Defining a role for TPX2 in the nucleus – Regulation of the DNA damage response
Date
2013-03-28
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The Targeting Protein for Xenopus kinesin-like protein 2 (TPX2) was discovered over a decade ago as nuclear protein. Since, TPX2 has been defined as a factor that is essential for mitotic spindle assembly and cell division. However, no function has yet been assigned to TPX2 in the nucleus, although this protein is actively imported into this cellular compartment throughout interphase. Data presented in this thesis now document that human TPX2 is involved in the cellular response to cytotoxic and pathogenic DNA double strand breaks (DSBs) induced by ionizing radiation (IR). Specifically, TPX2 regulates the formation of serine139 phosphorylated histone H2AX (γ-H2AX), a key-step of DNA damage response (DDR). Loss of TPX2 leads to inordinately strong and transient accumulation of γ-H2AX at DSBs during G0 and G1 phases of the cell cycle. Conversely, cells overexpressing TPX2 have reduced levels of γ-H2AX after irradiation. Importantly, this regulation of γ-H2AX by TPX2 is not an epiphenomenon of apoptosis and is independent of the mitotic functions of TPX2. Compatible with a role in DDR, TPX2 was found to be recruited to DSBs and was detected in complex with MDC1 and the ATM kinase, two proteins known to generate the majority of γ-H2AX. Additionally, cells lacking TPX2 have defects in recruitment and disengagement of DNA repair factors (53BP1 and RAD51) at sites of chromosomal damage, accumulate DSBs and ultimately, exhibit increased expression of IR-induced apoptotic markers. Interestingly, increased γ-H2AX upon depletion of TPX2 is paralleled by a decrease in histone H4 acetylated at lysine16 (H4K16ac). H4K16ac is a substrate of the SIRT1 deacetylase that was found to associate with TPX2 in a DNA damage-dependent manner. Thus, TPX2 might impact γ-H2AX via regulating the composition of chromatin. Of note, TPX2 dysfunction also causes aberrant chromatin architecture in unirradiated cells, indicating a constitutive role for TPX2 in chromatin-biology. In sum, this thesis reveals the first functions for TPX2 in the nucleus: regulation of DDR and chromatin. Since TPX2 is a suspected oncogene, novel insights into TPX2’s biology reported herein may advance our understanding of carcinogenesis.
Description
Keywords
Cell, Biology--Molecular, Biology--Molecular
Citation
Neumayer, G. (2013). Defining a role for TPX2 in the nucleus – Regulation of the DNA damage response (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/25537