SPACRCAN, a Novel Human Interphotoreceptor Matrix Hyaluronan-binding Proteoglycan Synthesized by Photoreceptors and Pinealocytes*
- Shreeta Acharyaद,
- Victoria C. Foletta§‖,
- Jung Wha Lee**,
- Mary E. Rayborn‡,
- Ignacio R. Rodriguez**,
- W. Scott Young III‖ and
- Joe G. Hollyfield‡‡
- From the ‡Cole Eye Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, ‖The National Institute of Mental Health, and **The National Eye Institute, The National Institutes of Health, Bethesda, Maryland 20892
Abstract
The interphotoreceptor matrix is a unique extracellular complex occupying the interface between photoreceptors and the retinal pigment epithelium in the fundus of the eye. Because of the putative supportive role in photoreceptor maintenance, it is likely that constituent molecules play key roles in photoreceptor function and may be targets for inherited retinal disease. In this study we identify and characterize SPACRCAN, a novel chondroitin proteoglycan in this matrix. SPACRCAN was cloned from a human retinal cDNA library and the gene localized to chromosome 3q11.2. Analysis of SPACRCAN mRNA and protein revealed that SPACRCAN is expressed exclusively by photoreceptors and pinealocytes. SPACRCAN synthesized by photoreceptors is localized to the interphotoreceptor matrix where it surrounds both rods and cones. The functional protein contains 1160 amino acids with a large central mucin domain, three consensus sites for glycosaminoglycan attachment, two epidermal growth factor-like repeats, a putative hyaluronan-binding motif, and a potential transmembrane domain near the C-terminal. Lectin and Western blotting indicate an M r around 400,000 before and 230,000 after chondroitinase ABC digestion. Removal ofN- and O-linked oligosaccharides reduces theM r to approximately 160,000, suggesting that approximately 60% of the mass of SPACRCAN is carbohydrate. Finally, we demonstrate that SPACRCAN binds hyaluronan and propose that associations between SPACRCAN and hyaluronan may be involved in organization of the insoluble interphotoreceptor matrix, particularly as SPACRCAN is the major proteoglycan present in this matrix.
Footnotes
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↵* This work was supported by Grant EY 02362 from the National Institutes of Health, The Foundation Fighting Blindness, Hunt Valley, MD, The Retina Research Foundation, Houston, TX, and funds from The Cleveland Clinic Foundation.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) .
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↵§ Contributed equally to this analysis.
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↵¶ Recipient of an award from the Knights Templar Eye Foundation, Chicago, Il.
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↵‡ Recipient of the 1999 Ocular Cell and Molecular Biology Prize from Allergan Laboratory for career contributions to vision research. To whom correspondence should be addressed. Tel.: 216-445-3252; Fax: 216-445-3670.
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↵2 V. C. Foletta, unpublished data.
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↵3 E. A. Turley and J. K. K. Choe, personal communication.
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↵4 S. Acharya, V. C. Foletta, J. W. Lee, M. E. Rayborn, I. R. Rodriguez, W. S. Young III, and J. G. Hollyfield, unpublished data.
- Abbreviations:
- IPM
-
interphotoreceptor matrix
- SPACR
-
sialoprotein associated with cones and rods
- ABC
-
avidin-biotin-peroxidase complex
- ΔDi6S
-
chondroitin-6-sulfate Δdisaccharide
- PNA
-
peanut agglutinin
- HA
-
hyaluronan
- PCR
-
polymerase chain reaction
- PBS
-
phosphate-buffered saline
- PAGE
-
polyacrylamide gel electrophoresis
- BSA
-
bovine serum albumin
- CPC
-
cetylpyridinium chloride
- EFEMP-1
-
EGF fibrillin-like extracellular matrix protein-1
- EGF
-
epidermal growth factor
- GAG
-
glycosaminoglycan
- Healon
-
the trade name for highly purified HA used in ophthalmic surgery
- Nonidet P-40
-
nonylpenoxyethanol
- PG10.2
-
rat pineal gland clone 10.2
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- Received August 9, 1999.
- Revision received December 3, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
