Differential responsiveness to agents which stimulate cAMP production in normal versus neoplastic mouse lung epithelial cells

Activity of β2-adrenergic receptor in oral squamous cell carcinoma is mediated by overexpression of the ADRBK2 gene: a pilot study

The β2-adrenergic receptor is most frequently involved in carcinogenic processes. Earlier studies have established a relation between the β2-adrenergic receptor and various characteristics of cancer including cell proliferation, apoptosis, chemotaxis, metastasis, tumor growth and angiogenesis. Our goal was to determine differential expression of the genes involved in adrenergic receptors using DNA microarrays and to confirm their under- or overexpression using real-time quantitative PCR. Five of the nine genes investigated showed significantly altered expression levels in tumor cells (p < 0.05). The gene product with the highest Z-score (restrictive statistical technique for selection of appropriate genes to study) was ADRBK2. Significantly, most of the overexpressed genes were related to β-adrenergic receptors. Real-time PCR analysis confirmed the up regulation observed in the microarrays, which indicated overexpression in 100% of the tumors. In oral squamous cell carcinomas, malignant cells and surrounding tissue overexpress the ADRBK2 gene.

Altered expression of splicing factor, heterogeneous nuclear ribonucleoprotein A2/B1, in mouse lung neoplasia

Our previous proteomic investigation of lung neoplasia in vitro demonstrated a high concentration of the lung cancer biomarker and splicing factor, hnRNP A2/B1, in the transformed mouse lung epithelial cell line, E9. Since changes in pre-mRNA splicing profoundly affect neoplastic progression, we examined hnRNP A2/B1 expression in chemically induced primary mouse lung tumors, an in vivo model of pulmonary adencocarcinoma. Tumor hnRNP A2/B1 content and spatial distribution assessed by immunohistochemistry varied with stage of progression, genetic background, and whether tumors were induced by a single agent (urethane) or by 2-stage initiation/promotion (3-methylcholanthrene/butylated hydroxytoluene) carcinogenesis. To address mechanisms governing hnRNP A2/B1 expression changes, we utilized in vitro models. hnRNP A2/B1 protein was overexpressed in E9, the spontaneous tranformant of immortalized but non-neoplastic E10 cells, but expression was not strictly a function of enhanced proliferative rate in neoplastic cells. Elevated mRNA content was positively associated with cell division in both E10 and E9, but hnRNP A2/B1 protein levels decreased in proliferating E10 cells. The increased mRNA reflected enhanced mRNA stability, as shown by measuring time-dependent mRNA decay after inhibiting transcription. Dysregulation of hnRNP A2/B1 expression during lung neoplasia in vivo thus depends on complex gene-environmental interactions that affect cell type-specific changes in mRNA processing and, most probably, the rates of translation and/or protein degradation.

The alpha2-adrenergic receptor agonist UK 14,304 inhibits secretin-stimulated ductal secretion by downregulation of the cAMP system in bile duct-ligated rats

Secretin stimulates ductal secretion by activation of cAMP --> PKA --> CFTR --> Cl(-)/HCO(3)(-) exchanger in cholangiocytes. We evaluated the expression of alpha(2A)-, alpha(2B)-, and alpha(2C)-adrenergic receptors in cholangiocytes and the effects of the selective alpha(2)-adrenergic agonist UK 14,304, on basal and secretin-stimulated ductal secretion. In normal rats, we evaluated the effect of UK 14,304 on bile and bicarbonate secretion. In bile duct-ligated (BDL) rats, we evaluated the effect of UK 14,304 on basal and secretin-stimulated 1) bile and bicarbonate secretion; 2) duct secretion in intrahepatic bile duct units (IBDU) in the absence or presence of 5-(N-ethyl-N-isopropyl)amiloride (EIPA), an inhibitor of the Na(+)/H(+) exchanger isoform NHE3; and 3) cAMP levels, PKA activity, Cl(-) efflux, and Cl(-)/HCO(3)(-) exchanger activity in purified cholangiocytes. alpha(2)-Adrenergic receptors were expressed by all cholangiocytes in normal and BDL liver sections. UK 14,304 did not change bile and bicarbonate secretion of normal rats. In BDL rats, UK 14,304 inhibited secretin-stimulated 1) bile and bicarbonate secretion, 2) expansion of IBDU luminal spaces, and 3) cAMP levels, PKA activity, Cl(-) efflux, and Cl(-)/HCO(3)(-) exchanger activity in cholangiocytes. There was decreased lumen size after removal of secretin in IBDU pretreated with UK 14,304. In IBDU pretreated with EIPA, there was no significant decrease in luminal space after removal of secretin in either the absence or presence of UK 14,304. The inhibitory effect of UK 14,304 on ductal secretion is not mediated by the apical cholangiocyte NHE3. alpha(2)-Adrenergic receptors play a role in counterregulating enhanced ductal secretion associated with cholangiocyte proliferation in chronic cholestatic liver diseases.

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.

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.

Reduced beta adrenoceptor density in vivo in human lung tumours: a preliminary study with positron emission tomography

BACKGROUND

Reduced beta adrenergic receptor density in tumours has been reported in previous in vitro studies. The aim of the present study was to assess whether this occurs in vivo.

METHODS

Pulmonary beta adrenoceptors were imaged and quantified in vivo using positron emission tomography (PET) and the beta antagonist radioligand (S)-[11C]CGP-12177 in five men with lung tumours of mean age 58 years (range 42-68). The histology of the tumours was squamous cell carcinoma in two cases, adenocarcinoma in one, carcinoid tumour in one, and large cell carcinoma in one. The regional blood volume and extravascular tissue density were also measured using PET. Regions of interest were drawn for both non-tumour and tumour lung tissue.

RESULTS

The mean (SD) blood volume was 0.142 (0.025) ml/ml in tumour regions and 0.108 (0.010) ml/ml in normal lung regions--a difference of 31%. Mean (SD) extravascular tissue density was 0.653 (0.133) g/ml in tumour regions, substantially higher than in normal lung regions (0.157 (0.021) g/ml). On the contrary, beta receptor density was 5.1 (1.8) pmol/g in tumour regions, lower than the value of 9.9 (1.6) pmol/g found in adjacent normal lung--a difference of 48%.

CONCLUSIONS

In vivo beta adrenoceptor density is reduced in human lung tumours.

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.