Normal growth and differentiation in a spontaneously immortalized near-diploid human keratinocyte cell line, NIKS

We report the isolation and characterization of a spontaneously immortalized human keratinocyte cell line, NIKS. The cell line is not tumorigenic in athymic nude mice and maintains cell-type-specific requirements for growth in vitro. NIKS cells express steady-state levels of transforming growth factor-alpha, transforming growth factor-beta1, epidermal growth factor receptor, c-myc, and keratin 14 mRNAs comparable with the parental BC-1-Ep keratinocyte strain. BC-1-Ep and NIKS keratinocytes produce similar levels of cornified envelopes and nucleosomal fragmentation in response to loss of substrata attachment. DNA fingerprinting results confirm that the NIKS cells originated from the parental BC-1-Ep keratinocytes. NIKS cells contain 47 chromosomes due to an extra isochromosome of the long arm of chromosome 8, and the near-diploid karyotype appears to be stable with repeated passage. A fully stratified squamous epithelium is formed by the NIKS keratinocytes in organotypic culture. Ultrastructural analysis of both the parental and immortalized keratinocytes reveals abundant desmosomes, hemidesmosomes, and the production of a basal lamina. Our findings with the NIKS cells support the observation that spontaneous immortalization is not linked to alterations in squamous differentiation or the ability to undergo apoptosis. The NIKS human keratinocyte cell line is an important new tool for the study of growth and differentiation in stratified squamous epithelia.

Transforming growth factor-beta 1 inhibits nucleosomal fragmentation in human keratinocytes following loss of adhesion

We have investigated the role of transforming growth factor-beta 1 (TGF-beta 1) in suspension-induced programmed cell death of cultured human keratinocytes. Suspension of keratinocytes in semisolid medium induces TGF-beta 1 mRNA levels and synthesis of bioactive TGF-beta 1 protein. Concomitant with the suspension-induced increase in secreted TGF-beta 1 levels, steady state mRNA levels for c-myc are decreased. Both exogenously added and endogenously produced TGF-beta 1 attenuate suspension-induced nucleosomal fragmentation in keratinocytes. We propose that TGF-beta 1 may function to protect keratinocytes from DNA fragmentation following loss of cell-substratum and/or cell-cell contact. Taken together, our findings suggest that loss of cell-substratum and/or cell-cell adhesion is an important component of an apoptotic signal transduction cascade regulated by TGF-beta 1 in normal human stratified squamous epithelia.

Fibronectin levels are enhanced in human fibroblasts overexpressing the c-sis protooncogene

We studied human dermal fibroblasts transfected with a human c-sis cDNA (coding for the platelet-derived growth factor B-chain). Dermal fibroblasts overexpressing c-sis exhibited a stellate morphology with focus formation, enhanced colony formation in methylcellulose-containing growth medium, and increased levels of soluble and extracellular matrix-associated fibronectin. Gene expression of fibronectin was enhanced 10-fold in c-sis-overexpressing fibroblasts relative to controls. Pro-alpha 1 (I) collagen mRNA was not increased in these same c-sis-overexpressing fibroblasts. Transforming growth factor beta 1 treatment of c-sis-transfected cells caused a modest increase (77%) in fibronectin mRNA levels with no increase in soluble fibronectin production after 24 h. In contrast, transforming growth factor beta 1 caused at least a 10-fold increase in fibronectin mRNA and a 2-fold increase in soluble fibronectin from medium conditioned by control fibroblasts. Transforming growth factor beta 1 increased pro-alpha 1 (I) collagen mRNA approximately 3-fold in both control and c-sis-transfected fibroblasts. These studies reveal that a primary biological function of the platelet-derived growth factor B-chain is upregulation of fibronectin gene expression and extracellular matrix formation. The anchorage-independent phenotype of c-sis-overexpressing cells was blocked by the cell adhesion sequence of fibronectin, Arg-Gly-Asp-Ser. Our results demonstrate that interaction of cells with extracellular adhesion receptors is necessary for proliferation in semisolid medium even when cells are overproducing growth factors known to act via autocrine stimulation.