Larry W. Fisher, Ph.D.

Senior Investigator

Craniofacial and Skeletal Diseases Branch/Matrix Biochemistry Section

NIDCR

Building 30, Room 223
30 Convent Drive
Bethesda, MD 20892

301-496-5769

lfisher@dir.nidcr.nih.gov

Research Topics

I am interested in the evolution, function, and genetic diseases of the five members of the Small Integrin-Binding LIgand, N-Linked Glycoprotein (SIBLING) family of secreted phosphoproteins. The five proteins are Bone Sialoprotein (BSP), Dentin Matrix Protein-1 (DMP1), Dentin Sialophosphoprotein (DSPP), Matrix Extracellular Protein (MEPE), and Osteopontin (OPN). The proteins' respective genes (IBSP, DMP1, DSPP, MEPE and SPP1) are always found in tandem on a single chromosome and are conserved in all mammals although the (toothless) anteaters have only vestigial remnants of their DSPP gene. Shared exon-intron structures, protein motifs (ex. the integrin-binding tripeptide, RGD) and post translational modifications (including phosphorylation, attachment of glycosaminoglycan chains and specific protease cleavage) all suggest that they are the result of ancient gene duplication and divergent evolution from a single gene hundreds of millions of years ago. We've shown by NMR that BSP and OPN are disordered proteins.  Computer modeling as well as the rapid genetic drift of all other SIBLINGS suggest that they likely disordered also. Reptiles and mammals appear to have used different copies of a duplicated DMP1 gene to co-evolve different but chemically similar DSPP proteins. Evolution has generally retained the integrin-binding RGD tripeptide in most SIBLINGs back through the common ancestors of mammals and reptiles.  Half of the mammals species studied,however, have lost their RGD motif in DSPP suggesting that this protein's critical function may no longer require binding to the cell surface via RGD-integrins. Three SIBLINGs, BSP, OPN and DMP1, have been shown to specifically bind and activate proMMP2, proMMP3, and proMMP9 respectively.  On an equimolar basis, tissue inhibitors of metalloproteinases (TIMPs) lose their ability to inhibit active MMP2, MMP3, and MMP9 in the presence of their SIBLING partners.  In each case, complement Factor H inactivates the SIBLINGs' ability to interact with their partner proMMP and active MMPs and has been shown to interfere with the detection of SIBLING proteins in serum assays. SIBLINGs have been shown to be up-regulated by a variety of cancers including oral, prostate, breast, thyroid, and lung.  Recently we have shown that surgically removed oral precancerous lesions that expressed DSPP (but not BSP) were associated with those patients that tended to progress to local frank oral cancer within four years of the "successful" surgery.

Our most recent work has defined the mechanisms leading to the dominant negative effects of all but one (Y6D) of the many mutations in DSPP (discovered by this laboratory and by others) that cause all nonsyndromic forms of Dentin Dysplasia (DD-II) and Dentinogenesis Imperfecta (DGI-II and III).  We propose that all of the many and diverse 5' mutations in the DSPP gene (including a proposed nonsense mutation) ultimately result in changes in the first three amino acids of the mature DSPP protein. Mutations in this tripeptide (isoleucine-proline-valine, IPV) result in inefficient trafficking of the defective DSPP out of the rough endoplasmic reticulum (rER).  We hypothesize that an 'IPV' receptor in the rER is responsible for trafficking and/or packaging of DSPP (and other acidic proteins) into the ER exit vesicles.  A second class of mutations we discovered, loss of one or four DNA bases in the ~ 2000 basepair 3' repeat domain (encoding ~ 700 tandem copies of the nominal tripeptide, serine-serine-aspartic acid, SSD), causes the mutant DSPP protein to become very hydrophobic, to insert into the membrane, and therefore also be retained in the rER.  Mutant DSPP retained in the rER cause their dominant negative effects by then capturing the normal DSPP protein encoded by the patients' second (normal) allele thereby further decreasing the amount of DSPP secreted into the dentin matrix.  We showed that the milder DD was likely caused by the subset of mutations in the DSPP proteins that were less effective at capturing the normal DSPP protein thereby permitting more of the normal allele's DSPP to be secreted into the dentin matrix.

Biography

After receiving my B.S. in biology/biochemistry from Cornell University in 1974, I remained for one year working as a research assistant in the laboratory of Dr. Efraim Racker on the reconstitution of both Ca2+ and Na+/K+ ion pumps in liposomes. My Ph.D. thesis project at Pennsylvania State University (1980) was studying the timing of sulfated proteins made in the highly synchronous, estrogen-induced medullary bone in birds. These proteins were later called biglycan, decorin, and bone sialoprotein.  After a brief postdoctoral fellowship at Case Western University, I began my career at NIDCR in 1981. I received tenure in 1990 and became chief of the Matrix Biochemistry Section of what is now the Craniofacial & Skeletal Diseases Branch, NIDCR, in 2000.


This page was last updated on May 25th, 2012