Biology subjects

Abankwa, D. K.

Publications and source records attributed to Abankwa, D. K..

4 recordsLinked to original sources

bioRxiv2024

A general Bioluminescence Resonance Energy Transfer (BRET) protocol to measure and analyze protein interactions in mammalian cells

Bioluminescence resonance energy transfer (BRET) allows to quantitate protein interactions in intact cells. Here we provide a step-by-step protocol for measuring BRET due to transient interactions of oncogenic K-RasG12V in plasma membrane nanoclusters of HEK293-EBNA cells. We describe how to seed, transfect and replate cells, followed by their preparation for BRET-measurements on a microplate reader and detailed data analysis steps. For details on how to apply this protocol, please refer to Steffen et al., 2024 1. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/602189v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@152e8c2org.highwire.dtl.DTLVardef@2f2aacorg.highwire.dtl.DTLVardef@9a8e9borg.highwire.dtl.DTLVardef@108833f_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2023

RAS isoform specific activities are disrupted by disease associated mutations during cell differentiation

The Ras-MAPK pathway is aberrantly regulated in cancer and developmental diseases called RASopathies. While typically the impact of Ras on the proliferation of various cancer cell lines is assessed, it is poorly established how Ras affects cellular differentiation. Here we implement the C2C12 myoblast cell line to systematically study the effect of Ras mutants and Ras-pathway drugs on differentiation. We first provide evidence that a minor pool of Pax7+ progenitors replenishes a major pool of transit amplifying cells that are ready to differentiate. Our data indicate that Ras isoforms have distinct roles in the differentiating culture, where K-Ras is more important than N-Ras to maintain the progenitor pool and H-Ras is significant for terminal differentiation. This assay could therefore provide significant new insights into Ras biology and Ras-driven diseases. In line with this, we found that all oncogenic Ras mutants block terminal differentiation of transit amplifying cells. Notably, while RASopathy K-Ras variants that are also NF1-GAP resistant also block differentiation, albeit less than their oncogenic counterparts. Profiling of targeted Ras-pathway drugs on oncogenic Ras mutants revealed their distinct abilities to restore normal differentiation as compared to triggering cell death. In particular, the MEK-inhibitor trametinib could broadly restore differentiation, while the mTOR-inhibitor rapamycin broadly suppressed differentiation. We expect that this quantitative assessment of the impact of Ras-pathway mutants and drugs on cellular differentiation has great potential to complement cancer cell proliferation data.

cell biology↗

bioRxiv2023

Identification of an H-Ras nanocluster disrupting peptide

The Ras-MAPK pathway is critical to regulate cell proliferation and differentiation. Its dysregulation is implicated in the onset and progression of numerous types of cancers. To be active, Ras proteins are membrane anchored and organized into nanoclusters, which realize high-fidelity signal transmission across the plasma membrane. Nanoclusters therefore represent potential drug targets. However, targetable protein components of signalling nanoclusters are poorly established. We previously proposed that the nanocluster scaffold galectin-1 (Gal1) enhances H-Ras nanoclustering by stabilizing stacked dimers of H-Ras and Raf via a direct interaction of dimeric Gal1 with the Ras binding domain (RBD) in particular of B-Raf. Here, we provide further supportive evidence for this model. We establish that the B-Raf preference emerges from divergent regions of the Raf RBDs that were proposed to interact with Gal1. We then identify the L5UR peptide, which disrupts this interaction by binding with low micromolar affinity to the B-Raf-RBD. Its 23-mer core fragment is thus sufficient to interfere with Gal1-enhanced H-Ras nanocluster, reduce MAPK-output and cell viability in HRAS-mutant cancer cell lines. Our data therefore suggest that the interface between Gal1 and the RBD of B-Raf can be targeted to disrupt Gal1-enhanced H-Ras nanoclustering. Collectively, our results support that Raf-proteins are integral components of active Ras nanoclusters.

biochemistry↗

bioRxiv2023

An improved PDE6D inhibitor combines with Sildenafil to synergistically inhibit KRAS mutant cancer cell growth

The trafficking chaperone PDE6D (or PDE) was proposed as a surrogate target for K-Ras, leading to the development of a series of inhibitors that block its prenyl-binding pocket. These inhibitors suffered from low solubility and intracellular potency, preventing their clinical development. Here we developed a highly soluble PDE6D inhibitor (PDE6Di), Deltaflexin3, which has the currently lowest off-target activity, as we demonstrate in dedicated assays. We further increased the K-Ras focus, by exploiting that PKG2-mediated phosphorylation of Ser181 lowers K-Ras binding to PDE6D. Thus, the combination of Deltaflexin3 with the approved PKG2-activator Sildenafil synergistically inhibits cell- and microtumor growth. However, the overall cancer survival of the high PDE6D/ low PKG2 target population is higher than of the group with the opposite signature. Our results therefore suggest re-examining the interplay between PDE6D and K-Ras in cancer, while recommending the development of PDE6Di that plug, rather than stuff the hydrophobic pocket of PDE6D. SignificanceCombinations of a novel PDE6D inhibitor with Sildenafil synergistically focus the inhibition on K-Ras, however, survival data of the target population suggest an interplay of K-Ras and PDE6D that needs further exploration.

biochemistry↗