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J E Strickland

Publications and source records attributed to J E Strickland.

At least 19 recordsLinked to original sources
PubMed1995

Analysis of v-Ha-ras and v-fos oncogene transduction into a mouse epidermal cell line with "initiated" phenotype in culture but normal skin phenotype in vivo.

Cell line SCR722 was derived from adult SENCAR mouse epidermal cells initiated in culture by treatment with the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine and selection for foci proliferating in medium with calcium levels that induce terminal differentiation in normal cells. Expansion of one of these foci and two additional cell clonings produced cell line SCR722, which was near-tetraploid and formed normal skin when grafted to athymic nude mouse hosts. However, unlike normal keratinocytes, SCR722 cells fail to suppress papilloma formation when grafted along with papilloma cell line SP-1. For optimum growth in culture, SCR722 cells required fibroblast-conditioned medium and 0.5 mM Ca2+. SCR722 cells had a wild-type c-Ha-ras gene but had lost their requirement for conditioned medium in culture and produced dysplastic papillomas in grafts when transduced with the v-Ha-ras gene. SCR722 cells stably expressing the v-fos gene produced normal epidermis in grafts, but when these cells were transduced with the v-Ha-ras gene, they produced carcinomas. Clones with greater expression of the transfected v-fos gene had a more invasive phenotype in vivo. These results indicate that carcinogen treatment of epithelial cells can result in an altered but nontumorigenic phenotype that may be at risk for becoming a more advanced neoplastic state with additional genetic alterations.

Animals↗
PubMed1995

Loss of heterozygosity on chromosome 11 q in breast cancer.

AIMS: Chromosome 11q23 seems to be a site of frequent mutation in cancer. It also contains loci such as ataxia telangiectasia with possible importance in the pathogenesis of breast tumours. The short arm of chromosome 11 has been studied extensively in breast cancer, but the long arm, in particular the distal part, has been studied less frequently. Cytogenetic analysis has shown possible involvement of chromosome 11q in breast tumours. Chromosome transfer experiments have also implicated chromosome 11q in breast cancer. A high frequency of mutations might therefore be expected to occur on chromosome 11q in breast cancers. METHODS: Using restriction fragment analysis, the primary tumours of 41 patients with breast cancer were screened for mutations at five loci on chromosome 11q (D11Z1, INT2, (FGF3), DRD2, NCAM, and D11S29). RESULTS: Allelic loss occurred at a high frequency (59%) at D11S29. At NCAM, novel alleles were frequently seen on autoradiographs. Relatively low frequencies of mutation were detected at the other loci. Allelic loss at D11S29 was associated with the presence of lymph node metastases, but this may be a chance association. CONCLUSIONS: The frequency of allelic loss at the DS11S29 locus is high. The significance of novel alleles at NCAM and their relation to allelic loss at D11S29 are unclear. The results presented here do not permit fine mapping of a region of allelic loss, but suggest that the region of greatest loss lies distal to DRD2. The results provide further evidence for the importance of gene(s) near 11q23 in the pathogenesis of breast cancer, and of tumours in general.

Breast Neoplasms↗
PubMed1994

Use of melarsomine dihydrochloride (RM 340) for adulticidal treatment of dogs with naturally acquired infections of Dirofilaria immitis and for clinical prophylaxis during reexposure for 1 year.

Heartworm-infected dogs were treated therapeutically with a new heartworm adulticide (melarsomine dihydrochloride, RM 340) and then put on a Strategic Program with treatment every 4 months for clinical prophylaxis to take advantage of the drug's potent activity against 4-month-old immature as well as adult Dirofilaria immitis. Ten random-source dogs with naturally acquired heartworm infections (microfilariae- and antigen-positive) were given melarsomine (2.2 mg kg-1 twice 3 h apart) by i.m. injection in the lumbar muscles to clear their existing infections. They were then placed outdoors (August 1988) in a high-risk area in Georgia (USA) for heartworm transmission and given melarsomine at the same posology every 4 months (Strategic Program) for 12 months as a clinical prophylactic measure. Five nontreated heartworm-naive beagles placed at this site during the same period served as 'controls' to monitor heartworm transmission. After exposure for 12 months, the ten treated and five 'control' dogs were taken indoors and held for 5 months. Microfilaremia and antigenemia levels were monitored in both groups by testing at 4-5 month intervals throughout the study and the intensity of infection was determined at necropsy. Microfilaremia levels in treated dogs dropped dramatically following the initial therapeutic treatment and remained either negative or low. Only two of the five 'control' dogs became microfilaremic, and this occurred near the end of the study. Nine of the ten treated dogs were antigen-negative 4 months after the initial therapeutic treatment, and all of them were antigen-negative at all bleedings thereafter. Four of the five 'control' dogs were antigen-positive at necropsy, and only one of these was positive 4 months earlier. Based on these antigen data, the initial treatment cleared 90% of the dogs of worms, and no worms were detected in any of the treated dogs thereafter. However, it is possible that undetectable immature heartworms were present. Although all of the treated dogs were antigen-negative at necropsy, three of them had a total of eight heartworms, seven of which were clearly immature, as determined by worm length measurements, and the remaining worm was a young adult female that was probably too young to be detected. All of the five 'control' dogs had heartworms (average 7.4; range 1-16), and about half of these worms were clearly immatures. Therapeutic treatment followed by strategic treatment with melarsomine every 4 months during reexposure was at least 89.2% effective overall.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

SENCAR mouse skin tumors produced by promotion alone have A to G mutations in codon 61 of the c-rasHa gene.

SENCAR mice, developed by selective breeding for high susceptibility to skin carcinogenesis by initiation with 7,12-dimethylbenz[a]anthracene and promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA), form squamous papillomas in approximately 20% of animals treated repeatedly with TPA, without chemical initiation. DNA from eight skin tumors produced by a TPA-only protocol and four cell lines derived from these tumors was amplified by polymerase chain reaction and analyzed by discriminative oligonucleotide hybridization using oligomers specific for various c-rasHa gene codon 61 sequences. Five tumors and three cell lines had CAA (wild-type) to CGA mutations. In addition, one tumor had a CAA to CTA mutation, for a total of six of eight tumors having an activating mutation at this codon. Two tumors and one cell line had no codon 61 mutations detectable by this method. Since tumors derived from promotion-only protocols presumably originated from constitutively initiated cells, we examined tumor-free skins of untreated newborn and eight-month-old retired breeders and of 78-88-week-old SENCAR mice of both sexes, which were treated with TPA for 10 weeks starting at age 16-28 weeks and were untreated thereafter. Only the wild-type c-rasHa gene codon 61 sequence was seen, suggesting that the constitutively initiated cell population, if present, is below the limit of detection by this method.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1993

Inhibition of tumor formation from grafted murine papilloma cells by treatment of grafts with staurosporine, an inducer of squamous differentiation.

The microbial alkaloid staurosporine induces responses associated with protein kinase C activation, resulting in terminal differentiation in cultures of both normal and neoplastic mouse epidermal cells. As a cancer chemotherapy model, we treated grafts of mouse epidermal tumor cell lines 308 and SP-1 repeatedly with staurosporine. A dose-dependent inhibition of tumor formation, maximal at 0.025 nmol per treatment, was observed. Higher and lower doses were less effective, suggesting a specific target for staurosporine action. A single, low-dose treatment 2 weeks after grafting also markedly reduced tumor formation. Although in vitro evidence suggests that staurosporine-induced terminal squamous differentiation results from activation of protein kinase C, we found no inhibition of tumor growth in similar studies with the protein kinase C activator 12-O-tetradecanoylphorbol-13-acetate. These results indicate that staurosporine is an effective antitumor agent for eradicating squamous cell tumors in vivo.

Alkaloids↗
PubMed1993

Critical aspects of initiation, promotion, and progression in multistage epidermal carcinogenesis.

Carcinogenesis in mouse skin can be divided into three distinct stages: initiation, promotion, and progression (malignant conversion). Initiation, induced by a single exposure to a genotoxic carcinogen, can result from a mutation in a single critical gene (e.g., rasHa), apparently in only a few epidermal cells. The change is irreversible. Promotion, resulting in the development of numerous benign tumors (papillomas), is accomplished by the repeated application of a nonmutagenic tumor promoter. The effects of single applications of tumor promoters are reversible since papillomas do not develop after insufficient exposure of initiated skin to promoters or when the interval between individual promoter applications is increased sufficiently. The reversibility of promotion suggests an epigenetic mechanism. Promoter treatment provides an environment that allows the selective clonal expansion of foci of initiated cells. The conversion of squamous papillomas to carcinomas (termed progression or malignant conversion) occurs spontaneously at a low frequency. The rate of progression to malignancy can be significantly increased by treatment of papilloma-bearing mice with certain genotoxic agents. These progressor agents or converting agents are likely to act via a second genetic change in papillomas already bearing the initiating mutation. Progression in the skin is characterized by genetic changes that result in several distinct changes in the levels or activity of structural proteins, growth factors, and proteases. The mechanisms involved in progression are being studied in epidermal cell culture. In order to determine the in vivo phenotype of cultured cells, a grafting system was developed in which the cells were transferred from culture to a prepared skin bed in athymic mice. Introduction of an activated v-fos oncogene into initiated cells bearing an activated rasHa gene produced cells with a carcinoma phenotype, i.e., carcinomas formed when the cells were grafted as part of reconstituted skin. Grafted keratinocytes containing the rasHa gene alone produced papillomas; with v-fos alone, normal skin formed when grafted. The rasHa/fos carcinomas showed changes in differentiation markers characteristic of chemically induced carcinomas. A cell culture assay utilizing cells initiated by the introduction of an activated rasHa oncogene was developed to study progression. After exposure of initiated cells to progressor agents under conditions in which the proliferation of the rasHa-initiated cells was suppressed, proliferating foci developed, with a good correlation of activity in the assay with activity in the progression stage in vivo. The cell culture assay provides a quantitative model to study chemically induced neoplastic progression and may be useful to identify potential progressor agents.

Animals↗
PubMed1992

A model for initiated mouse skin: suppression of papilloma but not carcinoma formation by normal epidermal cells in grafts on athymic nude mice.

The availability of a skin grafting system on nude mouse hosts and of epidermal cell lines which form papillomas when grafted has made possible the creation of a model for initiated skin in vivo from cultured cells. When grafted with 6-8 x 10(6) primary dermal fibroblasts, 10 x 10(6) primary epidermal cells form an apparently normal skin, and cell line SP-1 (0.5 x 10(6) cells) forms papillomas. Cell line SP-1 was derived from papillomas produced on SENCAR mice by initiation with 7,12-dimethylbenzaadaa]anthracene and promotion with 12-O-tetradecanoylphorbol-13-acetate. Grafting of 0.5 x 10(6) SP-1 cells along with 10 x 10(6) SENCAR newborn primary epidermal cells resulted in a 90% reduction in the average papilloma volume per mouse compared to controls without primary epidermal cells. Suppression occurred specifically with epidermal cells, either cultured or freshly prepared, and was not seen when an equivalent number of SENCAR primary dermal fibroblasts was grafted in place of epidermal cells. Nor did suppression occur when primary epidermal cells were replaced with a carcinogen-altered cell line, SCR722. SCR722 cells have a normal-skin phenotype when grafted. Furthermore, suppression of tumor formation did not occur when a malignant variant of SP-1 cells replaced benign SP-1 cells in grafts. Repeated treatment of suppressed grafts with 12-O-tetradecanoylphorbol-13-acetate resulted in an increased number of mice with papillomas and a larger mean papilloma volume per mouse compared to controls treated with solvent alone, whereas treatment of nonsuppressed grafts of papilloma cells with promoter produced no change in tumor size. These results support the concepts that normal epidermal cells suppress the growth of initiated cells and that repeated treatment with phorbol ester tumor promoters overcomes the suppression, leading to benign tumor formation.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1991

v-Ha-ras-induced mouse skin papillomas exhibit aberrant expression of keratin K13 as do their 7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13-acetate -induced analogues.

Introduction of the v-Ha-ras gene into primary epidermal keratinocytes, followed by grafting of these cells to animals, leads to the formation of benign epidermal tumors that resemble papillomas induced chemically by a two-stage carcinogenesis protocol. In this study, we investigated v-Ha-ras-induced papillomas for aberrant expression of type I keratin K13, previously described in 7,12-dimethylbenz[a]anthracene/12-O-tetradecanoylphorbol-13- acetate (DMBA/TPA)-induced mouse epidermal tumors. Papillomas produced from three independent infection series were removed 3 wk after grafting concomitant with control grafts originating from mock-, neo-, and v-fos-infected primary keratinocytes. Combined analysis of the grafts by western blotting of extracted keratins and immunofluorescence studies of frozen sections with a K13-monospecific antibody revealed K13 expression in all v-Ha-ras-induced papillomas and absence of this keratin in all control grafts. K13-positive cells in papillomas were restricted to the suprabasal cell layers of the lesions and, at this stage of papilloma development, occurred as foci of varying extensions. Analysis of genomic DNA from v-Ha-ras-induced papillomas for the methylation state of a CpG dinucleotide in the distant promoter region of the K13 gene revealed the occurrence of unmethylated DNA copies that were generated at the expense of methylated DNA copies ubiquitously present in normal epidermis. The ratio of unmethylated to methylated DNA copies correlated with the extent of suprabasal K13 protein expression. Thus, all features of aberrant K13 expression previously described in DMBA/TPA-induced papillomas were shared by v-Ha-ras-induced papillomas.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1989

Spontaneous Ha-ras gene activation in cultured primary murine keratinocytes: consequences of Ha-ras gene activation in malignant conversion and malignant progression.

The activation of the c-Ha-ras gene and its contribution to the tumorigenic phenotype were examined in cultured mouse keratinocytes and squamous tumors using transfection into NIH 3T3 cells and nucleic acid hybridization. When normal keratinocytes were cultured in medium with 0.05 mM Ca2+ (low Ca2+ medium), many cells died within 2-3 wk, while others formed rapidly growing foci that could be subcultured. These rapidly growing cells produced benign tumors when grafted to nude mice and possessed a heterozygous mutation in the c-Ha-ras gene with an A----T transversion in codon 61. Fibroblast-conditioned low Ca2+ medium prevented cell death, focus formation, c-Ha-ras gene mutation, and tumorigenicity. Thus, suboptimal culture conditions favored a spontaneous mutation in codon 61 of the c-Ha-ras gene of keratinocytes. When a v-Ha-ras gene was introduced into normal keratinocytes by a replication-defective retrovirus, the recipient cells produced papillomas in vivo, and after 2 mo, 60% of the tumors converted to squamos cell carcinomas. None of the 22 converted tumors had an endogenous c-Ha-ras gene mutation at codon 61. However, the A----T transversion mutation developed when these carcinoma cells were cultured in low Ca2+ medium but not in fibroblast-conditioned medium. Cells with both an exogenous v-Ha-ras and an activated c-Ha61-ras gene produced undifferentiated, rapidly lethal carcinomas, while cells with only v-Ha-ras maintained the squamous carcinoma phenotype. Undifferentiated carcinomas also developed when the v-Ha-ras gene was introduced into papilloma cells with a chemically induced endogenous c-Ha61-ras gene mutation. These results suggest that mutation in the c-Ha-ras gene can contribute to initiation, malignant conversion, and malignant progression in skin carcinogenesis, and gene dosage may determine the phenotype expressed.

Amino Acids↗
PubMed1988

Development of murine epidermal cell lines which contain an activated rasHa oncogene and form papillomas in skin grafts on athymic nude mouse hosts.

We have developed four murine epidermal cell lines which form squamous papillomas when grafted to athymic nude mice in a reconstituted skin. Two of the lines, SP-1 and BP-4, were derived from pools of papillomas produced on SENCAR and BALB/c mouse skin, respectively, by initiation with 7,12-dimethylbenz(a)anthracene and promotion with 12-O-tetradecanoylphorbol-13-acetate. Line 308 was derived from BALB/c mouse skin initiated in vivo with 7,12-dimethylbenz(a)anthracene, culture of the epidermal cells, and selection of cells resistant to Ca2+-induced terminal differentiation. Line LC14 was derived from untreated, cultured newborn BALB/c mouse primary epidermal cells which spontaneously developed resistance to Ca2+-induced terminal differentiation. Each line has an activated rasHa gene with a mutation within codon 61. Cells from all four lines, in contrast to normal primary epidermal cells, survive in medium with Ca2+ levels greater than 0.1 mM. Clonal growth studies in culture showed a unique growth pattern for each of the four lines in medium with 1.4 mM and 0.05 mM Ca2+, with or without 12-O-tetradecanoylphorbol-13-acetate. Early passage cells of these lines should provide a valuable resource for detecting genes or genetic alterations which complement an activated ras gene to cause malignant conversion and for studying the biology of tumor promotion.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1988

TGF alpha stimulates growth of skin papillomas by autocrine and paracrine mechanisms but does not cause neoplastic progression.

To investigate the role of transforming growth factor alpha (TGF alpha) in tumor development, we introduced the human TGF alpha (hTGF alpha) cDNA into cultured primary mouse epidermal cells or papilloma cells using a replication-defective retroviral vector and analyzed skin grafts constructed with such cells. Expression of the exogenous gene was confirmed by detection of hTGF alpha mRNA by northern RNA blot analysis, and the secreted hTGF alpha was measured by ELISA of culture supernatants. Tumor cells expressing hTGF alpha produced benign tumors (papillomas), which were 1.5- to 2-fold larger than tumors of parental cells when tested as skin grafts on nude mice. Grafts of normal cells that expressed hTGF alpha produced normal skin. When mixtures of parental tumor cells and normal mouse keratinocytes were grafted to nude mice, papilloma formation was suppressed and tumors that did form were small. Grafts of hTGF alpha-producing papilloma cells combined with either normal epidermal cells or hTGF alpha-producing epidermal cells yielded large tumors. Mixed grafts containing keratinocytes expressing hTGF alpha and parental papilloma cells also produced large tumors. While the tumor size was substantially increased by hTGF alpha expression, the tumors that developed in all groups were histologically benign and reached a stable size 4-5 wk after grafting. These results indicate that expression of hTGF alpha by either tumor cells (autocrine) or adjoining normal cells (paracrine) can stimulate tumor growth, particularly when tumor growth is suppressed by normal tissue. However, expression of this growth factor did not appear to influence tumor progression directly.

Animals↗
PubMed1987

Analysis of the rasH oncogene and its p21 product in chemically induced skin tumors and tumor-derived cell lines.

Mouse skin papillomas and squamous cell carcinomas induced by initiation with 7,12-dimethylbenz[a]anthracene and promotion with phorbol esters, such as 12-O-tetradecanoyl phorbol-13-acetate, frequently contain an activated Harvey ras gene. Six murine epidermal cells lines established from pooled skin papillomas previously tested negative in the NIH-3T3 assay, but have an altered differentiation program by a variety of criteria. The Harvey ras gene and its p21 protein product from these cell lines have been analyzed for alterations responsible for their altered growth and differentiation properties that were undetectable by 3T3 transfection assays. In comparison with primary papillomas and carcinomas, shown to have a point mutation in codon 61 of the Harvey ras gene, resulting in a p21 product with the diagnostic alteration in SDS-PAGE, the papilloma cell lines exhibited neither the codon 61 mutation, nor p21 product with altered migration in SDS-PAGE. These findings suggest that these papilloma cell lines contain a genetic lesion(s), other than Harvey ras activation, that may be responsible for their altered epithelial differentiation patterns and thus may serve as a useful model for identifying lesions involved in malignant conversion.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1986

In vitro comparisons of SENCAR and BALB/c primary epidermal cells.

Grafting experiments show that the enhanced sensitivity of the SENCAR mouse to skin carcinogenesis by initiation and promotion is a property of the skin itself, suggesting the usefulness of in vitro studies to elucidate the mechanism. Such studies have indicated that cultured epidermal cells of SENCAR mice and the resistant BALB/c strain are remarkably similar in a variety of respects. DNA repair and carcinogen binding are quantitatively similar in cultured cells of SENCAR and more resistant mouse strains. Epidermal Langerhans cell (LC) number and LC-mediated functions were indistinguishable in SENCAR and BALB/c mice. Primary epidermal cells cultured in the presence of various concentrations of 12-O-tetradecanoylphorbol-13-acetate (TPA), retinoic acid, epidermal growth factor (EGF), hydrocortisone, or fluocinolone acetonide failed to reveal differences in growth between BALB/c and SENCAR cells. Cells from these animals bound comparable amounts of EGF with similar kinetics, and the modulation of this binding by TPA and retinoic acid was indistinguishable between strains. Spontaneous expression of infectious, endogenous xenotropic type C RNA virus at very low levels could be demonstrated in primary BALB/c epidermal cells and both BALB/c and SENCAR epidermal lines resistant to Ca2+-induced terminal differentiation. The number of foci of initiated cells after exposure to carcinogens in vivo or in vitro did not differ significantly between SENCAR and BALB/c, suggesting that SENCAR sensitivity is primarily to promotion. However, there are qualitative differences between SENCAR and BALB/c foci. The appearance of foci of cells resistant to terminal differentiation in untreated SENCAR cultures supports the evidence from in vivo studies for the existence of a constitutively initiated cell population in SENCAR mouse skin.

Animals↗
PubMed1985

Association of resistance to terminal differentiation with initiation of carcinogenesis in adult mouse epidermal cells.

Primary adult mouse epidermal cells were maintained as a monolayer culture with a high proliferation rate in fibroblast-conditioned medium with low Ca2+ concentration (less than 0.1 mM). Terminal differentiation of the cultures was induced by raising the Ca2+ level in the medium above 0.1 mM. Treatment of adult mouse epidermal cells either in vivo or in vitro with 7,12-dimethylbenz(a)anthracene or N-methyl-N'-nitro-N-nitrosoguanidine yielded colonies which were resistant to terminal differentiation induced by Ca2+. The number of resistant colonies was dependent upon the dose of each carcinogen used whether exposure was in vivo or in vitro. Cultures derived from skin initiated in vivo with 7,12-dimethylbenz(a)anthracene, a strong initiator, resulted in more colonies than were derived from skin initiated with N-methyl-N'-nitro-N-nitrosoguanidine, a moderately potent initiator. Two mouse strains, BALB/c and SENCAR, which differ in sensitivity to skin carcinogenesis, yielded similar numbers of Ca2+-resistant colonies following carcinogen exposure. However, colonies developed spontaneously from untreated SENCAR cells (the sensitive strain), but not from BALB/c cells (the resistant strain). These results support the concept that cells resistant to terminal differentiation are initiated cells. The results also suggest that initiation may occur spontaneously in SENCAR skin, a finding consistent with the reported occurrence of tumors in mice of this strain receiving promoters without exogenous initiator.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1985

Similar effects of phospholipase C and phorbol ester tumor promoters on primary mouse epidermal cells.

Interaction of tumor promoting phorbol esters with specific high affinity receptors is probably essential for many of the biological responses elicited by these agents. Since diacylglycerols which can be produced enzymatically from phospholipids by phospholipase C are postulated to be the physiological ligands for the phorbol ester receptor, we have examined primary cultures of mouse epidermal basal cells exposed to phospholipase C (Clostridium perfringens) for several biological and biochemical responses characteristic of treatment with 12-O-tetradecanoyl-phorbol-13-acetate, the most potent phorbol ester tumor promoter. Formation of diacylglycerols by treatment with phospholipase C was demonstrated by the dose-dependent release of radioactive diacylglycerols in cells prelabeled with [3H]arachidonic acid. Treatment with phospholipase C at 0.05 units/ml for 30 min led to the morphological changes and to the reduction in epidermal growth factor binding (90%) associated with 12-O-tetradecanoylphorbol-13-acetate treatment. Continuous treatment at the same dose led to the induction of the enzymes ornithine decarboxylase and transglutaminase with a time course and extent similar to the inductions by 12-O-tetradecanoylphorbol-13-acetate. Treatment with phospholipase C at 0.1 enzyme unit/ml yielded substantial suppression of the binding affinity of phorbol-12,13-dibutyrate for its receptors without reduction in total number of binding sites, consistent with the production by phospholipase C of a competitive inhibitor of phorbol ester binding. Several diacylglycerols at concentrations of 250 microM and above effectively competed for phorbol-12,13-dibutyrate binding, reduced epidermal growth factor binding, and to a lesser extent induced ornithine decarboxylase and transglutaminase. These results support the hypothesis that diacylglycerols can act through the phorbol ester receptors and thus produce biological and biochemical responses similar to those of the phorbol esters.

Animals↗
PubMed1984

Interaction of epidermal growth factor with basal and differentiating epidermal cells of mice resistant and sensitive to carcinogenesis.

Epidermal growth factor (EGF) interactions with primary epidermal cells in culture were examined in BALB/c and SENCAR mice, strains resistant and sensitive, respectively, to carcinogenesis by initiation-promotion. Using low (less than 0.1 mM) calcium growth conditions, which select for basal cells, and calcium-induced terminal differentiation, we determined the effects of retinoids, the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), and cell density on binding of 125I-labeled EGF. Over the range tested, EGF binding increased with increasing cell density similarly in basal cells of both strains, which at similar densities bound similar amounts of EGF. Increasingly differentiated epidermal cells of both strains bound less EGF. Responses of basal and differentiating cells were dissimilar in several respects. Most notably, differentiating cells bound but failed to metabolize EGF. TPA treatment of basal cells from either strain led to a rapid, pronounced reduction in EGF binding, while treatment with retinoic acid, an antipromoter in vivo, increased binding. In contrast, EGF binding by differentiating cells was much less affected by TPA treatment, and retinoic acid had no effect or was slightly inhibitory, while combined treatment was more inhibitory than either alone. Given an adequate plating density, inclusion of 1 ng EGF per ml of media significantly enhanced growth of basal cells. Because of the similarities in binding patterns between the two strains, it seems unlikely that differential responses of BALB/c and SENCAR epidermal cells to EGF and to modulators of EGF binding are involved in the differences in susceptibility of these strains to carcinogenesis.

Animals↗