We demonstrated previously that leukotriene D-4 (LTD4) regulates proliferation of intestinal epithelial cells through a CysLT receptor by protein kinase C (PKC)epsilon-dependent stimulation of the mitogen-activated protein kinase ERK1/2. Our current study provides the first evidence that LTD4 can activate 90-kDa ribosomal S6 kinase (p90(RSK)) and cAMP-responsive element-binding protein (CREB) via pertussis-toxin-sensitive G(i) protein pathways. Transfection and inhibitor experiments revealed that activation of p90(RSK), but not CREB, is a PKCepsilon/Raf-1/ERK1/2-dependent process. LTD4-mediated CREB activation was not affected by expression of kinase-dead p90(RSK) but was abolished by transfection with the regulatory domain of PKCalpha (a specific dominant-inhibitor of PKCalpha). Kinase-negative mutants of p90(RSK) and CREB (K(-)p90(RSK) and K-CREB) blocked the LTD4-induced increase in cell number and DNA synthesis (thymidine incorporation). Compatible with these results, flow cytometry showed that LTD4 caused transition from the G(0)/G(1) to the S+G(2)/M cell cycle phase, indicating increased proliferation. Similar treatment of cells transfected with K-p90(RSK) resulted in cell cycle arrest in the G(0)/G(1) phase, consistent with a role of p90(RSK) in LTD4-induced proliferation. On the other hand, expression of K-CREB caused a substantial buildup in the sub-G(0)/G(1) phase, suggesting a role for CREB in mediating LTD4-mediated survival in intestinal epithelial cells. Our results show that LTD4 regulates proliferation and survival via distinct intracellular signaling pathways in intestinal epithelial cells.
- Cancer och onkologi