The Matrix Biochemistry Section?s research focuses on the functions of five major noncollagenous proteins found in the mineralized matrix of bones and teeth. These include: bone sialoprotein (BSP); osteopontin (OPN); dentin matrix protein 1 (DMP1); dentin sialophosphoprotein (DSPP); and matrix extracellular phosphoglycoprotein (MEPE). We have made a strong case for the genetic relatedness of these seemingly different proteins and have called them the SIBLING (Small Integrin-Binding LIgand, N-linked Glycoprotein) family. The genes encoding these proteins are all clustered in a tandem fashion within a short stretch of human chromosome 4, have similar exon-intron structures, and are likely a result of gene duplication and subsequent divergence millions of years ago. One of the few conserved motifs among the different SIBLING members and among animal species for any single protein is the integrin-binding tripeptide, arginine-glycine-aspartate (RGD). In recent years we have shown that at least three members of the SIBLING family bind and activate three different members of the matrix metalloproteinase (MMP) family further suggesting that these proteins are functionally related.? ? While generally thought to be limited to bones and teeth, we and our collaborators have shown over the last decade that BSP, OPN and DMP1 are frequently highly expressed in a number of specific cancers. Continuing in this line of research, it has now been shown that DSPP, once considered to be specific to the dentin portion of teeth, is highly expressed in prostate cancer but not in the normal gland. In fact the level of DSPP expression was positively correlated with the severity of the tumor as measured by both pathological stage and Gleason score. Given our past successes with correlating the blood levels of SIBLING proteins BSP and OPN with tumor expression, we will investigate the possibility of using serum DSPP levels as an adjunct marker with PSA for prostate cancer detection and to monitor any unfortunate return of the tumor after treatment.? ? Earlier we had shown that BSP could not only bind and activate highly purified matrix metalloproteinase-2 (MMP-2) but also enhanced the ability of many type of cancer cells to penetrate an artificial basement membrane barrier in a model of cancer metastasis. Cells derived from breast, prostate, lung, and thyroid cancers could all use BSP to be more invasive in this assay. Now we have shown that normal bone precursor cells can also use BSP to enhance their ability to move through model matrix barriers. Bone is made by mature cells called osteoblasts. They are derived from stem cells that reside in the marrow. The stem cell divides and one more highly committed cell migrates out of the marrow space toward the bone surface. Along the way the migrating cell develops into a preosteoblast which upon receiving the proper signal, then migrates to the bone surface and matures into the matrix-producing osteoblasts. During this migration process, the cells probably must traverse matrix barriers. Our results suggest that BSP bridges the matrix-destroying enzyme, MMP-2, to the cell surface of both the pluripotent bone marrow fibroblast and the preosteoblast where it can best aid the cells? migration through matrix barriers. This may be the normal process that cancer cells mimic when metastasizing from the primary tumor to distant sites.? ? The up regulation of BSP expression in both normal and cancer cells is an important area of study. In most cases, a cancer patient suffers the most and often dies due not to the primary tumor itself, but due to complications from secondary sites of invasion during late stage metastasis. One hypothesis is that the ability to turn off BSP production by cancer cells may help prevent metastasis of the disease to distant locations in the body. BSP had been known for several years to be up regulated by transforming growth factor beta (TGF-b). Furthermore in carcinogenesis, TGF-b is known to function as a prometastatic factor in late stage disease. Working with our colleagues in the NCI, it was shown that treatment with a neutralizing monoclonal antibody to TGF-b significantly suppressed metastasis of a breast cancer cell line injected into syngeneic mice. When the cells were recovered from the lungs of treated and untreated mice, the most differentially expressed gene was BSP. Cells from the less aggressive, monoclonal-treated tumors expressed much less BSP than cells from the untreated and more aggressive tumors. Down regulation of BSP in the cancer cell line by siRNA reduced the ability of the original cell line to degrade matrix barriers in vitro and reduced the number of lung tumors in the mice. Thus BSP is not only an excellent marker for numerous cancer studies, it can now be considered a target for treatments that may lessen a tumor?s ability to metastasize.? ? The Matrix Biochemistry Unit freely gives probes (antisera, cDNA, proteins etc.) to any laboratory in the world that makes a reasonable request. In FY05 we sent ~250 probes to nearly 100 laboratories (20% were in the dental field) around the world. Others in the Branch have sent these same probes during this time as well.
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