DNA-damage protective effect, telomerase activation and cell proliferation induction of one small peptide, GSE4, derived from GSE24.2.

<p>Panel A. One small peptide derived from GSE24.2, GSE4, and GSE24.2 were expressed in F9_A353V cells that were transfected with the pRRL-CMV-IRES-EGFP vector, either empty (Vector) or expressing GSE24.2 or GSE4. Twenty four hours later cells were lysed and the presence of γH2AX and α-tubulin (loading control) analyzed by western blot. Un-transfected F9 and F9-A353V cells were used as controls. The values at the bottom of the panel indicate the estimated ratio between γH2AX and α-tubulin expression levels referred to those found in cells transfected with the empty vector (F9-A353V vector). The amino acid sequences of GSE24.2 and GSE4 are indicated at the lower part of the panel. Panel B. The telomerase activity of F26IIB cells transfected with the pRRL-CMV-IRES-GFP vector empty (vector), expressing GSE24.2 (GSE24.2) or GSE4 (GSE4) was determined using the Telomeric Repeat Amplification Protocol (TRAP) assay. The amplification products obtained using three decreasing amounts of cell extracts for each cell line are shown in the right panel. Quantification of the amplification products, normalized to the internal control provided in the assay (indicated by an arrow at the right panel) is shown in the left panel. Panel C. Expression of Ki67 was determined by immunocytochemistry in F26IIB cells transfected as described in panel B. The percentage of cells expressing Ki67 is represented for each type of transfected cells. The experiments were repeated three times with similar results. Asterisks indicated the statistical significance (* p<0.05, **p<0.01, ***p<0.001).</p

GSE4, a Small Dyskerin- and GSE24.2-Related Peptide, Induces Telomerase Activity, Cell Proliferation and Reduces DNA Damage, Oxidative Stress and Cell Senescence in Dyskerin Mutant Cells

<div><p>Dyskeratosis congenita is an inherited disease caused by mutations in genes coding for telomeric components. It was previously reported that expression of a dyskerin-derived peptide, GSE24.2, increases telomerase activity, regulates gene expression and decreases DNA damage and oxidative stress in dyskeratosis congenita patient cells. The biological activity of short peptides derived from GSE24.2 was tested and one of them, GSE4, that probed to be active, was further characterized in this article. Expression of this eleven amino acids long peptide increased telomerase activity and reduced DNA damage, oxidative stress and cell senescence in dyskerin-mutated cells. GSE4 expression also activated c-myc and TERT promoters and increase of c-myc, TERT and TERC expression. The level of biological activity of GSE4 was similar to that obtained by GSE24.2 expression. Incorporation of a dyskerin nuclear localization signal to GSE24.2 did not change its activity on promoter regulation and DNA damage protection. However, incorporation of a signal that increases the rate of nucleolar localization impaired GSE24.2 activity. Incorporation of the dyskerin nuclear localization signal to GSE4 did not alter its biological activity. Mutation of the Aspartic Acid residue that is conserved in the pseudouridine synthase domain present in GSE4 did not impair its activity, except for the repression of c-myc promoter activity and the decrease of c-myc, TERT and TERC gene expression in dyskerin-mutated cells. These results indicated that GSE4 could be of great therapeutic interest for treatment of dyskeratosis congenita patients.</p></div