The Matrix Biochemistry Unit has been directed by Dr Larry W. Fisher directly working with Dr. Abdullah Karadag (Research Fellow, VP), Dr. Kalu Ogbereke (NIDCR Clinical Research Fellow) and an IPA, Dr. Neal S. Fedarko (Johns Hopkins Univ.). We have continued to focus on structure-function studies of the noncollagenous proteins of bones and teeth, with particular emphasis on matrix protein-protein and matrix protein-cell interactions. It is highly likely that both the assembly of the matrix and its subsequent mineralization is controlled by cells via the use of some of these noncollagenous proteins. Other noncollagenous proteins are likely used in cell-cell and cell-matrix signal transduction. This year we have reached at least intermediate goals in several areas discussed below. We have continued to present evidence to support our hypothesis that five small integrin-binding proteins [bone sialoprotein (BSP), osteopontin (OPN), dentin matrix protein 1 (DMP1), dentin sialophosphoprotein (DSPP) and matrix extracellular phosphoglycoprotein (MEPE)] whose genes are clustered within 375,000 base pairs on human chromosome 4 (mouse chromosome 5) are a genetically related family with overlapping fuctions. We have named this family the SIBLINGs (Small Integrin-Binding LIgand, N-linked Glycoproteins.) MEPE was convincingly added to the family with our discovery of exons 4 and 5 that are characteristic of the family. Enamelin, another gene on chromosome 4 was proposed to possibly be another, more distantly related member of the family. All of these proteins are clearly expressed in bones and teeth and are generally thought to be rarely expressed outside of the skeleton. We are currently challenging this concept by documenting the presence of these gene products in various epithelial tissues including salivary gland. Previously, with our colleagues in Belgium,we have shown that BSP and OPN are frequently up-regulated in many tumors. This year we discovered on a human tumor array that a third member of the SIBLING family, DMP1, was highly expressed in lung cancers but not in the normal lung. Again working with our Belgium colleagues, we have expanded this observation to include use of our antibodies and in situ probes to verify these results in human lung tumor sections. This continues to support our hypothesis (and patent) that all of the SIBLING family members are up-regulated in various tumors and that their elevation in the blood, urine and saliva of patients may be good markers for the presence of such tumors.We have also begun to study another member of the SIBLING family, dentin sialophosphoprotein (DSPP). Using our new antisera against this protein, our colleagues in the Skeletal Biology Section have been able to show that DSPP is expressed in their dental pulp stem cells (SHED) upon transplantation in nude mice. This is strong evidence that the matrix made by these cells is authentic dentin perhaps opening the door to future use of pulp cells in repair of dental lesions. The Matrix Biochemistry Unit freely gives probes (antisera, cDNA, proteins etc.) to any laboratory in the world that makes a reasonable request. In FY03 we sent ~350 probes to 130 laboratories (~15% 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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