Biology subjects

Whitaker, R. H.

Publications and source records attributed to Whitaker, R. H..

3 recordsLinked to original sources

bioRxiv2021

CDK4/6 inhibitors induce replication stress to cause long-term cell cycle withdrawal

AO_SCPLOWBSTRACTC_SCPLOWCDK4/6 inhibitors arrest the cell cycle in G1-phase. They are approved to treat breast cancer and are also undergoing clinical trials against a range of other tumour types. To facilitate these efforts, it is important to understand why a cytostatic arrest in G1 causes long-lasting effects on tumour growth. Here we demonstrate that a prolonged G1-arrest following CDK4/6 inhibition downregulates replisome components and impairs origin licencing. This causes a failure in DNA replication after release from that arrest, resulting in a p53-dependent withdrawal from the cell cycle. If p53 is absent, then cells bypass the G2-checkpoint and undergo a catastrophic mitosis resulting in excessive DNA damage. These data therefore link CDK4/6 inhibition to genotoxic stress; a phenotype that is shared by most other broad-spectrum anti-cancer drugs. This provides a rationale to predict responsive tumour types and effective combination therapies, as demonstrated by the fact that CDK4/6 inhibition induces sensitivity to chemotherapeutics that also cause replication stress.

cancer biology↗

bioRxiv2020

Rab27b regulates the release, autophagic clearance, and toxicity of alpha-synuclein

Alpha synuclein (syn) is the primary component of proteinaceous aggregates termed Lewy Bodies that pathologically define synucleinopathies including Parkinsons disease (PD) and Dementia with Lewy Bodies (DLB). Syn is hypothesized to spread through the brain in a prion-like fashion by misfolded protein forming a template for aggregation of endogenous syn. The release and uptake of syn from cell to cell are considered important processes for this prion-like spread. Rab27b is one of several GTPases essential to the endosomal-lysosomal pathway and is implicated in protein secretion and clearance but has yet to be characterized in its role in syn spread. In this study, we used a paracrine syn in vitro model to test the impact of Rab27b on syn release, clearance, and toxicity. shRNA-mediated knockdown (KD) of Rab27b increased syn-mediated paracrine toxicity. While Rab27b reduced syn release primarily through non-exosomal pathways, the syn released under KD conditions was of higher molecular weight species by size exclusion chromatography. Rab27b KD increased intracellular insoluble syn levels and led to an accumulation of endogenous LC3 positive puncta. Rab27b KD also decreased LC3 turnover with chloroquine treatment, indicating a defect in autophagic flux. Rab27b protein levels were increased in postmortem human brain lysates from PD and DLB subjects compared to healthy controls. These data indicate a role for Rab27b in the release, clearance, and toxicity of syn and ultimately in the pathogenesis of synucleinopathies.

neuroscience↗

bioRxiv2019

Specific inhibition of DPY30 activity by ASH2L-derived peptides suppresses blood cancer cell growth

DPY30 facilitates H3K4 methylation by directly binding to ASH2L in the SET1/MLL complexes and plays an important role in hematologic malignancies. However, the domain on DPY30 that regulates cancer growth is not evident, and the potential of pharmacologically targeting this chromatin modulator to inhibit cancer has not been explored. Here we have developed a peptide-based strategy to specifically target DPY30 activity. We have designed cell-penetrating peptides derived from ASH2L that can either bind to DPY30 or show defective or enhanced binding to DPY30. The DPY30-binding peptides specifically inhibit its activity in interacting with ASH2L and enhancing H3K4 methylation. Treatment with the DPY30-binding peptides significantly inhibited the growth of MLL-rearranged leukemia and other MYC-dependent hematologic cancer cells. We also revealed subsets of genes that may mediate the effect of the peptides on cancer cell growth, and showed that the DPY30-binding peptide sensitized leukemia to other types of epigenetic inhibitors. These results strongly support a critical role of the ASH2L-binding groove of DPY30 in promoting blood cancers, and demonstrate a proof-of-principle for the feasibility of pharmacologically targeting the ASH2L-binding groove of DPY30 for potential cancer inhibition.

cancer biology↗