Shortage of mitogen-activated protein kinase is responsible for resistance to AP-1 transactivation and transformation in mouse JB6 cells.
The JB6 mouse epidermal cell system, which includes tumor promotion-sensitive (P+) and tumor promotion-resistant (P-) cells, is a well-established and extensively used cell culture model for studying the mechanism of late-stage tumor promotion. Tumor promoters, such as 12-O-tetradecanoylphorbol 13-acetate (TPA) or epidermal growth factor (EGF), induce high levels of activator protein 1 (AP-1) activity and large, tumorigenic, anchorage-independent colonies in soft agar at a high frequency in JB6 P+ cells, but not in JB6 P- cells. We report here a molecular explanation for the defect in the AP-1 activation and promotion-resistant phenotype of P- cells. We demonstrate that the lack of AP-1 activation and cell transformation responses to TPA and EGF in P- cells appears attributable to the low level of mitogen-activated protein kinase (MAPK) (extracellular signal-regulated protein kinase, Erk) in these cells. TPA and EGF induce transactivation of AP-1 activity in P+ cells but not in P- cells. Nonphosphorylated forms and TPA- or EGF-induced phosphorylated forms of Erks (Erk1 and Erk2) in P- cells were much lower than those in P+ cells. Stable transfection of wild-type MAPK (Erk2) into P- cells restored its response to TPA and EGF for both AP-1 activation and cell transformation. These results suggest that the shortage of MAPK (Erk1 and Erk2) appears to be an important contributor to the tumor promotion-resistant phenotype in JB6 cells.
Huang
C
C
The Hormel Institute, University of Minnesota, Austin, MN 55912, USA.
Ma
W Y
WY
Young
M R
MR
Colburn
N
N
Dong
Z
Z
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002273:Carcinogens / Q000494:pharmacology; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004817:Epidermis / Q000201:enzymology; D051379:Mice; D010766:Phosphorylation; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D015533:Transcriptional Activation
D002273:Carcinogens; D018808:Transcription Factor AP-1; D004815:Epidermal Growth Factor; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D013755:Tetradecanoylphorbol Acetate