Biology subjects

Somuncu, O. S.

Publications and source records attributed to Somuncu, O. S..

2 recordsLinked to original sources

bioRxiv2026

A RAD18 SAP domain PIP motif enables PCNA mono-ubiquitination and USP1-BRCA1 synthetic lethality

The proliferating cell nuclear antigen (PCNA) sliding clamp is mono-ubiquitinated by RAD6-RAD18 in response to DNA damage, initiating the DNA damage tolerance pathway of translesion synthesis. The molecular basis by which RAD18 engages PCNA has, however, remained incompletely defined. Mono-ubiquitinated PCNA is subsequently poly-ubiquitinated with K48-linked chains that target PCNA for degradation. Ubiquitin-specific protease 1 (USP1) reverses PCNA mono- and poly-ubiquitination; accordingly, inhibiting USP1 causes the accumulation of mono-ubiquitinated PCNA at replication forks and a reduction in total PCNA levels. USP1 inhibitors promote the accumulation of ssDNA gaps (ssGAPs) in newly replicated DNA and are synthetic lethality in BRCA1-deficient cells. Here, we combine computational and structural approaches to identify and characterize a PCNA-interacting peptide (PIP) motif in RAD18. This PIP motif is required for RAD18-dependent DNA damage-induced PCNA ubiquitination and PCNA turnover. Mutation of the RAD18-PCNA interface reduces ssGAP accumulation and USP1 inhibitor sensitivity in BRCA1-deficient cells. Furthermore, cells adapted to prolonged USP1 inhibition exhibit reduced RAD18 levels, suggesting that deregulation of RAD18 contributes to a biologically relevant drug resistance mechanism. This resistance could be overcome by inhibiting the Ataxia telangiectasia and Rad3-related (ATR) kinase. Together, these findings define a molecular interface required for RAD18-dependent PCNA mono-ubiquitination and identify it as a key determinant of USP1-BRCA1 synthetic lethality.

biochemistry↗

bioRxiv2022

ΔNp63 controls stemness and inflammation in the adult epidermis

The p63 transcription factor is critical for epidermis formation in embryonic development, but its role in the adult epidermis is poorly understood. Here we show that acute genetic ablation of {Delta}Np63, the main p63 isoform, in adult epidermis disrupts keratinocyte proliferation and self-maintenance and, unexpectedly, triggers an inflammatory psoriasis-like condition. Mechanistically, single-cell RNA sequencing revealed down-regulation of the cell cycle genes, up-regulation of differentiation markers, and induction of several pro-inflammatory pathways in {Delta}Np63-ablated keratinocytes. Intriguingly, {Delta}Np63-ablated cells disappear three weeks post-ablation, at the expense of the remaining non-ablated cells. This is not associated with active cell death mechanisms, but rather with reduced self-maintenance capacity. Indeed, in vivo wound healing assay, a physiological readout of the epidermal stem cell function, is severely impaired in {Delta}Np63-ablated mice. We found that the Wnt signaling pathway (Wnt10a, Fzd6, Fzd10) and the AP1 factors (JunB, Fos, FosB) are the likely {Delta}Np63 effectors responsible for keratinocyte proliferation/stemness and suppression of differentiation, respectively, while interleukins IL-1a, IL-18, IL-24, and IL-36{gamma} are the likely negative effectors responsible for the suppression of inflammation. These data establish {Delta}Np63 as a critical node that coordinates epidermal homeostasis, stemness, and suppression of inflammation in the adult epidermis, upstream of known regulatory pathways.

cell biology↗