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Elevation of intracellular cAMP inhibits growth factor-mediated matrix metalloproteinase-9 induction and keratinocyte
L J McCawley1, S Li, M Benavidez
1Department of Cell Biology, Vanderbilt University, Nashville, TN, USA.
Abstract:
Receptor tyrosine kinases are regulators of diverse cellular functions including cell growth, cell survival, differentiation, locomotion, and morphogenesis. Activation of the cAMP-dependent protein kinase A inhibits receptor tyrosine kinase-stimulated growth responses in a number of cell types. In this study, we investigated the consequences of elevated cAMP on growth factor-mediated keratinocyte migration and matrix metalloproteinase (MMP)-9 induction in a human keratinocyte cell line. We found that elevation of intracellular cAMP by forskolin abolishes epidermal growth factor (EGF)- or scatter factor/hepatocyte growth factor-dependent colony dispersion. Concentrations of forskolin that inhibit growth factor-induced motility also eliminate EGF- or scatter factor/hepatocyte growth factor-dependent induction of the 92-kDa gelatinase/MMP-9. In contrast to findings obtained in fibroblasts, elevated intracellular cAMP did not interfere with growth factor-dependent activation of the p42/44 extracellular signal-regulated kinases, indicating that cAMP-dependent inhibition of migration and MMP-9 induction does not occur through perturbation of the extracellular signal-regulated kinases/mitogen-activated protein kinase pathway. However, forskolin effectively inhibited EGF-dependent activation of c-Jun N-terminal kinase and p38, demonstrating that cAMP selectively interferes with a different subset of growth factor-induced mitogen-activated protein kinase signaling cascades than reported previously in fibroblasts. These findings illustrate that EGF concurrently activates multiple mitogen-activated protein kinase signaling cascades in keratinocytes and suggests that each pathway contributes to maximal EGF-dependent migration and proteinase induction.
Insights
Elevated cyclic AMP (cAMP) inhibits human keratinocyte migration and matrix metalloproteinase-9 (MMP-9) induction by growth factors like epidermal growth factor (EGF). This inhibition occurs independently of the extracellular signal-regulated kinases/mitogen-activated protein kinase pathway.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Receptor tyrosine kinases regulate critical cellular processes like growth, survival, and migration.
- Cyclic AMP-dependent protein kinase A activation can inhibit receptor tyrosine kinase-stimulated growth.
- Understanding cAMP's role in keratinocyte responses to growth factors is crucial for cell migration and tissue remodeling insights.
Purpose of the Study:
- To investigate the effects of elevated intracellular cyclic AMP (cAMP) on growth factor-induced keratinocyte migration.
- To determine the impact of increased cAMP on matrix metalloproteinase-9 (MMP-9) induction in human keratinocytes.
- To elucidate the specific mitogen-activated protein kinase (MAPK) signaling pathways affected by cAMP in keratinocytes.
Main Methods:
- Human keratinocyte cell line utilized for experiments.
- Elevation of intracellular cAMP achieved using forskolin.
- Epidermal growth factor (EGF) and scatter factor/hepatocyte growth factor (SF/HGF) used as growth factors.
- Assays performed to measure colony dispersion, cell motility, and MMP-9 induction.
- Western blotting used to assess the activation of MAPK pathways, including ERK, JNK, and p38.
Main Results:
- Elevated intracellular cAMP abolished epidermal growth factor (EGF) or scatter factor/hepatocyte growth factor (SF/HGF)-dependent colony dispersion.
- Forskolin inhibited growth factor-induced keratinocyte motility and the induction of 92-kDa gelatinase/MMP-9.
- Unlike in fibroblasts, elevated cAMP did not inhibit growth factor-dependent activation of p42/44 extracellular signal-regulated kinases (ERK).
- Forskolin inhibited EGF-dependent activation of c-Jun N-terminal kinase (JNK) and p38, indicating selective interference with MAPK pathways.
- Findings suggest that EGF activates multiple MAPK cascades in keratinocytes, each contributing to migration and proteinase induction.
Conclusions:
- Elevated intracellular cAMP selectively inhibits growth factor-mediated keratinocyte migration and MMP-9 induction.
- The inhibitory mechanism of cAMP in keratinocytes differs from that in fibroblasts, not involving the ERK pathway.
- cAMP interferes with EGF-induced activation of JNK and p38 signaling in keratinocytes.
- These results highlight the complex interplay of MAPK pathways in regulating keratinocyte behavior and suggest distinct signaling roles for each pathway.