Eight cell lines exhibiting resistance to Ca2+ induced terminal differentiation were derived from primary mouse epidermal cultures and their properties analyzed. The lines developed either spontaneously (2 lines) or after exposure of primary cultures to carcinogens or carcinogens and tumor promoter. All but one of the lines were of epithelial or epitheloid morphology but 3 of the 8 lines lacked desmosomes, keratin filaments and immunoprecipitable keratin proteins, and thus could not be defined as keratinocytes. Two of the 5 keratinocyte lines were tumorigenic in syngeneic Balb/c newborns after 4 months in medium containing 1.2 mM Ca2+, and 3 lines remained non-tumorigenic even after 11 months in 1.2 mM Ca2+. All three of the non-keratinizing lines were tumorigenic. Tumorigenic potential of the 5 keratinocyte lines did not correlate with ploidy (as determined by DNA content), transglutaminase activity or growth in soft agar. However, the 2 tumorigenic keratinocyte lines contained cells which stained intensely red for gamma glutamyl transpeptidase activity, while the non-tumorigenic keratinocyte lines did not. Only those lines lacking desmosomes and keratin filaments grew in soft agar, but these lines were negative for gamma glutamyl transpeptidase activity. Ploidy and transglutaminase activity did not correlate with tumorigenicity in these non-keratinizing lines. These results show that cell lines derived from cultured mouse epidermal cells and selected on the basis of their resistance to Ca2+ induced terminal differentiation may be preneoplastic. Furthermore the association of additional markers with malignant change in these cell lines depended on whether or not the cells were keratinizing.

Abstract. Epidermal growth factor (EGF) and insulin in combination have previously been shown to initiate S-phase in primary cultures of adult rat hepatocytes. We here describe the detailed time course and dosedependency of the effects of EGF and insulin on DNA synthesis in cultured hepatocytes. The DNA synthesis was assessed either biochemically or autoradiographically with a fairly good correlation between the two methods. DNA synthesis started 24–30 h after plating of the cells and peaked at approximately 70 h. Up to 70% of the cells entered DNA synthesis during this period. EGF and insulin acted synergistically on the DNA synthesis. Dexamethasone raised the DNA synthesis slightly, maximal effect occurred at concentrations above 2.5 nm and this agent was routinely used in the experiments with EGF and insulin. In the presence of 0.4 μm insulin from the time of plating, EGF dose-dependently increased the DNA synthesis with maximal effect at 5–15 nm. When added in combination with 1.7 nm EGF, insulin enhanced the DNA synthesis over the concentration range from 0.1 to 3 nm. These studies show that primary cultures of hepatocytes are useful in assessing the quantitative aspects of the interactions between the growth stimulating effects of hormones.

This study evaluates the histological changes, especially the presence of possible precancerous lesions, in the nasal mucosa ofworkers exposed to formaldehyde. Nasal biopsies of 37 workers occupationally exposed to formaldehyde for more than five years and 37 age matched referents showed a higher degree of metaplastic alterations in the former group. In addition, three cases of epithelial dysplasia were observed among the exposed. These results indicate that formaldehyde may be potentially carcinogenic to man. Combination of this finding with the inconclusive epidemiological studies suggests that formaldehyde is a weak carcinogen and that occupational exposure to formaldehyde alone is insufficient to induce nasal cancer.The inhalation of formaldehyde has been shown to induce squamous cell carcinoma in the nasal cavity of rats at exposure levels ranging from 6 to 14 3 ppm12 and mice at an exposure level of 14 3 ppm.3 Although these findings aroused considerable concern about the possible long term effects in man, epidemiological studies conducted to date have not provided unequivocal evidence that exposure can induce nasal or other types of cancer.45 Like most other types of epithelial malignancies, it is reasonable to assume that nasal cancer is preceded by preneoplastic states and that the prevalence of such lesions is considerably higher than that of cancer. Experimental studies have shown that animals exposed to formaldehyde concentrations of 2 ppm or more develop dysplasia and metaplasia of

No abstract

No abstract