Up-regulation of Nucleolin mRNA and Protein in Peripheral Blood Mononuclear Cells by Extracellular-regulated Kinase

Abstract

The signal transduction pathways regulating nucleolin mRNA and protein production have yet to be elucidated. Peripheral blood mononuclear cells treated with phorbol 12-myristate 13-acetate showed steady state levels of nucleolin mRNA that were 2-2.5-fold greater than untreated control cells. The up-regulation of nucleolin mRNA was substantially repressed by U0126, a specific inhibitor that blocks phosphorylation of extracellularregulated kinase (ERK). Calcium ionophores A23187 and ionomycin also activated ERK and substantially elevated nucleolin mRNA levels, demonstrating phorbol 12-myristate 13-acetate and calcium signaling converge on ERK. Drugs that affected protein kinase C, protein kinase A, and phospholipase C signal transduction pathways did not alter nucleolin mRNA levels significantly. The half-life of nucleolin mRNA increased from 1.8 h in resting cells to 3.2 h with phorbol ester activation, suggesting ERK-mediated posttranscriptional regulation. Concomitantly, full-length nucleolin protein was increased. The higher levels of nucleolin protein were accompanied by increased binding of a 70-kDa nucleolin fragment to the 29-base instability element in the 3-untranslated region of amyloid precursor protein (APP) mRNA in gel mobility shift assays. Supplementation of rabbit reticulocyte lysate with nucleolin decreased APP mRNA stability and protein production. These data suggest ERK up-regulates nucleolin posttranscriptionally thereby controlling APP production.

Identification of Nucleolin as an AU-rich Element Binding Protein Involved in bcl-2 mRNA Stabilization

“…Stabilization of interleukin 2 mRNA in response to T-cell activation involves binding of nucleolin to a response element in the 5Ј-UTR of interleukin 2 mRNA. Nucleolin also has been shown to bind to a 29-nucleotide element in the 3Ј-UTR of amyloid precursor protein mRNA (43) and contribute to the stabilization of the mRNA (44). Interestingly, the predicted secondary structure of bcl-2 ARE 1 contains a stem-loop with a sequence in the loop (UCCCA) that is similar to the loop sequence (UCCCGA) in the nucleolin recognition element in pre-rRNA (45).…”

RNA-binding protein nucleolin in disease

“…In phorbol ester-treated peripheral blood mononuclear treated cells, the levels of NCL mRNA, which encodes nucleolin, increased transcriptionally via the activity of extracellular-regulated kinase (ERK). 40 At the post-transcriptional level, HuR was found to interact with the 3' UTR of NCL mRNA and promoted its translation, while miR-494 competed with HuR and repressed nucleolin translation. 13 Post-translationally, nucleolin abundance was shown to be controlled by proteolysis.…”

“…The 3' UTR of APP mRNA was found to be a substrate for association by nucleolin, as well as by the RBPs hnRNP C and fragile X mental retardation protein (FMRP). [38][39][40][41] The helicase activity of nucleolin was proposed to accelerate APP mRNA degradation in response to stress, an effect that was counteracted by the stabilizing influence of hnRNP C. 41 IL2 mRNA. Interleukin (IL)-2 is a major cytokine implicated in the response against microbial infection and is used in certain cancer therapies.…”

Functional Implication of Nucleolin in the Mouse First Molar Development

“…The amount of nucleolin mRNA fluctuates in parallel with the status of DNA synthesis (11). The intact 110-kDa nucleolin molecule is the major species in actively dividing cells, and degraded forms are relatively abundant in nondividing cells (12). In addition, nucleolin has been known to participate in the packaging and shuttling of the ribosome between the nucleus and cytoplasm (13).…”