Defining a role for TPX2 in the nucleus – Regulation of the DNA damage response

Neumayer, Gernot

Defining a role for TPX2 in the nucleus – Regulation of the DNA damage response

atmire.migration.oldid	776
dc.contributor.advisor	Nguyen, Minh Dang
dc.contributor.author	Neumayer, Gernot
dc.date.accessioned	2013-03-28T16:43:53Z
dc.date.available	2013-06-15T07:01:50Z
dc.date.issued	2013-03-28
dc.date.submitted	2013	en
dc.description.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.	en_US
dc.identifier.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	en_US
dc.identifier.doi	http://dx.doi.org/10.11575/PRISM/25537
dc.identifier.uri	http://hdl.handle.net/11023/577
dc.language.iso	eng
dc.publisher.faculty	Graduate Studies
dc.publisher.institution	University of Calgary	en
dc.publisher.place	Calgary	en
dc.rights	University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.
dc.subject	Cell
dc.subject	Biology--Molecular
dc.subject	Biology--Molecular
dc.subject.classification	TPX2	en_US
dc.subject.classification	DNA damage response	en_US
dc.subject.classification	ionizing radiation	en_US
dc.subject.classification	DNA double strand break	en_US
dc.subject.classification	Cell cycle	en_US
dc.title	Defining a role for TPX2 in the nucleus – Regulation of the DNA damage response
dc.type	doctoral thesis
thesis.degree.discipline	Biochemistry and Molecular Biology
thesis.degree.grantor	University of Calgary
thesis.degree.name	Doctor of Philosophy (PhD)
ucalgary.item.requestcopy	true