Mitotic and DNA Damage Response Proteins: Maintaining the Genome Stability and Working for the Common Good

The oxidative-stress-senescence axis in keratoconus: new insights into corneal degeneration

Keratoconus is a bilateral and asymmetric degenerative eye disease that causes corneal thinning and bowing, leading to irregular astigmatism and vision loss. Although environmental and genetic factors contribute to the disease's development, the exact cause and underlying pathological mechanism remain unknown. In this review, we comprehensively explore the latest pathophysiological mechanisms of keratoconus, focusing on oxidative damage and inflammation. Senescence emerges as a key driver of keratoconus pathogenesis. Understanding these common elements enhances our understanding of the disease and paves the way for innovative therapeutic approaches to keratoconus.

Pharmaceutical inhibition of the Chk2 kinase mitigates cone photoreceptor degeneration in an iPSC model of Bardet-Biedl syndrome

Bardet-Biedl syndrome (BBS) is a syndromic ciliopathy leading to progressive blindness starting in childhood, but the mechanism of photoreceptor degeneration remains unclear. The basal body of the photoreceptor primary cilium originates from the centrosome's mother centriole, and BBS-related proteins form a complex at basal body. Centrosomes also organize microtubules of the mitotic spindle. We show here that photoreceptors from Bbs10 -/- mouse pups present a DNA damage response (DDR) that becomes persistent and localizes to the basal body. In patient-derived induced pluripotent stem cells (iPSCs) carrying BBS10 mutations, BBS retinal progenitor cells (RPCs) present a DDR that correlates with activation of the mitotic spindle checkpoint. Pharmaceutical inhibition of the Chk2 kinase in BBS RPCs mitigates cell death and genomic instability and restores the phospho-proteome. Drug treatment of BBS retinal organoids improves tissue organization, cone survival, and outer segment maturation, thus opening a possible therapeutic avenue to delay photoreceptor degeneration in BBS.

The involvement of cyclin-dependent kinase 7 (CDK7) and 9 (CDK9) in coordinating transcription and cell cycle checkpoint regulation

Cells regulate the expression of cell cycle-related genes, including cyclins essential for mitosis, through the transcriptional activity of the positive transcription elongation factor b (P-TEFb), a complex comprising CDK9, cyclin T, and transcription factors. P-TEFb cooperates with CDK7 to activate RNA polymerase. In response to DNA stress, the cell cycle shifts from mitosis to repair, triggering cell cycle arrest and the activation of DNA repair genes. This tight coordination between transcription, cell cycle progression, and DNA stress response is crucial for maintaining cellular integrity. Cyclin-dependent kinases CDK7 and CDK9 are central to both transcription and cell cycle regulation. CDK7 functions as the CDK-activating kinase (CAK), essential for activating other CDKs, while CDK9 acts as a critical integrator of signals from both the cell cycle and transcriptional machinery. This review elucidates the mechanisms by which CDK7 and CDK9 regulate the mitotic process and cell cycle checkpoints, emphasizing their roles in balancing cell growth, homeostasis, and DNA repair through transcriptional control.

Post-translational modifications of epigenetic modifier TIP60: their role in cellular functions and cancer

TIP60 is a crucial lysine acetyltransferase protein that catalyzes the acetylation of histone and non-histone proteins. This enzyme plays a crucial role in maintaining genomic integrity, by participating in DNA damage repair, ensuring accurate chromosomal segregation, and regulating a myriad of cellular processes such as apoptosis, autophagy, and wound-induced cell migration. One of the primary mechanisms through which TIP60 executes these diverse cellular functions is via post-translational modifications (PTMs). Over the years, extensive studies have demonstrated the importance of PTMs in controlling protein functions. This review aims to summarize the findings on PTMs occurring on the TIP60 protein and their functional implications. We also discuss previously uncharacterized PTM sites identified on TIP60 and examine their relationship with cancer-associated mutations, with a particular focus on residues potentially modified by various PTMs, to understand the cause of deregulation of TIP60 in various cancers.

BUB1 Inhibition Overcomes Radio- and Chemoradiation Resistance in Lung Cancer

Background: Despite advances in targeted therapies and immunotherapies, traditional treatments like microtubule stabilizers (paclitaxel, docetaxel), DNA-intercalating platinum drugs (cisplatin), and radiation therapy remain essential for managing locally advanced and metastatic lung cancer. Identifying novel molecular targets could enhance the efficacy of these treatments. Hypothesis: We hypothesize that BUB1 (Ser/Thr kinase) is overexpressed in lung cancers and its inhibition will sensitize lung cancers to chemoradiation. Methods: BUB1 inhibitor (BAY1816032) was combined with cisplatin, paclitaxel, a PARP inhibitor olaparib, and radiation in cell proliferation and radiation-sensitization assays. Biochemical and molecular assays evaluated the impact on DNA damage signaling and cell death. Results: Immunostaining of lung tumor microarrays (TMAs) confirmed higher BUB1 expression in non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) compared to normal tissues. In NSCLC, BUB1 overexpression correlated directly with the expression of TP53 mutations and poorer overall survival in NSCLC and SCLC patients. BAY1816032 synergistically sensitized lung cancer cell lines to paclitaxel and olaparib and enhanced cell killing by radiation in both NSCLC and SCLC. Molecular analysis indicated a shift towards pro-apoptotic and anti-proliferative states, evidenced by altered BAX, BCL2, PCNA, and Caspases-9 and -3 expressions. Conclusions: Elevated BUB1 expression is associated with poorer survival in lung cancer. Inhibiting BUB1 sensitizes NSCLC and SCLC to chemotherapies (cisplatin, paclitaxel), targeted therapy (olaparib), and radiation. Furthermore, we present the novel finding that BUB1 inhibition sensitized both NSCLC and SCLC to radiotherapy and chemoradiation. Our results demonstrate BUB1 inhibition as a promising strategy to sensitize lung cancers to radiation and chemoradiation therapies.

BUB1 inhibition sensitizes lung cancer cell lines to radiotherapy and chemoradiotherapy

Background

Lung cancer is a major public health concern, with high incidence and mortality. Despite advances in targeted therapy and immunotherapy, microtubule stabilizers (paclitaxel, docetaxel), DNA intercalating platinum drugs (cisplatin) and radiation therapy continue to play a critical role in the management of locally advanced and metastatic lung cancer. Novel molecular targets would provide opportunities for improving the efficacies of radiotherapy and chemotherapy.

Hypothesis

We hypothesize that BUB1 (Ser/Thr kinase) is over-expressed in lung cancers and that its inhibition will sensitize lung cancers to chemoradiation.

Methods

BUB1 inhibitor (BAY1816032) was combined with platinum (cisplatin), microtubule poison (paclitaxel), a PARP inhibitor (olaparib) and radiation in cell proliferation and radiation sensitization assays. Biochemical and molecular assays were used to evaluate their impact on DNA damage signaling and cell death mechanisms.

Results

BUB1 expression assessed by immunostaining of lung tumor microarrays (TMAs) confirmed higher BUB1 expression in NSCLC and SCLC compared to that of normal tissues. BUB1 overexpression in lung cancer tissues correlated directly with expression of TP53 mutations in non-small cell lung cancer (NSCLC). Elevated BUB1 levels correlated with poorer overall survival in NSCLC and small cell lung cancer (SCLC) patients. A BUB1 inhibitor (BAY1816032) synergistically sensitized lung cancer cell lines to paclitaxel and olaparib. Additionally, BAY1816032 enhanced cell killing by radiation in both NSCLC and SCLC. Molecular changes following BUB1 inhibition suggest a shift towards pro-apoptotic and anti-proliferative states, indicated by altered expression of BAX, BCL2, PCNA, and Caspases 9 and 3.

Conclusion

A direct correlation between BUB1 protein expression and overall survival was shown. BUB1 inhibition sensitized both NSCLC and SCLC to various chemotherapies (cisplatin, paclitaxel) and targeted therapy (PARPi). Furthermore, we present the novel finding that BUB1 inhibition sensitized both NSCLC and SCLC to radiotherapy and chemoradiation. Our results demonstrate BUB1 inhibition as a promising strategy to sensitize lung cancers to radiation and chemoradiation therapies.

Loss of ORP3 induces aneuploidy and promotes bladder cancer cell invasion through deregulated microtubule and actin dynamics

We have recently shown that loss of ORP3 leads to aneuploidy induction and promotes tumor formation. However, the specific mechanisms by which ORP3 contributes to ploidy-control and cancer initiation and progression is still unknown. Here, we report that ORP3 is highly expressed in ureter and bladder epithelium while its expression is downregulated in invasive bladder cancer cell lines and during tumor progression, both in human and in mouse bladder cancer. Moreover, we observed an increase in the incidence of N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN)-induced invasive bladder carcinoma in the tissue-specific Orp3 knockout mice. Experimental data demonstrate that ORP3 protein interacts with γ-tubulin at the centrosomes and with components of actin cytoskeleton. Altering the expression of ORP3 induces aneuploidy and genomic instability in telomerase-immortalized urothelial cells with a stable karyotype and influences the migration and invasive capacity of bladder cancer cell lines. These findings demonstrate a crucial role of ORP3 in ploidy-control and indicate that ORP3 is a bona fide tumor suppressor protein. Of note, the presented data indicate that ORP3 affects both cell invasion and migration as well as genome stability through interactions with cytoskeletal components, providing a molecular link between aneuploidy and cell invasion and migration, two crucial characteristics of metastatic cells.

CAMK2D serves as a molecular scaffold for RNF8-MAD2 complex to induce mitotic checkpoint in glioma

MAD2 is a spindle assembly checkpoint protein that participates in the formation of mitotic checkpoint complex, which blocks mitotic progression. RNF8, an established DNA damage response protein, has been implicated in mitotic checkpoint regulation but its exact role remains poorly understood. Here, RNF8 proximity proteomics uncovered a role of RNF8-MAD2 in generating the mitotic checkpoint signal. Specifically, RNF8 competes with a small pool of p31comet for binding to the closed conformer of MAD2 via its RING domain, while CAMK2D serves as a molecular scaffold to concentrate the RNF8-MAD2 complex via transient/weak interactions between its p-Thr287 and RNF8's FHA domain. Accordingly, RNF8 overexpression impairs glioma stem cell (GSC) mitotic progression in a FHA- and RING-dependent manner. Importantly, low RNF8 expression correlates with inferior glioma outcome and RNF8 overexpression impedes GSC tumorigenicity. Last, we identify PLK1 inhibitor that mimics RNF8 overexpression using a chemical biology approach, and demonstrate a PLK1/HSP90 inhibitor combination that synergistically reduces GSC proliferation and stemness. Thus, our study has unveiled a previously unrecognized CAMK2D-RNF8-MAD2 complex in regulating mitotic checkpoint with relevance to gliomas, which is therapeutically targetable.

An Aurora B-RPA signaling axis secures chromosome segregation fidelity

Errors in chromosome segregation underlie genomic instability associated with cancers. Resolution of replication and recombination intermediates and protection of vulnerable single-stranded DNA (ssDNA) intermediates during mitotic progression requires the ssDNA binding protein Replication Protein A (RPA). However, the mechanisms that regulate RPA specifically during unperturbed mitotic progression are poorly resolved. RPA is a heterotrimer composed of RPA70, RPA32 and RPA14 subunits and is predominantly regulated through hyperphosphorylation of RPA32 in response to DNA damage. Here, we have uncovered a mitosis-specific regulation of RPA by Aurora B kinase. Aurora B phosphorylates Ser-384 in the DNA binding domain B of the large RPA70 subunit and highlights a mode of regulation distinct from RPA32. Disruption of Ser-384 phosphorylation in RPA70 leads to defects in chromosome segregation with loss of viability and a feedback modulation of Aurora B activity. Phosphorylation at Ser-384 remodels the protein interaction domains of RPA. Furthermore, phosphorylation impairs RPA binding to DSS1 that likely suppresses homologous recombination during mitosis by preventing recruitment of DSS1-BRCA2 to exposed ssDNA. We showcase a critical Aurora B-RPA signaling axis in mitosis that is essential for maintaining genomic integrity.

Therapeutic targets in cancer treatment: Cell cycle proteins

Cancer has been linked to the uncontrolled proliferation of cells and the overexpression of cell-cycle genes. The cell cycle machinery plays a crucial role in the regulation of the apoptosis to mitosis to growth phase progression. The mechanisms of the cell cycle also play an important role in preventing DNA damage. There are multiple members of the protein kinase family that are involved in the activities of the cell cycle. Essential cyclins effectively regulate cyclin-dependent kinases (CDKs), which are themselves adversely regulated by naturally occurring CDK inhibitors. Despite the fact that various compounds can effectively block the cell cycle kinases and being investigated for their potential to fight cancer. This chapter explains the detail of cell cycle and checkpoint regulators, that are crucial to the malignant cellular process. The known CDKs inhibitors and their mechanism of action in various cancers have also been addressed as a step toward the development of a possibly novel technique for the design of new drugs against cell cycle kinase proteins.