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D Collepardo

Publications and source records attributed to D Collepardo.

7 recordsLinked to original sources
PubMed1995

Reactive oxygen intermediates mediate angiotensin II-induced c-Jun.c-Fos heterodimer DNA binding activity and proliferative hypertrophic responses in myogenic cells.

Angiotensin II (Ang-II) receptor engagement activates many immediate early response genes in both vascular smooth muscle cells and cardiomyocytes whether a hyperplastic or hypertrophic response is taking place. Although the signaling pathways stimulated by Ang-II in different cell lines have been widely characterized, the correlation between the generation of different second messengers and specific physiological responses remains relatively unexplored. In this study, we report how in both C2C12 quiescent myoblasts and differentiated myotubes Ang-II significantly stimulates AP1-driven transcription and c-Jun.c-Fos heterodimer DNA binding activity. Using a set of different protein kinase inhibitors, we could demonstrate that Ang-II-induced increase in AP1 binding is not mediated by the cAMP-dependent pathway and that both protein kinase C and tyrosine kinases are involved. The observation that in quiescent myoblasts Ang-II increase of AP1 binding and induction of DNA synthesis and, in differentiated myotubes, Ang-II stimulation of protein synthesis are abolished by the cysteine-derivative and glutathione precursor N-acetyl-L-cysteine strongly suggests a role for reactive oxygen intermediates in the intracellular transduction of Ang-II signals for immediate early gene induction, cell proliferation, and hypertrophic responses.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Reactive oxygen intermediates (ROIs) are involved in the intracellular transduction of angiotensin II signal in C2C12 cells.

Increasing evidence suggests that angiotensin II may act as a growth factor for several muscle cell types. Angiotensin II stimulation activates many immediate early response genes like c-Fos, c-Jun, c-Myc and Egr-1 in both vascular smooth muscle cells and cardiomyocytes, independently of whether a hyperplastic or hypertrophic response is taking place. In this study we report that angiotensin II significantly stimulates AP1-driven transcription in mouse skeletal muscle cells C2C12 stably transfected with a TRE-tk-CAT plasmid in a dose-dependent manner (peak stimulation at 10(-5) M of angiotensin II). Moreover, angiotensin II increases the binding of the AP1 complex to its DNA target in both quiescent C2C12 myoblasts and in differentiated C2C12 myotubes. Most of the TRE-bound complexes in both unstimulated and angiotensin II-treated cells consist of c-jun/c-fos heterodimers. Using a set of different protein kinase inhibitors, including HA1004, H7, tyrphostin, genistein and staurosporine, we could demonstrate that the angiotensin II-induced AP1 binding increase is not mediated by the cAMP-dependent pathway and that protein kinase C and tyrosine kinases are involved. Treatment of C2C12 cells with H2O2 induces a dose-dependent increase in c-jun/c-fos heterodimer binding, specifically reverted by the cysteine derivative and glutathione precursor N-acetyl-L-cysteine (NAC). The observation that the induction by angiotensin II of both the AP1 DNA binding activity and DNA synthesis in quiescent C2C12 myoblasts is abolished by NAC strongly suggests a role for reactive oxygen intermediates (ROIs) in the intracellular transduction of angiotensin II signals for immediate early gene induction and for cell proliferation.

Angiotensin II↗
PubMed1995

Modulation of intracellular signal transduction pathways by the hepatitis B virus transactivator pX.

The mechanisms by which pX, the transactivator of the hepatitis B virus (HBV), exerts its effects on transcription of viral and cellular genes and affects cell-growth regulation have not yet been fully defined. Previous reports suggested the possibility of a direct interaction of pX, which lacks intrinsic DNA-binding activity, with components of the cellular transcription machinery. More recent investigations support the hypothesis that pX might activate cellular kinases involved in transcriptional regulation and growth control. We characterized the mechanisms of AP-1 transcription factor activation by pX and, in particular, the role of cellular proteins involved in the intracellular signal transduction of growth-factor receptors. The observation that the overexpression of c-fos and c-jun in the cells results in a clear augmentation of the effects of pX on TRE-directed transcription and the induction of the DNA-binding activity of c-jun/c-fos heterodimers by AP1-depleted nuclear extracts from pX-expressing cells strongly supports the involvement of post-translational modifications. In both HeLa and undifferentiated F9 cells, pX was able to increase the activity of exogenous transfected c-jun but not of c-jun mutants bearing mutations in the serine residues located in the amino-terminal transcriptional activation domain. Moreover, by use of Ha-ras and Raf-1 dominant negative mutants, we show that both Ha-ras and Raf-1 are required for pX-induced activation of c-jun transcriptional activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The hepatitis B virus (HBV) pX transactivates the c-fos promoter through multiple cis-acting elements.

The hepatitis B virus (HBV) X protein (pX) stimulates transcription regulated by cis-acting elements that control many viral and cellular genes, including the c-myc and the c-fos proto-oncogenes. Using several c-fos promoter deletion mutants, we found the serum-responsive element (SRE) located at -315, the modified TPA-responsive element located at -296 (fos-AP-1 binding site, FAP) and the region spanning from nucleotide -220 to -120, which contains an NF1-like site and several stretches of sequence homologous to the AP-2 consensus binding sites, to be responsive to pX. pX does not modify the pattern of the retarded complexes bound to the SRE/FAP region which, in our system, appears to be occupied by SRE-binding factors. The activation of the SRE does not involve complex formation between SRE-binding factors and pX, it is not associated with an increase in serum response factor binding to the SRE and it does not determine changes in SRE mobility-shift pattern.

Animals↗
PubMed1992

Truncated pre-S/S proteins transactivate multiple target sequences.

In order to investigate the transactivational function of HBV truncated preS/S proteins we have constructed two sets of plasmids and have tested their transactivational potential on the c-myc regulatory sequences and the TPA-responsive element. We found that preS/S proteins only become transactivationally active when truncated at the carboxy terminal end. Furthermore, using immunofluorescence microscopy we determined that the proteins are located exclusively in the cytoplasm, apparently ruling out DNA binding and activation of factors in the nucleus.

Chloramphenicol O-Acetyltransferase↗
PubMed1992

Characterization of the hepatitis B virus preS/S region encoded transcriptional transactivator.

A transactivating function generated by carboxy-terminal truncation of the HBV envelope proteins has been recently described. To characterize the preS/S protein domains responsible for transactivation, preS1/S2/S and preS2/S 3' deletion mutants under the control of the adenoviral major late promoter were tested for their transactivating potential in cotransfection experiments using the c-myc and c-fos regulatory sequences as targets. Deletion of the carboxyterminal hydrophobic domain of the S protein and the presence of the endoplasmic reticulum insertion signal I (ER signal I) are required for the generation of the preS/S transactivating function. Multiple transcription factors binding sites (i.e., TRE, SRE, and NFkB sites) mediated the truncated preS/S-induced activation of the target regulatory sequences. The transactivation phenomenon is linked, at least in part, to the protein kinase C signaling pathway.

Cloning, Molecular↗