Notch in normal and leukemic cells

Anna Bigas and Lluís Espinosa, of the Stem Cell and Cancer group of the IMIM are two principal investigators who have joined forces to investigate different aspects of cancer development. Together with their jointed group of 14 researchers, Bigas focuses on hematopoietic stem cells, while Espinosa concentrates on solid cancer and intestinal stem cells.

Bigas aims to understand how a pluripotent stem cell becomes a hematopoietic stem cell during embryogenesis. `It is a great challenge in the regenerative medicine field to understand where these stem cells come from and how they conserve this self- renewing capacity which enables them to maintain a tissue´, she explains. She focuses on a major signalling pathway controlling decisions in both normal and leukemic cells and which is also important for tissue maintenance: the Notch pathway.

Searching for Notch target genes

In order to specify the molecular mechanisms driving an undifferentiated cell towards the hematopoietic lineage or to the leukemic phenotype, the group’s current objective is to find Notch target genes and to describe their mechanism of function.

The researchers use techniques like such as chromatin precipitation and promoter arrays. This results in lists of possible candidate genes from which the real targets have to be isolated and validated in a series of experiments, including FACS to isolate the cells of interest and to determine whether the candidate gene is expressed. Further molecular and biochemical analysis, as well as experiments using mutant mice, help define possible interactions of the target molecules and their effect in the organism.

One target gene is GATA2, an important hematopoietic transcription factor that is not expressed in Notch mutant mice and is altered in human leukaemia. The Bigas group have characterized the GATA2 promoter and found that Notch exerts both positive and negative signals that restrict the intensity and the duration of GATA2 expression in hematopoietic cells.

In parallel, Espinosa is studying whether Notch cooperates with other signalling pathways in different contexts. He found that specific elements of the NF-κB pathway, which is involved in cancer development, directly regulate the transcription of genes which are known to be Notch-dependent.

In a common work Bigas and Espinosa identified a new role of the Notch signalling pathway in the maintenance of leukemic stem cells. Previous studies had shown that both the NF-κB and the Notch pathway are involved in T-cell acute lymphoblastic leukaemia, and future therapeutical strategies may employ both Notch and NF-kB inhibitors to fight this leukaemia.

However only the recent findings of Bigas and Espinosa describe the exact mechanism by which Notch activates the NF-kB transcription factor. These new insights published in Cancer Cell, could be translated to clinical trials and result in better pharmaceutical treatments with less side effects.

Despite all the advances in the field, it is not yet known whether Notch is also important for the leukaemia initiating cells, a question that Bigas would like to answer in the close near future. These cells are of major interest, since they are resistant to standard leukaemia treatments, remain in the organism and ultimately are the source of a recurrent outbreak.

Bigas and Espinosa maintain collaborations both inside and outside of the PRBB. `It is a great advantage to have so many scientists within a few square metreers´ Bigas states, `and we just have a great collaborative work in progress, including involving scientists from the CRG, the UPF, Hospital del Mar and others´.

This article was published in the El·lipse publication of the PRBB.

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