CELL-CYCLE GENE-EXPRESSION AND E2F TRANSCRIPTION FACTOR COMPLEXES IN HUMAN-MELANOMA CELLS INDUCED TO TERMINALLY DIFFERENTIATE

Defects in cellular differentiation are a common occurrence in human c ancers, The combination of recombinant human fibroblast interferon (IF N-beta) and the antileukemic compound mezerein (MEZ) results in an irr eversible loss of proliferative capacity and terminal cell differentia tion in H0-1 human melanoma cells, In contrast, either agent alone ind uces reversible growth arrest and/or specific components of the differ entiation process without inducing terminal differentiation, The curre nt study investigates changes in cell cycle, cell cycle gene expressio n and E2F transcription factor complex formation during the processes of reversible and irreversible (terminal) differentiation, Induction o f both terminal differentiation and reversible differentiation (MEZ tr eatment) results in a temporal decrease in DNA synthesis and the perce ntage of cells in S phase and a decrease in the expression of cell cyc le and growth regulated genes, including cdc2, cyclin A, cyclin B, his tone H1, histone H4, nm23-H1, p53 and c-myc, Persistent gene expressio n changes occur in terminally differentiated cells, but not in reversi bly differentiated cells, H0-1 cells contain several E2F binding activ ities, including uncomplexed E2F, an E2F-p107-cyclin A-cdk2 kinase com plex and an Rb-E2F complex, Induction of growth arrest by MEZ results in a slow migrating gel-shift band that contains E2F associated with t he pRb2/p130 protein. There is also a loss of the Rb-E2F complex. Indu ction of terminal differentiation after treatment with IFN-beta+MEZ ge nerates a second pRb2/p130-E2F complex that migrates considerably fast er than the pRb2/p130-E2F complex resulting from growth arrest, The sl ower migrating complex may contribute to growth arrest, whereas the fa ster migrating complex may play a role in terminal differentiation. Ou r results demonstrate that terminal cell differentiation involves a co -ordinate and continuous suppression of a number of cell cycle and gro wth related genes and results in the development of a novel E2F transc ription factor complex not apparent in growth arrested and reversibly differentiated human melanoma cells.