Transcriptional mechanisms in development and tumor formation

Scientific Interests

The role of Prep1 and Meis1 homeobox proteins in hematopoietic development and oncogenesis.

Prep1 is an homeodomain transcription factor, essential in various steps of embryonic development and adult life. Prep1 acts by dimerizing with Pbx proteins, which allows its nuclear localization and DNA binding. Prep1 hypomorphic mice (Prep1ⁱ) develop spontaneous tumors and Prep1 haploinsufficiency accelerates the insurgence of tumors, i.e. Prep1 acts as a tumor suppressor. For this reason we are analyzing cohorts of breast cancer patients to determine the level of Prep1 expression and the mechanisms inducing its down regulation in human tumors. Prep1 hypomorphic embryos have a major deficiency in Hematopoietic Stem Cells (HSC). We have identified genes that are differentially expressed in HSCs of the Prep1ⁱ mice, and on this basis are analyzing signaling pathways affecting HSC asymmetric cell division.

A minority of the Prep1ⁱ mice are born and live a normal length life. In addition to developing tumors, we have found a phenotype also in the mammary gland which may be due to deficiencies in mammary stem cells. Unlike Prep1-hypomorphic, Prep1-null embryos die before gastrulation because the epiblast cells go into p53-dependent apoptosis. Therefore we are interested in determining the molecular basis for the apoptosis phenotype, whether it is possibly caused by accumulation of DNA damage due to aberrant chromatin modifications, and to determine the molecular basis. This interest is being pursued in both mice (crosses with mice Ko for important signaling pathways) as well as in cells, HSC, embryonic fibroblasts and Embryonic Stem cells (ES).

Meis1 is a Prep1 family member that, like Prep1, binds Pbx forming a DNA-binding complex and sharing with Prep1 three homologous domain, including the DNA-binding and the Pbx-interacting domains. Importantly, Meis1 is an oncogene, i.e. has a function opposite to Prep1. Interestingly, both Meis1-null and Prep1 hypomorphic embryos have a very similar phenotype, in particular hematopoietic stem cells (HSC) deficiency. However, double heterozygous Prep1-Meis1 mice are perfectly normal, indicating that despite, their phenotype similarity, Prep1 and Meis1 affect different, but essential, pathways in HSCs.

We are also interested in identifying the genes that are regulated by Prep1 on a global basis. We have already obtained data by chromatin immunoprecipitation using a mouse promoters array and are now completing the study by ChIP-Seq. In parallel, we are doing the same experiment with Meis1, the Prep1 homologue. This will lead to an analysis of why two proteins, having homologous DNA binding and identical Pbx-interacting domains, can affect transcription of different genes.

Ongoing projects.

1. Structure determination of the Prep1/Pbx1/DNA complex.
2. Molecular and biological analysis of the Prep1-null ES cells.
3. Molecular and biological analysis of the aymmetric cell division in Prep1-null HSC.
4. Molecular mechanisms in the tumor suppressor function of Prep1. Mechanisms inducing DNA damage in Prep1-hypomorphic cells.
5. Molecular and biological analysis comparing the Meis1/Prep1 functions in tumorigenesis.
6. Molecular analysis of the Prep1-p53 relationship in Prep1 and Meis1 null embryos.
7. Prep1-p53 interrelation in tumorigenesis.
8. Identification of the Prep1 and Meis1 target genes. Relationship to their function in tumorigenesis.