Pharmacologic Inactivation of Kinase Suppressor of Ras1 Sensitizes Epidermal Growth Factor Receptor and Oncogenic Ras-Dependent Tumors to Ionizing Radiation Treatment

Multiomics Study of a Novel Naturally Derived Small Molecule, NSC772864, as a Potential Inhibitor of Proto-Oncogenes Regulating Cell Cycle Progression in Colorectal Cancer

Colorectal cancer (CRC) is one of the most prevalent malignant tumors, and it contributes to high numbers of deaths globally. Although advances in understanding CRC molecular mechanisms have shed significant light on its pathogenicity, current treatment options, including combined chemotherapy and molecular-targeted agents, are still limited due to resistance, with almost 25% of patients developing distant metastasis. Therefore, identifying novel biomarkers for early diagnosis is crucial, as they will also influence strategies for new targeted therapies. The proto-oncogene, c-Met, a tyrosine kinase that promotes cell proliferation, motility, and invasion; c-MYC, a transcription factor associated with the modulation of the cell cycle, proliferation, apoptosis; and cyclin D1 (CCND1), an essential regulatory protein in the cell cycle, all play crucial roles in cancer progression. In the present study, we explored computational simulations through bioinformatics analysis and identified the overexpression of c-Met/GSK3β/MYC/CCND1 oncogenic signatures that were associated with cancer progression, drug resistance, metastasis, and poor clinical outcomes in CRC. We further demonstrated the anticancer activities of our newly synthesized quinoline-derived compound, NSC772864, against panels of the National Cancer Institute's human CRC cell lines. The compound exhibited cytotoxic activities against various CRC cell lines. Using target prediction tools, we found that c-Met/GSK3β/MYC/CCND1 were target genes for the NSC772864 compound. Subsequently, we performed in silico molecular docking to investigate protein-ligand interactions and discovered that NSC772864 exhibited higher binding affinities with these oncogenes compared to FDA-approved drugs. These findings strongly suggest that NSC772864 is a novel and potential antiCRC agent.

praja2 regulates KSR1 stability and mitogenic signaling

The kinase suppressor of Ras 1 (KSR1) has a fundamental role in mitogenic signaling by scaffolding components of the Ras/MAP kinase pathway. In response to Ras activation, KSR1 assembles a tripartite kinase complex that optimally transfers signals generated at the cell membrane to activate ERK. We describe a novel mechanism of ERK attenuation based on ubiquitin-dependent proteolysis of KSR1. Stimulation of membrane receptors by hormones or growth factors induced KSR1 polyubiquitination, which paralleled a decline of ERK1/2 signaling. We identified praja2 as the E3 ligase that ubiquitylates KSR1. We showed that praja2-dependent regulation of KSR1 is involved in the growth of cancer cells and in the maintenance of undifferentiated pluripotent state in mouse embryonic stem cells. The dynamic interplay between the ubiquitin system and the kinase scaffold of the Ras pathway shapes the activation profile of the mitogenic cascade. By controlling KSR1 levels, praja2 directly affects compartmentalized ERK activities, impacting on physiological events required for cell proliferation and maintenance of embryonic stem cell pluripotency.

Roles of glucose transporter-1 and the phosphatidylinositol 3‑kinase/protein kinase B pathway in cancer radioresistance (review)

The mechanisms underlying cancer radioresistance remain unclear. Several studies have found that increased glucose transporter‑1 (GLUT‑1) expression is associated with radioresistance. Recently, the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway was reported to be involved in the control of GLUT‑1 trafficking and activity. Activation of the PI3K/Akt pathway may itself be associated with cancer radioresistance. Thus, increasing attention has been devoted to the effects of modifying the expression of GLUT‑1 and the PI3K/Akt pathway on the increase in the radiosensitivity of cancer cells. This review discusses the importance of the association between elevated expression of GLUT‑1 and activation of the PI3K/Akt pathway in the development of radioresistance in cancer.

PARP inhibitor attenuated colony formation can be restored by MAP kinase inhibitors in different irradiated cancer cell lines

Abstract Purpose: Sensitizing cancer cells to irradiation is a major challenge in clinical oncology. We aimed to define the signal transduction pathways involved in poly(ADP-ribose) polymerase (PARP) inhibitor-induced radiosensitization in various mammalian cancer lines.

MATERIALS AND METHODS

Clonogenic survival assays and Western blot examinations were performed following telecobalt irradiation of cancer cells in the presence or absence of various combinations of PARP- and selective mitogen-activated protein kinase (MAPK) inhibitors.

RESULTS

HO3089 resulted in significant cytotoxicity when combined with irradiation. In human U251 glioblastoma and A549 lung cancer cell lines, Erk1/2 and JNK/SAPK were found to mediate this effect of HO3089 since inhibitors of these kinases ameliorated it. In murine 4T1 breast cancer cell line, p38 MAPK rather than Erk1/2 or JNK/SAPK was identified as the main mediator of HO3089's radiosensitizing effect. Besides the aforementioned changes in kinase signaling, we detected increased p53, unchanged Bax and decreased Bcl-2 expression in the A549 cell line.

CONCLUSIONS

HO3089 sensitizes cancer cells to photon irradiation via proapoptotic processes where p53 plays a crucial role. Activation of MAPK pathways is regarded the consequence of irradiation-induced DNA damage, thus their inhibition can counteract the radiosenzitizing effect of the PARP inhibitor.

The RhoGEF GEF-H1 is required for oncogenic RAS signaling via KSR-1

Cellular transformation by oncogenic RAS engages the MAPK pathway under strict regulation by the scaffold protein KSR-1. Here, we report that the guanine nucleotide exchange factor GEF-H1 plays a critical role in a positive feedback loop for the RAS/MAPK pathway independent of its RhoGEF activity. GEF-H1 acts as an adaptor protein linking the PP2A B' subunits to KSR-1, thereby mediating the dephosphorylation of KSR-1 S392 and activation of MAPK signaling. GEF-H1 is important for the growth and survival of HRAS(V12)-transformed cells and pancreatic tumor xenografts. GEF-H1 expression is induced by oncogenic RAS and is correlated with pancreatic neoplastic progression. Our results, therefore, identify GEF-H1 as an amplifier of MAPK signaling and provide mechanistic insight into the progression of RAS mutant tumors.

The role of pseudokinases in cancer

Kinases play a critical role in regulating many cellular functions including development, differentiation and proliferation. To date, over 518 proteins with kinase activity, comprising ~2-3% of total cellular proteins, have been identified from within the human kinome. Interestingly, approximately 10% of kinases are categorised as pseudokinases since they lack one or more conserved catalytic residues within their kinase domain and were originally thought to have no enzymatic activity. Recently, there has been strong evidence to suggest that some pseudokinsases can not only function as scaffold proteins, but may also possess kinase activity leading to modulation of cell signalling pathways. Altered activity of these pseudokinases can result in impaired cellular function, particularly in malignancies. In this review we are discussing recent evidence that apart from a scaffolding role, pseudokinases also orchestrate cellular processes as active kinases per se in signalling pathways of malignant cells.

Suppression of Ras/Mapk pathway signaling inhibits Myc-induced lymphomagenesis

Although the Myc transcription factor has been shown necessary for the oncogenic function of Ras, the contribution of Ras pathway signaling to the oncogenic function of Myc remains unresolved. We report the novel findings that Myc alone induced Ras/Mapk pathway signaling, and increased signaling following growth factor stimulation. Deletion of the scaffold protein kinase suppressor of Ras 1 (Ksr1) attenuated signaling through the Ras/Mapk pathway, including activation following Myc induction. B cells that lacked Ksr1 exhibited reduced proliferation and increased cytokine deprivation-induced apoptosis. Overexpression of Myc rescued the proliferation defect of Ksr1-null B cells, but loss of Ksr1 increased sensitivity of B cells to Myc-induced apoptosis. Notably, there was a significant delay in lymphoma development in Ksr1-null mice overexpressing Myc in B cells (Eμ-myc transgenic mice). There was an elevated frequency of p53 inactivation, indicative of increased selective pressure to bypass the p53 tumor suppressor pathway, in Ksr1-null Eμ-myc lymphomas. Therefore, loss of Ksr1 inhibits Ras/Mapk pathway signaling leading to increased Myc-induced B-cell apoptosis, and this results in reduced B-cell transformation and lymphoma development. Our data indicate that suppression of Myc-induced Ras/Mapk pathway signaling significantly impairs Myc oncogenic function. These results fill a significant gap in knowledge about Myc and should open new avenues of therapeutic intervention for Myc-overexpressing malignancies.

Protein-intrinsic and signaling network-based sources of resistance to EGFR- and ErbB family-targeted therapies in head and neck cancer

Agents targeting EGFR and related ErbB family proteins are valuable therapies for the treatment of many cancers. For some tumor types, including squamous cell carcinomas of the head and neck (SCCHN), antibodies targeting EGFR were the first protein-directed agents to show clinical benefit, and remain a standard component of clinical strategies for management of the disease. Nevertheless, many patients display either intrinsic or acquired resistance to these drugs; hence, major research goals are to better understand the underlying causes of resistance, and to develop new therapeutic strategies that boost the impact of EGFR/ErbB inhibitors. In this review, we first summarize current standard use of EGFR inhibitors in the context of SCCHN, and described new agents targeting EGFR currently moving through pre-clinical and clinical development. We then discuss how changes in other transmembrane receptors, including IGF1R, c-Met, and TGF-β, can confer resistance to EGFR-targeted inhibitors, and discuss new agents targeting these proteins. Moving downstream, we discuss critical EGFR-dependent effectors, including PLC-γ; PI3K and PTEN; SHC, GRB2, and RAS and the STAT proteins, as factors in resistance to EGFR-directed inhibitors and as alternative targets of therapeutic inhibition. We summarize alternative sources of resistance among cellular changes that target EGFR itself, through regulation of ligand availability, post-translational modification of EGFR, availability of EGFR partners for hetero-dimerization and control of EGFR intracellular trafficking for recycling versus degradation. Finally, we discuss new strategies to identify effective therapeutic combinations involving EGFR-targeted inhibitors, in the context of new system level data becoming available for analysis of individual tumors.