Jeffrey R. Jasper

Tissue- and subunit-specific regulation of G-protein expression by hypo- and hyperthyroidism

Thyroid hormone status has profound effects on signal transduction in various tissues throughout the body. Therefore, we quantified the signal transducing G-proteins in the rat heart, cerebral cortex, vas deferens and liver by immunoblotting and pertussis toxin labeling in response to chemically induced hypothyroidism (treatment with propylthiouracil) and hyperthyroidism (treatment with triiodothyronine). Levels of the pertussis toxin (PTX) substrates Gi alpha and Go alpha in the heart and vas deferens were inversely correlated with thyroid hormone levels, i.e. Gi alpha and Go alpha were decreased or unchanged in hyperthyroid rats and increased in hypothyroid rats compared to control animals. The cerebral cortex and liver expression of PTX substrates Gi alpha and Go alpha was not affected by changes in thyroid hormone. Regulation of Gs alpha protein was more complex in that Gs alpha was unaffected in the other tissues tested. Expression of G-protein beta-subunits was not affected by thyroid status in the heart, liver, or cerebral cortex. Our results suggest that tissue- and G-protein-specific factors are involved in the regulation of G-protein subunits by thyroid hormone. Moreover, cardiac expression of Gs alpha is upregulated by increases or decreases in the normal level of thyroid hormone.

Decreased serum insulin-like growth factor-I associated with growth failure in newborn lambs with experimental cyanotic heart disease.

To determine whether chronic hypoxemia results in alterations in endocrine function that may contribute to growth failure, we measured growth hormone (GH), somatomedins (insulin-like growth factors I and II, IGF-I and IGF-2), hepatic growth hormone receptors, and circulating IGF-binding proteins IGFBP-3 and IGFBP-2 in 12 newborn lambs with surgically created pulmonic stenosis and atrial septal defect, and in 10 controls. During chronic hypoxemia (oxygen saturation of 60-74% for 2 wk), weight gain was 60% of control (hypoxemic, 135 +/- 20 vs. control, 216 +/- 26 g/d, P less than 0.02). IGF-I was decreased by 43% (hypoxemic 253.6 +/- 29.3 SE vs. control 448.0 +/- 75.5 ng/ml, P = 0.01), whereas GH was unchanged (19.9 +/- 5.1 vs. 11.9 +/- 3.0 ng/ml, NS). The increase in IGF-1 was associated with a decrease in IGFBP-3 (hypoxemic, 5.09 +/- 1.25 vs. control, 11.2 +/- 1.08 arbitrary absorbency units per mm (Au.mm), P less than 0.01), and increase in IGFBP-2 (0.47 +/- 0.03 vs. 0.19 +/- 0.13 Au.mm, P less than 0.05), but no significant downregulation of hepatic GH receptors (hypoxemic, 106.1 +/- 20.1 vs. control, 147.3 +/- 25.9 fmol/mg, NS). Thus, chronic hypoxemia in the newborn is associated with a decrease in IGF-I and IGFBP-3 in the face of normal GH. This suggests peripheral GH unresponsiveness, similar to protein-calorie malnutrition or GH receptor deficiency dwarfism, but mediated at a level distal to the hepatic GH receptor.

Transcriptional regulation of left ventricular beta-adrenergic receptors during chronic hypoxia.

beta-Adrenergic receptor downregulation is the end result of cellular adaptation to prolonged agonist exposure. The factors mediating receptor downregulation include receptor phosphorylation, receptor movement from the plasma membrane to intracellular sites, and alterations in nascent receptor synthesis. We have previously demonstrated a downregulation of the left ventricular beta-receptor during chronic hypoxia in vivo. To determine the mechanism of this downregulation, we produced chronic hypoxia in seven newborn lambs by creating right ventricular outflow obstruction and an atrial septal defect. Oxygen saturation was reduced to 65-74% for 2 weeks. Six lambs served as normoxic controls. Sarcolemmal membrane and cytosolic fractions were prepared from left ventricular free wall samples. beta-Receptor density in each fraction was determined with the radioligand [125I]iodocyanopindolol. Steady-state levels of beta-receptor mRNA were determined by Northern blot analysis using a beta 1-adrenergic receptor cDNA probe. During chronic hypoxia, left ventricular membrane beta-adrenergic receptor density decreased by 55% (153 +/- 28 fmol/mg for hypoxic lambs versus 342 +/- 79 fmol/mg for control lambs, p < 0.05). There was no corresponding increase in beta-receptor density in the cytosolic fraction (23 +/- 3 fmol/mg for hypoxic lambs versus 33 +/- 9 fmol/mg for control lambs, p = NS), nor was there a significant change in the ratio of beta 1-receptor/beta 2-receptor subtypes as assessed by radioligand binding (beta 1 subtype, 84.1 +/- 10.1% for hypoxic lambs versus 93.2 +/- 8.8% for control lambs; p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Primary structure of the mouse β1-adrenergic receptor gene

Abstract The mouse β 1 - adrenergic receptor was isolated from a genomic library and cloned into pBluescript SK − . Characterization of the clone revealed an open reading frame which encodes a predicted protein of 466 amino acids. The mouse β 1 receptor is 92.7% identical to the human sequence, 98.5% identical to the rat sequence, and contains a consensus site for N-linked glycosylation at Asn-15 and a cAMP-dependent protein kinase phosphorylation site at Ser-301.