Molecular Mechanisms of Oncogenesis
via Cosimo il Vecchio 2, Firenze
Principal Investigator: Dr. Silvo Conticello
Staff
- Andrea Chicca, PostDoc
e-mail: andrea.chicca@ittumori.it - Angelika Zotter, PostDoc
e-mail: angelika.zotter@ittumori.it
The Unit "Molecular Mechanisms of Oncogenesis" has started its research activities in January 2008. Our current research is focused on the identification and characterization of factors and pathways involved in the onset of genetic alterations in cancer.
Main Research Themes
- Cancer is the outcome of a multistep path that progressively leads to uncontrolled cellular growth. Underlying this progression of events is the presence of genetic alterations or mutations that provide the framework characterizing the type and evolution of the tumor. Mostly, we have access only to the ending point of this path - with the diagnosis of cancer - and it is not easy to intervene on this succession of events. However, understanding the factors and processes leading to the genetic alterations can improve our diagnostic and therapeutic options by a finer characterization of the tumorigenesis - the final aim being a more targeted treatment.
Surprisingly there is a gene family, the AID/APOBECs, whose only role is to introduce mutations in DNA and RNA molecules. The founder member, Activation Induced Deaminase (AID), is a DNA mutator that, after recruitment to the transcribed immunoglobulin gene, deaminates cytosine residues to uracil and thus initiates the antigen-driven antibody diversification processes.
AID is a powerful tool to improve the immune response, but its ability to mutate DNA represents a double edged sword: transgenic mice constitutively expressing AID develop cancer, and there is increasing evidence linking AID to the onset of mature B cells lymphomas.
Other AID-like cytidine deaminases are able to introduce mutations in nucleic acids while fulfilling quite diverse physiological functions. Thus the APOBEC3s are involved in an innate pathway of immunity against retroviruses, and APOBEC1, an RNA editing enzyme, can mutate DNA as well. As with AID, there is evidence suggesting their association to the onset of cancer.
In fact, while chromosomal aberrations are usually caused by the failure of a given cellular processes (e.g. DNA repair), the intrinsic role of the AID/APOBECs set them on a different level: the processes in which they are involved are designed to maximize the chance of DNA lesions. Thus, any situation in which the AID/APOBECs are induced can potentially lead to the initiation of the path towards cancer. But it needs to be ascertained whether this is due to stochastic events - unavoidable side effects of a mutational machinery - or there are specific conditions that might induce an aberrant function. - The main objective of our research is to investigate the role of AID and of its paralogs in the onset and progression of human cancer through two converging approaches:
- We will define molecules and pathways controlling the function of the AID/APOBECs - While overexpression of AID induces a generalized increase in mutations, under physiological conditions the primary target for AID is a specific region in the immunoglobulin locus. This suggests the existence of a targeting machinery and the possibility that AID misregulation could lead to DNA lesions and tumorigenesis. Intriguingly this is what might be happening in Chronic Lymphocytic Leukemia (B-CLL) where expression of AID is inversely correlated with the mutational status of the immunoglobulin locus. Unfortunately, a part from the role the AID/APOBECs play in their respective pathways, little is known about the factors involved in their regulation and targeting. We will thus investigate the targeting of AID to the immunoglobulin locus to determine whether misregulation of these pathways is involved in the onset of genetic alterations.
To this aim we use a number of tools, ranging from biochemical and bacterial assays to cellular assays. In particular, DT40 cells – a chicken lymphoma cell line – allows efficient gene targeting and provides a reliable assay system for AID function, and primary murine B cells can be induced to study both the AID ability to initiate Class Switch Recombination and to induce cancer-like c-myc/IgH chromosomal translocations, analogous to those found in Burkitt’s Lymphoma. The information gathered through this research will be then used in transgenic mice to investigate whether forced expression of AID mutants and AID regulators makes B-cells more/less susceptible to tumorigenesis. - We will analyze human tumors in order to assess whether the AID/APOBECs are expressed or induced, and whether patterns of expression are associated with specific types of cancer and with their prognosis.
a) AID in the progression of B-cell lineage tumors - With AID expression being associated to the prognosis of B-cell lineage tumors, we intend to study whether AID is merely a relic of the developmental stage at the origin of the tumor or it plays an active role in the progression of the cancer.
b) AID/APOBECs in other cancers - Up to now, the reports on the role and expression of the AID/APOBECs in non-B-cell tumors are fragmentary. We will therefore survey the expression of the AID/APOBECs in carcinomas for which their presence has been reported. We will correlate their expression pattern with known prognostic factors and parameters affecting the clinical outcome (progression free survival, overall survival). Moreover, given the role of AID in the genesis of chromosomal translocations, we will analyze the correlation between the AID/APOBECs and the amount/heterogeneity of chromosomal aberrations.
- We will define molecules and pathways controlling the function of the AID/APOBECs - While overexpression of AID induces a generalized increase in mutations, under physiological conditions the primary target for AID is a specific region in the immunoglobulin locus. This suggests the existence of a targeting machinery and the possibility that AID misregulation could lead to DNA lesions and tumorigenesis. Intriguingly this is what might be happening in Chronic Lymphocytic Leukemia (B-CLL) where expression of AID is inversely correlated with the mutational status of the immunoglobulin locus. Unfortunately, a part from the role the AID/APOBECs play in their respective pathways, little is known about the factors involved in their regulation and targeting. We will thus investigate the targeting of AID to the immunoglobulin locus to determine whether misregulation of these pathways is involved in the onset of genetic alterations.
Publications
- S.G. Conticello, R.S. Harris, and M.S. Neuberger (2003). The Vif protein of HIV triggers degradation of the human antiretroviral DNA deaminase APOBEC3G. Curr Biol, 13(22), 2009-13.
- S.G. Conticello, C.J. Thomas, S.K. Petersen-Mahrt, and M.S. Neuberger (2005). Evolution of the AID/APOBEC Family of Polynucleotide (Deoxy)cytidine Deaminases. Mol Biol Evol, 22(2), 367-77.
- M.A. Langlois, R.C. Beale, S.G. Conticello, and M.S. Neuberger (2005). Mutational comparison of the single-domained APOBEC3C and double-domained APOBEC3F/G anti-retroviral cytidine deaminases provides insight into their DNA target site specificities. Nucleic Acids Res, 33(6), 1913-1923.
- S.G. Conticello, M.A. Langlois, and M.S. Neuberger (2007). Insights into DNA deaminases. Nat Struct Mol Biol, 14(1), 7-9.
- S.G. Conticello, M.A. Langlois, Z. Yang, and M.S. Neuberger (2007). DNA deamination in immunity: AID in the context of its APOBEC relatives. Advances in Immunology, 94, 37-73.
- S.G. Conticello (2008). The AID/APOBEC family of nucleic acid mutators. Genome Biology. 9:6, 229.
Collaborations
- Medical Reasearch Council - Laboratory of molecular Biology (Cambridge, Uk)
- U.O.C Ematologia e Trapianti - Università di Siena (Siena, Italy)
