Studies of penta-decameric binding proteins: AP-4 and CBF-A

Abstract

Each immunoglobulin (Ig) V gene segment contains an upstream promoter region. The octamer element and the TATA box are the only elements that are conserved in all Ig promoters. The presence of the octamer element is necessary, but not sufficient to support high levels of transcription. Therefore, the activity of other co-stimulatory elements is required. This investigation has focused on the study of one such regulatory region: the penta-decameric (pd) element. The pd element is an integral part of the SP6 V-kappa promoter and shows functional synergism with the octamer element at the late stages in B cell differentiation. The pd element is comprised of an E2A type of E-box (5’-CAGCTG-3-) and an AT-rich region. Previous work had identified CArG box-binding factor-A (CBF-A) as the protein interacting with the AT-rich moiety. However, the ligand for the E-box was an unknown. Our work has now identified the bHLH-Zip protein AP-4 as the E-box binding factor. In addition, AP-4 has been found to bind to the second E-box (5’-CAGCTG-3’) found 3’ from the octamer site. E-boxes are conserved within human V-kappa promoter subgroups I, III, IV, V and VII, and related families, hence reinforcing the idea that the natural ligand for Ig-kappa promoter E-boxes is AP-4. Lastly, we pursued the study of CBF-A by searching for interacting partners by using a yeast Two-Hybrid screen. We have now characterised two important proteins interacting with CBF-A, the nucleolar phosphoprotein nucleophosmin(NPM/B23) and hnRNP H. Furthermore, CBF-A shows selectivity in its interactions, since CBF-A/NPM complexes are detected in the nucleus only, as opposed to the cytoplasmic only CBF-A/hnRNP H heterotypic complexes. Interestingly, we have shown that CBF-A undergoes self-oligomerisation in both the nuclear and cytoplasmic compartments. In addition, we have evidence to suggest that CBF-A might be shuttling between the nucleus and the cytoplasm. Specifically, we show that mitogenic stimulation of resting B cells promotes CBF-A accumulation in the nucleus. We have mapped the region responsible for the import/export activity of CBF-A to the most carboxyl-terminal 13 amino acid residues.

Abstract (Swedish)

Popular Abstract in Swedish

Vårt immunsystem är uppbyggt runt två typer av celler som har som uppgift att försvaraoss mot infektioner. T lymfocyterna står för det cellmedierade immunförsvaret som är speciellt viktigt för att bekämpa virusinfektioner med B lymfocyterna har som uppgift att producera antikroppar. Antikroppar finns i alla kroppsvätskor och kan interagera med toxiner, virus och bakterier innan dessa kan ställa till skada. Innan en B lymfocyt kan producera antikroppar genomgår den en komplicerad utmognadsprocess som inleds i benmärgen och sedan fortsätter ute i kroppen. Under denna process är det helt avgörande att olika geners uttryck regleras på ett mycket exakt sätt. I vår arvsmassa finns över 30.000 gener och dessas uttryck styrs av proteiner som interagerar direkt med DNA; sk. transkriptionsfaktorer. I denna avhandling studeras två sådana proteiner, AP-4 och CBF-A, som reglerar uttrycket av en antikroppsgen. Det visas att även transkriptionsfaktorer som uttrycks i alla celltyper kan ha en mycket speciell funktion för en gen som uttrycks i bara en celltyp såsom antikroppsgener. Denna funktion möjliggörs sannolikt av att transkriptionsfaktorn interagerar med olika andra proteiner i olika celler och det är summan av dessa interaktioner som styr när och hur en gen uttrycks. Vidare har sådana proteininteraktioner studerats och karakteriserats. Det har då kunnat definieras att ett protein kan interagera specifikt med vissa proteiner i cellens cytoplasma och med andra i cellkärnan. Genom att förstå dessa interaktioner kan en ökad förståelse för mekanismerna som styr cellers utmognad erhållas.

• author: Aranburu, Alaitz
• supervisor: [unknown] [unknown]
• opponent: Dr Mårtensson-Bopp, Inga-Lill
• organization: Immunology (research group)
• publishing date: 2004
• type: Thesis
• publication status: published
• subject: Immunology in the medical area
• keywords: Biochemistry, transplantation, Metabolism, serologi, metabolism, Biokemi, serology, Immunology, hnRNP H, NPM, CBF-A, AP-4, transcription, B cells, immunoglobulin, Immunologi
• pages: 208 pages
• defense location: Runne Grubb Salen, BMC, Sölvegatan 21, Lund
• defense date: 2004-10-08 09:00:00
• ISBN: 91-628-6193-X
• language: English
• LU publication?: yes
• additional info: Article: I. Aranburu A., Carlsson R., Persson C. & Leanderson T. Transcription factor AP-4 is a ligand for immunoglobulin-kappa promoter E-box elements. Biochem. J. 354, 431-438 (2001). Article: II. Aranburu A., Bennett M. & Leanderson T. The promoter pentadecamer binding protein CBF-A can modify its sequence specificity by interactions with nucleophosmin. Submitted for publication. Article: III. Aranburu A. & Leanderson T. CBF-A shuttles between, and exhibits exclusive interacting partners in the nucleus and the cytoplasm. Manuscript.
• id: 0f861c74-643c-4483-bcc6-18e2e5790015 (old id 467306)
• date added to LUP: 2016-04-04 11:33:27
• date last changed: 2018-11-21 21:05:37