Increased Uridine Incorporation Research Articles

Analysis of ribosomal RNA in human fibroblasts continuously treated with hydrocortisone

The prolongation of the limited lifespan of human embryonic lung fibroblasts by hydrocortisone was previously associated with increased uridine incorporation into ribosomal RNA (rRNA). Using polyacrylamide gel electrophoresis, we show here that the continuous treatment with 12 μM hydrocortisone results in increased uridine incorporation into rRNA precursors in cells stimulated to grow by serum, but not in resting cells, suggesting that the hormone does not directly activate rRNA transcription. Chase experiments indicate that the stability of 28S and 18S rRNA is enhanced by hydrocortisone in quiescent cells but not after serum refeeding. Similar results were also observed for transfer RNA (tRNA). Therefore, these effects of hydrocortisone seem to be indirect consequences of pleiotropic actions of glucocorticoid, such as stimulation of processes involved in cell proliferation and inhibition of lysosomal enzymes.

Factors involved in the control of RNA synthesis during regeneration of the optic nerve in the frog

The incorporation of tritiated uridine into retinal ganglion cells was studied following intra- and extracranial section of the optic nerve in the frog. It was found that incorporation increased to above control levels by two days following extracranial section of the optic nerve and by two weeks following intracranial section and was maintained at an elevated level until the regenerating optic nerve reached the diencephalon, at which point the rate of incorporation fell back to control levels. It is suggested that the signal for turning off increased uridine incorporation lies in the diencephalon, and that functional reconnection is not the signal.

Human lymphocyte complement receptors. Stimulation of lymphocyte RNA synthesis by complement-coated human red cells

A subpopulation of human lymphocytes (CR+ lymphocytes) possesses receptors for the third component of complement (C3). This paper examines the rate of incorporation of uridine in RNA of CR+ lymphocytes compared to lymphocytes without complement receptors (CR− lymphocytes) and the effect of interaction of lymphocytes with human complement-coated autologous red cells (EC). CR+ lymphocytes had a greater baseline RNA synthesis than CR− lymphocytes. Stimulation of RNA synthesis was observed in CR+ lymphocytes after 3 hr of incubation with EC, as compared to lymphocytes incubated with red cells which lacked membrane-bound complement (E). RNA synthesis in CR− lymphocytes was unaffected by incubation with EC. This increased uridine incorporation into RNA in CR+ lymphocytes was due neither to increased intracellular flux of uridine nor to decreased degradation of RNA. Lymphocytes incubated with EC had increased incorporation of amino acids into intracellular proteins as compared to controls. Thus, the interaction of complement-coated red cells with complement-receptor-bearing human lymphocytes causes an immediate increase in lymphocyte RNA synthesis.

The effect of intermittent hypoxia on RNA synthesis in the isolated rat heart

To determine whether hypoxia per se could initiate myocardial RNA synthesis, isolated rat hearts were subjected to varying degrees of hypoxic perfusion in a modified Langendorff apparatus. Hearts were perfused for 30 min with media equilibrated with gas mixtures containing 96, 48, 24, 12 and 0% O 2, 4% CO 2, balance N 2; then for an additional 30 min with aerobic (96% O 2, 4% CO 2) media containing [ 14C]-uridine and incorporation into RNA determined. Hearts which showed significantly decreased performance during hypoxic perfusion (24% O 2 or less) exhibited significant increases in uridine incorporation into RNA post-hypoxia. To assess the effect of hypoxia in the absence of contraction, hearts were arrested with media containing a high potassium concentration (26 mEq/l). Potassium-arrest during the aerobic labelling period only did not prevent increased incorporation of uridine following 30 min of hypoxia (12% and 0% O 2). Potassium-arrest during hypoxia as well as the labelling period prevented increased uridine incorporation in all but anoxia (0% O 2) exposed hearts. The myocardial content of high energy compounds (creatine phosphate, ATP, ADP, and AMP) was determined after 30 min of hypoxia in the absence and presence of potassium arrest. Only those hearts in which significant decreases in high energy phosphate content were observed, exhibited significant increases in uridine incorporation. It is concluded that intermittent hypoxia per se initiates events leading to increases in RNA synthesis, but only if energy depletion occurs.

TheIn VitroEffects of Androgens on RNA Synthesis by Cultured Rat Epididymal Tubules

The incorporation of [14C]uridine into RNA by cultured rat epididymal tubules was tested after different times in culture. Incorporation after 3 days in culture was twice that found after 1 day in culture, and reached a maximum after 5 days. The presence of androgen in the culture medium for a 3-day period produced significant stimulation of [14C]uridine incorporation into RNA. 10 μM Dihydrotestosterone (DHT) or testosterone (T) caused 52 and 68% increases, respectively. 0.1 μM DHT enhanced incorporation by 79%. The effects of androgens became detectable only 10 hours after the addition of the hormone. Neither estradiol-17ß, progesterone nor corticosterone was able to mimic the effect of DHT or T, while 10 μM 5α-androstane-3α-17ß-diol produced a 40% stimulation ofuridine uptake. The effect of 10 μM DHT was blocked by the simultaneous presence of 0.1 mM cyproterone acetate.Fetal calf serum contains 0.35 ng T/ml. When the culture media were prepared with charcoal-treated serum in which T is undetectable by radioimmunoassay, the tissues responded with increased uridine incorporation to the addition of 5 nm DHT or T. Under these conditions, 1 μM DHT covalently linked to bovine serum albumin was without effect.

Effect of the inhibition of RNA synthesis on in vitro ovulation by frog ovaries.

OVULATION can be stimulated in isolated segments of frog ovary by the addition of hormones1,2 but is prevented by actinomycin D3; this has led to the suggestion that ovulation is contingent on the synthesis of RNA3,4. Indeed, actinomycin D is known to inhibit RNA synthesis in ovaries as well as ovulation4, while hormonal stimulation is followed by increased uridine incorporation into the cells of the peritoneal surface of the ovary5, through which ovulation occurs.

Ribonucleic acid and protein synthesis in ovary

The incorporation of isotopic uridine and valine into RNA and protein of rabbit ovarian slices in vitro is enhanced by pretreatment in vivo with pituitary follicle-stimulating hormone (FSH), pituitary luteinizing hormone (LH), and human chorionic gonadotropin (HCG). Significant changes in RNA and protein turnover in the ovarian slice are detectable within 60 min after hormone treatment. When ovarian follicles and ovarian interstitial tissue were incubated separately, it was found that FSH pretreatment stimulated uridine and valine incorporation only in the Graafian follicles; whereas LH pretreatment stimulated uridine and valine uptake by both follicles and interstitial tissue, with the latter showing the greater increment. Increased uridine incorporation following LH administration in vivo occurred mainly in the nuclear and post-mitochondrial cellular fractions. The stimulatory effect of gonadotropin on uridine incorporation was blocked by actinomycin D in vitro.