The relationship between oncogenic KRas and wild-type Ras activity and signaling
Creators: name: Kewagamang, Kitso Ata
Publisher: name: TU Dortmund
Year: 2024
Subjects: subject: Ras
subject: Oncogenic KRas
subject: Signaling dynamic
subject: Chemically induced dimerization
subject: 570
subject: 540
subject: Krebs
subject: Maligne Transformation

description: Ras proteins play an important role in various signaling cascades, transducing external signals into phenotypic and behavioral responses. In many cancers, however, Ras-mediated signaling is dysregulated, with mutated, constitutively active KRas proteins being the most pervasive in pancreatic ductal carcinoma and colorectal cancer. The mechanisms driving this dysregulation are complex. Wild-type Ras isoforms, including the cognate wild-type Ras counterpart to the oncogenic Ras, are thought to play distinct roles in how they mediate Ras signaling and alter cell behavior in cancerous cells. Moreover, overexpressed oncogenic Ras proteins can cause senescence when heterogeneously expressed with wild-type Ras isoforms. The molecular mechanism of this oncogene-induced senescence is not fully understood, although the involvement of tumor suppressor proteins such as p53 has been shown. Whether an interaction between oncogenic and wild-type Ras also plays a role here remains unclear. To investigate how oncogenic KRas activity affects wild-type Ras activity and subsequent signaling, a two-component chemical genetic approach was developed. This technique allows bioorthogonal chemical control of the amount of KRas oncoproteins at the plasma membrane. It leverages the important feature of plasma membrane localization of Ras proteins in signal transduction. The results herein show that a reversible, chemically-induced dimerization system can effectively control plasma membrane localization of ectopically expressed KRas in cells. Using this approach, we found that cytosolic oncogenic KRas (possessing G12V or G12D mutations) has higher GTP-loading compared to wild-type KRas, providing further evidence for its constitutive activity. We also show that acutely enriching overexpressed wild-type KRas and oncogenic KRas at the plasma membrane resulted in transient activation of endogenous wild-type Ras and the downstream signaling effectors ERK and AKT. As Epidermal Growth Factor (EGF) – mediated-Ras signaling is often dysregulated in cancer, an investigation into the effects of plasma membrane localization of oncogenic KRas on this network was performed by way of EGF dose-response experiments. Results suggest that accumulation of oncogenic KRas proteins at the plasma membrane causes an ultrasensitive response in endogenous wild-type Ras activity and downstream effectors at lower EGF doses, compared to wild-type cells. Additionally, clonogenic assays revealed that over-expressed KRas G12V and G12D oncoproteins were associated with reduced proliferation, regardless of whether they were localized in the cytosol or at the plasma membrane. Collectively, these findings indicate that KRas oncoproteins have an activating interaction with the wild-type Ras proteins at the plasma membrane and initiate downstream signaling. Furthermore, oncogenic Ras may increase the sensitivity of transformed cells to growth factor stimulation by this interaction with wild-type Ras. However, these effects alone are likely insufficient to drive tumorigenesis when oncogenic KRas is overexpressed, as proliferation was suppressed. Thus, further mechanisms may be required for cancer formation. Altogether, these results help to explain some of the changes in signaling responses to growth factors in KRas-driven carcinogenesis.