AID/APOBEC protein family members share the common ability to deaminate cytosine into uracil and, by doing so, to mutate both RNA and DNA. In physiological conditions APOBECs activity against viruses, retroviruses, and mobile elements is carried on safely, thanks to cellular repair mechanisms that take care of possible self-inflicted DNA damage. The effects of their aberrant activity in cancer have been observed in the form of their mutational signature in the cancer genomes, in some cancers representing up to 90% of all genetic alterations. Yet, it is still to be defined their weight in driving tumorigenesis and tumor progression. It has been shown that APOBEC mutagenesis is driven by short bursts of expression rather than a stable overexpression, presumably because prolonged APOBECs activation might be cytotoxic. The hypothesis that drove my PhD work focuses on the possibility that APOBEC expression might represent a last-ditch effort to prevent cells to go through the final steps towards cellular transformation: as regulatory pathways and tumor suppressors fail to induce apoptosis, APOBEC induced DNA damages might not be counterbalanced by DNA repair pathways and genotoxic stress would eventually lead to cell death. I thus investigated the behavior of a human breast cancer cell-line (MCF-7) where the APOBEC3B gene was inactivated to assess its proliferation and colony forming capability, also after exogenous reconstitution of APOBEC3B. Intriguingly, doxycycline-mediated overexpression of APOBEC3B caused a small but significative decrease in both clonogenicity and proliferative capacity on the APOBEC3B-/- cells, while cells with the parent cell line no difference after APOBEC3B induction. Moreover, I assessed whether expression of known oncogenes -mutated forms of TP53, KRAS and CTNNB1- could affect APOBEC3B-/- cells: cells expressing endogenous APOBEC3B acquired a larger boost in proliferation compared to APOBEC3B-/- ones but only APOBEC3B-/- showed an increase in clonogenicity. This suggests that lack of APOBEC3B might indeed favor the onset of tumorigenic features. Altogether these results suggest that, during the very early stages of tumorigenesis, APOBEC3B-mutagenesis might play a different role compared to later stages, providing a new perspective on APOBECs as a potential ‘tumor suppressor’.

Tarantino, D. (2021). The weight of APOBEC mutations in cancer development [10.25434/danilo-tarantino_phd2021].

The weight of APOBEC mutations in cancer development

Danilo Tarantino
2021-01-01

Abstract

AID/APOBEC protein family members share the common ability to deaminate cytosine into uracil and, by doing so, to mutate both RNA and DNA. In physiological conditions APOBECs activity against viruses, retroviruses, and mobile elements is carried on safely, thanks to cellular repair mechanisms that take care of possible self-inflicted DNA damage. The effects of their aberrant activity in cancer have been observed in the form of their mutational signature in the cancer genomes, in some cancers representing up to 90% of all genetic alterations. Yet, it is still to be defined their weight in driving tumorigenesis and tumor progression. It has been shown that APOBEC mutagenesis is driven by short bursts of expression rather than a stable overexpression, presumably because prolonged APOBECs activation might be cytotoxic. The hypothesis that drove my PhD work focuses on the possibility that APOBEC expression might represent a last-ditch effort to prevent cells to go through the final steps towards cellular transformation: as regulatory pathways and tumor suppressors fail to induce apoptosis, APOBEC induced DNA damages might not be counterbalanced by DNA repair pathways and genotoxic stress would eventually lead to cell death. I thus investigated the behavior of a human breast cancer cell-line (MCF-7) where the APOBEC3B gene was inactivated to assess its proliferation and colony forming capability, also after exogenous reconstitution of APOBEC3B. Intriguingly, doxycycline-mediated overexpression of APOBEC3B caused a small but significative decrease in both clonogenicity and proliferative capacity on the APOBEC3B-/- cells, while cells with the parent cell line no difference after APOBEC3B induction. Moreover, I assessed whether expression of known oncogenes -mutated forms of TP53, KRAS and CTNNB1- could affect APOBEC3B-/- cells: cells expressing endogenous APOBEC3B acquired a larger boost in proliferation compared to APOBEC3B-/- ones but only APOBEC3B-/- showed an increase in clonogenicity. This suggests that lack of APOBEC3B might indeed favor the onset of tumorigenic features. Altogether these results suggest that, during the very early stages of tumorigenesis, APOBEC3B-mutagenesis might play a different role compared to later stages, providing a new perspective on APOBECs as a potential ‘tumor suppressor’.
2021
CONTICELLO, SILVESTRO
Tarantino, D. (2021). The weight of APOBEC mutations in cancer development [10.25434/danilo-tarantino_phd2021].
Tarantino, Danilo
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11365/1143954