TOXICOLOGY AND APPLIED PHARMACOLOGY 116,240-247 ( 1992) Lead Inhibits Secretion of Osteonectin/SPARC without Significantly Altering Collagen or Hsp47 Production in Osteoblast-like ROS 17/2.8 Cells JOHN J. SAUK,* TIMOTHY SMITH,* ELLEN K. SILBERGELQt BRUCE A. FOWL&t AND MARTHA J. SOMERMAN# *Department ofPathology, University of Maryland Dental School. Baltimore, Maryland 21201; t Toxicology Program, Department of Pathology, University of Maryland School of Medicine, Baltimore, Maryland; and *Department of Periodontics, Prevention and Geriatrics, University of Michigan School of Dentistry, Ann Arbor, Michigan Received February 28, 1992; accepted June 8, 1992 Richter et al., 1968; Choie et al., 1975; McLachlin et al., Lead Inhibits Secretion of Osteonectin/SPARC without Sig- 1980; Shelton and Egle, 1982), two glucose regulated proteins nificantly Altering Collagen or Hsp47 Production in Osteoblast- (Shelton et al., 1986) and by deminishing the levels of the like ROS 17/2.8 Cells. SAUK, J. J., SMITH, T., SILBERGELD, bone related protein, osteocalcin (Angle et al., 1990; Long E.K.,FowLER,B. A.,AND SOMERMAN,M.J. (1992). Toxicol. Appl. Pharmacol. 116,240-247. et al., 1989, 1990). In addition to osteocalcin, there is increasing evidence In an effort to better understand the consequences of lead that other noncollagenous proteins associated with miner- (Pb’+) on skeletal growth, the effects of Pb*+ were investigated alized tissues play a critical role in the regulation of osteo- using ROS 17/2.8 bone-like cells in vitro. These studies revealed genesis. This has led to increased research emphasis on pu- that Pb2+ (4.5 X 10m6 M - 4.5 X 10M7 M) has little or no effect on cell shape except when added immediately following seeding rifying, characterizing, and identifying the role of these pro- of the cells. However, proliferation of ROS cells was inhibited, teins in the mineralization process (for reviews see Butler in the absence of serum, at concentrations of 4.5 X 10m6M Pb*+. 1985; Fisher et al.. 1987; Glimcher and Lian, 1989). Many Protein production was generally increased, however, the major of these proteins are acidic and are known to bind both Ca2+ structural protein of bone, type I collagen, production was only and hydroxylapatite, suggesting a role for them in the initial slightly altered. Following treatment of ROS cells with Pb*+, phases of mineralization. Also, some bone related proteins intracellular levels of the calcium-binding protein osteonectin/ such as osteonectin/SPARC (secreted protein, acid and rich SPARC were increased. Osteonectin/SPARC secretion into the in cysteine) mRNA have been localized to areas of active media was delayed or inhibited. Coincident with retention of tissue morphogenesis and are expressed in cells and tissues osteonectin/SPARC there was a decrease in the levels of osteo- that exhibit high rates of turnover, secretion, and remodeling nectin/SPARC mRNA as determined by Northern analysis. (Funk and Sage, 199 1). In the studies reported here we seek These studies suggest that processes associated with osteonectin/ to determine if Pb2+ alters the characteristics of ROS 17/2.8 SPARC translation and secretion are sensitive to Pb2+. o 1992 bone-like cells in vitro. Also, this study determines whether Academic Press, Inc. Pb2+ affects the production of two recognized bone matrix components, collagen and osteonectin/SPARC. Further- Lead (Pb”) is a toxic substance that is known to impair more, we examine the effect of Pb2+ on Hsp47, a resident skeletal growth even at levels of exposure for the general endoplasmic reticulum protein of cells producing type I col- population (0.75 PM) (Mooty et al., 1975; Angle and Huse- lagen (Nakai et al., 1990; Sauk et al., 1990b). man, 1989; Shukla et al., 1989; Schwartz et al., 1986; Fri- sanch and Ryan, 1991). There are several indications that MATERIALS AND METHODS Pb2+ by its interactions with calcium (Ca2+) may perturb Cell culture. Cloned bone cell lines (ROS 17/2.8) derived from AC19935 many normal calcium regulatory processes, e.g., its action rat osteosarcoma were used. These cells have the advantage that their os- as a second messenger, interactions with calcium binding teoblastic-like phenotypic characteristics are maintained in vitro (Majeska and other extracellular proteins associated with mineralized et al.. 1980). Cells were cultured in Dulbecco’s modified Eagle’s medium tissues and subcellular functions at the level of the mito- (DMEM) supplemented with 1.16 g/l glutamine, 100 units/ml penicillin, 100 &ml streptomycin, and 10% fetal bovine serum (FBS). Lead glutamate chondria, synaptosomes, and membrane vesicles. Further- was prepared by preparing a stock solution containing 4.5 X lo-’ M lead more, lead is known to affect protein synthesis (Shelton et nitrate (Sigma) and 5.0 X lo-’ M glutamic acid in water. al., 1986), particularly by increasing proteins that constitute Proliferation rate. To evaluate the effects of lead on cell proliferation, nuclear and cytoplasmic inclusion bodies (Moore et al., 1973; ROS 17/2.8 cells were seeded into tissue culture wells (35 mm Falcon), 0041-008X/92 $5.00 240 Copyright 0 1992 by Academic Press, Inc. All rights of reproduction in any form reserved. LEAD INHIBITS SECRETION OF OSTEONECTIN/SPARC 241 ~8.0 X lo3 cells/well. with DMEM supplemented with 10% FBS and an- (Kirkegaard & Perry Labs, Inc., Gaithersburg, MD) was diluted to 0.9 pg/ tibiotic and incubated overnight at 37°C. On the following day, the medium ml and incubated with the paper for 2 hr. Washing between steps was per- was removed from each well and medium added as follows: (a) DMEM + formed three times for 30 min with 50 mM Tris-HCl, 0.9 M NaCI, 0.05% 10% FBS + glutamic acid; (b) DMEM + 2% FBS + glutamic acid; (c) DMEM Tween, pH 7.4. Staining was accomplished with 4-chloro-naphthol. For + 0% FBS + ghrtamic acid; (d) DMEM + 2% FBS t lead glutamate; and Hsp47, polyclonal rabbit antibodies were prepared against a 22-mer peptide (e) DMEM t 0% FBS + lead glutamate. The effects of lead glutamate on corresponding to the N-terminal sequence of chick Hsp47 (Hirayoshi et al.. cell proliferation were evaluated at three different concentrations, 4.5 X lo-’ 199 1) that was conjugated to Keyhole limpit hemocyanin (Sauk et al., 1990b). M, 4.5 X 10m6M and 4.5 X lo-’ M. Cell proliferation, on Day 2, Day 4. and Zmmunoprecipitation. Cell layers having equal cell numbers were ho- Day 6 after seeding, was determined by trypsinizing cells and counting elec- mogenized in 2X immunoprecipitation buffer (0.2 M Tris-HCI, 0.3 M NaCl., tronically using a Coulter counter. 2% Triton X-100, 2% deoxycholate, 0.2% SDS, pH 7.2) and diluted with Determination of total protein and collagen production. The methods cold distilled water to 1 X. while the culture media was diluted 3: 1 with 4X for labeling cells have been reported previously (Somerman et al.. 1987). immunoprecipitation buffer. The homogenates and media were then cen- Briefly, 1.0 X lo4 cells per test well (Falcon, 35-mm wells) were seeded in trifuged for 5 min at 10,OOOgin an Eppendorfcentrifuge and a 50-r] sample wells in DMEM with 10% FBS and antibiotics. After cells attached and of the radiolabeled supernatant was added to a mixture of GammaBind G- spread, medium was removed and cells were incubated for 48 hr in serum- Agarose (Genex, Gaithersburg, MD) and antibody in PBS-azide. The samples free DMEM with 20 &i/ml L-5-[3H]proline and (a) glutamic acid (control) were then incubated at 4°C with constant shaking and then centrifuged at or(b) 4.5 X 1O-6 M lead glutamate. Media and cell samples were then dialyzed 10,OOOg for 10 min. The resulting immunoprecipitate pellets were then extensively against cold buffer (pH 7.4,0.05 M Tris-HCI, 0.2 M NaCI, 0.005 washed twice with PBS-azide. The final pellets were suspended in 2X gel M CaCl,). Following dialysis, aliquots of these samples were counted in a electrophoresis sample buffer, heated for IO min at 90°C. and then centrifuged liquid scintillation spectrometer (Packard Tri Carb 460C) in Aquasol- (New to remove GammaBind G-agarose. Samples ofthe supematants were counted England Nuclear (NEN) Boston. MA). These counts represented total non- in a scintillation counter and another sample analyzed by PAGE and au- dialyzable radioactive material and were taken as a measure of total protein toradiography as described above. Autoradiograms were densitometrically production. scanned and data were reported as ratio of treated to control samples. To estimate collagen production, an ahquot of the above dialyzed material Northern analysis. Total RNA from 4 X lo6 ROS 17/2.8 cells was sol- was reacted for 6 hr at 37°C with chromatographicahy purified bacterial ubilized in 500 ~14 M guanidinium thiocyanate containing 25 mM sodium collagenase (Form III, Advance Biofactures) according to methods of Pe- acetate (pH 5.0) and 100 IIIM fl-mercaptoethanol, transferred to an Eppendorf terkofsky and Diegelmann ( 197 1). Undigested proteins were precipitated tube containing 20-pg of calf liver tRNA, and precipitated by addition of with 5% trichloroacetic acid/0.5% tannic acid and samples were centrifuged. 450 r.d of 100% ethanol. RNA pellets were reprecipitated in the presence of An aliquot of the supernatant was counted in Aquasol- (NEN) with a liquid 80% ethanol containing 100 mM sodium acetate (pH 5.0) at -20°C. and scintillation counter. To provide a background value for the collagenase equal amounts of RNA were immediately loaded onto Northerns. RNA assays, additional aliquots of dialyzate were treated as above except that was transferred to nitrocellulose and bound to the paper by baking at 80°C bacterial collagenase was excluded from these samples.