Grafting assay distinguishes promotion sensitive from promotion resistant JB6 cells

The JB6 mouse epidermal cell system has been used extensively as an invitro transformation model for the study of tumor promotion. The standardJB6 cell assay for promotion of transformation is carried out in soft agaror other anchorage independent conditions. The present study was directedto the development of an in vivo model to distinguish the promotionresistant (P-) and promotion sensitive (P+) progression phenotypes. Resultsindicate that the grafting assay distinguishes P- and P+ cells in vivo withP+ but not P- cells forming tumors within 7-9 weeks. Expression of dominantnegative mutant jun TAM67 blocks both anchorage independent transformationresponse and graft bed tumor formation by P+ cells, suggesting that therequirement for AP-1 activation in transformation now applies in vivo.Expression of mutated p53 produced a gain of P+ phenotype in P- cells invitro, but not in vivo. Histochemical and Northern blot analysis forexpression of various keratinocyte markers revealed no evidence forexpression, suggesting a loss of keratinocyte markers followingestablishment in culture. In summary, the skin-grafting assay described inthis study appears to be a valid in vivo assay for distinguishing thepreneoplastic progression phenotypes represented by JB6 P- and P+ cells.