Selective regulation of the amount of catalytic subunit of cyclic AMP-dependent protein kinases during isoprenaline-induced growth of the rat parotid gland

TSH control of PKA catalytic subunit activity in thyroid cell cultures

The protein expression and the enzyme activity of the catalytic subunit (C) of the cAMP-dependent protein kinases were studied in porcine thyroid cell primary cultures stimulated with two doses of TSH (0.1 mU/ml and 1 mU/ml) for 1 to 3 days. In TSH-stimulated cells the desensitization of the catalytic subunit activity was accompanied by a simultaneous and parallel decrease of its immunoreactivity. The loss of catalytic subunit was rapid and reached its maximum after 1 day of culture. It is similar in the two subcellular compartments: cytosol and particulate extracts. Contrary to the observed loss of the C subunit protein molecules in TSH-stimulated cells, the expression of the Cbeta subunit mRNA in these cells was increased fivefold compared to controls, while no significant change was observed on the Calpha subunit mRNA. These results suggest that TSH controls the Cbeta subunits of PKA at two levels: at the transcriptional level it increases Cbeta mRNA expression, and at the translational or posttranslational level TSH decreases the amount and the activity of the Cbeta protein molecules.

Regulation of protein kinase A subunits during germination of Mucor rouxii sporangiospores

Levels of protein kinase A (PKA) subunits and of cAMP have been measured during aerobic germination of the sporangiospores of the dimorphic fungus Mucor rouxii; further, the holoenzyme and its catalytic (C) and regulatory (R) subunits have been visualized through sucrose gradient centrifugation. Sporangiospores contain around 0.06 microM of a dimeric holoenzyme species of 5.5 S and a sixfold excess of a free R subunit of 2.7 S. Both these species are proposed to be derived by proteolysis from the native forms. Enzymic activity at this stage is highly inhibited, as demonstrated with permeabilized cells. Immediately upon germination, and after a transient increase in cAMP concentration from 10 microM to 90 microM, C-subunit levels fall to 30%. After the onset of germination, the specific activity and concentration of both the 5.5 S holoenzyme species and the 2.7 S species of free R subunit decrease in parallel to the increase in total protein and volume. Net synthesis of C and R subunits to form a native holoenzyme species of 8.8 S is apparent 4 h onwards after germination. A significant increase in cellular concentration is observed at 6 h. At 7 h of growth, when germ-tube emission is complete, the holoenzyme concentration is around 0.23 microM; there is almost no free R subunit and the intracellular concentration of cAMP is around 3 microM. A role for PKA during germination and morphogenesis is discussed.

TSH action on cAMP binding to the regulatory subunits of cAMP-dependent protein kinases in pig thyroid cell cultures

This study examines the mechanism of TSH action on the cAMP-dependent protein kinases (PKA) by measuring the catalytic activity of the two PKA isozymes (PKA I and PKA II) and their capacity to bind cAMP to the regulatory subunits (RI and RII) in thyroid cell cultures exposed for two days to different doses of TSH. In TSH-treated cell cultures a selective down regulation (up to 60%) of the catalytic activity was found; the PKA I was down regulated at lower TSH doses (0.1 mU/ml and even 0.05 mU/ml) than was the PKA II (1.0 mU/ml TSH). At the dose of 1.0 mU/ml the loss of the catalytic activity in PKA I and PKA II was respectively 60% and 40%. No free catalytic activity was found either in control or in TSH-treated cells. Binding of cAMP to regulatory subunits (R) measured under exchange conditions at 37 degrees C, showed that no change in total regulatory subunit protein content occurs in TSH-treated cells. Binding of cAMP to R subunits at 4 degrees C (when only free cAMP binding sites are measured) revealed an important endogenous occupancy of cAMP binding sites of RI and RII isoreceptors under basal conditions (40%) and a significantly increased occupancy after exposure of cells to TSH (60%). Pools of regulatory subunits with more than 50% of sites occupied, which were devoid of enzyme activity, were found both, in control and TSH-exposed cells. They were identified as RI subunits which represented a mixed population of native and partly degraded molecules.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of cAMP-kinase subunits is correlated with growth in rat mammary carcinomas and uterus

The expression of the regulatory (RI and RII) and catalytic (C) subunits of cAMP-dependent protein kinase was found to depend on the growth-state in oestrogen-dependent DMBA-induced mammary adenocarcinomas as well as in uteri of the rat. Castration-induced atrophy of the oestrogen-dependent tissues was accompanied by a decrease of the concentration of regulatory subunits (RI and RII) relative to both the catalytic subunit (C) and total protein, decreasing the R/protein and R/C ratios. A hyperplastic burst caused by high-dose oestrogen-replacement treatment was associated with an increased level of RI and little change in RII and C levels. Only minor differences were noted for the expression of mRNA for the alpha and beta subtypes of RI, RII and C between rat uteri from castrated and oestrogen-treated animals, or between mammary tumours from normal and castrated animals. Expression of RI beta-mRNA was detected only in the uterus. Our findings provide an experimental correlate for the reported value of the parameter R/protein in human mammary cancer biopsies to predict prognosis and outcome of therapy. Due to the sensitivity of the R/protein ratio towards changes in extracellular protein content, we recommend the biologically more meaningful R/C ratio in further clinical evaluations of mammary tumour biopsies.

Programmed cell death (apoptosis) is induced rapidly and with positive cooperativity by activation of cyclic adenosine monophosphate-kinase I in a myeloid leukemia cell line

Programmed death (apoptosis) of the rat myelocytic leukemic cell line IPC-81 was triggered by cyclic adenosine monophosphate (cAMP) analogs or by agents (cholera toxin, prostaglandins) increasing the endogenous cAMP level. The induction of cell death by cholera toxin was preceded by increased activation of cAMP-kinase. Cell lysis started already 5 hr after cAMP challenge and was preceded by internucleosomal DNA fragmentation and morphological changes characteristic of apoptosis. The cell suicide could be prevented by inhibitors of macromolecular synthesis. cAMP analogs induced cell death in a positively cooperative manner (apparent Hill coefficient of 2.9), indicating that triggering of the apoptotic process was under stringent control. There was a strong synergism between cAMP analogs complementing each other in the activation of cAMP-dependent protein kinase I (cAKI). No such synergism was noted for analogs complementing each other in the activation of cAKII. It is concluded that apoptosis can be induced solely by activation of cAKI. The IPC-81 cells expressed about four times more cAKI than cAKII. The expression of cAK subunits, on the protein and mRNA levels, was only minimally affected by cholera toxin treatment.

Co-ordinated changes in the cyclic AMP signalling system and the phosphorylation of two nuclear proteins of Mr 130,000 and 110,000 during proliferative stimulation of the rat parotid gland by isoprenaline. Possible identity of the two proteins with pp135 and nucleolin

Parotid glands were stimulated to growth by repeated injection of the beta-agonist isoprenaline into rats. Incubation of intact parotid-gland lobules with [32P]Pi and subsequent analysis of nuclear proteins revealed in the stimulated glands an increased 32P incorporation into two acid-soluble non-histone proteins with apparent Mr values of 110,000 and 130,000 (p110 and p130). After a single injection of isoprenaline, leading to a biphasic increase in DNA synthesis (maximum at 24 h), the same two proteins showed a transiently increased 32P incorporation at 17 h after injection. At this time point at the onset of DNA synthesis the total activity of soluble cyclic AMP-dependent protein kinase decreased. No change in p110/p130 phosphorylation was observed at 0.3 h after stimulation, a time of maximal stimulation of secretion. Administration of the beta-antagonist propranolol 8 h after the injection of isoprenaline suppressed the increase in DNA synthesis, the preceding changes in the concentration of cyclic AMP and in the activity of cyclic AMP-dependent protein kinase, as well as the increased phosphorylation of p110 and p130. Cross-reactivity of p110 and p130 with specific antisera against two nucleolar phosphoproteins of similar molecular mass (nucleolin and pp135), as well as their localization in a nucleolar cell fraction, indicated a possible identity of p110 and p130 with these two proteins. Our results suggest that nucleolin and pp135 are nuclear target proteins of cyclic AMP in the cyclic AMP-influenced regulation of the transition of cells from the G1 to the S phase.