Overexpression of FRA1 (FOSL1) Leads to Global Transcriptional Perturbations, Reduced Cellular Adhesion and Altered Cell Cycle Progression.

FRA1 (FOSL1) is a transcription factor and a member of the activator protein-1 superfamily. FRA1 is expressed in most tissues at low levels, and its expression is robustly induced in response to extracellular signals, leading to downstream cellular processes. However, abnormal FRA1 overexpression has been reported in various pathological states, including tumor progression and inflammation. To date, the molecular effects of FRA1 overexpression are still not understood. Therefore, the aim of this study was to investigate the transcriptional and functional effects of FRA1 overexpression using the CGL1 human hybrid cell line. FRA1-overexpressing CGL1 cells were generated using stably integrated CRISPR-mediated transcriptional activation, resulting in a 2-3 fold increase in FRA1 mRNA and protein levels. RNA-sequencing identified 298 differentially expressed genes with FRA1 overexpression. Gene ontology analysis showed numerous molecular networks enriched with FRA1 overexpression, including transcription-factor binding, regulation of the extracellular matrix and adhesion, and a variety of signaling processes, including protein kinase activity and chemokine signaling. In addition, cell functional assays demonstrated reduced cell adherence to fibronectin and collagen with FRA1 overexpression and altered cell cycle progression. Taken together, this study unravels the transcriptional response mediated by FRA1 overexpression and establishes the role of FRA1 in adhesion and cell cycle progression.

Identification of Radiation-Induced miRNA Biomarkers Using the CGL1 Cell Model System.

MicroRNAs (miRNAs) have emerged as a potential class of biomolecules for diagnostic biomarker applications. miRNAs are small non-coding RNA molecules, produced and released by cells in response to various stimuli, that demonstrate remarkable stability in a wide range of biological fluids, in extreme pH fluctuations, and after multiple freeze-thaw cycles. Given these advantages, identification of miRNA-based biomarkers for radiation exposures can contribute to the development of reliable biological dosimetry methods, especially for low-dose radiation (LDR) exposures. In this study, an miRNAome next-generation sequencing (NGS) approach was utilized to identify novel radiation-induced miRNA gene changes within the CGL1 human cell line. Here, irradiations of 10, 100, and 1000 mGy were performed and the samples were collected 1, 6, and 24 h post-irradiation. Corroboration of the miRNAome results with RT-qPCR verification confirmed the identification of numerous radiation-induced miRNA expression changes at all doses assessed. Further evaluation of select radiation-induced miRNAs, including miR-1228-3p and miR-758-5p, as well as their downstream mRNA targets, Ube2d2, Ppp2r2d, and Id2, demonstrated significantly dysregulated reciprocal expression patterns. Further evaluation is needed to determine whether the candidate miRNA biomarkers identified in this study can serve as suitable targets for radiation biodosimetry applications.

PACAP-regulated phenylethanolamine N-methyltransferase gene expression.

Pituitary adenylate cyclase activating polypeptide (PACAP) induces the proximal -893 bp of rat phenylethanolamine N-methyltransferase (PNMT) gene promoter in PC12 cells via PACAP type I receptors. Deletion mutation analysis suggested that the initial -392 bp of promoter, containing early growth response protein (Egr-1), specificity protein 1 (Sp1) and activator protein 2 (AP-2) binding sites (-165, -168 and -103 bp, respectively), was sufficient for PACAP activation. Egr-1 and AP-2 involvement was supported by PACAP induction of their mRNA and protein. Mutation of the Egr-1, Sp1 and AP-2 elements showed that the Egr-1 site was essential for PACAP stimulation. Mutation of the -103 bp AP-2 site partially reduced PACAP activation of the promoter. Mutation of two upstream AP-2 sites at -573 and -650 bp, separately or in tandem, also prevented promoter induction by PACAP. siRNA knock-down of Egr-1 and AP-2 suppressed promoter activation for the -893 bp construct. Egr-1 siRNA knock-down also eliminated the residual activation observed for the -103 bp AP-2 mutant construct, suggesting that Egr-1 and AP-2 through respective -165 and -650/-573/-103 bp sites cooperatively stimulate the promoter. PACAP responses appear orchestrated through cAMP-protein kinase A and phospholipase C signaling as MDL12,330A, H89 and U73122, respectively, inhibited promoter induction by PACAP and reduced PACAP-stimulation of Egr-1, AP-2 and PNMT mRNA and protein and Egr-1 and AP-2 protein/DNA complex formation. Findings are the first to show that PACAP stimulates PNMT promoter-driven gene expression via PACAP type I receptors and cAMP-protein kinase A and phospholipase C signaling, recruiting Egr-1 and AP-2 as cooperative regulators, and the first to associate the transcription factor AP-2 to PACAP-mediated gene induction.

Cholinergic and peptidergic regulation of phenylethanolamine N-methyltransferase gene expression.

The splanchnic nerve, innervating the adrenal medulla, releases a variety of neurotransmitters that stimulate genes involved in catecholamine biosynthesis. In particular, cholinergic agonists have been shown to induce phenylethanolamine N-methyltransferase (PNMT) gene expression through activation of both nicotinic and muscarinic receptors in vivo and in vitro. By contrast, the role of peptidergic neurotransmitters in adrenal medullary PNMT gene expression remains unclear. Using transient transfection assays, we demonstrate that rat PNMT promoter-luciferase reporter gene constructs are markedly activated by 10 nM PACAP when expressed in PC12 cells. PACAP appears to mediate its effects primarily through PAC1 receptors and, subsequently, cAMP-protein kinase A (PKA) and extracellular Ca(2+) signaling mechanisms. Activation of these signal transduction pathways markedly increases nuclear levels of the immediately early gene transcription factor Egr-1 and the developmental factor AP2. A slight decrease in Sp1 expression may also occur, whereas MAZ and glucocorticoid receptor expression remains unaltered. Although PACAP stimulates rapid changes in transcription factor expression and PNMT promoter activity, its effects are long lasting. PNMT promoter induction continues to rise and is sustained for > or=48 hours. By contrast, while muscarine, nicotine, or carbachol (100 micro M) also evoke rapid increases in rat PNMT promoter activity, peak activity is observed at 6 hours, followed by a decline and restoration to basal levels by 24 hours. Cholinergic activation of the PNMT promoter also seems to involve the cAMP-PKA signaling mechanism. However, the magnitude of stimulation and antagonist blockade with H-89 or the polypeptide inhibitor PKI suggests that the extent of activation is much less than that with PACAP.