Human serum alpha 2HS-glycoprotein modulates in vitro bone resorption.

We previously isolated a family of bone-resorbing proteins from human cancer ascites fluid and established that the three purified bone-resorbing proteins were chemically and immunochemically related to each other and to alpha-2HS glycoprotein (alpha 2HS). After this finding we purified the normal human serum counterpart of these ascites proteins and studied its effects on bone resorption. The bone-resorbing properties of normal human serum alpha 2HS were examined in vitro over a wide dose range. This normal human serum glycoprotein had a biphasic effect on 45Ca2+ release from bone. More specifically, this protein stimulated bone resorption at the lower concentrations tested, with a maximum effect [treated over control ratio of 2.5 +/- 0.30 (+/- SE); P less than 0.01] at 40 micrograms/mL. In contrast, at doses above 40 micrograms/mL, a sharp decline in calcium mobilization occurred, with a return to baseline occurring above 80 micrograms/mL. These results suggest that serum alpha 2HS may participate in the regulation of bone metabolism in vivo.

Three forms of BRP-2 (bone resorptive proteins) from human cancer ascites fluid and their relationship to human serum alpha-2 HS-glycoprotein.

Two new forms of BRP-2, a previously described bone resorptive protein, were purified from ascites fluids obtained from patients with hypercalcemia and metastatic bone cancer. The apparent molecular weights of BRP-2 and of these two proteins were 52,000, 48,000, and 46,000, respectively, as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The three proteins have essentially the same amino acid compositions but differ with respect to their carbohydrate moieties. The amino-terminal amino acid sequences of the three glycoproteins were identical to each other as well as to human serum alpha 2HS-(human serum) glycoprotein. The relationship of the three forms of BRP-2 to alpha 2HS was also established immunochemically. The ascites proteins, as well as alpha 2HS, on a molar basis, were approximately one-tenth as potent as bovine parathyroid hormone fragment (1-34) in their abilities to stimulate calcium release from bone in vitro. This study describes for the first time a possible function for human serum alpha 2HS.

Purification and partial characterization of a Mr 52,000 glycoprotein from human cancer ascites fluid which stimulates bone resorption in vitro.

A glycoprotein which stimulates bone resorption in vitro has been purified at least 375-fold from human cancer ascites fluid. Purification was accomplished utilizing fractionation with ammonium sulfate, anion exchange chromatography, high-performance size exclusion chromatography, adsorptive chromatography on hydroxylapatite, and high-performance anion exchange chromatography. The homogeneous bone-resorptive protein possesses an apparent molecular weight of 52,000 as calculated from electrophoresis in sodium dodecyl sulfate:polyacrylamide gels. On polyacrylamide gels at pH 8.9 in the absence of sodium dodecyl sulfate, the bone-resorptive protein migrates with the mobility of an alpha 2-globulin. The amino acid composition of this protein is marked by the absence of methionine and by a relatively high content of nonpolar amino acids. The protein possesses a single amino- and a single carboxyl-terminal amino acid, alanine, and leucine, respectively. The carbohydrate moiety, comprising 20% of the total weight, consists of neutral hexoses, galactosamine and glucosamine, and sialic acids. With respect to its biological activity, the ascites glycoprotein is one-fourth as potent as parathyroid hormone, on a molar basis, in its ability to stimulate calcium release from bone explants in vitro. Calcium release is significantly decreased on heating at 60 degrees C but is not inhibited by indomethacin.

Purification and partial characterization of a protein from cancer ascites fluid which stimulates the resorption of bone explants in vitro.

A protein capable of stimulating bone resorption in vitro has been purified approximately 1250-fold from cancer ascites fluid. Purification was accomplished employing successive fractionation with ammonium sulfate, ion exchange, and Cibacron blue affinity chromatography, isoelectric focusing, and selective adsorption on hydroxylapatite. The bone-resorptive protein obtained by this procedure appeared homogeneous in polyacrylamide gels at pH 9.5, migrating with the mobility of an alpha 2-globulin, and in sodium dodecyl sulfate polyacrylamide gels from which an apparent molecular weight of 43,000 was calculated. The amino acid composition of the bone-resorptive protein distinguished itself by the absence of methionine and by its relatively high content of glycine (17%) and proline (11%). Furthermore, the protein possesses a single NH2-terminal amino acid residue (glycine). The ascites protein was found to contain 19% carbohydrate by weight including a high content of sialic acid (15 residues/mol) as compared to the other sugars (27 residues/mol). As to its biological properties, the homogeneous ascites glycoprotein proved to be as potent as parathyroid hormone in its ability to stimulate bone resorption in vitro.

Isolation of a bone-resorptive factor from human cancer ascites fluid.

A protein fraction that induces the resorption of bone explants in organ culture was isolated from the ascitic fluid of patients with advanced cancer metastatic to the peritoneal cavity. Partial purification was achieved by means of gel filtration, affinity chromatography, and ion-exchange chromatography. The isolated fraction, the components of which have an apparent molecular weight of 60,000, was found to be heterogeneous by disc gel electrophoresis and to be composed primarily of proteins with relatively acidic electrophoretic properties. The specific bone-resorptive activity of this protein fraction was greatly increased over that of the unfractionated starting material, and the activity could be completely destroyed upon incubation with pronase and on heating. As determined by immunoassay and extraction procedures with various solvents, the bone-resorptive action of the isolated fraction was not attributable to the presence of parathyroid hormone, prostaglandin E2 or vitamin D-like sterols. In parallel experiments the supernatants of phytohemagglutinin-stimulated normal human peripheral leukocytes were subjected to identical chromatographic techniques, and a proten fraction with a molecular weight of 60,000, which resembled the resorptive fraction isolated from cancer ascites fluid and which contained significant bone-resorptive activity, was also partially purified.

Effects of prostaglandins and other drugs on the cyclic AMP content of cultured bone cells.

Prostaglandins of the E-series (PGE1 and PGE2) may be involved in disease-related, localized loss of bone. E-prostaglandins increase the cyclic AMP content of many cells; and, to determine if their effects on bone are mediated by cyclic AMP, we examined the effects of E-prostaglandins and of other agents on the cyclic AMP content of cultured bone cells. PGE2 produced a rapid, marked and dose-related increase in the cyclic AMP content of confluent monolayers of bone cells isolated from newborn rat calvaria. At 2.8 X 10(-6) M, PGE1 and PGE2 had approximately the same effect, while the effect of PGF2alpha was much less pronounced. In the presence of theophylline, PGE2 had a more marked effect than parathyroid hormone (PTH) and the combination of PGE2 and PTH had a synergistic effect. The divalent, cationic, ionophore, A23187, produced an increase in cellular cyclic AMP and had an additive effect in combination with PGE2. Synthetic salmon calcitonin (CT), which inhibits the bone resorptive effect of PGE2, increased cellular cyclic AMP and had an additive effect in combination with PGE2. A prostaglandin antagonist, SC-19220, partially inhibited the resorptive effect of PGE2 and reduced its effect on cellular cyclic AMP. The calcium antagonist, D600, inhibited the bone resorptive effects of PGE2 but had no effect on increased cellular cyclic AMP produced by PGE2. The marked effect of PGE2 on bone cell cyclic AMP suggests that this action is involved in the mechanism of PGE2-related bone loss. The fact that agents with different effects on PGE2-induced increases in cellular cyclic AMP can inhibit its resorptive actions, suggests that PGE2-induced changes in cyclic AMP may be related less to its resorptive actions than to its inhibitory effect on bone formation.