Bone sialoprotein, matrix metalloproteinase 2, and alpha(v)beta3 integrin in osteotropic cancer cell invasion.
BACKGROUND
Bone sialoprotein (BSP) interacts separately with both matrix metalloproteinase 2 (MMP-2) and integrin alpha(v)beta3 and is overexpressed in many metastatic tumors. Its role in tumor biology, however, remains unclear. We investigated whether BSP enhances cancer cell invasiveness by forming a trimolecular complex with MMP-2 and cell-surface integrin alpha(v)beta3.


METHODS
Invasiveness of breast, prostate, lung, and thyroid tumor cell lines was measured with a modified Boyden chamber assay. Binding and co-localization of BSP, MMP-2, and integrin alpha(v)beta3 were investigated with immunoprecipitation and in situ hybridization. All statistical tests were two-sided.


RESULTS
Treatment with BSP increased invasiveness of many breast, prostate, lung, and thyroid cancer cells through Matrigel in a dose-dependent manner. BSP at 50 nM increased the invasiveness of SW-579 thyroid cancer cells (95.2 units, 95% confidence interval [CI] = 90.4 to 100 units) by approximately 10-fold compared with that of untreated control SW-579 cells (9.1 units, 95% CI = 5.7 to 12.5 units) (P<.001). Addition of an inactive mutated BSP, in which BSP's integrin-binding RGD tripeptide was altered, or addition of integrin alpha(v)beta3-blocking antibodies resulted in invasiveness equivalent to that of untreated cells. Inhibiting cellular MMP-2 activity with chemical inhibitors or a specific antibody also blocked BSP-enhanced invasiveness. Osteopontin and dentin matrix protein 1, proteins related to BSP that also bind integrin alpha(v)beta3 and form complexes with other MMPs (but not MMP-2), did not enhance invasiveness. Immunoprecipitation showed that a complex containing BSP, integrin alpha(v)beta3, and MMP-2 formed in vitro. Addition of BSP increased the amount of MMP-2 bound by cells in an integrin-dependent fashion. Co-expression of BSP, integrin alpha(v)beta3, and MMP-2 in papillary thyroid carcinoma cells was shown by in situ hybridization.


CONCLUSIONS
Cancer cells appear to become more invasive when BSP forms a cell-surface trimolecular complex by linking MMP-2 to integrin alpha(v)beta3.
Karadag
Abdullah
A
Craniofacial and Skeletal Diseases Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892-4320, USA. akaradag@dir.nidcr.nih.gov
Ogbureke
Kalu U E
KU
Fedarko
Neal S
NS
Fisher
Larry W
LW
D001859:Bone Neoplasms / Q000378:metabolism / Q000556:secondary*; D001943:Breast Neoplasms / Q000378:metabolism; D045744:Cell Line, Tumor; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D017403:In Situ Hybridization; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D058574:Integrin-Binding Sialoprotein; D008175:Lung Neoplasms / Q000378:metabolism; D008297:Male; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D009361:Neoplasm Invasiveness; D009369:Neoplasms / Q000378:metabolism*; D012516:Osteosarcoma / Q000378:metabolism; D011233:Precipitin Tests; D011471:Prostatic Neoplasms / Q000378:metabolism; D012795:Sialoglycoproteins / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000378:metabolism
C546871:IBSP protein, human; D039302:Integrin alphaVbeta3; D058574:Integrin-Binding Sialoprotein; D012795:Sialoglycoproteins; D020778:Matrix Metalloproteinase 2