Wellome Investigator award in Science

Protein Phosphatases in Chromatin Organisation

Reversible protein phosphorylation is one of the major mechanisms used by cells to control biological processes in space and time and to respond to environmental stimuli. A healthy situation is when cells can balance the level of protein phosphorylation (mediated by kinases) and de-phosphorylation (mediate by phosphatases) by regulating these binary switches.A great deal of research has been conducted to discover disease-relevant kinases with the ultimate goal of designing molecules that can control their activity. However, despite the equal importance of phosphatases in these systems, the knowledge and discoveries on phosphatases have lagged behind. This is mainly due to the lack of basic knowledge of their structure and regulation. Recent discoveries on protein phosphatases have changed the game and have opened new avenues towards the understanding of these enzymes and their potential use as therapeutic targets.

In human cells, Protein Phosphatase 1 (PP1) and Protein Phosphatase 2A (PP2A) account for 90% of all serine/threonine phosphatase activity in most tissues and their malfunction is associated with a variety of diseases.

The activity and specificity of phosphatases is highly regulated in space and time and it is achieved with the help of other proteins (regulatory subunits) that activate/inhibit or direct the phosphatases function towards specific targets. Therefore understanding how this occurs represents one of the priorities in the field.

My laboratory is interested in understanding how our genomes are maintained in a stable state throughout our lifespan and how they can respond correctly to external stimuli. Therefore our aim is to identify which phosphatases are important for genome maintenance.

Identification of the molecular pathways linking H2A.Z to chromosome segregation fidelity

Cell division is a fundamental process that is at the basis of our existence. From the single cell, about 37.2 trillion cells are generated to make up an adult human being. Divisions need to occur in an extremely accurate manner in order to produce daughter cells that are healthy and viable. Defects in cell division are at the basis of several human pathologies ranging from Down syndrome to cancer. Understanding how cell division occurs faithfully and how mistakes are avoided would lead us to better diagnostic tools and intervention opportunity to either prevent or cure some of these diseases. The key machinery for segregating the chromosomes during cell division is the centromere/kinetochore. This structure is composed of DNA and proteins that are directly linked to DNA and forms a special DNA structure at the centromere, which is essential for chromosome segregation. We have discovered that one of the H2A.Z variant (H2A.Z.2 but not H2A.Z.1) is also a key regulator of this process. We revealed that the two variants that only differ by 3 amino acids have distinct functions in cell cycle regulation. Loss of H2A.Z.2 leads to increased chromosome instability and premature loss of sister chromatid cohesion; concomitantly, it also causes a reduction in CENP-A and CENP-C at the centromere. We will investigate how H2A.Z.2 influences centromeric function by identifying the protein complexes that are specifically recruited to chromatin by the H2A.Z variants and identifying the link between H2A.Z and CENP-A deposition/stability.

Investigating the role of the MYCN-CDCA2 axis in neuroblastoma

Neuroblastoma is a paediatric cancer whose high risk, metastatic form still causes death in the majority of affected children. Amplification of the MYCN transcription factor is a common feature of advanced neuroblastoma and associated with a poor outcome of the disease. When overexpressed in the nervous system, MYCN induces neuroblastomas and medulloblastomas, demonstrating a causative role in cell transformation. Thus, clinical approaches aiming at inhibiting its expression or activity should benefit patients with aggressive forms of these childhood cancers. In spite efforts from different laboratories, strategies to inhibit MYCN are of difficult application, given the high levels of MYCN protein present in tumour cells and the difficulty in designing small molecule inhibitors for transcription factors.

For these reasons, we have focussed our attention to molecular pathways upstream or downstream of MYCN that could lead to the identification of more tractable targets for cancer therapy. Recently, using web databases such as Oncomine and Oncogenomics, we have identified a number of genes co-expressed with MYCN in tumours that could be relevant for its pathophysiological functions. Among other candidates, cdca2, also known as Repo-Man (ref), is of considerable interest.

The overall aim of the research is to elucidate the molecular mechanisms used by CDCA2 and MYCN to regulate each other. Dissection of this novel pathway could have important implications for the identification of new molecular targets and the development of alternative therapeutic approaches for MYC bearing tumours. Specific aims will be

1) To identify the molecular pathways downstream of cdca2 that result in elevated MYCN.

2) To inactivate the cdca2/PP1 phosphatase complex as a proof-of-principle study that could lead to the identification of drugs for the treatment of MYCN driven tumours.

Research Goal

To understand the molecular basis of the coordination between chromosome structure/dynamics in anaphase and the reformation of a functional G1 nucleus in heath and diseases