Short dysfunctional telomeres impair tumorigenesis in the INK4a(delta2/3) cancer-prone mouse.

Maintenance of telomere length is predicted to be essential for bypass of senescence and crisis checkpoints in cancer cells. The impact of telomere dysfunction on tumorigenesis was assessed in successive generations of mice doubly null for the telomerase RNA (mTR) and the INK4a tumor suppressor genes. Significant reductions in tumor formation in vivo and oncogenic potential in vitro were observed in late generations of telomerase deficiency, coincident with severe telomere shortening and associated dysfunction. Reintroduction of mTR into cells significantly restored the oncogenic potential, indicating telomerase activation is a cooperating event in the malignant transformation of cells containing critically short telomeres. The results described here demonstrate that loss of telomere function in a cancer-prone mouse model possessing intact DNA damage responses impairs, but does not prevent, tumor formation.

Visualization of single RNA transcripts in situ.

Fluorescence in situ hybridization (FISH) and digital imaging microscopy were modified to allow detection of single RNA molecules. Oligodeoxynucleotide probes were synthesized with five fluorochromes per molecule, and the light emitted by a single probe was calibrated. Points of light in exhaustively deconvolved images of hybridized cells gave fluorescent intensities and distances between probes consistent with single messenger RNA molecules. Analysis of beta-actin transcription sites after serum induction revealed synchronous and cyclical transcription from single genes. The rates of transcription initiation and termination and messenger RNA processing could be determined by positioning probes along the transcription unit. This approach extends the power of FISH to yield quantitative molecular information on a single cell.

Sorting of beta-actin mRNA and protein to neurites and growth cones in culture.

The transport of mRNAs into developing dendrites and axons may be a basic mechanism to localize cytoskeletal proteins to growth cones and influence microfilament organization. Using isoform-specific antibodies and probes for in situ hybridization, we observed distinct localization patterns for beta- and gamma-actin within cultured cerebrocortical neurons. beta-Actin protein was highly enriched within growth cones and filopodia, in contrast to gamma-actin protein, which was distributed uniformly throughout the cell. beta-Actin protein also was shown to be peripherally localized after transfection of beta-actin cDNA bearing an epitope tag. beta-Actin mRNAs were localized more frequently to neuronal processes and growth cones, unlike gamma-actin mRNAs, which were restricted to the cell body. The rapid localization of beta-actin mRNA, but not gamma-actin mRNA, into processes and growth cones could be induced by dibutyryl cAMP treatment. Using high-resolution in situ hybridization and image-processing methods, we showed that the distribution of beta-actin mRNA within growth cones was statistically nonrandom and demonstrated an association with microtubules. beta-Actin mRNAs were detected within minor neurites, axonal processes, and growth cones in the form of spatially distinct granules that colocalized with translational components. Ultrastructural analysis revealed polyribosomes within growth cones that colocalized with cytoskeletal filaments. The transport of beta-actin mRNA into developing neurites may be a sequence-specific mechanism to synthesize cytoskeletal proteins directly within processes and growth cones and would provide an additional means to deliver cytoskeletal proteins over long distances.

Activation of the Ig germ-line gamma 1 promoter. Involvement of C/enhancer-binding protein transcription factors and their possible interaction with an NF-IL-4 site.

Ig isotype switching in B lymphocytes is preceded by transcription of the corresponding unrearranged, or germ-line (GL), CH gene. The promoter of mouse GL C gamma 1 transcripts has been shown to be located within a 349-bp KpnI/Bg/II fragment, extending from -147 to +202 bp relative to the first transcription initiation site. By the electrophoretic mobility shift assay, we have analyzed nuclear extracts from three B cell lines and splenic B cells for the presence of proteins binding to this fragment. We show that they give different patterns of DNA binding, implying significant complexity in the regulation of this locus. We focused on the sIgM+ mouse B lymphoma line L10A6.2 that has been shown able to confer responsiveness of the GL gamma 1 promoter to phorbol ester plus IL-4. Activation of this cell line results in altered expression of several nuclear DNA-binding complexes involving two members of the C/enhancer-binding protein (EBP) family of transcription factors, namely C/EBP beta (nuclear factor (NF)-IL-6/LAP) and Ig/EBP-1 (C/EBP gamma). The complexes bind to two C/EBP elements, one at about -115 bp and one near the first RNA start site. In normal B cells stimulated by LPS or IL-4, new complexes appear that bind to C/EBP and NF-IL-4 elements, respectively, located within the -125/-101 region. The -125/-101 segment previously has been shown to be required for transcriptional activation. We discuss these findings in relation to the presence of consensus C/EBP binding sites in other IL-4-regulated promoters.

Androgen and estrogen dynamics in the female baboon (Papio anubis).

Androgen and estrogen dynamics were studied in 5 female baboons (Papio anubis) using constant infusions of [3H]androstenedione/[14C]estrone and [3H]testosterone/[14C]estradiol. Blood samples were obtained prior to the infusions and both blood and plasma was used for measurements of androstenedione (A), testosterone (T), dihydrotestosterone (DHT), estrone (E1), estradiol (E2). Plasma was used for measurements of sex-hormone binding globulin (SHBG), and the percents of T and E2 free, bound to SHBG, and to albumin. Blood samples obtained during the infusions were analyzed for radioactivity as purified androgens and estrogens. Metabolic clearance rates (MCR), and transfer factors ([rho]BB; fraction of steroid infused which is converted to and measured in blood as product) and blood production rates were calculated from whole blood data. All urine was collected for 96 h and an aliquot analyzed for radioactivity as the glucuronides of estrone and estradiol and the % peripheral aromatization calculated. The MCR's, calculated in whole blood, of A, E1, E2 and T were 53 +/- 6 1/day/kg, 39.3 +/- 3 1/day/kg, 29.9 +/- 5.2 1/day/kg and 10.1 +/- 2.3 1/day/kg, respectively. Each MCR was different (P less than 0.05) from the others. The PB of E1 was 15 +/- 2 micrograms/day and was not different from that of E2 (12 +/- 3 micrograms/day). The PB of A, 231 +/- 55 micrograms/day, was greater than that of T, 13 +/- 5 micrograms/day. The interconversions of both the androgens (18.9 +/- 3.4% vs 3.9 +/- 1.0%) and the estrogens (48.8 +/- 10.7% vs 4.0 +/- 0.8%) favored the oxidative pathway, i.e. conversion of 17-OH to 17-oxo steroids. The conversion ratio of A to DHT was greater than that of T to DHT (16.4 +/- 2.1% vs 5.3 +/- 0.7%), and A is a more important source of DHT than is T. The percent of T bound to SHBG (80.7 +/- 0.9%) was greater than percent of E2 (36.9 +/- 9.8%) and inversely the percents of T bound to albumin and free (17.5 +/- 0.8% and 1.65 +/- 0.16%) were less than the respective percents for estradiol (60.5 +/- 9.5% and 2.40 +/- 0.27%). The mean SHBG concentration was 54 +/- 6 nM. The peripheral aromatization of androstenedione, 1.36 +/- 0.05%, was greater than of testosterone, 0.18 +/- 0.02%. This difference is, in part, due to the lack of SHBG-binding of androstenedione. The general pattern of androgen and estrogen dynamics is similar to that in women. This similarity is due, in part, to the presence of SHBG in both baboons and women.

Inhibition of peripheral aromatization in baboons by an enzyme-activated aromatase inhibitor (MDL 18,962).

The peripheral aromatization ([rho]BM) of androstenedione (A) and testosterone (T) was measured before and after administration of the aromatase inhibitor 10-(2 propynyl)estr-4-ene-3,17-dione (MDL-18,962) to five mature female baboons, Papio annubis. The measurements were made by infusing [3H]androstenedione/[14C]estrone or [3H]testosterone/[14C]estradiol for 3.5 h and collecting blood samples during the infusions and all urine for 96 h from the start of the infusion. Blood samples were analyzed for radioactivity as infused and product steroids, and the data were used to calculate MCRs. An aliquot of the pooled urine was analyzed for the glucuronides of estrone and estradiol and used to calculate the [rho]BM. MDL-18,962 was administered as a pulse in polyethylene glycol-400 (1-5 ml) either iv or via gastric tube 30 min before administration of the radiolabeled steroids. Control studies were done with and without polyethylene glycol-400 administration. When MDL-18,962 was given iv at 4 mg/kg, the aromatization of A was decreased 91.8 +/- 0.9% from the control value of 1.23 +/- 0.13% to 0.11 +/- 0.01%. At the same dose, aromatization of T was decreased 82.0 +/- 7.1%, from a control value of 0.20 +/- 0.03% to 0.037 +/- 0.018%. When MDL-18,962 was given iv at doses of 0.4, 0.1, 0.04, and 0.01 mg/kg, the values for aromatization of A were 0.16 +/- 0.03%, 0.18 +/- 0.06%, 0.37 +/- 11%, and 0.65 +/- 0.09%, respectively. The administration of MDL-18,962 via gastric tube at 4 mg/kg as a pulse decreased the aromatization of A from 1.35 +/- 0.06% to 0.43 +/- 0.12%, an inhibition of 67.2 +/- 10.7%. When administered via gastric tube daily for 5 days at 4 mg/kg, the aromatization of A fell from 1.35 +/- 0.06% to 0.063 +/- 0.003%, an inhibition of 84.4 +/- 0.5%. The MCRs of A and estrone were not altered by any dose of MDL-18,962 regardless of the mode of administration, but there was an increase in the MCRs of T and estradiol at the only dose (4 mg/kg, iv) at which these steroids were infused. The interconversions between the androgens and between the estrogens were not altered by the administration of MDL-18,962 at 4 mg/kg, iv. The enzyme-activated inhibitor MDL-18,962 is an effective inhibitor of [rho BM] in female baboons and could prove to be a useful therapeutic agent in treating estrogen-dependent breast cancer.

Estrogen and androgen dynamics in the cynomolgus monkey.

We studied the dynamics of androgen, estrogen, and cortisol (F) production, metabolism, and protein binding in cynomolgus monkeys (M. fascicularis) to provide baseline data and to compare these parameters with those obtained in other primates. Constant infusions of 3H-labeled androgens, 14C-labeled estrogens, and [3H]F were administered to 11 male cynomolgus monkeys (M. fascicularis) for 3.5 h. Blood samples were obtained from a peripheral vein during the infusion, and all urine was collected for 96 h. In each of 3 monkeys, a catheter was inserted into the hepatic vein, and during the infusions blood samples were obtained from the hepatic and peripheral veins and the femoral artery. All blood and urine samples were analyzed for radioactivity as testosterone (T), androstenedione (A), dihydrotestosterone (DHT), estradiol (E2), and estrone (E1). When indicated, blood samples were also analyzed for radioactivity as F. Blood samples taken before the infusions were analyzed for endogenous T, A, DHT, E1, E2, and F concentrations; percent free T, free E2, and free F; and sex hormone-binding globulin and F-binding globulin capacities. The mean +/- SE MCRs for T, A, E2, E1, and F were 44 +/- 4, 407 +/- 40, 175 +/- 17, 315 +/- 28, and 57 +/- 6 liters/day, respectively. The mean blood production rates were 128 +/- 19, 91 +/- 14, 3.3 +/- 0.5, and 9.2 +/- 1.1 micrograms/day and 13.4 +/- 1.9 mg/day for T, A, E2, E1, and F, respectively. The aromatization of androgens was 1.30 +/- 0.10% for A to E1 and 0.28 +/- 0.03% for T to E2. The percent free F (4.34 +/- 0.42%) was greater than the percent free T (1.73 +/- 0.16%) or free E2 (2.75 +/- 0.22%), and the concentration of F-binding globulin was greater than that of sex hormone-binding globulin (227 +/- 35 vs. 60 +/- 7 nM). In the three monkeys who had hepatic venous catheterization, the mean extraction, across the splanchnic bed of T was 32 +/- 3%, that of E was 62 +/- 2%, and that of cortisol was 12 +/- 5%. Across peripheral tissues (leg) the mean extractions were 13 +/- 1%, 18 +/- 1%, and 6 +/- 4%, respectively. In general, the dynamics of androgen, estrogen, and F production and metabolism are similar in male cynomolgus and rhesus monkeys and in man. The similarity is especially close for peripheral aromatization despite differences in adipose tissue content between man and nonhuman primates.

The effects of l-thyroxine and dexamethasone on steroid dynamics in male cynomologous monkeys.

Male cynomologous monkeys (M. fascicularis) were infused with [3H]androgens, [14C]estrogens and [3H]cortisol before and after the administration of l-thyroxine, (l-T4) 150 micrograms/day for 6 wk, dexamethasone 8 mg every 8 h for 3 doses and dexamethasone 1.0 mg/day for 8 days. Blood samples were obtained before each of the infusions and analyzed for endogenous T, A, E1, E2 and F concentrations, % free T and % free E2, sex hormone-binding globulin (SHBG) and cortisol binding globulin (CBG) capacity. When l-T4 was being administered, T4 and triiodothyronine (T3) concentrations were also measured. Blood samples were obtained during the infusions and analyzed for radioactivity as testosterone (T), androstenedione (A), dihydrotestosterone (DHT), estradiol (E1), estrone (E2), and cortisol (F). All urine was collected for 96 h and an aliquot of the pooled urine was analyzed for radioactivity as estrone and estradiol glucuronide. The administration of l-T4 for 6 wk to 3 monkeys resulted in a marked rise in T4 and T3 levels, from 4.8 +/- 0.4 micrograms/dl and from 136 +/- 6 to 515 +/- 71 ng/dl, respectively. MCRT, MCRE2 and MCRE1 did not change, but MCRA values increased slightly and MCRF increased 2-3 fold. [rho]T.E2 did not change but [rho]A.E1BM showed a slight but significant increase. The inter-conversions between the androgens and between the estrogens were not altered. There was a 2-3-fold increase in SHBG and a decrease in %FT but no change in %FE2 or CBG. The concentrations of T, A and DHT rose but there was no trend in the levels of the estrogens. The administration of dexamethasone 8 mg every 8 h for 3 doses or 1 mg/day for 8 days caused no changes in the MCRs for T, A, E1 and E2 but did cause a significant decrease in MCRF. Measurement of splanchnic and peripheral tissue extractions before and after acute dexamethasone administration in 1 monkey showed that the decrease in MCRF was the result of a marked decrease, 11-2%, in splanchnic extraction of F. The extractions of T and E2 were relatively unaffected. The concentrations of T and F fell but E2 remained the same. % FT and % FE2 rose slightly and the concentrations of SHBG and CBG were unchanged. The androgen interconversions and estrogen interconversions were not affected but [rho]T,E2BM and [rho]A,E1BM showed slight decreases.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolism of 2-methoxyestrone in normal men.

We studied, in four normal men, the metabolism of 2-methoxyestrone (2-MeOE1) using pulse injections of either [3H]2MeOE1 (two men) or [14C]methoxy-2-MeOE1 plus [3H]2-MeOE1 (two men) by analysis of blood samples drawn at increasing time intervals after the pulse and of urine collected for 5 days. The disappearance from the blood of radioactivity as 2-MeOE1 could be characterized as a function that was the sum of three exponentials. The mean +/- SE value for the initial volume of distribution was 32 +/- 9 liters, and the mean MCR was 2470 +/- 770 liters/day. The disappearance of total 3H radioactivity from the blood was considerably slower, with a mean MCR of 290 +/- 30 liters/day, indicating the presence of a slowly turning over pool of 2-MeOE1 metabolites, probably including the 2-MeOE1 3-sulfate conjugate. The disappearance of total 14C radioactivity was slower than that of total 3H, indicating considerable demethylation of 2-MeOE1 with a very slow excretion of 14C from the released methyl group. In none of the subjects could we find in the blood radioactivity as unconjugated [3H]2-hydroxyestrone ( [3H]2-OHE1). However, examination of the urine indicated that considerable demethylation of [3H]2-MeOE1 had occurred. At least 64% of the urinary 3H-containing metabolites from the mixed dose had lost the 14C-bearing methoxylcarbon atom. The fractionated metabolites were qualitatively and quantitatively similar to those found earlier for [3H]2-OHE1. We conclude that 2-MeOE1, which of itself has little biological activity, can act as a pool of potentially active 2-OHE1 in the tissues.