Inhibition of protein synthesis in LLC-PK1 cells increases calcitonin-induced plasminogen-activator gene transcription and mRNA stability

Abstract

The peptide hormone calcitonin induces the accumulation of urokinase-type plasminogen activator (uPA) mRNA in pig kidney LLC-PK1 cells. By itself, inhibition of protein synthesis had a negligible effect on uPA mRNA accumulation. Inhibition of protein synthesis led to two superinductive effects: an increase in calcitonin-induced uPA mRNA accumulation over time, and a shift in the dose-response curve so that lower calcitonin doses became more potent. To explain these two superinductive effects of protein-synthesis inhibition on calcitonin treatment, we demonstrated that the inhibition of protein synthesis increased both calcitonin-induced uPA-gene transcription and uPA-mRNA stability. Different protein-synthesis inhibitors had similar actions, arguing against the possibility that the results were attributable to an anomalous action of a particular inhibitor. The superinductive effects of protein-synthesis inhibition could not be mimicked when a tumour promoter, 12-O-tetradecanoylphorbol 13-acetate (TPA), was used instead of calcitonin as an inducer. Calcitonin and TPA exert their effects through different pathways, suggesting a clue to the mechanism of superinduction. Although inhibition of protein synthesis has been reported to increase transcription and mRNA stability in a number of other systems, the one described here appeared unique in combining both effects in the context of hormonal regulation.

Regulation of c-myc mRNA stability in vitro by a labile destabilizer with an essential nucleic acid component.

“…The necessity for such precise regulation is consistent with the finding that inappropriate expression of these and other mRNAs and their protein products can interfere with cell replication and differentiation (1,7,12,30,31,39,47). mRNAs whose decay rates seem to be regulated include those expressed from proto-oncogenes (13,15,20,35,41,72); genes related to cell division, including the histones (reviewed in reference 36); acute-phase response and inflammatory response genes (3,19); interferon genes (80); heat shock protein genes (65,71); and developmentally regulated gehes (16,62,73).…”

NMDA induces post-transcriptional regulation of α2-guanylyl-cyclase-subunit expression in cerebellar granule cells

“…These results suggest that the effect of NMDA does not depend on translation and augments the abundance of ␣ 2 mRNA by decreasing its degradation rate because the accumulation of a particular mRNA species is the result of the equilibrium between the rate of synthesis and the rate of degradation. Moreover, it has been shown that inhibition of protein synthesis increases AREs-containing mRNA stability in different systems (Altus et al, 1987;Oliveira and McCarthy, 1995;Ross, 1995;Guhaniyogi and Brewer, 2001) and, here, we observed an increase in ␣ 2 mRNA after cycloheximide treatment. To determine whether the stability of ␣ 2 mRNA is affected by NMDA, control and NMDA-treated cells were incubated in the presence of actinomycin D for different periods of time and the amount of ␣ 2 transcripts was measured.…”

“…These results suggest that both cycloheximide and NMDA share the mechanism by which they increase the levels of ␣ 2 mRNA, and imply that these mRNA transcripts are more stable under these conditions. This is further supported by the fact that the inhibition of protein synthesis increases mRNA stability in several different systems (Altus et al, 1987;Oliveira and McCarthy, 1995;Ross, 1995), mainly in relation to mRNA transcripts that contain AU-rich elements (AREs) (Guhaniyogi and Brewer, 2001) such as ␣ 2 mRNA. Cycloheximide is thought to interact with some aspects of mRNA translation itself, elements that are coupled to the activation of ARE-mRNA degradation (Savant-Bhonsale and Cleveland, 1992).…”

Enhanced expression of the urokinase-type plasminogen activator gene and reduced colony formation in soft agar by ectopic expression of PU.1 in HT1080 human fibrosarcoma cells

“…In murine macrophages, Ets-2 activates the uPA enhancer by binding to the PEA3 site, whereas other Ets family transcription factors such as PU. I and PEA3 do not activate the enhancer (Stacey et al, 1995 (Henderson et al, 1991; uPA mRNA stability is specifically increased by a synergistic effect of Ca2+ and cAMP in renal epithelial cells (Altus et al, 1987(Altus et al, , 1991Zeigler et al, 1990); and cycloheximide, an inhibitor of protein synthesis, increases the uPA mRNA half-life from 70 min to >20 h (Altus et al, 1991). Therefore, there may be a protein(s) of shorthalf life, potentially attaching to the A+U-rich elements in the 3'-untranslated region of the uPA mRNA and responsible for specific degradation of the mRNA (Altus et al, 1991;Henderson and Kefford 1991).…”