Osteoblastic differentiation and P-glycoprotein multidrug resistance in a murine osteosarcoma model.
A recent study of multidrug resistance (MDR) 1 gene transfected osteosarcoma cells found a cause-effect relationship between increased expression of P-glycoprotein (P-gp) and a low aggressive phenotype. However, several experimental and clinical studies have observed contradictory findings in that P-gp expression has been associated with tumour progression. In the present study, we characterized P-gp-positive and P-gp-negative single-cell clones of a murine osteosarcoma, to further investigate the relationship between P-gp expression and changes in cell phenotype. Although these clones were all selected by doxorubicin (DOX) exposure, they were heterogeneous with respect to MDR1 gene expression. The P-gp-positive clones revealed MDR phenotype, whereas the P-gp-negative clones showed no resistance to drugs. Morphological and functional analysis showed that both the P-gp-positive and P-gp-negative clones were more differentiated than the parent cells in terms of enhanced activity of cellular alkaline phosphatase, an increase in well-organized actin stress fibres and enhanced osteogenic activity. Moreover, these subclones all displayed a decrease in malignant potential such as oncogenic activity, tumour growth rate and metastatic ability, regardless of their P-gp status. These results indicate that the observed osteoblastic differentiation and less aggressive phenotype in DOX-selected osteosarcoma cells may not only be explained by the direct effect of P-gp, and accordingly, consideration of the effect of DOX, as well as P-gp, appears to be important.
Takeshita
H
H
Department of Orthopaedic Surgery, Kyoto Prefectural University of Medicine, Japan.
Kusuzaki
K
K
Murata
H
H
Suginoshita
T
T
Hirata
M
M
Hashiguchi
S
S
Ashihara
T
T
Gebhardt
M C
MC
Mankin
H J
HJ
Hirasawa
Y
Y
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis* / Q000235:genetics; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D002454:Cell Differentiation; D002471:Cell Transformation, Neoplastic; D004195:Disease Models, Animal; D004317:Doxorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D051379:Mice; D010006:Osteoblasts / Q000166:cytology*; D012516:Osteosarcoma / Q000473:pathology*; D010641:Phenotype; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D004317:Doxorubicin