EGF-receptor and extracellular matrix changes in mouse pulmonary carcinogenesis

Reduced receptor expression for platelet-derived growth factor and epidermal growth factor in dividing mouse lung epithelial cells

The roles of growth factors in mouse lung neoplasia were investigated by examining receptors for platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) in epithelial cell lines. Whereas nontumorigenic lung cells expressed mRNA and protein for PDGF receptor (PDGFR)-alpha, PDGFR-beta, and EGF receptor (EGFR), five of six neoplastic lines did not. Because this exceptional tumorigenic cell line grows slowly, we hypothesized that receptor levels increased with cell stasis. To test this hypothesis, serum concentrations were manipulated, and log-phase and post-confluent cells were compared. Consistent with our hypothesis, PDGFR-alpha and EGFR contents, but not PDGFR-beta contents, increased at stasis. Ki-ras mutation initiates lung tumorigenesis in mice, but activation of Ki-ras did not affect receptor expression. This was determined both by transfecting nontumorigenic cells with activated Ki-ras and neoplastic cells with a Ki-ras antisense construct and by diminishing Ki-ras activation by using a farnesyltransferase inhibitor. Stasis-associated upregulation of growth-factor receptor expression suggests a function in lung cell differentiation that is abrogated during neoplastic growth.

Mouse lung epithelial cell lines--tools for the study of differentiation and the neoplastic phenotype

Several dozen lung epithelial cell lines have been established in culture over the past 20 years from normal lung explants and their spontaneous transformants, and from lung tumors that arose spontaneously or were induced with chemicals, viruses, or oncogenic transgenes. To provide information from which to choose appropriate lines for investigating problems in lung cell biology and pulmonary neoplasia, this review describes the origins of these lines and some of their characteristics. These include growth, morphology, tumorigenicity, ability to metastasize, xenobiotic metabolism, mutational status, signal transducing activities, cytogenetics, ability to form domes, and electric conductance. In addition to collecting this information in a single place for the first time, we describe previously unpublished apoptosis features of some of these lines. An increasing number of investigations are beginning to use these lines and this review contains references into 1997.

Altered dexamethasone responsiveness and loss of growth control in tumorigenic mouse lung cell lines

Glucocorticoid hormones induce differentiation, inhibit proliferation, and, in mice, reduce carcinogen-induced tumorigenesis of lung epithelial cells. Therefore we examined dexamethasone effects on tumorigenic and non-tumorigenic mouse lung epithelial-derived cell lines. Non-tumorigenic cells were growth inhibited and exhibited CAT activity in pMMTV-CAT transfectants in response to dexamethasone. Tumorigenic cell lines exhibited a range of responses to dexamethasone. While one tumorigenic line was growth-inhibited and responsive in CAT assays, 2 other tumorigenic cell lines were unresponsive both in CAT and in growth assays. A fourth tumorigenic cell line exhibited intermediate sensitivity in CAT assays and was actually growth-enhanced by dexamethasone. Although no difference between cell lines was observed in the abundance of glucocorticoid receptor protein on Western blots, the least dexamethasone-responsive tumorigenic lines exhibited very little binding of 3H-dexamethasone. Clones of tumorigenic lines stably transfected with the rat glucocorticoid receptor gene were more dexamethasone-sensitive in CAT assays and were growth-inhibited by dexamethasone. These data suggest that the neoplastic progression of cell lines derived from mouse lung frequently involves the acquisition of diminished glucocorticoid responsiveness.

Ki-ras mRNA regulation in untransformed mouse lung cells

Although the Ki-ras gene is an often-observed transforming gene in lung tumors, little is understood of the factors that regulate the expression of the normal gene in lung cells. Therefore, we used untransformed mouse lung epithelial cells to determine the effect of serum, growth factors, and cell confluence on the regulation of Ki-ras mRNA expression. In subconfluent cells synchronized by 24-h serum deprivation, the refeeding of media containing serum resulted in the expression of both Ki-ras and H4 histone mRNA. No change in the expression of either gene was observed in cells refed with media alone. In confluent cell cultures, the refeeding of media with serum had no effect on the expression of these genes, suggesting that cell-density-dependent mechanisms can override the serum-induced stimuli for Ki-ras and H4 histone mRNA expression. Confluent cells expressed low but detectable Ki-ras mRNA levels consistent with constitutive expression of this gene independent of its role in mitogenic stimuli. EGF (10 ng/mL) and TGF-alpha (10 ng/mL) were found to induce transient increases in Ki-ras mRNA but large increases in H4 histone mRNA levels. Similarly, 48-h-conditioned media obtained from two transformed mouse lung cells containing activated Ki-ras genes and overexpressing Ki-ras mRNA were observed to increase both Ki-ras and H4 histone mRNA in the untransformed mouse lung cells. The expression of these genes in mouse lung cells therefore appeared to be linked to stimuli provided by specific growth factors as well as by autocrine factors elaborated by lung tumor cells. The studies reported here provide insight into the regulation of the Ki-ras mRNA in untransformed lung cells and the factors that may contribute to the elevated levels of Ki-ras mRNA often observed in transformed lung cells.

Altered levels and protein kinase C-mediated phosphorylation of substrates in normal and transformed mouse lung epithelial cells

Protein phosphorylation and protein kinase C (PKC) levels were analyzed in intact cultures of spontaneously transformed, chemically transformed, and untransformed mouse pulmonary epithelial cell lines. It was found that although the transformed cell lines contained about 80% less protein kinase C, measured as total enzyme activity or binding of [3H]phorbol ester, phosphorylation events after phorbol ester treatment could still be easily detected. A commonly described Mr 80-kDa protein kinase C substrate (p80, 80 K, MARKS) was identified using 2D-PAGE, following phosphorylation in intact cells, and found to have reduced availability for phosphorylation in the transformed cell lines C4SE9, C1SA5 and NULB5 in comparison to the untransformed C4E10 and C1C10. Available levels of p80 were further analyzed in heat-denatured extracts from all cell lines using partially purified bovine brain PKC and correlated well with changes seen in intact cells. It was also noted that all transformed cell lines contained large amounts of a family of phosphoproteins of Mr 55-65 kDa, that could not be detected in the untransformed cell lines and whose phosphorylation state was increased by protein kinase C activation. This protein was found to be located in the nucleus. Hence, spontaneously and chemically transformed mouse pulmonary epithelial cells exhibit reduced levels of PKC, along with an altered pattern of PKC-mediated phosphorylation.