Protein kinase: altered regulation in a hepatoma cell line deficient in adenosine 3',5'-cyclic monophosphate-binding protein

Regulation of yeast trehalase by a monocyclic, cyclic AMP-dependent phosphorylation-dephosphorylation cascade system

Mutation at the GLC1 locus in Saccharomyces cerevisiae resulted in simultaneous deficiencies in glycogen and trehalose accumulation. Extracts of yeast cells containing the glc1 mutation exhibited an abnormally high trehalase activity. This elevated activity was associated with a defective cyclic AMP (cAMP)-dependent monocyclic cascade which, in normal cells, regulates trehalase activity by means of protein phosphorylation and dephosphorylation. Trehalase in extracts of normal cells was largely in a cryptic form which could be activated in vitro by ATP . Mg in the presence of cAMP. Normal extracts also exhibited a correlated cAMP-dependent protein kinase which catalyzed incorporation of label from [gamma-32P]ATP into protamine. In contrast, cAMP had little or no additional activating effect on trehalase or on protamine phosphorylation in extracts of glc1 cells. Similar, unregulated activation of cryptic trehalase was also found in glycogen-deficient strains bearing a second, independently isolated mutant allele, glc1-2. Since trehalase activity was not directly affected by cAMP, the results indicate that the glc1 mutation results in an abnormally active protein kinase which has lost its normal dependence on cAMP. Trehalase in extracts of either normal or mutant cells underwent conversion to a cryptic form in an Mg2+-dependent, fluoride-sensitive reaction. Rates of this reversible reduction of activity were similar in extracts of mutant and normal cells. This same, unregulated protein kinase would act on glycogen synthase, maintaining it in the phosphorylated low-activity D-form. The glc1 mutants provide a novel model system for investigating the in vivo metabolic functions of a specific, cAMP-dependent protein kinase.

Inhibition of hepatoma cell growth by analogs of adenosine and cyclic AMP and the influence of enzymes in mammalian sera

The following evidence suggests that inhibition of hepatoma cell (HTC) growth by cyclic nucleotides is an adenosine-like effect that is greatly modified by the type and treatment of serum used in the culture medium and is probably not mediated by cyclic AMP-dependent protein kinase: 1) Heating serum reduces its phosphodiesterase content, thereby slowing metabolism of cyclic AMP and reducing the inhibition of HTC cell growth by cyclic AMP; 2) Using medium that contains phosphodiesterase but lacks adenosine deaminase causes adenosine to accumulate from cyclic AMP and increases the toxicity of cyclic AMP; 3) Uridine or cytidine reverses the growth inhibition caused by adenosine, 5'-AMP or cyclic AMP; 4) adenosine, 5'-AMP and N6-(delta 2-isopentenyl) adenosine are more toxic for HTC cells than is cyclic AMP, and N6,O2-dibutyryl cyclic AMP is not toxic; and 5) N6,O2'-dibutyryl cyclic AMP inhibits growth of Reuber H35 cells, but uridine prevents this inhibition of growth. We conclude that most, if not all, of the inhibitory effects of cyclic AMP and N6,O2'-dibutyryl cyclic AMP on HTc and Reuber H35 hepatoma cell growth are due to the generation of toxic metabolites.

Adenosine 3',5'-monophosphate-dependent protein kinase(s) in diploid and SV40 transformed human fibroblasts

Cyclic AMP-dependent protein kinases (EC 2.7.1.37; ATP:protein phosphotransferase) in the human diploid fibroblast WI-38 and an SV40-transformant WI-38-VA13-2RA (VA13) have been compared on the basis of their concentrations in cells, isoenzyme composition and susceptibility to hormonal activation. In high population density cultures, total soluble cyclic AMP-dependent kinase activities measured with histone were essentially the same in WI-38 and VA13. Two soluble protein kinase forms separated by chromatography on DEAE-cellulose were present in both cell lines. The concentration of cyclic AMP required for half-maximal activation of both enzyme forms was 10-30 nM. Overall kinase stimulation was greater for the Peak I enzymes. Kinase activation induced in the presence of 0.5 M KCl was more rapid and complete for the Peak I enzymes. Under conditions which elevated the concentration of cyclic AMP in WI-38 and VA13 cells the activities of the soluble histone kinases were increased. Incubation of the cells with either of 5.7 micronM prostaglandin E1 or 1 micronM isopropylnorepinephrine induced complete activation of the cyclic AMP-dependent histone kinases within 5 min and maintained the effect for 20 min. When intracellular cyclic AMP levels were raised by prostaglandin E1, activation of glycogen phosphorylase (assayed-AMP) suggested that this enzyme cascade involving cyclic AMP-dependent protein kinase(s) was intact and responsive in both cell lines.

Studies of cAMP metabolism in cultured hepatoma cells: presence of functional adenylate cyclase despite low cAMP content and lack of hormonal responsiveness

The ability of isoproterenol, glucagon, PGE1 and cholera toxin to stimulate the synthesis of cAMP and protein kinase activity in line of liver cells (BRL) and a line of rat hepatoma cells (H35) has been determined. The concentration of cAMP in BRL cells (approximately 10 pmoles/mg protein) is in the range reported for other cultured cell lines but H35 cells contain extraordinarily low amounts of this cyclic nucleotide (approximately 0.05 pmoles/mg protein). Isoproterenol and PGE1 caused an increase in cAMP content, and protein kinase activation in BRL cells, although glucagon was ineffective. H35 cells, in contrast, were completely insensitive to all hormonal agonists. Despite this fact, cholera toxin was able to produce a marked increase in cAMP content, adenylate cyclase activity and protein kinase activation in H35 cells. binding studies with [125 I]-iodohydroxybenzylpindolol, a specific beta-adrenergic receptor antagonist, revealed that each H35 cell possesses fewer than 10 beta-adrenergic receptors whereas BRL cells contain 2-5,000 receptors per cell. The low level of cAMP in H35 cells appears to result from a combination of totally unstimulated adenylate cyclase and apparently elevated phosphodiesterase activities.

Regulation of macromolecular synthesis in Morris hepatomas

In this review, some studies are discussed in which an attempt has been made to determine the nature of changes in macromolecular synthesis in Morris hepatomas. The incorporation of isotope labeled precursors into nucleic acids and proteins has suggested greatly increased rates of DNA synthesis in comparison with rat liver of normal and tumor bearing rats, but for RNA and proteins the changes may be impressive for individual macromolecular species but total synthesis is not greatly changed. Fractionation of nuclear proteins has indicated altered patterns of synthesis which are related to the growth rates of the tumors and are much more pronounced than in regenerating liver despite a growth rate similar to that of the most rapidly growing hepatomas. Investigations with drugs which inhibit synthesis of macromolecules has suggested that liver neoplasia may be accompanied by changes in response which may make the tumor less sensitive or more sensitive to regulation than the tissue of origin.

Cyclic nucleotide metabolism in solid tumor tissues

The examination of the regulation of the system of 3'-5' cyclic nucleotide monophosphates has only begun in cancer tissues. In human cancers, these studies are notably non-existent. However, in animal cancers, especially the Morris hepatomas, enough data has been gathered that, while risky, certain trends seem to begin to appear. Cyclic AMP is constant or lowered, while cyclic GMP is elevated in the fast growing hepatomas. Regulation of adenylate cyclase by protein hormones is reduced, while regulation by epinephrine may be increased. Binding of glucagon is decreased in the fast growing hepatomas. Guanylate cyclase, while being predominantly cytoplasmic in the normal liver, is predominantly membrane bound in the tumors. The liver enzyme is also readily stimulated by several chemical carcinogens. The cyclic GMP phosphodiesterases are decreased in these tumors; while the cAMP phosphodiesterases are increased. Although the cyclic nucleotide dependent protein kinases (histone as substrate) are altered in the hepatomas, observations of unique cyclic nucleotide binding proteins or cAMP independent protein kinases in cancer tissues may be of even greater significance for the development of or the maintenance of the neoplastic state of cells.

Altered regulation of cyclic AMP-dependent protein kinase in a mouse lymphoma cell line

The ability of cyclic AMP to inhibit growth, cause cytolysis and induce synthesis of cyclic AMP-phosphodiesterase in S49.1 mouse lymphoma cells is deficient in cells selected on the basis of their resistance to killing by 2 mM dibutyryl cyclic AMP. The properties of the cyclic AMP-dependent protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37) in the cyclic AMP-sensitive (S) and cyclic AMP-resistant (R) lymphoma cells were comparatively studied. The cyclic AMP-dependent protein kinase activity or R cells cytosol exhibits an apparent Ka for activation by cyclic AMP 100-fold greater than that of the enzyme from the parental S cells. The free regulatory and catalytic subunits from both S and R kinase are thermolabile, when associated in the holoenzyme the two subunits are more stable to heat inactivation in R kinase than in S kinase. The increased heat stability of R kinase is observed however only for the enzyme in which the catalytic and cyclic AMP-binding activities are expressed at high cyclic AMP concentrations (10(-5)--10(-4) M), the activities expressed at low cyclic AMP concentrations (10(-9)--10(-6) M) being thermolabile. The regulatory subunit of S kinase can be stabilized against heat inactivation by cyclic AMP binding both at 2-10(-7) and 10(-5) M cyclic AMP concentrations. In contrast, the regulatory subunit-cyclic AMP complex from R kinase is stable to heat inactivation only when formed in the presence of high cyclic AMP concentrations (10(-5)M). The findings indicate that the transition from a cyclic AMP-sensitive to a cyclic AMP-resistant lymphoma cell phenotype is related to a structural alteration in the regulatory subunit of the cyclic AMP-dependent protein kinase which has affected the protein's affinity for cyclic AMP and its interaction with the catalytic subunit.

Hyperglucagonemia and altered responsiveness of hepatic adenylate cyclase-adenosine 3',5'-monophosphate system to hormonal stimulation during chronic ingestion of DL-ethionine

Basal activity and hormonal responsiveness of the adenylate cyclase-adenosine 3',5'-monophosphate system were examined in premalignant liver from rats chronically fed the hepatic carcinogen DL-ethionine, and these data were correlated with endogenous levels of plasma glucagon. By 2 weeks basal hepatic cyclic AMP levels, determined in tissues quick-frozen in situ, were 2-fold higher in rats ingesting ethionine than in the pair-fed control. Enhanced tissue cyclic AM content was associated with an increase in the adenylate cyclase activity of whole homogenates of fresh liver from rats fed ethionine (68 +/- 5 pmol cyclic AMP/10 min per mg protein) compared to control (48 +/- 4). Cyclic AMP-dependent protein kinase activity ratios were also significantly higher (control, 0.38 +/- 0.04; ethionine 0.55 +/- 0.05) and the percent glycogen synthetase activity in the glucose 6-phosphate-independent form was markedly reduced (control, 52 +/- 7%; ethionine, 15 +/- 1.5%) in the livers of ethionine-fed rats compared to the controls, suggesting that the high total hepatic cyclic AMP which accompanied ethionine ingestion was bilogically effective. These changes persisted throughout the 38 weeks of drug ingestion. Immunoreactive glucagon levels, determined in portal venous plasma, were 8-fold higher than control after 2 weeks of the ethionine diet (control, 185 +/- 24 pg/ml; ethionine, 1532 +/- 195). Analogous to the changes in hepatic parameters, plasma glucagon levels remained elevated during the entire period of drug ingestion until the development of hepatomas. The hepatic cyclic AMP response to a maximal stimulatory dose of injected glucagon was blunted in vivo in ethionine-fed rats (control, 14 -fold increase over basal, to 8.63 +/- 1.1 pmol/mg wet weight; ethionine, 4.6-fold rise over basal, to 5.42 +/- 0.9). Reduced cyclic AMP responses to both maximal and submaximal glucagon stimulation were also evident in vitro in hepatic slices prepared from rats fed the drug, and the reduction was specific to glucagon. Absolute or relative hepatic cyclic AMP responses to maximally effective concentrations of protaglandin E1 or isoproterenol in hepatic slices from ethionine-fed rats were greater than or equal to those observed in control slices. Parallel alterations in hormonal responsiveness were observed in adenylate cyclase activity of whole homogenates of these livers, implying that the changes in cyclic AMP accumulation following hormone stimulation were related to an alteration in cyclic AMP generation in the premalignant tissue. In view of the recognized hepatic actions of glucagon and the desensitization of adenylate cyclase which can occur during sustained stimulation of the liver with this hormone, the endogenous hyperglucagonemia that accompanies ethionine ingestion could play a role in the pathogenesis of both the basal alterations in hepatic cyclic AMP metabolism and the reduced responsiveness to glucagon observed in liver from rats fed this carcinogen.

Sequential alterations in the hepatic content and metabolism of cyclic AMP and cyclic GMP induced by DL-ethionine: evidence for malignant transformation of liver with a sustained increase in cyclic AMP

There is evidence than adenosine 3',5'-monophosphate (cAMP) and guanosine 3',5'-monophosphate (cGMP) may have antagonistic actions on cell growth, with cAMP inhibiting and cGMP stimulating this process. However, reductions in cAMP and increases in cGMP are not charactersitic of all neoplastic tissues. Thus, benign and malignant tissues from hepatoma-bearing rats exposed to the hepatic carcinogen DL-ethionine have elevated rather than depressed cAMP, compared to control liver, and parenteral administration of this drug increases hepatic cAMP within hours. In the present study, the effects of ethionine ingestion on the hepatic content and metabolism of both cAMP and cGMP were examined sequentially in rats at 2 and then 6 wk intervals, from the initiation of drug administration until the development of hepatomas. After 2 wk, cAMP content of quick-frozen liver from rats receiving ethionine (E) was significantly increased (826 +/- 91 pmole/g wet weight) above that of liver from pair-fed controls (C, 415 +/- 44), whether calculated by tissue wet weight, protein, or DNA content. In benign tissue from E, higher cAMP was still evident after in vitro incubations of slices with 2 mM 1-methyl-3-iso-butylxanthine (MIX) and was associated with enhanced adenylate cyclase and unchanged high or low Km cAMP-phosphodiesterase activities. These findings are compatible with accelerated cAMP generation in liver from E. Protein kinase activity ratios were significantly increased in frozen liver from E (0.52 +/- 0.04 versus 0.36 +/- 0.03 in C), and the percent glycogen synthetase in the I form was clearly reduced (19% +/- 2% in E versus 47% +/- 5% in c). incubation of hepatic slices from E or C with MIX and/or 10 muM glucagon further increased cAMP and protein kinase activity ratios, data which imply higher effective, as well as total, cellular cAMP in E. Changes in cAMP metabolism and action observed at 2 wk persisted throughout the 38-wk period of drug ingestion. Adenylate cyclase activity, cAMP content, and protein kinase activity ratios of ethionine-induced hepatomas exceeded those of both the surrounding liver from tumor-bearing rats and that of control liver, but alterations in these parameters were qualitatively similar in both tissues from E. By contrast, while cGMP in quick-frozen surrounding liver from tumor-bearing rats (36 +/- 4 pmole/g wet weight) did not differ from that of control liver (30 +/- 3), cGMP in the hepatomas was increased. This change was evident in both frozen tumor (89 +/- 10) and in tumor slices incubated in vitro with MIX (C, 90 +/- 11; surrounding liver, 85 +/- 10; hepatoma 231 +/- 29). These results indicate that malignant conversion can occur in liver with a sustained elevation of both total and effective cAMP during the premalignant phase. The increase in cGMP detected in ethionine-induced hepatomas could also be a key determinant of malignant transformation in the model, although premalignant changes in cGMP were not apparent.

Studies on cyclic nucleotides in cancer. I. Adenylate guanylate cyclase and protein kinases in the prostatic sarcoma tissue

Adenylate, guanylate cyclase and protein kinases in a fibrous sarcoma originating from rat prostate have been studied. A decrease in levels of adenosine 3', 5'-monophosphate (cyclic AMP) and adenylate cyclase activities and an increase in levels of guanosine 3',5'-monophosphate (cyclic GMP) and guanylate cyclase activities were observed in the tumor tissue when compared with the normal prostatic tissue of rats. Protein kinases from the tumor and the prostate were both responsive to exogenous cyclic AMP, with an apparent Ka of 0.08 muM in the tumor and of 0.11 muM in the prostate. It is of interest that the protein kinases from the tumor responded to cyclic AMP to the same extent as was observed in the enzyme preparation from the prostate. The protein kinase from the tumor was more sensitive to cyclic GMP than that from the prostate, showing an apparent Ka of 0.88 muM in the tumor and of 4.85 muM in the prostate. This tumor has been characterized with an increase in guanylate cyclase activities with a subsequent rise in cellular cyclic GMP and an increased sensitivity of the protein kinase to cyclic GMP.

An evaluation of adenosine 3',5'-cyclic monophospate-dependent protein kinase activity in atopic dermatitis

Activity of adenosine 3',5'-cyclic monophosphate-dependent protein kinase has been measured in the skin of normal controls, patients with non-atopic skin disorders, and those with atopic dermatitis. All samples analyzed displayed the presence of this enzymatic activity. However, the enzyme from the atopic skin did not seem to be dependent on cyclic AMP for activity. Whether this is due to an artifact of isolation of protein kinase or is indeed the true in vivo nature of the enzyme remains to be established.

Chromosomal proteins of rat brain: increased synthesis and affinity for DNA following a pulse of the carcinogen ethyinitrosourea in vivo

A single pulse of ethlnitrosourea (EtNU), administered to 10-day-old BD IX-rats, specifically results in a high incidence of neuroectodermal tumors in the central and peripheral nervous system. At five days after an EtNU-pulse, analyses of protein-DNA interactions were performed using chromatin dissociation and re-association experiments, following incorporation of radioactive leucine into brain chromosomal proteins (CP) during short-term suspension culture. In comparison with 15-day-old control animals, the brain cells of EtNU-treated rats exhibited (i) an increased rate of CP synthesis, and (ii) an increased affinity of the newly-synthesized CP for brain DNA of both control and EtNU-treated animals.

Phosphorylation of the lysine-rich histones throughout the cell cycle

The phosphorylating of the lysine-rich histone at various stages in the cell cycle has been studied. In rapidly dividing cell populations the lysine-rich histone is phosphorylated rapidly after synthesis and more slowly once bound to the chromosome. The half-life of hydrolysis of such interphase phosphorylation in 5 hr except during mitosis when the phosphata hydrolysis increases almost three-fold. During mitosis there is extensive phosphorylation at sites different from those phosphorylated during interphase and a smaller measure of sites common to both mitotic and interphase cells. The sites of mitotic phosphorylation are most critically distinguished from those phosphorylated in interphase by the rapidly hydrolysis of M-phase phosphohistone when the cells divide and enter the G1 phase of the cell cycle.

The phosphorylation region of lysine-rich histone in dividing cells

N-Bromosuccinimide cleavage of in vivo 32P-labelled lysine-rich histone isolated from rapidly dividing cells has been studied. N-Bromosuccinimide cleaves F1-histone into two fragments, a small N-terminal piece and a larger C-terminal portion. The phosphate-induced microheterogeneity and associated radioactivity which has been linked to cell replication, is found in the carboxyterminal fragment, No phosphorous is found associated with the amino-terminal fragment when histone phosphorylation is associated with cell division. The specific tryptic phosphopeptides obtained from in vivo labelled F1 are clearly different from those obtained from in vitro incubations of free F1-histones and cytoplasmic protein kinase.

Regulation of phosphoenolpyruvate carboxykinase and tyrosine transaminase in hepatoma cell cultures. 3. Comparative studies in H35, HTC, MH1C1 and RLC cells

The ability of N(6), O(2)'-dibutyryl cyclic AMP (DBcAMP) to regulate a number of metabolic events in four lines of cultured rat hepatomas has been examined. Although dexamethasone induces tyrosine transaminase in all four lines, DBcAMP induces this enzyme normally only in H35 cells. A slight increase in transaminase activity was seen with MH(1)C(1) cells and HTC cells, but no effect was detectable in RLC cells. In contrast, phosphoenolpyruvate carboxykinase activity is increased by both agents in H35 and MH(1)C(1) cells, but neither had any effect in HTC or RLC cells. DBcAMP caused a rapid inhibition of the growth rate and DNA synthesis and an increase in protein content in both H35 and MH(1)C(1) cells but not in HTC or RLC cells. The effect of DBcAMP on DNA synthesis in MH(1)C(1) cells could be reversed by deoxycytidine as is also the case with H35 cells. The resistance of HTC and RLC cells to DBcAMP was not due to reduced uptake or deacylation as judged by studies with [(3)H]DBcAMP. The cyclic nucleotide appears to enter the cells by passive diffusion as the intracellular concentration approaches that in the medium within 30-60 min. Possible explanations for the differential responses observed are discussed.