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Self-association of class II transactivator correlates with its intracellular localization and transactivation
A Kretsovali1, C Spilianakis, A Dimakopoulos
1Foundation for Research and Technology, Institute of Molecular Biology and Biotechnology, Heraklion, 711 10 Crete, Greece. papamath@imbb.forth.gr
Insights
Class II transactivator (CIITA) controls gene expression by regulating its movement between the nucleus and cytoplasm. Specific protein regions and self-interactions are key to CIITA
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Class II transactivator (CIITA) is essential for major histocompatibility complex (MHC) class II gene expression.
- CIITA regulates both B lymphocyte-specific and interferon-gamma-inducible gene expression pathways.
Purpose of the Study:
- To identify specific protein regions of CIITA responsible for its intracellular distribution.
- To investigate the mechanisms governing CIITA's nucleocytoplasmic trafficking and transcriptional activity.
Main Methods:
- Analysis of CIITA protein regions involved in nuclear export.
- Examination of interactions between CIITA and the export receptor CRM-1.
- Assessment of CIITA self-association and its impact on function.
Main Results:
- Two distinct regions (amino acids 1-114 and 408-550) of CIITA mediate nuclear export via CRM-1 interaction.
- The 408-550 region of CIITA is crucial for both homotypic self-association and heterotypic interactions.
- Impaired nuclear import and abolished activation function in CIITA mutants correlate with reduced self-association.
Conclusions:
- CIITA's nucleocytoplasmic trafficking is controlled by its protein configuration, which is determined by homo- and heterotypic interactions.
- These interactions are critical for proper CIITA function in regulating MHC class II gene expression.
Abstract:
Class II transactivator (CIITA) is the master regulator of major histocompatibility complex class II genes that regulates both B lymphocyte-specific and interferon gamma-inducible expression. Here we identify protein regions and examine mechanisms that determine the intracellular distribution of CIITA. We show that two separate regions of CIITA mediate nuclear export: amino acids 1-114 and 408-550. Both regions interact with the export receptor CRM-1. The CIITA region spanning amino acids 408-550 of CIITA also determines its ability for homotypic self-association as well as heterotypic interactions with other regions residing at the amino and carboxyl termini of the protein. These observations are in line with data demonstrating that co-expression of amino- and carboxyl-terminal parts of CIITA promote subcellular relocalization and, remarkably, rescue transcriptional activation by individually inert molecules. CIITA point mutations that impair nuclear import and abolish its activation function show reduced self-association. We propose that the concerted action of homo- and heterotypic interactions of CIITA determine proper protein configuration that in turn controls its nucleocytoplasmic trafficking.