Faculty Bibliography

Infection of human epidermal keratinocytes by the oncogenic virus SV40 leads to progressive inhibition of the normal differentiation process in vitro. Treatment of infected cells with 5-azacytidine (5-aza-CR) over a 24-h period produced a striking enlargement and pronounced flattening of cells within 5-7 days following removal of the agent. This morphological change was accompanied by a several-fold increase in the number of cells staining positively for the cell envelope precursor protein, involucrin, and in the exfoliation of cornified envelope bearing cells from the monolayer. The drug-treated cultures at high passage levels were stained by immunofluorescence using monoclonal antibodies to keratin classes associated with different epidermal layers. These experiments revealed that 5-aza-CR caused the re-expression of two keratin classes (suprabasal and stratum corneum-associated), whose synthesis had been suppressed during the transformation process. 5-Aza-CR also brought about re-expression of 58 and 56 kD keratin markers of epithelial keratinization and stratification, as well as of 40 and 49-52 kD keratin markers of viral transformation. However, the responsiveness to the drug was gradually lost over time following infection

We have studied the appearance of transformed properties following infection of human epidermal keratinocytes by the oncogenic virus SV40. Shortly after infection, only a small fraction of the cells are positive for SV40 T antigen by immunofluorescence; this fraction progressively increases upon serial subcultivation concomitant with an increase in plating/colony-forming efficiency and growth rate. The capacity of the cells to differentiate progressively decreases, as indicated by cytochemical staining and cornified cell-envelope formation induced by suspension in methyl cellulose. The infected cells enter a period of growth crisis characterized by cytopathology and cell death as the level of T antigen synthesis reaches about 90 percent positive cells at about the tenth serial passage. Viable cells emerging from the crisis period are found to exhibit anchorage-independent growth, as indicated by the formation of viable colonies in semisolid media, but there is considerable variability in colony formation among clones isolated from anchorage-independent populations. The emergent population also manifests phenotypic instability in terms of the appearance of variants, which, in contrast to uninfected cells, expresses a well-defined actin cytoskeleton. The infected cells eventually become 'immortalized,' as evidenced by an indefinite lifespan, i.e., replication capability maintained well beyond the ordinary time of senescence for uninfected cells. We present these findings in the context of a stage-specific model of epithelial transformation in vitro

We have studied the changes in the surface ultrastructure of human epidermal keratinocytes after infection by the oncogenic virus, SV40. The surfaces of uninfected cells show patterns of dense microvilli and microridges in varying proportion with microridges predominating in the center of the developing keratinocyte colony and on the fully mature keratinocytes (squames) and the microvilli being more prevalent on the immature proliferative cells at the colony periphery. As the transformation process progressed over time highly microridged surfaces became less numerous. After many months in culture cell surfaces were found to exhibit more sparse, predominantly villous ultrastructure. The surface characteristics of the infected cells in long term culture were similar to those observed in a cell line derived from a squamous cell carcinoma

We have studied the effects of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate on the differentiation of human epidermal keratinocytes infected by the oncogenic virus Simian Virus 40. The cells in monolayers exposed to a concentration of 12-O-tetradecanoylphorbol-13-acetate as low as 5 X 10(-10) M redistributed into dense patches within 48 hr. This morphological change was accompanied by a 10- to 30-fold increase in the production of cells cytochemically stained by orange G:acid fuchsin indicating keratinization and a 2- to 3-fold increase in the exfoliation of cornified envelope-bearing cells. The induced cellular differentiation occurred in parallel with an inhibition of cell growth. The biologically inactive congener 4 alpha-phorbol-12,13-didecanoate at equimolar concentrations did not affect the growth or differentiation of these cells. Binding studies using [3H]12-O-tetradecanoylphorbol-13-acetate revealed a binding site with characteristics similar to those found for other cell types (Kd = 17 nM; 1.25 X 10(5) available sites/cell)