Role of proto-oncogenes in the regulation of proenkephalin mRNA expression induced by repeated nicotine injections in rat adrenal medulla

We have studied the effect of repeated systemic administrations of nicotine (3 mg/kg) at 30 min intervals on proenkephalin (proENK) mRNA level in rat adrenal gland. Northern blot analysis has shown that proENK mRNA expression was enhanced by repeated nicotine administrations. Additionally, repeated administrations of nicotine transiently induced the c-fos and c-jun mRNA levels after the first-third nicotine administration, and the c-fos and c-jun mRNA levels were returned to the basal level after the seventh administration of nicotine. c-Fos, c-Jun and Fra-2 protein levels were persistently increased until the seventh administration. The repeated nicotine administrations also elevated phospho-CREB without altering total CREB level in all tested groups. Immunohistochemical analysis showed that the increase of c-Fos and c-Jun proteins by repeated nicotine administrations is mostly medulla specific, while Fra-2 immuno reactivity was shown both in medulla and cortex. The repeated nicotine administrations enhanced the AP-1 and ENKCRE-2 DNA binding activities. Furthermore, the cross-competition studies revealed that the AP-1 proteins, rather than CREB, actively bind to ENKCRE-2 DNA domain. These results suggest that proENK mRNA expression induced by repeated nicotine administrations may be mediated by AP-1 proteins, such as c-Fos, c-Jun and Fra-2 rather than CREB via interacting to the ENKCRE-2 DNA binding domain in rat adrenal medulla.     

PTHrP modulates chondrocyte differentiation through AP-1 and CREB signaling

During the process of differentiation, chondrocytes integrate a complex array of signals from local or systemic factors like parathyroid hormone-related peptide (PTHrP), Indian hedgehog, bone morphogenetic proteins and transforming growth factor beta. While PTHrP is known to be a critical regulator of chondrocyte proliferation and differentiation, the signaling pathways through which this factor acts remain to be elucidated. Here we show that both cAMP response element-binding protein (CREB) and AP-1 activation are critical to PTHrP signaling in chondrocytes. PTHrP treatment leads to rapid CREB phosphorylation and activation, while CREB DNA binding activity is constitutive. In contrast, PTHrP induces AP-1 DNA binding activity through induction of c-Fos protein expression. PTHrP activates CRE and TRE reporter constructs primarily through PKA-mediated signaling events. Both signaling pathways were found to be important mediators of PTHrP effects on chondrocyte phenotype. Alone, PTHrP suppresses maturation and stimulates proliferation of the chondrocyte cultures. However, in the presence of dominant negative inhibitors of CREB and c-Fos, these PTHrP effects were suppressed, and chondrocyte maturation was accelerated. Moreover, in combination, the effects of dominant negative c-Fos and CREB are synergistic, suggesting interaction between these signaling pathways during chondrocyte differentiation.     

Excretory/secretory products from plerocercoids of Spirometra erinaceieuropaei suppress interleukin-1beta gene expression in murine macrophages

The present study shows that ES products from plerocercoids of Spirometra erinaceieuropaei suppressed interleukin-1beta mRNA expression in lipopolysaccharide-stimulated RAW 264.7 macrophages in the absence or presence of a cyclic AMP analogue, dibutyryl cyclic AMP. Investigation using the inhibitors of mitogen-activated protein kinase (MAPK) pathways revealed that extracellular signal-regulated protein kinase 1/2 and p38 mitogen-activated protein kinase pathways are crucial for full induction of interleukin-1beta mRNA expression. ES products additionally suppressed interleukin-1beta mRNA expression in the cells treated with p38 mitogen-activated protein kinase inhibitor (SB203580) or extracellular signal-regulated protein kinase 1/2 inhibitor (PD98059). Western blot analysis showed that dibutyryl cyclic AMP enhanced lipopolysaccharide-induced phosphorylation of extracellular signal-regulated protein kinase 1/2, p38 mitogen-activated protein kinase and cyclic AMP responsive element binding protein (CREB) and, in turn, we demonstrated that ES products reduced the lipopolysaccharide and dibutyryl cyclic AMP-induced phosphorylation of extracellular signal-regulated protein kinase 1/2 and p38 mitogen-activated protein kinase, but not cyclic AMP responsive element binding protein. These data demonstrate that ES products from the plerocercoids of S. erinaceieuropaei may evade induction of interleukin-1beta mRNA by inhibiting extracellular signal-regulated protein kinase 1/2 and p38 mitogen-activated protein kinase pathways in lipopolysaccharide and/or dibutyryl cyclic AMP-stimulated macrophages.