Cell interactions control the fate of malignant keratinocytes in an organotypic model of early neoplasia

The role of cell interactions during early neoplastic progression in human skin is not well understood. We report that the fate and behavior of low-gr ade malignant cells in stratified epithelium is dependent on their interact ions with neighboring cells and with extracellular matrix during the early events in neoplastic progression. We utilized an organotypic tissue model w hich mimics premalignancy to monitor malignant cells (II-4) genetically mar ked with beta-gal and grown in the context of either normal human keratinoc ytes or the immortalized cell line HaCaT. HaCaT cells were permissive for c lonal expansion of II-4 cells at ratios of 4:1, 12:1, and 50:1 (HAC:II-4) w hen compared with coculture with normal human keratinocytes. This II-4 cell expansion was associated with the failure of neighboring HaCaT cells to in duce differentiation and cell cycle withdrawal of II-4, as had been seen in the context of normal human keratinocytes. When 12:1 mixtures (NHK:II-4) w ere stripped of all suprabasal cells and regrown, all beta-gal cells were l ost showing that these normal human keratinocyte-suppressed II-4 cells had been actively sorted to a suprabasal position where their clonal expansion was limited. These growth-suppressive effects of normal human keratinocytes were found to be conditional on direct cell-cell contact, as II-4 formed c olonies when trypsinized from 12:1 (NHK:II-4) mixtures and grown at clonal density in submerged culture. The distribution and behavior of low-grade ma lignant cells was therefore dependent on the state of transformation of adj acent: keratinocytes and on cell-matrix interactions. These results demonst rate that alterations in the cellular microenvironment are central to the i nduction of clonal expansion and early neoplastic progression in stratified epithelium.