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

Desipramine inhibits the growth of a mouse skin squamous cell carcinoma cell line and affects glucocorticoid receptor-mediated transcription

The purpose of this study was to examine the effect of tricyclic antidepressant desipramine (DMI) on the growth inhibition and translocation of the glucocorticoid receptor (GR) from the cytoplasm to the nucleus in cancerous and noncancerous cell lines and the effect of DMI on GR-mediated transcription. Nontumorigenic, immortalized keratinocytes cell line (3PC), papilloma (MT1/2), and squamous cell carcinoma (Ca3/7) cell lines were initially used to study the cell growth inhibition by DMI. Although, the growth of all three cell lines was suppressed by DMI, it was more effective in Ca3/7 cells. Therefore, we next examined the effect of DMI on Ca3/7 cells, resistant to growth inhibition by the synthetic glucocorticoid fluocinolone acetonide (FA). DMI inhibited cell proliferation in a time-dependent manner. The translocation of GR was induced by FA alone, DMI alone, and combination of both agents. FA induced GR-mediated transcription in Ca3/7 cells transfected with a luciferase reporter gene under the control of glucocorticoid response element (GRE), but DMI alone did not affect GR-mediated transcription. However, DMI inhibited FA-induced, GR-mediated transcription when both agents were given together. Pretreatment with DMI followed by combination of DMI and FA decreased GR-mediated transcription more than pretreatment with FA. The expression of metallothionein-1 (Mt-1) gene, which is regulated by GR, was induced significantly by the combination of DMI and FA, and enhanced significantly by pretreatment with FA but not DMI. DMI is suggested to inhibit the growth of Ca3/7 cells and to affect GR-mediated transcription.

Role of inflammation in mouse lung tumorigenesis: a review

Peritumoral and intratumoral macrophages are associated with human and mouse lung cancer The mouse model allows manipulation of the macrophage population to experimentally evaluate its contribution to tumor growth. Genetic and pharmacologic strategies also permit testing the invol vement of specific inflammatory mediators in tumor progression. Among those endogenous mediators thus identified are interleukin (IL)-10, glucocorticoids, prostacyclin, nitric oxide, and surfactant apoprotein D (SP-D); serum SP-D levels are a useful biomarker to monitor tumor growth rate. The importance of understanding the mutually antagonistic roles of individual prostaglandins downstream from cycloxygenase (COX) and how this affects the efficacy of COX-inhibitory drugs is discussed. Promising drug candidates include synthetic glucocorticoids such as budesonide and the sulfone derivative of sulindac, apotosyn.

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.

Influence of the glucocorticoid receptor on c-fos inducibility in activated ras-containing mouse lung cells

Glucocorticoids inhibit the growth and promote the differentiation of normal lung cells. Transformed A5 mouse lung cells containing an activated Ki-ras gene are not responsive to glucocorticoid-induced growth inhibition and demonstrate increased cell proliferation. Activated ras genes may lead to constitutive activation of genes, such as the activating protein 1 (AP-1) transcription factor components fos and jun, which are downstream in the ras signal-transduction pathway. A5 cells and A5GR, a stable A5 transfectant containing excess copies of the glucocorticoid receptor (GR) gene, were examined for potential alterations in AP-1 that accompany the restoration of glucocorticoid-dependent growth inhibition. The established ability of the GR to antagonize AP-1 activity led us to examine the regulation and inducibility of c-fos and c-jun in these cells. Nontransformed C10 lung cells were found to have higher and more inducible AP-1 activity than the transformed A5 cells. The level of AP-1 activity could be reduced in C10 cells by transient transfection of constitutive fos and jun expression vectors. In A5 cells, stimulation with factors that activate the serum-response element on the fos promoter and induce c-fos mRNA had little effect on AP-1 activity, whereas treatment with 12-O-tetradecanoylphorbol-13-acetate, which acts at the fos-AP-1 binding sequence site on the fos promoter, efficiently induced c-fos mRNA. The c-fos mRNA in A5GR cells, however, was not inducible with all treatments, suggesting that one potential mechanism by which the GR restores glucocorticoid-induced growth inhibition in these cells may involve the desensitization of additional 12-O-tetradecanoylphorbol-13-acetate-inducible elements of the fos promoter.

Beta-adrenergic signalling in neoplastic lung type 2 cells: glucocorticoid-dependent and -independent defects

Tumorigenic mouse lung-derived type 2 cell lines have large reductions in both beta-adrenergic-stimulated cAMP production and ligand binding to beta-adrenergic receptors. These tumorigenic cells are also relatively insensitive to glucocorticoids. Because glucocorticoids regulate both beta-adrenergic receptor expression and receptor coupling to the stimulatory guanine nucleotide binding protein Gs interactions between the glucocorticoid and beta-adrenergic signalling systems were examined. This study demonstrates that beta-adrenergic ligand binding and agonist sensitivity are increased in a tumorigenic cell line stably expressing a normal glucocorticoid receptor transgene. However, although the transfected tumour cells and non-tumorigenic cells have similar amounts and affinities of beta-adrenergic agonist and antagonist binding, similar amounts of Gs subunits and similar forskolin-stimulated adenylyl cyclase activities, the former remain much less isoproterenol responsive. Competition binding studies demonstrate that tumour cell beta-adrenergic receptors have both high- and low-affinity agonist binding but are functionally uncoupled from Gs. This uncoupling may involve an alteration in Gs, as guanine nucleotides exhibit a reduced ability to stimulate adenylyl cyclase. Thus, some aspects of tumorigenic cell dysfunction in beta-adrenergic signalling can be ameliorated by interactions with the glucocorticoid pathway, but additional defects are also involved.

Loss of glucocorticoid-dependent growth inhibition in transformed mouse lung cells

Transformed A5 mouse lung cells were examined for mechanisms that may explain their loss of glucocorticoid-induced growth inhibition. These cells were compared to nontransformed C10 mouse lung cells, which retain this response. Southern blot analysis revealed no major differences in the amount or pattern of restriction fragments for the glucocorticoid receptor (GR) gene between the responsive and nonresponsive cells. Northern blot analysis demonstrated that both cell lines expressed GR mRNA at similar levels and that these mRNAs had similar relative stabilities. The mRNA from both cell lines was used for reverse transcription-polymerase chain reaction amplification and direct sequencing with primers for different regions of the GR cDNA. A conservative mutation previously shown not to affect receptor function was detected within the DNA-binding domain region of the GR from both cell lines. Because of the ability of the transcription factors for activator protein-1 to antagonize GR function, c-jun and c-fos mRNA levels were examined. A5 cells were found to have higher levels of c-jun mRNA than C10 cells both during active cell growth and after serum starvation. Stable transfection of the nonresponsive A5 cells with a rat GR expression vector (A5GR7) resulted in strong glucocorticoid-induced growth inhibition, demonstrating that these cells retain the ability to be growth inhibited by these steroids. The A5GR7 transfectants also had higher mouse mammary tumor virus (MMTV)-chloramphenicol acetyltransferase (CAT) activity than the parental A5 cells and lower levels of c-jun during active cell growth. Transient transfection of the C10 cells with c-jun expression vector strongly reduced glucocorticoid-inducible MMTV-CAT activity. These results suggest that the transformed A5 cells apparently contain functional GR but that the high level of c-jun mRNA expression (probably resulting from the activated Ki-ras allele in these cells) may antagonize their ability to respond to the growth-inhibitory signaling of glucocorticoids.

Dexamethasone enhances colonization of soft agar by tumorigenic mouse lung-derived cell lines

When cultured on plastic, tumorigenic mouse lung-derived cell lines exhibit different proliferative responses to glucocorticoids; some lines are inhibited while others are stimulated or unaffected. In contrast to the variable dexamethasone responses when cells are cultured on plastic, soft agar colonization by each of these cell lines is enhanced by dexamethasone. Enhanced soft agar growth is unlikely to result from expression of a mutant glucocorticoid receptor, since dexamethasone also enhanced colony formation in two cell lines that stably express a transfected normal glucocorticoid receptor gene. Thus, cell attachment influences the effect of glucocorticoids on cell cycle progression.

Effect of increased glucocorticoid responsiveness in transformed mouse lung cells

Many transformed mouse lung cells, including LM2 cells, contain activating mutations in the Ki-ras gene and show reduced responsiveness to growth inhibition by glucocorticoids. LM2GR cells, which are LM2 cells stably transfected with a rat glucocorticoid receptor (GR) gene, were used to determine whether increasing glucocorticoid responsiveness can influence aspects of the transformed phenotype. LM2GR cells grew slower and had a lower final saturation density than the parental LM2 cells. Expression of growth-related genes was examined by northern blot analysis. The cells were serum-deprived and treated with fetal bovine serum (FBS), steroid-stripped FBS (ssFBS), dexamethasone, or 12-O-tetradecanoylphorbol-13-acetate. The level and pattern of Ki-ras mRNA expression was similar in both LM2 and LM2GR cells, but histone H4 mRNA was expressed in a more regulated fashion in LM2GR cells. The induction of c-jun and c-fos mRNA expression lasted longer in the LM2GR cells treated with ssFBS; however, the maximal induction was greater in the LM2 cells treated with FBS. LM2GR cells demonstrated similar activator protein-1 (AP-1) activity but higher GR activity than LM2 cells as determined by using AP-1-chloramphenicol acetyltransferase (CAT) and mouse mammary tumor virus-CAT transient transfection assays, consistent with the higher level of GR mRNA in LM2GR cells. Both cell lines exhibited the ability to grow in soft agar and to form tumors in nude mice. These results indicate that introduction of a functional GR transgene into LM2 cells can increase glucocorticoid responsiveness and alter the expression of genes involved in growth regulation but cannot overcome anchorage-independent cell growth or tumorigenicity, apparently because of the presence of an activated Ki-ras gene.