Nucleic Acids Research Advance Access originally published online on July 2, 2008
Nucleic Acids Research 2008 36(13):4402-4416; doi:10.1093/nar/gkn413
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Nucleic Acids Research, 2008, Vol. 36, No. 13 4402-4416
© 2008 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Gene Regulation, Chromatin and Epigenetics |
Physical and functional characterization of the genetic locus of IBtk, an inhibitor of Bruton's tyrosine kinase: evidence for three protein isoforms of IBtk
1Department of Experimental and Clinical Medicine, University of Catanzaro ‘Magna Graecia’, 88100 Catanzaro, 2Department of Biochemistry and Medical Biotechnology, University of Naples ‘Federico II’, 3Telethon Institute of Genetics and Medicine, 80131 Naples, 4Institute of Food Sciences, CNR, Avellino and 5Department of Biotechnological Sciences, University of Naples ‘Federico II’, Naples, Italy
*To whom correspondence should be addressed. Tel: +39 0961 3694058 (office); Fax: +39 0961 3694090; Email: quinto{at}unicz.it Correspondence may also be addressed to Giuseppe Scala. Tel: +39 0961 3694059 (office); Fax: +39 0961 3694090; Email: scala{at}unicz.it
Received January 9, 2008. Revised June 12, 2008. Accepted June 13, 2008.
Bruton's tyrosine kinase (Btk) is required for B-cell development. Btk deficiency causes X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency (Xid) in mice. Btk lacks a negative regulatory domain and may rely on cytoplasmic proteins to regulate its activity. Consistently, we identified an inhibitor of Btk, IBtk, which binds to the PH domain of Btk and down-regulates the Btk kinase activity. IBtk is an evolutionary conserved protein encoded by a single genomic sequence at 6q14.1 cytogenetic location, a region of recurrent chromosomal aberrations in lymphoproliferative disorders; however, the physical and functional organization of IBTK is unknown. Here, we report that the human IBTK locus includes three distinct mRNAs arising from complete intron splicing, an additional polyadenylation signal and a second transcription start site that utilizes a specific ATG for protein translation. By northern blot, 5'RACE and 3'RACE we identified three IBTK
, IBTKβ and IBTK
mRNAs, whose transcription is driven by two distinct promoter regions; the corresponding IBtk proteins were detected in human cells and mouse tissues by specific antibodies. These results provide the first characterization of the human IBTK locus and may assist in understanding the in vivo function of IBtk.
Present address: Notis Argiriou, Center for Research and Technology-Hellas, 570 01 Thermi–Thessaloniki, Greece
The authors wish it to be known that, in their opinion, the first three authors should be regarded as joint First Authors