Induction of APOBEC3C Facilitates the Genotoxic Stress-Mediated Cytotoxicity of Artesunate

Cytidine deaminases APOBEC3C and APOBEC3D promote DNA replication stress resistance in pancreatic cancer cells

Gemcitabine is a potent inhibitor of DNA replication and is a mainstay therapeutic for diverse cancers, particularly pancreatic ductal adenocarcinoma (PDAC). However, most tumors remain refractory to gemcitabine therapies. Here, to define the cancer cell response to gemcitabine, we performed genome-scale CRISPR-Cas9 chemical-genetic screens in PDAC cells and found selective loss of cell fitness upon disruption of the cytidine deaminases APOBEC3C and APOBEC3D. Following gemcitabine treatment, APOBEC3C and APOBEC3D promote DNA replication stress resistance and cell survival by deaminating cytidines in the nuclear genome to ensure DNA replication fork restart and repair in PDAC cells. We provide evidence that the chemical-genetic interaction between APOBEC3C or APOBEC3D and gemcitabine is absent in nontransformed cells but is recapitulated across different PDAC cell lines, in PDAC organoids and in PDAC xenografts. Thus, we uncover roles for APOBEC3C and APOBEC3D in DNA replication stress resistance and offer plausible targets for improving gemcitabine-based therapies for PDAC.

Research on the influence of APOBEC family on the occurrence, diagnosis, and treatment of various tumors

BACKGROUND

Apolipoprotein B mRNA-editing catalytic polypeptide (APOBEC) is a family of highly efficient cytidine deaminase enzymes. APOBECs have been proven to deaminate cytidine on single-stranded DNA or RNA. Inducing the deamination of cytosine on the target gene into uracil, which exerts a variety of physiological functions, plays an important role in innate immunity, adaptive immunity, and antiviral. As the research progresses, APOBECs have been confirmed to be highly expressed in a variety of tumors, causing abnormal mutations in host genes, leading to inactivation of tumor suppressor genes or activation of proto-oncogenes, and their role in tumor development and as diagnostic and treatment markers gradually be found.

CONCLUSION

This article will review the mechanism of APOBECs and their impact on tumor occurrence, development, diagnosis, and treatment, and provide a theoretical basis for future tumor treatment.

Loop 1 of APOBEC3C Regulates its Antiviral Activity against HIV-1

APOBEC3 deaminases (A3s) provide mammals with an anti-retroviral barrier by catalyzing dC-to-dU deamination on viral ssDNA. Within primates, A3s have undergone a complex evolution via gene duplications, fusions, arms race, and selection. Human APOBEC3C (hA3C) efficiently restricts the replication of viral infectivity factor (vif)-deficient Simian immunodeficiency virus (SIVΔvif), but for unknown reasons, it inhibits HIV-1Δvif only weakly. In catarrhines (Old World monkeys and apes), the A3C loop 1 displays the conserved amino acid pair WE, while the corresponding consensus sequence in A3F and A3D is the largely divergent pair RK, which is also the inferred ancestral sequence for the last common ancestor of A3C and of the C-terminal domains of A3D and A3F in primates. Here, we report that modifying the WE residues in hA3C loop 1 to RK leads to stronger interactions with substrate ssDNA, facilitating catalytic function, which results in a drastic increase in both deamination activity and in the ability to restrict HIV-1 and LINE-1 replication. Conversely, the modification hA3F_WE resulted only in a marginal decrease in HIV-1Δvif inhibition. We propose that the two series of ancestral gene duplications that generated A3C, A3D-CTD and A3F-CTD allowed neo/subfunctionalization: A3F-CTD maintained the ancestral RK residues in loop 1, while diversifying selection resulted in the RK → WE modification in Old World anthropoids' A3C, possibly allowing for novel substrate specificity and function.