NF1 loss of function as an alternative initiating event in pancreatic ductal adenocarcinoma

Impact of Mutational Status on Intracellular Effects of Cell-Permeable CaaX Peptides in Pancreatic Cancer Cells

Prenyltransferases add a lipid group to the cysteine of a CaaX motif of proteins. This posttranslational modification enables proteins to attach to membranes where they are essential hubs for signaling, trafficking, and apoptosis. Recently, cell-permeable CaaX-peptides are developed as possible tools to interfere with the prenylation machinery. These peptides cause cytotoxic effects, particularly in KRas mutant pancreatic cancer cells (PANC-1) in which they also alter downstream signaling of Ras proteins. Herein, the aim is to get more clues about the relevance of the mutational status of KRas. Therefore, the activity of CaaX-peptides in KRas wildtype BxPC-3 and KRas mutated PANC-1 cells is compared. CaaX-peptides differently influence these two cell lines, although they internalize pretty much to the same extent. Indeed, an altered KRas plasma membrane localization in PANC-1 cells is observed, probably induced by disturbed KRas prenylation based on the presence of CaaX-peptides. The impact of CaaX-peptides on KRas signaling is likely dependent on the KRas mutation in PANC-1 cells in which they further trigger effects on KRas-dependent regulators, e.g., Neurofibromin -1 (NF1) and son of sevenless homolog 1 (SOS1). All in all, CaaX peptides are identified as promising tools for studying and manipulating the function of therapeutically important prenylated proteins.

New Therapeutic Targets in RAS Wild-type Pancreatic Cancer

OPINION STATEMENT

The landscape of treatment of advanced PDAC is witnessing significant changes. This is in part due to the advent of molecular profiling, which has highlighted molecularly-distinct subsets of pts, especially those with KRAS wild-type disease. We now know that these pts harbor genomic alterations that not only serve as molecular drivers but also pose as therapeutically relevant markers. In the absence of strong evidence to support the use of targeted therapy in the front-line setting, we continue to offer chemotherapy for treatment-naïve pts. However, an argument can be made for the front-line use of targeted therapy in pts who are not fit for chemotherapy or who are not interested in it. The challenge is ensuring that molecular profiling is done in a timely fashion to prevent significant delays in therapy. In our practice, we offer molecular testing to all pts with a new diagnosis of advanced PDAC. We prefer the utility of targeted therapy in the second line and beyond for pts who have an actionable target, over the use of further chemotherapy, as targeted therapy appears to confer deep and durable responses and longer survival. For pts with MSI-H or MMRd disease, the use of immunotherapy is indicated, although it has to be noted that MSI-H/MMRd PDAC performed worse that other MSI-H/MMRd cancers treated with immunotherapy. Therefore, in the presence of MSI-H/MMRd and an additional actionable target, we prefer treating with targeted therapy and reserving immunotherapy for later lines. Pt preference has to be taken into consideration at all times though.

Molecular and Clinical Features of Pancreatic Acinar Cell Carcinoma: A Single-Institution Case Series

Objectives: Acinar cell carcinoma (ACC) accounts for about 1% of pancreatic cancers. The molecular and clinical features of ACC are less characterized than those of pancreatic ductal adenocarcinoma. Methods: We retrospectively evaluated the clinical and molecular features of ACC patients who underwent germline and/or somatic molecular testing at The University of Texas MD Anderson Cancer Center from 2008 to 2022 and two cases from 2023-2024 who underwent RNA and TME analysis by Boston Gene. Patient information was extracted from our institutional database with the approval of the Institutional Review Board. Results: We identified 16 patients with available molecular testing results. Fourteen patients had metastatic disease, one had borderline resectable disease, and one had localized resectable disease at diagnosis. Fifteen patients were wild type for KRAS (one patient had unknown KRAS status). Somatic/germline mutations of DNA damage repair genes (BRCA1/2, PALB2, and ATM) were present in 5 of 12 patients tested for these genes. One patient was found to have RET fusion and responded favorably to selpercatinib for over 42 months. The median overall survival (OS) was 24 months for patients with metastatic disease. One of the additional two cases who underwent BostonGene testing was found to have NTRK1 fusion. RNA and TME analysis by Boston Gene of the two cases reported immune desert features and relatively lower RNA levels of CEACAM5, CD47, CD74, and MMP1 and higher RNA levels of CDH6 compared with PDAC.

K128 ubiquitination constrains RAS activity by expanding its binding interface with GAP proteins

The RAS pathway is among the most frequently activated signaling nodes in cancer. However, the mechanisms that alter RAS activity in human pathologies are not entirely understood. The most prevalent post-translational modification within the GTPase core domain of NRAS and KRAS is ubiquitination at lysine 128 (K128), which is significantly decreased in cancer samples compared to normal tissue. Here, we found that K128 ubiquitination creates an additional binding interface for RAS GTPase-activating proteins (GAPs), NF1 and RASA1, thus increasing RAS binding to GAP proteins and promoting GAP-mediated GTP hydrolysis. Stimulation of cultured cancer cells with growth factors or cytokines transiently induces K128 ubiquitination and restricts the extent of wild-type RAS activation in a GAP-dependent manner. In KRAS mutant cells, K128 ubiquitination limits tumor growth by restricting RAL/ TBK1 signaling and negatively regulating the autocrine circuit induced by mutant KRAS. Reduction of K128 ubiquitination activates both wild-type and mutant RAS signaling and elicits a senescence-associated secretory phenotype, promoting RAS-driven pancreatic tumorigenesis.

The oncogenic role of NF1 in gallbladder cancer through regulation of YAP1 stability by direct interaction with YAP1

BACKGROUND

Gallbladder cancer (GBC) is the most prevalent and invasive biliary tract malignancy. As a GTPase-activating protein, Neurofibromin 1 (NF1) is a tumor suppressor that negatively regulates the RAS signaling pathway, and its abnormality leads to neurofibromatosis type 1 (NF-1) disease. However, the role of NF1 playing in GBC and the underlying molecular mechanism has not been defined yet.

METHODS

A combination of NOZ and EH-GB1 cell lines as well as nude mice, were utilized in this study. mRNA expression and protein levels of NF1 and YAP1 were evaluated by quantitative real-time PCR (qRT-PCR), western blot (WB), and immunohistochemistry (IHC). In vitro and in vivo assays were performed to explore the biological effects of NF1 in NOZ and EH-GB1 cells via siRNA or lv-shRNA mediated knockdown. Direct interaction between NF1 and YAP1 was detected by confocal microscopy and co-immunoprecipitation (Co-IP), and further confirmed by GST pull-down assay and isothermal titration calorimetry assay (ITC). The stability of proteins was measured by western blot (WB) in the presence of cycloheximide.

RESULTS

This study showed that a higher level of NF1 and YAP1 was found in GBC samples than in normal tissues and associated with worse prognoses. The NF1 knockdown impaired the proliferation and migration of NOZ in vivo and in vitro by downregulating YAP1 expression. Moreover, NF1 co-localized with YAP1 in NOZ and EH-GB1 cells, and the WW domains of YAP1 specifically recognized the PPQY motif of NF1. The structural modeling also indicated the hydrophobic interactions between YAP1 and NF1. On the other hand, YAP1 knockdown also impaired the proliferation of NOZ in vitro, phenocopying the effects of NF1 knockdown. Overexpression of YAP1 can partially rescue the impaired proliferation in NF1 stably knockdown cells. In mechanism, NF1 interacted with YAP1 and increased the stability of YAP1 by preventing ubiquitination.

CONCLUSIONS

Our findings discovered a novel oncogenic function of NF1 by directly interacting with YAP1 protein and stabilizing YAP1 to protect it from proteasome degradation in NOZ cells. NF1 may serve as a potential therapeutic target in GBC.