An osteopontin fragment is essential for tumor cell invasion in hepatocellular carcinoma.
Tumor cell invasion is a primary event in the metastatic progression of hepatocellular carcinoma (HCC). Our recent results indicate a concordant elevated expression of osteopontin (OPN) and matrix metalloproteinase-9 (MMP-9) in primary metastatic HCC. This study hypothesizes an MMP-9-directed cleavage of OPN that biologically contributes to HCC metastasis. We found that MMP-9 cleaved OPN into specific fragments in vitro, of which three could be identified by Edman degradation amino-acid sequencing. One of these fragments (OPN-5 kDa, residues 167-210) induced low-metastatic HCC cellular invasion via CD44 receptors, which was effectively blocked by the addition of small peptides within the region of OPN-5 kDa. Increased expression of an OPN splice variant (OPN-c) was associated with clinical metastatic HCC. Overexpression of OPN-c with physiological levels of MMP-9 enhanced cellular invasion and coincided with elevated OPN-5 kDa levels. Our data suggest that an alternative splicing event (OPN-c) promotes extracellular cleavage of OPN by MMP-9, thus releasing a distinct region of OPN (OPN-5 kDa) that is essential for HCC cellular invasion and appears to correlate with metastatic potential. The findings of this study may help to improve advanced-stage HCC prognosis and suggest the utility of small peptides for novel therapies.
Takafuji
V
V
Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4258, USA.
Forgues
M
M
Unsworth
E
E
Goldsmith
P
P
Wang
X W
XW
D017398:Alternative Splicing; D000818:Animals; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000556:secondary*; D002448:Cell Adhesion; D002465:Cell Movement; D002846:Chromatography, Affinity; D018450:Disease Progression; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism; D047468:Immunoprecipitation; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D009361:Neoplasm Invasiveness; D053495:Osteopontin / Q000502:physiology*; D010446:Peptide Fragments / Q000502:physiology*; D011379:Prognosis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
D018960:Hyaluronan Receptors; D010446:Peptide Fragments; D012333:RNA, Messenger; D053495:Osteopontin; D020780:Matrix Metalloproteinase 9