Biology subjects

Fanunza, E.

Publications and source records attributed to Fanunza, E..

3 recordsLinked to original sources

bioRxiv2026

Endogenous APOBEC3B Promotes CHK1 Inhibitor Sensitivity

APOBEC3B (A3B) is a single-stranded DNA cytosine deaminase overexpressed in cancer, where it causes genomic DNA damage and mutations associated with tumor evolution. Enforced A3B overexpression triggers a dependency on the replication-stress response in different cellular models. However, whether endogenous A3B in cancer cells might yield a similar vulnerability is unclear. Here, we investigate how endogenous A3B expression and catalytic activity affect sensitivity to CHK1 inhibition, using two cancer cell lines, JHOC5 and U2OS. A3B-expressing cancer cells are sensitive to two chemically distinct CHK1 inhibitors, GDC-0575 and Prexasertib. CHK1 inhibitor sensitivity is reduced by A3B CRISPR knockout and restored by re-expressing wildtype A3B in knockout cells. Moreover, an endogenous A3B-E255A catalytic mutant generated by homology-directed repair phenocopies the reduced CHK1 inhibitor sensitivity of A3B-null cells, demonstrating a DNA deamination-dependent mechanism. CHK1 inhibition induces replication-associated DNA damage and cell-cycle perturbation dependent on A3B expression. As a result, A3B-expressing cells accumulate more pan-nuclear {gamma}H2AX, aberrant DNA-content profiles, and an expanded EdU-negative S-phase population, which are hallmarks of stalled DNA replication. In comparison, A3B-null and A3B-E255A cells retain defined cell-cycle distributions and are less sensitive to CHK1 inhibition. Together, these findings identify endogenous A3B-catalyzed deamination as a therapeutically actionable source of replication-associated DNA damage that renders tumor cells selectively dependent on CHK1 function. Statement of significanceAPOBEC3B causes mutations in cancer cells and simultaneously imposes DNA replication stress. This combines to sensitize tumor cells to chemical inhibitors of the DNA damage response kinase CHK1.

cancer biology↗

bioRxiv2023

Human cytomegalovirus mediates APOBEC3B relocalization early during infection through a ribonucleotide reductase-independent mechanism

The APOBEC3 family of DNA cytosine deaminases comprises an important arm of the innate antiviral defense system. The gamma-herpesviruses EBV and KSHV and the alpha-herpesviruses HSV-1 and HSV-2 have evolved an efficient mechanism to avoid APOBEC3 restriction by directly binding to APOBEC3B and facilitating its exclusion from the nuclear compartment. The only viral protein required for APOBEC3B relocalization is the large subunit of the ribonucleotide reductase (RNR). Here, we ask whether this APOBEC3B relocalization mechanism is conserved with the beta-herpesvirus human cytomegalovirus (HCMV). Although HCMV infection causes APOBEC3B relocalization from the nucleus to the cytoplasm in multiple cell types, the viral RNR (UL45) is not required. APOBEC3B relocalization occurs rapidly following infection suggesting involvement of an immediate early or early (IE-E) viral protein. In support of this mechanism, cycloheximide treatment of HCMV-infected cells prevents the expression of viral proteins and simultaneously blocks APOBEC3B relocalization. In comparison, the treatment of infected cells with phosphonoacetic acid, which is a viral DNA synthesis inhibitor affecting late protein expression, still permits A3B relocalization. These results combine to show that the beta-herpesvirus HCMV uses a fundamentally different, RNR-independent molecular mechanism to antagonize APOBEC3B. ImportanceHuman cytomegalovirus (HCMV) infections can range from asymptomatic to severe, particularly in neonates and immunocompromised patients. HCMV has evolved strategies to overcome host-encoded antiviral defenses in order to achieve lytic viral DNA replication and dissemination and, under some conditions, latency and long-term persistence. Here, we show that HCMV infection causes the antiviral factor, APOBEC3B, to relocalize from the nuclear compartment to the cytoplasm. This overall strategy resembles that used by related herpesviruses. However, the HCMV relocalization mechanism utilizes a different viral factor(s) and available evidence suggests the involvement of at least one protein expressed at the early stages of infection. This knowledge is important because a greater understanding of this mechanism could lead to novel antiviral strategies that enable APOBEC3B to naturally restrict HCMV infection.

microbiology↗

bioRxiv2019

Mutation of Ebola virus VP35 Ser129 uncouples interferon antagonist and replication functions

Ebolaviruses are non-segmented, negative-sense RNA viruses (NNSVs) within the order Mononegavirales that possess the multifunctional virion protein 35 (VP35), a major determinant of virulence and pathogenesis that is indispensable for viral replication and host innate immune evasion. VP35 is functionally equivalent to the phosphoprotein (P) of other mononegaviruses such as rhabdoviruses and paramyxoviruses. Phosphorylation of the P protein is universally regarded as functionally important however, a regulatory role(s) of phosphorylation on VP35 function remains unexplored. Here, we identified a highly conserved Ser129 residue near the homo-oligomerization coiled coil motif, which is essential for VP35 functions. Affinity-purification MS followed by post-translational modification (PTM) analysis predicted phosphorylation of Ser129. Co-immunoprecipitation, cross-linking, and biochemical characterization studies revealed a moderately decreased capacity of VP35-S129A to oligomerize. Functional analysis showed that Ser-to-Ala substitution of Ebola virus (EBOV) VP35 did not affect IFN inhibitory activity but nearly abolished EBOV minigenome activity. Further coimmunoprecipitation studies demonstrated a lost interaction between VP35-S129A and the amino terminus of the viral polymerase but not between viral nucleoprotein (NP) or VP35-WT. Taken together, our findings provide evidence that phosphorylation modulates VP35 function, supporting VP35 as a NNSV P protein and providing a potentially valuable therapeutic target.\n\nImportanceEbola virus (EBOV) can cause severe disease in humans. The 2013-2016 West African epidemic and the two recent outbreaks in the Democratic Republic of the Congo underscore the urgent need for effective countermeasures, which remain lacking. A better understanding of EBOV biology and the modulation of multifunctional viral proteins is desperately needed to develop improved therapeutics. We provide evidence here that function of virion protein 35 (VP35) is modulated by phosphorylation of Ser129, a conserved residue among other ebolavirus species. These findings shed light on EBOV biology and present a potential target for broad acting anti-ebolavirus therapeutics.

microbiology↗