Anjana Rao


Department of Pathology
Immune Disease Institute, Inc.
Harvard Medical School
200 Longwood Avenue, Room 152
Boston, MA 02115
Tel: (617) 278-3260/3261
Fax: (617) 278-3280
Email: arao@cbr.med.harvard.edu
14 postdoctoral fellows, 4 graduate students


Signalling to transcription: The NFAT transcription factor controls cell lineage specification in many different cell types. In immune cells, it controls both lymphocyte activation and tolerance. The first step of NFAT activation involves calcium entry through “CRAC” channels in the plasma membrane. The increase in intracellular calcium causes activation of the phosphatase calcineurin, which dephosphorylates NFAT and causes it to translocate from the cytoplasm to the nucleus. Using a genome-wide RNAi screen -based approaches to identify regulators of the Ca/ calcineurin/ NFAT pathway, we have identified CRAC channel components as well as a triad of kinases that deactivate NFAT (CK1, GSK3 and DYRK). We have shown that a mutation in a component of the CRAC channel pathway, Orai1, is responsible for the genetic defect in two severe combined immunodeficiency patients whose T lymphocytes lack the ability to open “CRAC” Ca channels in response to depletion of intracellular Ca stores. We are further investigating the pathway of calcium influx, particularly the mechanism by which depletion of calcium stores is coupled to CRAC channel opening. In addition, we are studying the structural changes that occur as a result of NFAT phosphorylation and dephosphorylation, the mechanisms of calcineurin and NFAT activation in living cells, and the structural aspects of the detailed interaction between calcineurin and NFAT.

 

The immune system as a model for understanding cell differentiation: Chronic stimulation with antigen and cytokines results in the differentiation of uncommitted precursor T cells into “effector” T cells with specific functions in the immune response. As expected, different classes of effector T cells are distinguished by specific patterns of gene expression, and deviation from balanced representation of the different effector classes is associated with diseases such as autoimmunity, asthma and allergy. We are defining the regulatory regions and nuclear processes that control chromatin accessibility of selected lineage-specific genes, leading to their activation or silencing in characteristic T cell subsets. T cells lacking either Dicer or the siRNA exonuclease mExo are skewed in the balance of T cell differentiation and lineage-specific gene expression, and we are also asking how microRNAs affect this balance.

 

Mechanisms of peripheral immune tolerance: We have shown that the transcriptional profile of activated T cells is driven by cooperative complexes of NFAT with its transcriptional partners Fos and Jun, while NFAT in the absence of Fos and Jun drives a transcriptional programme that is associated with anergy (a cell-intrinsic unresponsive state). In addition, autoimmune responses are further suppressed by a special class of regulatory T cells which express high levels of the transcription factor FoxP3, and we have shown that T regulatory function depends on a complex of NFAT with FOXP3 on DNA. Anergic T cells express characteristic patterns of negative regulators, ranging from tyrosine phosphatases and inhibitory cell surface receptors to transcriptional repressors and proteins involved in ubiquitin-mediated degradation. We are investigating the negative feedback mechanisms that operate in tolerant T cells and defining the proteins and processes involved. We are also investigating the transcriptional programmes and differentiation pathways involved in development and function of regulatory T cells.

 

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BBS webpage updated 12/02/2009