene promotor

Exogenously introduced wild-type and mutant p53 have recently been reported to enhance the human epidermal growth factor receptor (EGF-R) gene promoter activity in p53-deficient Saos2 osteosarcoma cells. A p53 binding site residing at position -265/-239 in the EGF-R proximal promoter has also been identified. We investigated the p53 regulation of EGF-R core promoter activity in human cell lines with varying endogenour p53 status. Wild-type and mutant p53Ala143 enhanced the EGF-R core promotor activity in cells that were either p53-deficient or contained wild-type or mutant endogenous p53. Upon further characterization of the various deletion fragments of the EGF-R promoter, we identified a wild-type p53 responsive 62 bp region residing at position -167/-105. The -167/-105 segment was responsive only to wild-type p53 but not to mutant p53Ala143 or p53His273. The -167/-105 segment of the EGF-R promotor contains one perfect and several imperfect consensus p53-binding half sites; indeed in gel shift experiments the 62 bp -167/-105 segment as well as the oligonucleotides corresponding to two p53 consensus half-sites within the 62 bp fragment, exhibited binding to p53-containing protein complexes. Thus, we have identified an additional wild-type p53 responsive site in the human EGF-R promoter. This site containing consensus p53-binding sequences resides at position -167/-105 and is proximal to recently identified p53 binding element located at position -265/-239 in the EGF-R promotor.

Characterization of the GADD45 response to ionizing radiation in WI-L2-NS cells, a p53 mutant cell line

We have previously reported that WI-L2-NS, a human lymphoblastoid cell line, has very high basal levels of GADD45 mRNA and protein in spite of a p53 mutation at amino acid 237. Regardless of the amount of Gadd45 in this cell line, no growth suppression activity was detected. We report here that in WI-L2-NS, the mutated p53 protein adopts predominantly a wild type (wt) conformation and binds to the p53 binding site in the GADD45 third intron. In this cell line, the already high levels of mutated p53 protein can be induced further by ionizing radiation (IR) but the response of the p53 downstream effector genes is altered. Induction of GADD45 and CIP1/WAF1 is reduced compared to p53 wt cell lines but is still substantially higher than the average fold induction obtained from 39 p53 mutant cell lines. Induction of the MDM2 gene was not detected in WI-L2-NS following IR. The induction pattern of the three p53 effector genes by the alkylating agent methylmethane sulfonate (MMS) was also attenuated in WI-L2-NS cells. In TK6 cells, a WI-L2-NS sister cell line having a p53 wt genotype, the induction of the p53 downstream effectors is normal, i.e. induced, both at the protein and the mRNA levels. These results indicate that the DNA binding activity of the mutated p53 protein in WI-L2-NS might be responsible, at least in part, for the high basal levels of GADD45 but can not mediate the full induction of the p53 downstream effector genes. The reason(s) for the inability of Gadd45 to suppress growth in this cell line remains however unknown.

The production and characterization of murine monoclonal antibodies to human Gadd45 raised against a recombinant protein

The production of two different murine monoclonal antibodies to human Gadd45, a protein that is induced in response to DNA damage, is reported. Antibodies were generated in a SJL mouse using a recombinant form of the human Gadd45 protein. Monoclonal antibody 4TCYA1, which recognizes the denatured form of human Gadd45 in Western blots, was selected based upon the recognition of Gadd45 induced by functional p53 in the human myeloid leukemia cell line, ML-1. A second monoclonal antibody, designated 30T.14, immunoprecipitates native human Gadd45 in lysates produced from RKO cells, a colorectal carcinoma cell line that expresses relatively high basal levels of Gadd45, as well as from cell lysates made from ML-1 cells after exposure to ionizing irradiation (IR). Since 4TCYA1 fails to immunoprecipitate Gadd45, and 30T.14 fails to bind to IR-induced Gadd45 in immunoblotting, these two monoclonal antibodies probably recognize different epitopes.

Characterization of human Gadd45, a p53-regulated protein

GADD45 (growth arrest and DNA damage) is a DNA-damage-inducible gene regulated in part by the tumor suppressor p53. A role in negative growth control has recently been suggested based on significant (more than 75%) reduction of colony formation following over expression of Gadd45. To better understand the role of Gadd45, we have developed specific rabbit and murine antibodies raised against the human recombinant protein. Using these antibodies, we have found that in ML-1 cells Gadd45 is predominantly a nuclear protein. MyD118, a protein induced by terminal differentiation sharing 57% homology with Gadd45, does not cross-react with any of the antibodies produced. As expected, the induction of Gadd45 protein by ionizing radiation (IR) was also found to be dependent on a wild type p53 phenotype. Interestingly, WI-L2-NS, a human lymphoid cell line, showed very high basal levels of Gadd45 mRNA and protein in addition to a high constitutive level of a mutated p53 protein. In this cell line, the high levels of GADD45 did not inhibit cellular growth in spite of the fact that no mutations were found in GADD45 sequence. These results indicate that some cell line(s) can tolerate high levels of Gadd45 and abrogate its growth suppression function.

Interaction of the regulatory domains of the murine Cyp1a1 gene with two DNA-binding proteins in addition to the Ah receptor and the Ah receptor nuclear translocator (ARNT)

The aromatic hydrocarbon (Ah) receptor complex is a ligand-activated transcriptional activator consisting of at least two protein components. The ligand-binding component is the AhR protein, a cytosolic receptor encoded by the Ahr gene, which, upon ligand binding, translocates to the nucleus in a heterodimeric complex with the ARNT (Ah receptor nuclear translocator) component. The complex binds to several discrete DNA domains containing aromatic hydrocarbon responsive elements (AhRE) present in the regulatory region of the murine cytochrome P(1)450 Cyp1a1 gene and of the other genes in the [Ah] gene battery. As a consequence of binding, a transcriptional complex is formed that activates the expression of these genes by as yet unidentified mechanisms. We have analyzed DNA-protein interactions in four of these domains, specifically, the AhREs located between -1085 and -482 (sites A, C, E, and D) of the upstream regulatory region of the murine Cyp1a1 gene. We found that two DNA-binding proteins, present in cytosolic and nuclear extracts of mouse Hepa-1 cells, showed overlapping DNA-binding specificities to those of the Ah receptor. One of these proteins had an apparent molecular mass of 35-40 kDa, bound only to AhRE3 (site D), and has been identified tentatively as a member of the C/EBP family of transcription factors. The second protein, purified by DNA-affinity chromatography, had an apparent molecular mass of 95 kDa and bound to a larger DNA motif that included the AhRE sequence, in AhRE3 and AhRE5 (sites D and A), but not in AhRE1 or AhRE2 (sites C and E). This protein was not AhR nor was it ARNT, since it was found in receptorless (Ahr-) and in nuclear translocation-defective (Arnt-) cells, as well as in cells that had not been exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin), a potent inducer of Cyp1a1 expression. Evidence from in vivo methylation protection indicated that two G residues flanking AhRE3, one of which is required for binding of the 95-kDa protein, may be protected from methylation in uninduced cells and become exposed upon dioxin treatment, suggesting that the 95-kDa protein may be constitutively bound to AhRE3, and be displaced by binding of the Ah receptor complex. These results lend support to the concept that the transcriptional regulation of the [Ah] battery genes could be modulated by combinatorial interactions of the Ah receptor complex with other transcription factors.

Activation of HIV type 1 long terminal repeat by ultraviolet light is serum and strain specific

We have studied the UV responsiveness of xeroderma pigmentosum (XP) and HeLa cell lines transfected with a CAT reporter gene under the control of the HIV-1 LTR promoter. XP fibroblasts grown in 10% newborn bovine serum (NBS) were three times more responsive to UV radiation than cells grown in 10% fetal calf serum (FCS). Moreover, cocultivation of UV-irradiated XP cells with XP cells containing stable integrants of HIV-LTR CAT was found to be more than four times more effective in inducing the CAT activity when cells were maintained in 10% NBS than in 10% FCS. The level of induction was also dependent on the serum concentration. These data indicate that a serum component, possibly a cytokine(s), can enhance the UV response of both irradiated cells and unirradiated cells cocultivated with irradiated cells. The magnitude of UV responsiveness seemed also to be strain dependent. CAT activity for the HIV LTR promoter from the HTLV-IIIB (HIV-IIIB) strain was induced more than 30-fold by UV irradiation whereas activity from the LAV-1BRU strain was less than 2-fold. In contrast, both constructs were strongly induced by Tat expression. This indicates that there are differences in the induction mechanism for these two stimuli, even though UV radiation has been previously reported to induce a cellular Tat-like factor (Valerie K, et al., Nature [London] 1988;333:78-81).

The gadd and MyD genes define a novel set of mammalian genes encoding acidic proteins that synergistically suppress cell growth

A remarkable overlap was observed between the gadd genes, a group of often coordinately expressed genes that are induced by genotoxic stress and certain other growth arrest signals, and the MyD genes, a set of myeloid differentiation primary response genes. The MyD116 gene was found to be the murine homolog of the hamster gadd34 gene, whereas MyD118 and gadd45 were found to represent two separate but closely related genes. Furthermore, gadd34/MyD116, gadd45, MyD118, and gadd153 encode acidic proteins with very similar and unusual charge characteristics; both this property and a similar pattern of induction are shared with mdm2, whic, like gadd45, has been shown previously to be regulated by the tumor suppressor p53. Expression analysis revealed that they are distinguished from other growth arrest genes in that they are DNA damage inducible and suggest a role for these genes in growth arrest and apoptosis either coupled with or uncoupled from terminal differentiation. Evidence is also presented for coordinate induction in vivo by stress. The use of a short-term transfection assay, in which expression vectors for one or a combination of these gadd/MyD genes were transfected with a selectable marker into several different human tumor cell lines, provided direct evidence for the growth-inhibitory functions of the products of these genes and their ability to synergistically suppress growth. Taken together, these observations indicate that these genes define a novel class of mammalian genes encoding acidic proteins involved in the control of cellular growth.

Induction of RNA-binding proteins in mammalian cells by DNA-damaging agents

A technique to detect RNA-binding proteins (RBP) involving hybridization of RNA probe to proteins transferred to a membrane was used to study RBP in different mammalian cells and in cells after genotoxic stress. With this approach, up to 13 proteins of different sizes were detected in crude nuclear extracts by using a viral RNA probe consisting of the trans-activation-responsive (TAR) element of human immunodeficiency virus type 1 (HIV-1). The TAR RNA probe contains a stem-loop structure found in nascent HIV-1 transcripts. A G+C-rich probe with similar structure also bound to many of these RBP. Only a 102-kDa protein strongly bound to other RNA probes lacking this structure, while a probe with an A+U-rich stem-loop structure fail to bind most RBP, thus indicating a RNA secondary structure preference. The expression of these RBP varied substantially in nine different human and hamster cell lines, with no detectable RBP in two human myeloid lines. Evidence for induction of these RBP was found in six of seven lines after treatment with DNA-damaging agents; UV radiation was the most effective agent. In Chinese hamster ovary cells, which showed the strongest response, all five RBP present in untreated cells rapidly increased in activity after UV irradiation, and eight additional RBP were detected. The induction of these RBP by DNA-damaging agents indicates one or more possible roles for these proteins in the cellular response to genotoxic stress and in viral activation after such stress.

Induction of cellular p53 activity by DNA-damaging agents and growth arrest

The tumor suppressor p53 can function as a sequence-specific transcription factor and is required for activation by ionizing radiation (IR) of one or more downstream effector genes, such as the human GADD45 gene. One important consequence of IR that is probably mediated by these downstream effector genes is activation of the p53-mediated G1 cell cycle checkpoint. While the induction of reporter constructs containing p53-binding sites has already been demonstrated with p53 expression vectors, we have now demonstrated the direct activation of such a construct after treatment of the human RKO line, which has a normal p53 phenotype, with various types of DNA-damaging agents and also after growth arrest produced by medium depletion (starvation). IR, UV radiation, and methylmethane sulfonate were found to induce p53 activity when a stably integrated reporter construct containing functional p53-binding sites was used and also in mobility shift assays with a p53-binding site from the GADD45 gene, and IR-inducible gene previously associated with growth arrest. The same cell treatments that induced this p53 activity also caused an increase in cellular p53 protein levels. The response in cells lacking normal p53 or in RKO cells expressing a dominant negative mutant p53 was markedly reduced. Interestingly, the spectrum of effective inducing agents for the above-described experiments was similar to that which induces GADD45 either in cells with a normal p53 status or, with the exception of IR, in cells lacking normal p53. These results indicate a role for p53 in the IR pathway, which is completely p53 dependent, and in other genotoxic stress responses, in which p53 has a cooperative effect but is not required.

Cyclobutane pyrimidine dimers in UV-DNA induce release of soluble mediators that activate the human immunodeficiency virus promoter

Ultraviolet (UV) irradiation of human cells induced expression of a stably maintained fusion gene consisting of the human immunodeficiency virus long terminal repeat promoter controlling the bacterial chloramphenicol acetyltransferase gene. Two experiments demonstrated that DNA damage can initiate induction: UV induction was greater in DNA repair-deficient cells from a xeroderma pigmentosum patient than in repair-proficient cells, and transfection of UV-irradiated DNA into unirradiated cells activated gene expression. Increased repair of cyclobutane pyrimidine dimers by T4 endonuclease V abrogated viral gene activation, suggesting that dimers in DNA are one signal leading to increased gene expression. This signal was spread from UV-irradiated cells to unirradiated cells by co-cultivation, implicating the release of soluble factors. Irradiation of cells from DNA repair-deficiency diseases resulted in greater release of soluble factors than irradiation of cells from unaffected individuals. These results suggest that UV-induced cyclobutane pyrimidine dimers can activate the human immunodeficiency virus promoter at least in part by a signal-transduction pathway that includes secretion of soluble mediators.

A mammalian cell cycle checkpoint pathway utilizing p53 and GADD45 is defective in ataxia-telangiectasia

Cell cycle checkpoints can enhance cell survival and limit mutagenic events following DNA damage. Primary murine fibroblasts became deficient in a G1 checkpoint activated by ionizing radiation (IR) when both wild-type p53 alleles were disrupted. In addition, cells from patients with the radiosensitive, cancer-prone disease ataxia-telangiectasia (AT) lacked the IR-induced increase in p53 protein levels seen in normal cells. Finally, IR induction of the human GADD45 gene, an induction that is also defective in AT cells, was dependent on wild-type p53 function. Wild-type but not mutant p53 bound strongly to a conserved element in the GADD45 gene, and a p53-containing nuclear factor, which bound this element, was detected in extracts from irradiated cells. Thus, we identified three participants (AT gene(s), p53, and GADD45) in a signal transduction pathway that controls cell cycle arrest following DNA damage; abnormalities in this pathway probably contribute to tumor development.

Dioxin induces expression of c-fos and c-jun proto-oncogenes and a large increase in transcription factor AP-1

Among environmental pollutants, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) is one of the most potent tumor promoters and teratogens known. The molecular mechanisms responsible for the biological activity of TCDD, however, remain largely unknown. In this report, we show that the first observable effects of TCDD in cultured murine hepatoma cells are a rapid, transient increase in Ca2+ influx and a minor but significant elevation of activated, membrane-bound protein kinase C. These changes are then followed by induction of the immediate early proto-oncogenes c-fos, jun-B, c-jun, and jun-D, and by large increases in AP-1 transcription factor activity. Induction of these changes by TCDD is delayed compared with that by phorbol esters, although the magnitude of the effects caused by both treatments is similar, and both induction processes can be blocked by staurosporine, a protein kinase C inhibitor. In cultured cells, proto-oncogene induction by TCDD appears to be independent of the presence of a functional aryl hydrocarbon (Ah) receptor or nuclear translocation protein. These results reveal early events that may lead to the elucidation of the molecular basis of TCDD-induced tumor promotion.

Dioxin-dependent activation of murine Cyp1a-1 gene transcription requires protein kinase C-dependent phosphorylation

Transcriptional activation of the murine Cyp1a-1 (cytochrome P(1)450) gene by inducers such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (dioxin) requires the aromatic hydrocarbon (Ah) receptor and the interaction of an inducer-receptor complex with one or more of the Ah-responsive elements (AhREs) located about 1 kb upstream from the transcriptional initiation site. We find that treatment of mouse hepatoma Hepa-1 cells with 2-aminopurine, an inhibitor of protein kinase activity, inhibits CYP1A1 mRNA induction by TCDD as well as the concomitant increase in CYP1A1 enzyme activity. Formation of DNA-protein complexes between the Ah receptor and its AhRE target is also inhibited by 2-aminopurine, as determined by gel mobility shift assays. Phosphorylation is required for the formation of Ah receptor-specific complexes, since in vitro dephosphorylation of nuclear extracts from TCDD-treated Hepa-1 cells abolishes the capacity of the Ah receptor to form specific complexes with its cognate AhRE sequences. To determine whether any one of several known protein kinases was involved in the transcriptional regulation of the Cyp1a-1 gene, we treated Hepa-1 cells with nine other protein kinase inhibitors prior to induction with TCDD; nuclear extracts from these cells were analyzed for their capacity to form specific DNA-protein complexes. Only extracts from cells treated with staurosporine, a protein kinase C inhibitor, were unable to form these complexes. In addition, staurosporine completely inhibited CYP1A1 mRNA induction by TCDD. Depletion of protein kinase C by prolonged treatment with phorbol ester led to the complete suppression of CYP1A1 mRNA induction by TCDD. We conclude that (i) phosphorylation is necessary for the formation of a transcriptional complex and for transcriptional activation of the Cyp1a-1 gene; (ii) the phosphorylation site(s) exists on at least one of the proteins constituting the transcriptional complex, possibly the Ah receptor itself; and (iii) the enzyme responsible for the phosphorylation is likely to be protein kinase C.

Solubilization and molecular characterization of the atrial natriuretic peptide (ANP) receptor in human platelets: comparison with ANP receptors in rat tissues

We have previously demonstrated the presence of binding sites for atrial natriuretic peptide (ANP) in human platelets. These sites have pharmacological characteristics similar to those of rat vascular smooth muscle. They are subject to regulation by circulating levels of ANP in plasma, varying inversely with the latter after high sodium intake, in arterial hypertension and congestive heart failure. We have now solubilized these platelet receptors with the nonionic detergent Triton X-100 (0.6%). The preparations were incubated with [125I]ANP in the presence of increasing concentrations of ANP-(99-126), ANP-(101-126), ANP-(103-126), and ANP-(103-123). The order of potency of these peptides to displace [125I]ANP was similar for the solubilized and particulate receptor. Bound [125I]ANP was covalently cross-linked to the receptor with 5 mM disuccinimidyl suberate. Autoradiography of the sodium dodecyl sulfate-polyacrylamide gel showed that [125I]ANP specifically interacts with a 125-kDa membrane component, some of which may be reduced by 2% mercaptoethanol or 10 mmol/L dithiothreitol to a 70-kDa species. A small proportion of a 70-kDa peptide is also found under nonreducing conditions. The concentration of ANP-(99-126) that inhibits binding of [125I]ANP by 50% to both the 125-kDa and the 70-kDa species was 0.1 nM, while that for ANP-(103-123) was 3 nM. The internally ring-deleted analog Des(Gln116,Ser117,Gly118,Leu119,Gly120)ANP -(102-121) or C-ANP displaced with equal potency ANP binding to the high and low mol wt (Mr) bands, as also found in cultured rat vascular smooth muscle cells, but not in the mesemteric arteries these cells are derived from. In the latter, C-ANP displaced only binding from the lower Mr band. These results show that the ANP receptor in human platelets is heterogeneous. There is one nonreducible species with of 125,000 Mr, another of similar Mr containing two disulfide-linked subunits of 70,000 Mr, and, to a lesser extent, a nonreducible 70-kDa species, in agreement with findings in other tissues in experimental animals.

Inhibition of protein phosphatases-1 and -2A with acanthifolicin. Comparison with diarrhetic shellfish toxins and identification of a region on okadaic acid important for phosphatase inhibition

Acanthifolicin (9,10-epithio-okadaic acid from Pandoras acanthifolium) inhibited protein phosphatase-1 (PP1) similarly to okadaic acid (IC50 = 20 nM and 19 nM, respectively) but was slightly less active against protein phosphatase-2A (PP2A) (IC50 = 1 nM and 0.2 nM, respectively). Methyl esterification of acanthifolicin sharply reduced its activity. PP2A was inhibited with an IC50 = 5.0 microM, whilst PP1 was inhibited less than 10% at 250 microM toxin. Okadaic acid methyl ester was similarly inactive whereas dinophysistoxin-1 (35-methyl okadaic acid) inhibited PP1/2A almost as potently as okadaic acid. Pure acanthifolicin/okadaic acid methyl ester may be useful as specific inhibitors of PP2A at 1-10 microM concentrations in vitro and perhaps in vivo. The data also indicate that a region on these toxins important for PP1/2A inhibition comprises the single carboxyl group.

Identification and characterization of atrial natriuretic factor receptors in the rat retina

The characteristics of atrial natriuretic factor (ANF) receptors where studied in rat retinal particulate preparations. Specific 125I-ANF binding to retinal particulate preparations was greater than 90% of total binding and saturable at a density (Bmax) of 40 +/- 8 fmol/mg protein with an apparent dissociation constant (Kd) of 6.0 +/- 2.0 pM (n = 3). Apparent equilibrium conditions were established within 30 min. The Kd value of 125I-ANF binding calculated by kinetic analysis was 4.0 pM. The Bmax of 60 +/- 10 fmol/mg protein and the Kd of 5 +/- 2 pM, calculated by competition analysis, were in close agreement with the values obtained from Scatchard plots or kinetic analysis. The 125I-ANF binding to retinal particulate preparations was not inhibited by 1 microM concentration of somatostatin, vasopressin, vasoactive intestinal peptide, adrenocorticotropin, thyrotropin releasing hormone, or leu-enkephalin. The rank order of potency of the unlabelled atrial natriuretic peptides for competing with specific 125I-ANF (101-126) binding sites was rANF (92-126) greater than rANF (101-126) greater than rANF (99-126) greater than rANF (103-126) greater than Tyro-Atriopeptin I greater than hANF (105-126) greater than rANF (1-126). Similar results have been obtained in peripheral tissues and mammalian brain, indicating that central and peripheral ANF-binding sites have somewhat similar structural requirements. Affinity cross-linking of 125I-ANF to retinal particulate preparations resulted in the labelling of two sites of molecular weight 140 and 66 kDa, respectively. This demonstration of specific high-affinity ANF receptors suggests that the peptide may act as a neurotransmitter or neuromodulator in the retina.

Radioreceptor assay for atrial natriuretic factor

Interest in accurate measurement of atrial natriuretic factor (ANF) in biological fluids and various tissues has been stimulated by recent data indicating the possible role of ANF in the homeostasis of salt and water. The presence of high-affinity binding sites for ANF in rat glomeruli has allowed us to develop a rapid, sensitive, and simple radioreceptor assay (RRA). A saturable high-affinity binding site on the membranes of rat glomeruli has been characterized by a dissociation constant of 33 pM and binding capacity of 396 fmol/mg protein. Rat plasma extracts or atrial homogenates or standards were incubated with radioiodinated ANF and a preparation of rat glomerular membranes. The receptor-bound and free radioactivity were separated by filtration on Whatman GF/C paper after 1 h incubation at room temperature. The sensitivity of the RRA was 2.08 fmol. The effective concentration of standard ANF that displaced 50% of labeled receptor-bound ANF (EC50) was 43.3 +/- 2.6 fmol/ml (n = 7). Both intra- and interassay coefficients of variation were smaller than 11%. This RRA assay has been compared with radioimmunoassay (RIA). High correlations for 19 plasma extracts and 34 atrial homogenates (r = 0.973 and r = 0.954, respectively) tested by RRA and RIA were obtained. This good correlation between the two methods suggests that the immunoreactive material found in rat plasma and atrial homogenates also displays biological activity.

Glomerular ANF receptor regulation during changes in sodium and water metabolism

The concentration of atrial natriuretic factor (ANF) in atria and plasma was investigated in relation to the regulation of renal glomerular ANF receptors in the rat during changes in water and sodium intake. A decrease in plasma immunoreactive ANF (IR-ANF) was observed after 4 days of water deprivation or after 1 wk on a low-sodium diet, whereas animals offered 1% NaCl in their drinking water had elevated plasma ANF values. Atrial IR-ANF was lower in water-deprived and higher in sodium-restricted rats than in their respective controls. A low-sodium intake or water deprivation increased the density of glomerular ANF receptors, whereas the inverse occurred with a high-salt consumption. It is concluded that an inverse correlation exists between ANF plasma concentration and renal glomerular ANF receptor sites.

Partial characterization and solubilization of receptors for atrial natriuretic factor in rat glomeruli

Specific receptors for atrial natriuretic factor (ANF) have been identified and solubilized in glomeruli from rat kidney. Radioiodinated synthetic ANF (Arg 101-Tyr 126) bound to a single class of high affinity (Kd 27 +/- 24 pM) sites with a density of 390 +/- 230 fmole/mg protein. The binding was time- and temperature-dependent, saturable and reversible. The ANF-receptor complex was not affected by angiotensin II, ACTH or vasopressin. Solubilization with 10 mM 3-[(3-cholamidopropyl)-dimethylammonio]- 1-propane sulfonate (CHAPS) slightly increased the affinity for ANF (Kd 5.0 +/- 3.3 pM) without affecting the density (250 +/- 110 fmole/mg protein). Similar results were found with 1% Triton X-100. ANF-related peptides interact generally in the same way with non-solubilized and solubilized receptors, indicating a fully preserved specificity of the receptors.

Structure-activity relationships of atrial natriuretic factor (ANF). I. Natriuretic activity and relaxation of intestinal smooth muscle

Atrial natriuretic factor-related peptides were produced from synthetic ANF (101-126) either by chemical hydrolysis at the N-terminal end or by treatment with carboxypeptidases at the C-terminal end. The biological activities of these peptides were characterized in vivo by a natriuretic bioassay and in vitro by relaxation of contracted intestinal smooth muscle (chick rectum). In the natriuretic assay, the removal of Asn122, Ser123 and Phe124 at the C-terminal end alters considerably the renal response. Deletion or extension of amino acids at the N-terminal end affects only slightly the natriuretic activity. Removal of N-terminal or C-terminal amino acids decreases the relaxant activity of ANF on the chick rectum. In both bioassays, simultaneous deletions of residues at both ends drastically affect the activity in an additive manner.

Interaction of filamentous actin with isolated liver plasma membranes

Actin-membrane interactions have been studied using purified liver plasma membranes and muscular filamentous actin. Despite the large quantity of endogenous actin present in membranes, exogenous muscular filamentous actin cosediments with membranes after a 30 min centrifugation at 30 000 g. The cosedimentation process is time-dependent and exhibits a complex relationship with actin concentration. The cosedimentation of actin with membranes can be partly explained by gelation as shown by low-shear viscosity and electron microscopy. The characterization of the gelation phenomenon as a function of time, actin and membrane concentrations, ionic strength, temperature and Ca2+ concentration is also presented. Gelation alone cannot however account for the overall cosedimentation data, and a more direct mode of association between actin and the membrane must be envisaged. The analogy that exists between the results obtained with liver plasma membranes and those obtained with other membrane systems suggests that a general mechanism may be involved in the interaction of actin with plasma membranes.