Receptors for 1,25(OH)2-vitamin D3 enriched in cloned osteoblast-like rat osteogenic sarcoma cells.
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Acid Phosphatase↗
Biomedical subjects
N C Partridge
Publications and source records attributed to N C Partridge.
Insulin inhibition of protein degradation in cell monolayers.
Protein degradation has been measured in confluent monolayers of eleven lines of contact-inhibited cells and ten transformed lines as the rate of release of trichloroacetic acid-soluble radioactivity after prelabeling cell protein with [3H]leucine. Insulin, at contrations from 10(-12) M to 10(-6) M, has been added at the beginning of the 4-hour degradation period to detect selective effects of this hormone as an inhibitor of the inducible proteolysis occurring in serum-free medium. In addition insulin binding measurements have been performed on selected cell lines in an attempt to relate receptor properties to insulin action. Substantial effects of insulin are found in most cells with a selective inhibition at low insulin concentrations noted in several of the transformed lines. The difference in insulin sensitivity is not entirely definitive because temperature-sensitive transformation mutants of NRK cells are not more sensitive to insulin at a temperature where they show the transformed phenotype. Although insulin receptors on different cell lines have similar binding properties, two of the hepatomas used, H35 and MH1C1, show inhibition of protein degradation at insulin concentrations where receptor occupancy is extremely low. Calvarial osteoblast-like cells have a high rate of protein degradation which can be reduced by growth factors but not by insulin. The lack of an insulin response is a consequence of poor insulin binding to the cells. Insulin binds to the osteogenic sarcoma cells in substantial amounts. However, its normal action to inhibit the induced proteolysis is restricted because with these cells no increase of proteolysis occurs in serum-free medium. Generally higher rates of protein degradation are observed in the contact-inhibited lines than the transformed cells. We suggest that this difference may provide a selective growth advantage to transformed cells.
Animals↗
Premature induction of glucokinase in the neonatal rat by thyroid hormone.
1. It was shown that the development of liver glucokinase in the rat coincided with a peak in the levels of circulating thyroid hormone at about the 16th postnatal day. 2. Administration of thyroid inhibitors blocked the development of the enzyme and administration of thyroid hormone restored activity to normal levels. 3. Glucokinase could be induced prematurely as early as the 2nd postnatal day by the administration of thyroid hormone followed by daily injection of glucose (10 mg/g body weight). 4. Glucocorticoids and corticotropin failed to induce glucokinase activity prematurely. 5. The postnatal increase in circulating thyroid hormone levels together with increased intake of carbohydrate at weaning may be the normal physiological stimulus for induction of this enzyme.
Adrenocorticotropic Hormone↗
New concepts in bone remodeling: an expanding role for the osteoblast.
Until recently, the prevailing view regarding the function of osteoblasts and osteoclasts was to attribute bone formation to the former and bone resorption to the latter. While the capacity of the osteoclast to degrade bone matrix remains unquestioned, there is now provocative evidence indicating that the osteoblast plays a critical role in regulating osteoclast resorptive activity as well as in contributing directly to matrix dissolution. The first of these points follows from observations indicating that the osteoblast (but not the osteoclast) 1) exhibits receptors and/or responses to resorption-promoting agents (including parathyroid hormone and vitamin D), and 2) releases agents capable of stimulating bone resorption. The second point is derived from studies demonstrating that the osteoblast produces neutral collagenase (an enzyme specialized to degrade type I collagen, the principal organic constituent of bone matrix) and an inhibitor capable of blocking collagenase activity. The synthesis of both of these proteins is, in part, regulated by parathyroid hormone and other resorption-stimulating agents and appears to involve control at the transcriptional, translational, and secretory levels. Thus, in both physiologic bone remodeling and modeling, as well as the altered bone turnover associated with some disease states, it is the osteoblast rather than the osteoclast that may hold the key to understanding the mechanism of tissue form and function.
Bone Resorption↗