Genetic influence on type 2 or Clara cell origin of pulmonary adenomas in urethan-treated mice

Urethan-induced lung adenomas arising from alveolar type 2 cells and from bronchiolar Clara cells have distinct histologic patterns; and examination of all lung adenomas found in A/J, SWR/J, BALB/cByJ, 129/J, and RIIIS/J inbred mice, 14-16 weeks after a single urethan injection, demonstrated that both tumor types were present in all five strains. The relative numbers of each tumor type varied significantly among the different strains. No correlation was observed between the type of tumor formed and tumor multiplicity. Augmentation of tumor multiplicity by chronic butylated hydroxytoluene (BHT) treatment following urethan injection did not change the proportion of the 2 tumors from that observed with urethan alone. This finding demonstrated that BHT stimulated the development of both tumor types equally. The tumors found 14 weeks after a single urethan injection into neonatal BALB mice were larger than those found 14 weeks after urethan injection into adult BALB mice, but the proportion of alveolar and papillary tumors was the same for both groups. Lymphocytic infiltration into tumors was mainly associated with Clara cell-derived tumors. The proportion of type 2 cell- and Clara cell-derived lung adenomas appeared to be controlled primarily by the genetic background.

Changes in cyclic adenosine 3':5'-monophosphate-dependent protein kinases during the progression of urethan-induced mouse lung tumors

The cyclic adenosine 3':5'-monophosphate (cAMP)-dependent protein kinases in lung adenomas are functionally different from those of normal lung. The relevance of this change to neoplastic conversion was examined by comparing tumor kinases with those obtained from the normal cell of origin and by studying the kinases at different stages of tumor growth. Lung tumors were collected from A strain mice at different times after a single injection of urethan. These tumors are predominantly of alveolar type two cell origin, and cAMP-binding proteins in extracts from isolated type two cells and from lung adenomas at various stages of tumor progression were compared. Both the incorporation of the cAMP photoaffinity analogue, cyclic 8-azidoadenosine 3':5'-[32P]monophosphate (8-N3-[32P]cAMP), into the regulatory subunits of the type I (RI) and type II (RII) cAMP-dependent protein kinases and the autophosphorylation of RII were similar in extracts from whole normal lung and from type two cells. Altered protein kinases are thus not characteristic of normal type two cells. Lung tumors showed a decrease in photodetectable RII which correlated in degree with tumor size and extent of anaplasticity. This decreased RII photolabeling during tumor growth was associated with increased RII autophosphorylation. In contrast, decreased RII photolabeling in extracts from neonatal lung is accompanied by a substantial decrease in RII autophosphorylation. The characteristics of RII during normal development thus clearly differ from those during neoplastic development. An increase in the amount of an Mr 37,000 proteolytic fragment derived from R-subunits was also noted as a function of tumor progression. DEAE-cellulose chromatography of tumor cytosol showed that the increase in the amount of Mr 37,000 protein was accompanied by increased subunit dissociation of the type I isozyme. The dissociated RI subunit has been shown to be more sensitive to cleavage by a Ca2+-dependent neutral protease than when RI was in the holoenzyme form. This protease is present in both normal lung and lung adenomas, and its activity increases during the later stages of tumor progression. A comparison of cAMP binding and the light-induced covalent incorporation of 8-N3-[32P]cAMP showed that, for both RI and RII, photoincorporation was about 75% as efficient as noncovalent binding. In contrast, although the Mr 37,000 fragment can be photolabeled with low concentrations of 8-N3-[32P]cAMP, noncovalent cAMP binding to the endogenous Mr 37,000 fragment could not be demonstrated with a standard filtration assay. Such altered cAMP binding characteristics following Ca2+-dependent proteolysis of R-subunits would all

Autoradiographic localization of specific [3H]dexamethasone binding in fetal lung

The cellular and subcellular localization of specific [3H]dexamethasone binding was examined in fetal mouse lung at various stages of development and in human fetal lung at 8 weeks of gestation using a rapid in vitro steroid incubation technique followed by thaw-mount autoradiography. Competition studies with unlabeled steroids demonstrate the specificity of [3H]dexamethasone labeling, and indicate that fetal lung mesenchyme is a primary glucocorticoid target during lung development. Quantitative binding studies, involving incubation of intact tissue with competing ligand and subsequent subcellular fractionation, show this to be specific, nuclear binding characteristic of glucocorticoid receptors. Autoradiographs of [3H]dexamethasone binding in lung tissue at early stages of development demonstrate that the mesenchyme directly adjacent to the more proximal portions of the bronchiolar network is heavily labeled. In contrast, the epithelium which will later differentiate into bronchi and bronchioles, is relatively unlabeled. Distal portions of the growing epithelium, destined to become alveolar ducts and alveoli, do show nuclear localization of [3H]dexamethasone. Because of the known importance of the mesenchyme in controlling lung development and the ability of glucocorticoids to stimulate lung development, these results suggest that many of the growth-promoting effects of glucocorticoids may be mediated through the mesenchyme. In addition, by utilizing a technique which allows the simultaneous examination of extracellular matrix components and [3H]dexamethasone binding, a relationship is observed between extensive mesenchymal [3H]dexamethasone binding and extensive extracellular matrix accumulation. Since glucocorticoids stimulate the synthesis of many extracellular matrix components, these results suggest a role for these hormones in affecting mesenchymal-epithelial interactions during lung morphogenesis.

Localization of specific [3H]dexamethasone binding in urethan-induced mouse lung tumors

Pulmonary tumors induced in A/J mice 14 months after a single i.p. injection of urethan vary greatly in size. Since glucocorticoids may play a major role in regulating lung cell proliferation, glucocorticoid binding was examined in these tumors to determine whether tumor size was related to any specific pattern of [3H]dexamethasone [( 3H]DEX) binding. Tumor samples were incubated in vitro with 17 nM [3H]DEX for 90 min at 37 degrees, washed extensively to reduce nonspecific binding, and either fractionated by differential centrifugation to quantify nuclear and cytosolic binding or processed for autoradiography. Quantitative binding studies demonstrate a reduction in specific nuclear [3H]DEX binding and an increase in nonspecific cytosolic binding in all of the tumors examined as compared to normal adult lung. Autoradiographic studies reveal pulmonary tumors of different morphology which vary in their [3H]DEX binding characteristics. Small tumors were of two histological patterns, alveolar adenomas which are probably derived from alveolar type II cells and papillary adenomas which are probably derived from bronchiolar Clara cells. The alveolar adenomas contain little nuclear [3H]DEX binding, whereas the papillary adenomas show extensive nuclear localization of [3H]DEX. These results indicate that nuclear localization of [3H]DEX can provide a biochemical criterion for distinguishing alveolar from papillary adenomas. Most of the larger tumors were either papillary or anaplastic in morphology and localized [3H]DEX in their nuclei. This suggests that these larger and possibly more malignant tumors are derived from papillary adenomas.

Functional changes in the regulatory subunit of the type II cyclic adenosine 3':5'-monophosphate-dependent protein kinase isozyme during normal and neoplastic lung development

The abilities of cyclic adenosine 3':5'-monophosphate (cAMP) and cyclic 8-azidoadenosine 3':5'-[32P]monophosphate (8-N3-[32P]cAMP) to bind to the regulatory subunit (RII) of the type II cAMP-dependent protein kinase isozyme and to cause subsequent dissociation of the holoenzyme were compared in extracts from adult and neonatal mouse lung and lung adenoma. RII in extracts from adult lung exhibits equal numbers of high- (Kd 15 nM) and low- (Kd 230 nM) affinity 8-N3-[32P]cAMP binding sites. In the neonate, the proportion of high-affinity sites is reduced to 20% while, in lung adenoma, only low-affinity RII binding is observed. Low-affinity RII binding is correlated with an inability of cAMP to dissociate the type II holoenzyme completely. Sucrose gradient sedimentation of adult lung cytosol in the presence of cAMP shows complete dissociation of the type I isozyme, while only some of the type II holoenzyme is dissociated. This is in contrast to the case with lung tumor cytosol, in which only low-affinity binding is observed and no apparent dissociation of the type II isozyme occurs. cAMP does promote RII dephosphorylation within the holoenzyme, however, suggesting that cAMP can bind to RII without dissociating the tetramer. Consistent with this interpretation, photoincorporation of 8-N3-[32P]cAMP prior to sucrose gradient sedimentation results in the formation of a photolabeled RII complex which sediments at the same rate as does the holoenzyme. Two-dimensional gel electrophoresis of RII photolabeled at low and high concentrations of 8-N3-[32P]cAMP suggests that these altered binding and dissociation characteristics of the type II isozyme are not due to the presence of a structurally altered RII molecule. After DEAE-cellulose chromatography of lung cytosol, only high-affinity RII binding is observed, and all of the RII can now be dissociated with cAMP. Low-affinity binding may thus reflect either an altered conformational state of RII or the interaction of the type II kinase with other cytosolic molecules which can affect RII binding and dissociation without altering the functional properties of the type I isozyme.

Developmental changes in the endogenous Ca2+-stimulated proteolysis of mouse lung cAMP-dependent protein kinases

Regulatory subunits (R subunits) of mouse lung cAMP-dependent protein kinases undergo age-dependent changes in endogenous proteolysis, with the greatest amount of the major Mr = 37,000 proteolytic fragment detectable during fetal and neonatal development. Homogenization of lung in the presence of various protease inhibitors does not affect this age-related difference, suggesting that the observed quantitative change in R subunit proteolysis occurs in vivo. Mechanisms were sought to account for this age-dependent change. The production of a Mr = 37,000 proteolytic fragment can be stimulated in lung extracts by the addition of exogenous calcium and is due to the action of an endogenous Ca2+-stimulated protease. Neonatal lung extracts show more Ca2+-stimulated proteolysis of R subunits than adult extracts, although only slight age-related differences in either the Ca2+-stimulated protease or its specific endogenous inhibitor were observed. Age-dependent differences in R subunits which may affect sensitivity to proteases were also examined. Analysis of the two-dimensional patterns of adult and neonatal 8-N3-[32P]cAMP-labeled R subunits before or after limited proteolysis with trypsin suggests that the R subunits are structurally similar. Differences are found, however, in the relative proportions of adult and neonatal Type I R subunits (RI) in the holoenzyme or dissociated forms. An increased proportion of neonatal R subunits exist in the dissociated state, whereas adult R subunits exist primarily in the holoenzyme form. Dissociated R subunits from mouse lung are more susceptible than the holoenzyme to limited proteolysis by the partially purified lung Ca2+-stimulated protease. Dissociation of the holoenzyme in vivo may be a major factor in the age-dependent proteolytic changes observed in mouse lung protein kinases.

Methods in laboratory investigation. Autoradiographic demonstration of the specific binding and nuclear localization of 3H-dexamethasone in adult mouse lung

This report describes the first autoradiographic demonstration of specific nuclear localization of 3H-dexamethasone in different cell types of the lung. Adult mouse lung tissue was incubated in vitro for 90 minutes with 17 nM 3H-dexamethasone in the presence or absence of various nonradioactive steroids. After extensive washing to remove any nonspecifically bound ligand, the specimens were processed for autoradiography using the thaw-mount method. In the absence of competing steroids, silver grains were localized in the nuclei of alveolar type II cells, bronchiolar and arteriolar smooth muscle cells, fibroblasts, and endothelial cells of the pulmonary vasculature. No significant nuclear concentration of label was observed in the bronchiolar epithelium, however. The specificity of 3H-dexamethasone labeling was demonstrated by incubating 17 nM 3H-dexamethasone with a 600-fold excess of either unlabeled dexamethasone, estrogen, dihydrotestosterone, or progesterone. These autoradiographic binding and steroid competition studies were confirmed by quantifying with liquid scintillation counting the specific 3H-dexamethasone binding in nuclear and cytosolic fractions prepared from lung tissues that had undergone identical incubation and washing procedures as those for autoradiography. These results demonstrate that many cell types in adult lung are targets for glucocorticoids and may respond to physiologic concentrations of this hormone.

Time course of the carbon tetrachloride-induced decrease in mitochondrial aldehyde dehydrogenase activity

Hepatic microsomal enzymes like cytochrome P-450 and glucose 6-phosphatase are inhibited after exposure to CCl4 in vivo. Since comparatively less is known about the effects of CCl4 on nonmicrosomal enzymes, we investigated the rapidity by which CCl4 inhibits the low Km mitochondrial aldehyde dehydrogenase (ALDH) isozyme, an enzyme known to be inhibited 24 hr after CCl4 treatment. The activity of this ALDH isozyme was significantly lowered 6 and 12 hr after a single 1 ml/kg intragastric dose of CCl4. The mitochondrial low Km ALDH specific activities exhibited a similar pattern of destruction/inhibition to the documented target enzyme microsomal cytochrome P-450 in that lowest values were observed 6 hr after CCl4. These values were 44 and 37% of control for cytochrome P-450 content and the low Km ALDH activity, respectively. Alcohol dehydrogenase activity, expressed as activity per gram liver, was depressed 12 hr after CCl4 dosing. Finally, the activity of the low Km cytosolic ALDH, the isozyme that metabolizes malondialdehyde at low concentrations, was not affected by CCl4 treatment. The CCl4-induced decline in the activity of the matrix ALDH isozyme occurs earlier than previously reported mitochondrial damage. The study of sensitive enzymes like the low Km ALDH may provide valuable information by which it may be possible to determine the relationship of the truly rapid biochemical effects of CCl4 such as microsomal lipid peroxidation with later effects on nonmicrosomal components.

Inhibition of rat liver aldehyde dehydrogenase by carbon tetrachloride

Current data suggests that aldehydic products of lipid peroxidation possess substantial cytotoxic properties. Carbon tetrachloride (CCl4), a potent stimulator of hepatic lipid peroxidation, was tested for possible effects on hepatocellular aldehyde metabolism. CCl4 (1 ml/kg) produced an elevation in serum alanine aminotransferase activity, hepatic fatty infiltration, centrilobular necrosis and significant decreases in the content of hepatic microsomal cytochrome P-450. Concurrently, the aldehyde dehydrogenase (E.C. 1.2.1.3) activity of mitochondrial and cytosolic fractions was significantly depressed. The lower Km aldehyde dehydrogenase located in the mitochondria showed the largest degree of inhibition (46%). An in vitro system which contained the low Km mitochondrial aldehyde dehydrogenase was employed to determine the role of microsomal lipid peroxidation in the inhibition of the enzyme. Aldehyde dehydrogenase was shown to be extremely sensitive to inhibition under conditions of NADPH or NADPH and CCl4-stimulated lipid peroxidation. Reduced glutathione (6 mM) provided complete protection of aldehyde dehydrogenase activity under conditions of NADPH-stimulated lipid peroxidation but could not protect activity loss during CCl4-stimulated microsomal lipid peroxidation. The degree of enzyme activity loss related well with the amount of thiobarbituric reacting substances present in the incubation mixture. These findings show that CCl4 decreases the activity of the aldehyde oxidizing enzyme, aldehyde dehydrogenase. This effect may accentuate cytotoxic effects of reactive aldehydic products generated during lipid peroxidation.