Redundant Intronic Repressors Function to Inhibit Fibroblast Growth Factor Receptor-1 α-Exon Recognition in Glioblastoma Cells*
- From the Section of Endocrine Neoplasia and Hormonal Disorders, Department of Medical Specialties, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030
Abstract
The human fibroblast growth factor receptor-1 primary transcript is alternatively processed to produce receptor forms that vary in their affinity for fibroblast growth factor. The inclusion of a single exon (α) in normal brain glial cells produces a low affinity form of the receptor. Recognition of the α-exon is dysregulated during neoplastic transformation of glial cells to produce a high affinity receptor form. In this study, we have identified a second intronic repressor of RNA splicing located approximately 250 nucleotides upstream of the α-exon. Deletion or mutation of this sequence resulted in a significant increase in exon recognition in glioblastoma cells. This intronic repressor was found to share significant sequence homology with an intronic repressor element located downstream of the α-exon. The two repressor elements are functionally redundant in that they are capable of inhibiting α-exon recognition when positioned upstream or downstream of the exon. Finally, the elements were found to mediate enhanced exclusion of an unrelated exon, but only the repressors were placed flanking the exon. However, under these conditions, the cell-specific exon exclusion was no longer maintained. These results suggest that although the α-exon inclusion is actively repressed in glioblastomas, the absence of trans-activators appears to be key to the production of the high affinity form of fibroblast growth factor receptor-1 in glioblastomas.
Footnotes
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↵* This work was supported by United States Public Health Service Grant CA-67946 from the National Cancer Institute (to G. J. C.). Additional support for The University of Texas M. D. Anderson Cancer Center DNA Sequencing Core Facility was provided by Public Health Service Grant 2P30-CA16672.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: The University of Texas M. D. Anderson Cancer Center, Section of Endocrinology, Box 15, 1515 Holcombe Blvd., Houston, TX 77030. Tel.: 713-792-2840; Fax: 713-794-4065. E-mail: gcote@mdanderson.org.
- Abbreviations:
- FGFR
-
fibroblast growth factor receptor
- FGF
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fibroblast growth factor
- ISS
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intronic splicing silencer
- PCR
-
polymerase chain reaction
- PTB
-
polypyrimidine tract-binding protein
- bp
-
base pair(s)
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- Received May 12, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
