Osteogenic potential of murine osteosarcoma cells: comparison of bone-specific gene expression in in vitro and in vivo conditions.
Bone tissue formation and the expression of osteoblast-specific genes were compared in vitro and in vivo for two well characterized murine clonal osteosarcoma cell lines (K7 and K8). In vitro studies were carried out under conditions that promoted extracellular matrix morphogenesis and mineralization. The K8 cells showed 8-fold greater alkaline phosphatase activity and mineral accumulation than did K7 cells during 21 days of in vitro growth. The K8 cell line showed high levels of bone sialoprotein (BSP), collagen type I (COL I), and alkaline phosphatase (APase) mRNA expression throughout its growth in vitro. In contrast, K7 cells showed an almost complete absence of BSP and COL I and very low levels of APase throughout the culture period. In vitro, both cell lines expressed very low levels of osteocalcin (OC). For in vivo studies, we used a three-dimensional culture device that permitted analysis of tissue formation by the cells after their implantation into syngeneic mice. The K8 cells consistently generated extensive mineralized woven bone after their subcutaneous implantation. The striking features distinguishing the bone formed by the implanted cells from normal recipient bone were the complete absence of osteoclasts or matrix resorption, the absence of OC protein, and very low levels of OC mRNA expression in the tissues formed by these cell lines. BSP, APase, and COL I expressions were maintained at high levels in the K8-produced tissues. In contrast to their near absence in vitro, APase, BSP, and COL I were expressed by K7 cells and increased with time in vivo. These findings demonstrate that the K7 cells in vitro are less differentiated than K8 cells, but that K7 cells in vivo undergo osteogenic maturation. Thus, expression of bone-specific genes in these osteogenic cell lines was dependent on systemic or local factors in recipient animals and was distinct for these cell lines when grown under in vitro conditions. OC protein does not appear to be needed for the mineralization of the extracellular matrix but may be needed to provide the necessary signals for the resorption and remodeling of the tissue.
Gerstenfeld
L C
LC
Laboratory for the Study of Skeletal Disorders and Rehabilitation, Children's Hospital, Boston, Massachusetts 02115, USA.
Uporova
T
T
Schmidt
J
J
Strauss
P G
PG
Shih
S D
SD
Huang
L F
LF
Gundberg
C
C
Mizuno
S
S
Glowacki
J
J
D000469:Alkaline Phosphatase / Q000235:genetics; D000818:Animals; D001857:Bone Matrix / Q000378:metabolism; D001859:Bone Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002113:Calcification, Physiologic; D002118:Calcium / Q000032:analysis; D003094:Collagen / Q000235:genetics; D004587:Electrophoresis, Agar Gel; D015870:Gene Expression; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D015675:Osteocalcin / Q000032:analysis / Q000235:genetics; D010012:Osteogenesis; D053495:Osteopontin; D012516:Osteosarcoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D012313:RNA / Q000032:analysis / Q000235:genetics; D012795:Sialoglycoproteins / Q000235:genetics; D014407:Tumor Cells, Cultured
D012795:Sialoglycoproteins; C506896:Spp1 protein, mouse; D015675:Osteocalcin; D053495:Osteopontin; D012313:RNA; D003094:Collagen; D000469:Alkaline Phosphatase; D002118:Calcium