ABSTRACT
In the course of modeling the naturally occurring tumor immunity seen in patients with paraneoplastic cerebellar degeneration (PCD), we discovered an unexpectedly high threshold for breaking CD8+ cytotoxic T cell (CTL) tolerance to the PCD autoantigen, CDR2. While CDR2 expression was previously found to be strictly restricted to immune-privileged cells (cerebellum, testes, and tumors), unexpectedly we have found that T cells also express CDR2. This expression underlies inhibition of CTL activation; CTLs that respond to epithelial cells expressing CDR2 fail to respond to T cells expressing CDR2. This was a general phenomenon, as T cells presenting influenza (flu) antigen also fail to activate otherwise potent flu-specific CTLs either in vitro or in vivo. Moreover, transfer of flu peptide-pulsed T cells into flu-infected mice inhibits endogenous flu-specific CTLs. Our finding that T cells serve as a site of immune privilege, inhibiting effector CTL function, uncovers an autorepressive loop with general biologic and clinical relevance.
Subject(s)
Antigens, Viral/immunology , Autoantigens/immunology , Nerve Tissue Proteins/metabolism , Nerve Tissue Proteins/pharmacology , T-Lymphocytes, Cytotoxic/drug effects , T-Lymphocytes, Cytotoxic/immunology , Animals , Autoimmune Diseases/immunology , Epithelial Cells/metabolism , HeLa Cells , Humans , Immunization , Influenza A virus , Mice , Mice, Inbred C57BL , Mice, Knockout , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/immunology , Nervous System Diseases/immunology , Paraneoplastic Cerebellar DegenerationABSTRACT
Cdr2 is a tumor antigen expressed in a high percentage of breast and ovarian tumors and is the target of a naturally occurring tumor immune response in patients with paraneoplastic cerebellar degeneration, but little is known of its regulation or function in cancer cells. Here we find that cdr2 is cell cycle regulated in tumor cells with protein levels peaking in mitosis. As cells exit mitosis, cdr2 is ubiquitinated by the anaphase promoting complex/cyclosome (APC/C) and rapidly degraded by the proteasome. Previously we showed that cdr2 binds to the oncogene c-myc, and here we extend this observation to show that cdr2 and c-myc interact to synergistically regulate c-myc-dependent transcription during passage through mitosis. Loss of cdr2 leads to functional consequences for dividing cells, as they show aberrant mitotic spindle formation and impaired proliferation. Conversely, cdr2 overexpression is able to drive cell proliferation in tumors. Together, these data indicate that the onconeural antigen cdr2 acts during mitosis in cycling cells, at least in part through interactions with c-myc, to regulate a cascade of actions that may present new targeting opportunities in gynecologic cancer.
Subject(s)
Nerve Tissue Proteins/physiology , Proto-Oncogene Proteins c-myc/metabolism , Ubiquitin-Protein Ligase Complexes/metabolism , Anaphase-Promoting Complex-Cyclosome , Animals , Antigens, Neoplasm/physiology , Cell Cycle , Cell Line, Tumor , Cell Proliferation , Gene Expression Regulation, Neoplastic , Humans , Mice , Mice, Nude , Mitosis , Nerve Tissue Proteins/metabolism , Proteasome Endopeptidase Complex/metabolism , Proto-Oncogene Proteins c-myc/genetics , Rats , Transcription, Genetic , UbiquitinationABSTRACT
The Runt domain proteins are transcription regulators of major developmental pathways. Here we present the crystal structures of the Runt domain (RD) of the human protein RUNX1 and its DNA binding site in their free states and compare them with the published crystal structures of RD bound to DNA and to the partner protein CBFbeta. We demonstrate that (1) RD undergoes an allosteric transition upon DNA binding, which is further stabilized by CBFbeta, and that (2) the free DNA target adopts a bent-helical conformation compatible with that of the complex. These findings elucidate the mechanism by which CBFbeta enhances RD binding to DNA as well as the role of the intrinsic conformation of the DNA target in the recognition process.
