Changes in cAMP-dependent and Ca2(+)-phospholipid-dependent protein kinase activities in suspension cultures of porcine thyroid cells

Interleukin-1beta (IL-1beta) induces a crosstalk between cAMP and ceramide signaling pathways in thyroid epithelial cells

Interleukin-1 beta (IL-1beta) is an important regulator of the thyroid cell function. This cytokine has been largely described to trigger an important biological signaling cascade: the sphingomyelin/ceramide pathway. In this report, we show that IL-1beta induces the transient activation of a neutral sphingomyelinase in porcine thyroid cells. Moreover, IL-1beta and ceramides are demonstrated to inhibit the TSH-induced cAMP production via the implication of alphaGi subunit of the adenylyl cyclase system. This crosstalk between cAMP and ceramide pathways constitutes a preponderant process in the TSH-controlled differentiation state of thyrocytes. All these results argue for the involvement of ceramides and IL-1beta in the thyroid function regulation, leading to a cell dedifferentiated state.

Forskolin mimics TSH action on the expression of protein kinase C isozymes in pig thyroid cell cultures

In porcine thyroid cell cultures, phospholipid-dependent protein kinases (PKCs) have the same characteristics as intact glands. The overall PKC activity, presence of PKC isozymes, chromatographic pattern and endogenous substrates specificity were not modified during the two-day culture period. Three PKC isozymes (cPKC epsilon, nPKC epsilon and aPKC zeta) were identified by immunoblot analysis in the two subcellular fractions: cytosol and particulate extract, both in intact glands and two-day-old cultures. In cells cultured for two days in the presence of TSH (0.1 mU/ml), the overall PKC activity was stimulated (ca. 200%) in the two compartments. This stimulation was parallel to the increase in protein expression of the three PKC isoforms (as demonstrated by immunoblot analysis) and was accompanied by a redistribution of cPKC alpha and nPKC epsilon toward the particulate fraction. In TSH-treated cells, hydroxyapatite chromatography of cytosolic PKC revealed an additional peak of PKC activity eluted at 195 mM potassium phosphate. Its elution molarity did not correspond to the molarity of any known PKC isozyme, and it did not cross-react with antibodies directed against cPKC isozymes--: alpha, beta, or gamma. When TSH was replaced by forskolin (10(-5) M), identical quantitative and qualitative modifications were obtained, suggesting that, in thyroid cells, the cyclic AMP-dependent regulatory cascade could be involved in the control of PKC isoforms expression by TSH.

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)

Protein kinase C activity in human thyroid carcinoma and adenoma

Protein kinase C (PKC) activity was examined in the cytosolic and particulate fractions of homogenates obtained from 12 papillary thyroid carcinomas, 12 follicular thyroid adenomas, and the adjacent normal thyroid tissue. Particulate PKC activity was elevated significantly in thyroid carcinomas compared with normal thyroid tissue (P < 0.01) and adenomas (P < 0.05). By contrast, cytosolic PKC activity of carcinomas and adenomas was lower significantly than that of normal thyroid tissue (P < 0.01). The percentage of particulate PKC activity in carcinoma and adenoma was higher than in normal thyroid tissue (carcinoma, P < 0.001; adenoma, P < 0.01). The average particulate PKC activity of carcinomas more than 3 cm in diameter was significantly lower than that of carcinomas less than or equal to 3 cm in diameter (P < 0.05). The average cytosolic PKC activity of carcinomas more than 3 cm also was lower significantly than that of smaller carcinomas (P < 0.05). These results suggest that alterations in PKC activity may be important in the development of papillary thyroid cancer.