ABSTRACT
The purpose of the present study was to determine whether skin fibroblasts from individuals, either with an inherited predisposition to cancer or with genetic disorders usually associated with a high risk of cancer, can be oncogenically transformed in vitro by a tumor promoter alone. The effects of chronic and limited applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) on several properties that are associated with transformation were examined using skin fibroblasts from individuals with polyposis coli, a familial cancer syndrome, xeroderma pigmentosum, Fanconi's anemia, and trisomy 21. The results of this study show that TPA treatment induces similar changes on cellular morphology, growth rate, saturation density, epidermal growth factor binding, and cytoskeleton in fibroblasts from both normal and genetically predisposed individuals. None of these cell lines, however, acquired anchorage-independent growth or unlimited growth potential in culture after chronic application of TPA. These observations suggest clearly that skin fibroblasts from individuals with either a genetic predisposition to or a high risk of cancer may not exist in a preneoplastic or "initiated" state susceptible to oncogenic transformation by TPA alone and that the mechanism of genetically determined cancer induction may be different from that of chemical carcinogenesis.
Subject(s)
Cell Transformation, Neoplastic , Fibroblasts/drug effects , Neoplasms/genetics , Phorbols/pharmacology , Tetradecanoylphorbol Acetate/pharmacology , Cell Adhesion/drug effects , Cell Division/drug effects , Cell Line , Cytoskeleton/drug effects , Disease Susceptibility , Down Syndrome , Epidermal Growth Factor/metabolism , Fanconi Anemia , Female , Fibroblasts/physiology , Humans , Intestinal Polyps , Male , Trypsin/pharmacology , Xeroderma PigmentosumABSTRACT
The data presented here show that normal skin fibroblasts from individuals with dominantly inherited retinoblastoma, polyposis coli, and nevoid basal cell carcinoma (predisposed cells), grown in the presence of [35S]methionine, contain more than 2.5-fold [35S]methionine-labeled actin as compared to normal fibroblasts from individuals without a prior history of predisposition to cancer (normal cells). The rate of incorporation of [35S]methionine into actin in predisposed cells is rapid and is not correlated with an increase in the total protein and actin contents of the cells, in the intracellular pool size of [35S]methionine, or in the synthesis of beta-actin-specific mRNA, as compared to normal cells. However, the half-life of actin in predisposed cells is less than 5 h, as compared to at least 48 h for normal cells. The significantly reduced half-life of actin and an increased incorporation of [35S]methionine specifically into actin in all predisposed cells studied may represent an inherited biochemical defect which leads to cytoskeletal disorganization previously observed in these cells. It can be speculated that the altered properties of actin in predisposed cells may be caused by the same genetic lesion(s) which is responsible for the induction of dominantly inherited cancers.
Subject(s)
Actins/metabolism , Neoplasms/genetics , Actins/analysis , Cells, Cultured , Electrophoresis, Polyacrylamide Gel , Fibroblasts/analysis , Fibroblasts/metabolism , Half-Life , Humans , Methionine/metabolism , Molecular Weight , Neoplasms/etiology , Neoplasms/metabolism , Polymers/analysis , RNA, Messenger/analysis , Skin/analysis , Skin/metabolism , Sulfur Radioisotopes , Vimentin/analysis , Vimentin/metabolismABSTRACT
There is now considerable evidence to suggest that genetic factors can influence the incidence of cancer. Although expression of this susceptibility to cancer appears to be tissue-specific, the normal skin fibroblasts from individuals predisposed to cancer (predisposed fibroblasts) have also been shown to express the risk of the target cell in the development of cancer. In the context of the 2-stage theory of chemical carcinogenesis predisposed fibroblasts may, therefore, exist in a pre-neoplastic or initiated state. The purpose of the present study was to determine whether predisposed fibroblasts would be oncogenically transformed in vitro by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) alone. TPA treatment induced similar changes in cellular morphology, cytoskeleton, and epidermal growth-factor binding, in predisposed and normal cells. None of these cell lines acquired anchorage-independent growth or an unlimited growth potential in culture after chronic application of TPA. Fluorescent microscopy with an F-actin probe, in the absence of TPA, showed a disorganization of the microfilament and intermediate filament network in skin fibroblasts from individuals with familial polyposis coli, hereditary and sporadic retinoblastoma, basal cell nevus syndrome, and Gardner's syndrome, as compared to normal skin fibroblasts. Single and 2-dimensional electrophoresis also indicated that the incorporation of 35S-methionine into actin in predisposed fibroblasts was 2-fold greater than in normal fibroblasts, and the turnover rate of actin in predisposed fibroblasts was less than 5 h, compared to 48 h in normal fibroblasts. These observations clearly suggest that predisposed fibroblasts may not exist in a pre-neoplastic or initiated state, and that the mechanism of genetic susceptibility to cancer may be different from that of chemical carcinogenesis. In contrast, the results of this study indicate that genetic susceptibility to a variety of cancers may be associated with a rapid turnover of actin and a disorganization of the microfilament and intermediate filament networks.