Density-induced down regulation of epidermal growth factor receptors

Summary Previous studies have shown that cell density can regulate the binding of several growth factors. To determine whether cell density exerts a uniform effect on the expression of epidermal growth factor (EGF) receptors, seven cell lines were examined in detail. For each cell line, EGF binding was found to decrease as cell density increases. Scatchard analysis of the binding data reveals that decreases in EGF binding are due to reductions in the number of cell surface EGF receptors. The only apparent exception is the effect of cell density on the binding of EGF to A-431 cells. For these cells, increases in cell density lead to two effects: decreases in the number of high affinity EGF receptors and increases in the total number of EGF receptors. In addition to the effects of cell density on EGF receptors, it was determined that increases in cell density can coordinately down-regulate receptors for as many as four different growth factors. Overall, the findings described in this report for EGF and those previously described for transforming growth factor type-β (TGF-β) and fibroblast growth factor (FGF) demonstrate the existence of a common mechanism for down-regulating growth factor receptors. This work was supported by grants from the Nebraska Department of Health (89-51), the National Cancer Institute (Laboratory Research Center Support Grant, CA36727), and the American Cancer Society (Core Grant ACS SIG-16). EDITOR'S STATEMENT The paper by Rizzino et al. demonstrates that receptor number decreases as a function of cell density. This may represent a mechanism by which cell proliferation is reduced as cell density increases.     

On the biology of bream, Abramis brama (L.) in Lake Peipsi in 1994

The population of bream in L. Peipsi was studied with respect to age, growth rate, condition factor (according to Fulton) and length-weight relationship in 1994. That autumn the bream population in L. Peipsi consisted of fishes aged from 0+ to 15+. During the first year bream reached an average body length of 7.9 cm (the commercial legal size (30 cm) was usually attained by the end of the 5th–6th year. The condition of bream in this lake was above the average of Estonian lakes. The relatively good growth rate and condition of bream in the lake indicates that the waterbody is appropriate for this fish.     

Effects of Nerve Growth Factor and Phorbol Derivative on Reactivation of Herpes Simplex Virus Type 1 in Cultured Cells of Latently Infected Adult Mouse Trigeminal Ganglia

Reactivation of herpes simplex virus type 1 (HSV-1) occurred rapidly in cells of latently infected adult mouse trigeminal ganglia which were cultured in serum-free medium in the presence of sufficient nerve growth factor (NGF). However, HSV-1 reactivation was delayed significantly in ganglionic cultures in the absence of exogenous NGF or in cultures treated with 2-aminopurine in the presence of NGF. The delayed viral reactivation in ganglionic cultures without NGF was accelerated by treatment with phorbol myristate acetate or dibutyryl cyclic AMP. Culture conditions which affected HSV-1 reactivation did not affect replication of HSV-1 in normal ganglionic cultures.     

Proliferation and Teratogenicity of Aino Virus in Chick Embryos

Aino virus (AIV; JaNAr 28 strain) 10³ TCID₅₀/0.2 ml was inoculated in the yolk sac of 8-day-old chick embryos. Recovery and titration of the virus from various organs including the central nervous system (CNS) and skeletal muscle were performed at 2, 4, 7, 10 and 13 days after inoculation (PI). AIV was systemically disseminated and proliferated even 2 days PI. The titers of the recovered virus from the CNS and from skeletal muscle was the highest at 4 days PI and declined with time, whereas hydranencephaly, arthrogryposis and cerebellar hypoplasia developed at 7 days PI and gradually progressed until 13 days PI.     

Phytochrome control of short-day-induced bud set in black cottonwood

In trees and other woody perennial plants, short days (SDs) typically induce growth cessation, the initiation of cold acclimation, the formation of a terminal bud and bud dormancy. Phytochrome control of SD-induced bud set was investigated in two northern clones of black cottonwood (Populus trichocarpa Torr. & Gray) by using night breaks with red light (R) and far-red light (FR). For both clones (BC-1 and BC-2), SD-induced bud set was prevented when R night breaks as short as 2 min were given in the middle of the night. When night breaks with 2 min of R were immediately followed by 2 min of FR, substantial reversibility of bud set was observed for BC-1 but not for BC-2. By comparing the effects of the R night breaks on bud set and the length of specific internodes, we determined that the R night breaks influenced internode elongation in two opposing ways. First, the addition of a R night break to the SD treatment prevented the cessation of internode elongation that is associated with bud set. Those internodes that would not have elongated under SDs (and would have been found within the terminal bud) elongated in the R treatment. Second, the R night breaks decreased internode length relative to the long-day (LD) control. In contrast to the clonal differences in reversibility that we observed for bud set, the decrease in internode length (i.e. the second effect of R) was R/FR reversible in both clones. Based on these results, we conclude that internode elongation is influenced by two distinct types of phytochrome-mediated response. The first response is a typical response to photpperiod, whereas the second response is a typical “end-of-day” response to light quality. Our results demonstrate that SD-induced bud set in black cottonwood is controlled by phytochrome but that clonal differences have an important influence on the R/FR reversibility of this response. The availability of an experimental system in which SD-induced bud set is R/FR reversible will be valuable for studying the physiological genetics of photoperiodism in trees.     

A cell-based reporter assay for the identification of protein kinase C activators and inhibitors

Transmission of extra cellular signals across biological membranes results in the generation of lipid metabolites which in turn influence specific cellular events such as cell growth or differentiation. Many of these lipid messengers can activate protein kinase C (PKC) isozymes of which one function is to perpetuate the extracellular signals to the nucleus by phosphorylating other targets proteins. We have engineered mammalian cell lines to identify and evaluate activators and inhibitors of PKC-dependent and independent signal transduction pathways. The A31 mouse fibroblast cell line, has been stably transfected with a construct containing a triplet repeat of the TPA response element (TRE) upstream of a thymidine kinase promoter fused to the human growth hormone (hGH) gene. A31 cells containing this reporter construct exhibit significant increases in hGH secretion following stimulation by phorbol esters or other mitogens. The levels of hGH secretion are modulated in this system using different pharmacological agents. We demonstrate that this assay can be used to identify specific and general inhibitors as well as activators of the signal transduction pathway mediated by PKC isozymes. (Mol Cell Biochem141: 129–134, 1994)     

The distribution, age and growth of wrasse (Labridae) in inshore waters of west Scotland

Wrasse were widely distributed in inshore waters of west Scotland in rocky and algal habitats. Ctenolabrus rupestris and Centrolabrus exoletus dominated commercial and experimental catches using creels, traps and fyke nets, but Crenilabrus melops, Labrus bergylta and L. mixtus were infrequent. Maximum age of sampled fish was 16yr in C. rupestris , 9 yr in C. exolefus , 5 yr in C. melops , 15 yr in L. bergylta , and 11 yr in L. mixtus . Growth was more rapid prior to maturation in all species. The von Bertalanffy growth model fitted data for C. rupestris and C. exoletus . Male C. rupestris and C. exoletus were significantly longer than females in most age groups and growth of all species captured in mid–Scottish areas was more rapid than in northern localities. Mortality (Z) of C. rupestris was 0–1861 per year and 0·4185 in C exoletus .     

Hormone- and growth factor-stimulated NADH oxidase

An NADH oxidase activity of animal and plant plasma membrane is described that is stimulated by hormones and growth factors. In plasma membranes of cancer cells and tissues, the activity appears to be constitutively activated and no longer hormone responsive. With drugs that inhibit the activity, cells are unable to grow although growth inhibition may be more related to a failure of the cells to enlarge than to a direct inhibition of mitosis. The hormone-stimulated activity in plasma membranes of plants and the constitutively activated NADH oxidase in tumor cell plasma membranes is inhibited by thiol reagents whereas the basal activity is not. These findings point to a thiol involvement in the action of the activated form of the oxidase. NADH oxidase oxidation by Golgi apparatus of rat liver is inhibited by brefeldin A plus GDP. Brefeldin A is a macrolide antibiotic inhibitor of membrane trafficking. A model is presented where the NADH oxidase functions as a thiol-disulfide oxidoreductase activity involved in the formation and breakage of disulfide bonds. The thiol-disulfide interchange is postulated as being associated with physical membrane displacement as encountered in cell enlargement or in vesicle budding. The model, although speculative, does provide a basis for further experimentation to probe a potential function for this enzyme system which, under certain conditions, exhibits a hormone- and growth factor-stimulated oxidation of NADH.