A role for the Cockayne Syndrome B (CSB)-Elongin ubiquitin ligase complex in signal-dependent RNA polymerase II transcription

Transcription-coupled repair: tangled up in convoluted repair

Significant progress has been made in understanding the mechanism of transcription-coupled nucleotide excision repair (TC-NER); however, numerous aspects remain elusive, including TC-NER regulation, lesion-specific and cell type-specific complex composition, structural insights, and lesion removal dynamics in living cells. This review summarizes and discusses recent advancements in TC-NER, focusing on newly identified interactors, mechanistic insights from cryo-electron microscopy (Cryo-EM) studies and live cell imaging, and the contribution of post-translational modifications (PTMs), such as ubiquitin, in regulating TC-NER. Furthermore, we elaborate on the consequences of TC-NER deficiencies and address the role of accumulated damage and persistent lesion-stalled RNA polymerase II (Pol II) as major drivers of the disease phenotype of Cockayne syndrome (CS) and its related disorders. In this context, we also discuss the severe effects of transcription-blocking lesions (TBLs) on neurons, highlighting their susceptibility to damage. Lastly, we explore the potential of investigating three-dimensional (3D) chromatin structure and phase separation to uncover further insights into this essential DNA repair pathway.

Perspectives in the investigation of Cockayne syndrome group B neurological disease: the utility of patient-derived brain organoid models

Cockayne syndrome (CS) group B (CSB), which results from mutations in the excision repair cross-complementation group 6 (ERCC6) genes, which produce CSB protein, is an autosomal recessive disease characterized by multiple progressive disorders including growth failure, microcephaly, skin photosensitivity, and premature aging. Clinical data show that brain atrophy, demyelination, and calcification are the main neurological manifestations of CS, which progress with time. Neuronal loss and calcification occur in various brain areas, particularly the cerebellum and basal ganglia, resulting in dyskinesia, ataxia, and limb tremors in CSB patients. However, the understanding of neurodevelopmental defects in CS has been constrained by the lack of significant neurodevelopmental and functional abnormalities observed in CSB-deficient mice. In this review, we focus on elucidating the protein structure and distribution of CSB and delve into the impact of CSB mutations on the development and function of the nervous system. In addition, we provide an overview of research models that have been instrumental in exploring CS disorders, with a forward-looking perspective on the substantial contributions that brain organoids are poised to further advance this field.

CS proteins and ubiquitination: orchestrating DNA repair with transcription and cell division

To face genotoxic stress, eukaryotic cells evolved extremely refined mechanisms. Defects in counteracting the threat imposed by DNA damage underlie the rare disease Cockayne syndrome (CS), which arises from mutations in the CSA and CSB genes. Although initially defined as DNA repair proteins, recent work shows that CSA and CSB act instead as master regulators of the integrated response to genomic stress by coordinating DNA repair with transcription and cell division. CSA and CSB exert this function through the ubiquitination of target proteins, which are effectors/regulators of these processes. This review describes how the ubiquitination of target substrates is a common denominator by which CSA and CSB participate in different aspects of cellular life and how their mutation gives rise to the complex disease CS.

Structure of the transcribing RNA polymerase II-Elongin complex

Elongin is a heterotrimeric elongation factor for RNA polymerase (Pol) II transcription that is conserved among metazoa. Here, we report three cryo-EM structures of human Elongin bound to transcribing Pol II. The structures show that Elongin subunit ELOA binds the RPB2 side of Pol II and anchors the ELOB-ELOC subunit heterodimer. ELOA contains a 'latch' that binds between the end of the Pol II bridge helix and funnel helices, thereby inducing a conformational change near the polymerase active center. The latch is required for the elongation-stimulatory activity of Elongin, but not for Pol II binding, indicating that Elongin functions by allosterically regulating the conformational mobility of the polymerase active center. Elongin binding to Pol II is incompatible with association of the super elongation complex, PAF1 complex and RTF1, which also contain an elongation-stimulatory latch element.

Reprogramming transcription after DNA damage: recognition, response, repair, and restart

Genome integrity is constantly challenged by endogenous and exogenous insults that cause DNA damage. To cope with these threats, cells have a surveillance mechanism, known as the DNA damage response (DDR), to repair any lesions. Although transcription has long been implicated in DNA repair, how transcriptional reprogramming is coordinated with the DDR is just beginning to be understood. In this review, we highlight recent advances in elucidating the molecular mechanisms underlying major transcriptional events, including RNA polymerase (Pol) II stalling and transcriptional silencing and recovery, which occur in response to DNA damage. Furthermore, we discuss how such transcriptional adaptation contributes to sensing and eliminating damaged DNA and how it can jeopardize genome integrity when it goes awry.

A Comprehensive Review of Biological Roles and Interactions of Cullin-5 Protein

Ubiquitination is a modification of proteins that has a powerful impact on protein function along with other cellular functions. This reaction is regulated through major enzymes, including E3 ligase as a chief enzyme. The Cullin-5 ubiquitin ligase (Cul5) possesses a variety of substrates that maintain the process of ubiquitination as well as proteasomal degradation. It regulates cell development, proliferation, and other physiological tasks in the human body. Moreover, it has been discovered that the expression of Cul5 plays a significant role in specific cancer cells while affecting the progression of tumor cells. This review is based on current knowledge about Cul5 and its expression, signaling pathways, regulation, virus-related responses, and inhibitors for therapeutic strategies.