Structural and functional studies of proteins in cell signaling and cancer

Abstract

Cancer is one of the most common causes of death in the western world. Cancer is an umbrella term for over 100 different diseases all caused by mutations in cells leading to uncontrolled cell division and metastasis. The control of the cell division is extremely important in order to maintain homeostasis and avoid development of cancer. The cells in the body have to communicate with each other to keep homeostasis. This can subsequently regulate the cell cycle that controls cell division. Many proteins are involved in the control mechanisms to pass the cell through the cycle where phosphorylation and dephosphorylation are important mechanism for regulation. The cell division is also controlled by tumor suppressors that sense, for example, DNA damage or cell stress, to ascertain reediness for cell division and to minimize the amount of mutations. Two important proteins in the cell signaling are Protein Phosphatase 2A that act as switch for the pocket proteins that control the cell cycle, and p53 which is labeled “the guardian of the genome”, both are tumor suppressor.

Protein Phosphatase 2A (PP2A), is together with PP1 responsible for 90% of all dephosphorylation events in the cell. Apart from controlling the cell cycle PP2A is involved in many other pathways making it a very important protein in cell signaling. Understanding its structure and function is crucial for understanding how it works at the molecular level and how difference cancer mutations are affecting its mechanism of action. PP2A consists of three subunits, a scaffolding (A), a catalytic (C) and a regulatory (B) for substrate recognition. In this thesis the structure and biochemical function of one of the regulatory subunits, B’’/PR70, is presented, a subunit who’s structure was unknown before the start of the doctoral project. A high-resolution structure of the core revealed 8 EF-hands where two were binding calcium. A mapping of the A-B’’ interaction is also presented.

p53 is a common tumor suppressor that is mutated in 50% of all cancer tumors. It is involved in key decisions for cell cycle progression and apoptosis and more detailed understanding of this protein could shed light on the role of different p53 mutations in cancer. P53 is acting as a transcription factor and has a DNA binding core domain that binds to a response element on the target gene. In this thesis, a novel method to study biochemical events in cells and cell extract is applied for the first time on p53, the Cellular Thermal Shift Assay (CETSA). It is shown that p53-DNA can indeed be studied using this strategy and that binding profiles to four different oligonucleotides representing target genes with response elements, give distinct profiles for each mutation. This suggest that the CETSA strategy allows for more detailed functional studies of p53 in cells and that oligonucleotide profiling might constitute a novel mean to profile cancer patient cells for differential p53 activity.