The Calcium Sensing Receptor and Its Alternatively Spliced Form in Keratinocyte Differentiation*
- From the Departments of Medicine and Dermatology and§Endocrinology, University of California San Francisco, Veterans Administration Medical Center, San Francisco, California 94121
Abstract
We have recently reported the presence of the calcium sensing receptor (CaR) in keratinocytes and suggested that it signaled calcium-induced differentiation of these cells. cDNA clones encoding the full-length CaR were isolated from human keratinocytes. In addition, an alternatively spliced form that lacks exon 5, encoding a portion of the extracellular domain, also was found. The in frame deletion of 231 nucleotides of exon 5 resulted in the loss of function of the CaR as measured by calcium-stimulated production of inositol phosphates when transfected into HEK293 cells or keratinocytes. This variant produced a smaller CaR protein with an altered glycosylation pattern compared with the full-length CaR. Coexpression of the spliced variant with the full-length CaR reduced the function of the full-length CaR. The full-length CaR was expressed in undifferentiated keratinocytes consistent with their greater response to elevated extracellular calcium in terms of increased intracellular free calcium and production of inositol phosphates. The full-length CaR decreased as the keratinocytes differentiated with an increase in the ratio of the spliced variant to the full-length form. The relative proportions of these two forms of CaR may regulate the calcium responsiveness of keratinocytes during their differentiation.
Footnotes
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↵* This work was supported by Grants R01-AR38386 and P01-AR39448 from the National Institutes of Health and Merit Review award from Veterans Affairs.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: Dept. of Dermatology (190), VA Medical Center, San Francisco, 4150 Clement St., San Francisco, CA 94121. Tel.: 415-751-2091 or 415-221-4810 (ext. 3428); Fax: 415-751-3927; E-mail: y2073{at}itsa.ucsf.edu.
- Abbreviations:
- [Ca2+]o
-
extracellular calcium concentration
- [Ca2+]i
-
intracellular calcium concentration
- CaR
-
calcium receptor
- IP
-
inositol phosphate
- IP3
-
inositol 1,4,5-trisphosphate
- ORF
-
open reading frame
- KGM
-
keratinocyte growth medium
- RT-PCR
-
reverse transcriptase-polymerase chain reaction
- PNGase F
-
peptide-N-glycosidase F
- Endo H
-
endoglycosidase H
- HEK293
-
human embryonic kidney cell 293
- bp
-
base pair(s)
- kb
-
kilobase pair(s)
- G3PDH
-
glyceraldehyde-3-phosphate dehydrogenase.
-
- Received May 1, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
