Dephosphorylation of p-ERK1/2 in relation to tumor remission after HER-2 and Raf1 blocking therapy in a conditional mouse tumor model

Targeting CRAF kinase in anti-cancer therapy: progress and opportunities

The RAS/mitogen-activated protein kinase (MAPK) signaling cascade is commonly dysregulated in human malignancies by processes driven by RAS or RAF oncogenes. Among the members of the RAF kinase family, CRAF plays an important role in the RAS-MAPK signaling pathway, as well as in the progression of cancer. Recent research has provided evidence implicating the role of CRAF in the physiological regulation and the resistance to BRAF inhibitors through MAPK-dependent and MAPK-independent mechanisms. Nevertheless, the effectiveness of solely targeting CRAF kinase activity remains controversial. Moreover, the kinase-independent function of CRAF may be essential for lung cancers with KRAS mutations. It is imperative to develop strategies to enhance efficacy and minimize toxicity in tumors driven by RAS or RAF oncogenes. The review investigates CRAF alterations observed in cancers and unravels the distinct roles of CRAF in cancers propelled by diverse oncogenes. This review also seeks to summarize CRAF-interacting proteins and delineate CRAF's regulation across various cancer hallmarks. Additionally, we discuss recent advances in pan-RAF inhibitors and their combination with other therapeutic approaches to improve treatment outcomes and minimize adverse effects in patients with RAF/RAS-mutant tumors. By providing a comprehensive understanding of the multifaceted role of CRAF in cancers and highlighting the latest developments in RAF inhibitor therapies, we endeavor to identify synergistic targets and elucidate resistance pathways, setting the stage for more robust and safer combination strategies for cancer treatment.

Regulation of cell proliferation and migration by keratin19-induced nuclear import of early growth response-1 in breast cancer cells

PURPOSE

Keratin19 (KRT19) is the smallest known type I intermediate filament and is used as a marker for reverse transcriptase PCR-mediated detection of disseminated tumors. In this study, we investigated the functional analysis of KRT19 in human breast cancer.

EXPERIMENTAL DESIGN

Using a short hairpin RNA system, we silenced KRT19 in breast cancer cells. KRT19 silencing was verified by Western blot analysis and immunocytochemistry. We further examined the effect of KRT19 silencing on breast cancer cells by cell proliferation, migration, invasion, colony formation assay, cell-cycle analysis, immunocytochemistry, immunohistochemistry, and mouse xenograft assay.

RESULTS

Silencing of KRT19 resulted in increased cell proliferation, migration, invasion, and survival. These effects were mediated by upregulation of Akt signaling as a result of reduced PTEN mRNA expression. Silencing of KRT19 decreased the nuclear import of early growth response-1 (Egr1), a transcriptional factor for PTEN transcription, through reduced association between Egr1 and importin-7. We also confirmed that silencing of KRT19 increased tumor formation in a xenograft model.

CONCLUSIONS

KRT19 is a potential tumor suppressor that negatively regulates Akt signaling through modulation of Egr1 nuclear localization.

From man to mouse and back again: advances in defining tumor AKTivities in vivo

AKT hyperactivation is a common event in human cancers, and inhibition of oncogenic AKT activation is a major goal of drug discovery programs. Mouse tumor models that replicate AKT activation typical of human cancers provide a powerful means by which to investigate mechanisms of oncogenic signaling, identify potential therapeutic targets and determine treatment regimes with maximal therapeutic efficacy. This Perspective highlights recent advances using in vivo studies that reveal how AKT signaling supports tumor formation, cooperates with other mutations to promote tumor progression and facilitates tumor-cell dissemination, focusing on well-characterized prostate carcinoma mouse models that are highly sensitive to AKT activation. The implications of these findings on the therapeutic targeting of AKT and potential new drug targets are also explored.

Isolation of fibroblasts for coating of meshes for reconstructive surgery: differences between mesh types

Aims: An extensive colonization of surgical meshes with autologous fibroblasts may reduce complications. Therefore, we aimed to establish a technique that allows isolation and propagation of fibroblasts from vaginal biopsies. Using these cells we tested the applicability of several clinically applied meshes for fibroblast coating. Materials & methods: Fibroblasts were isolated from vaginal tissue after digestion with collagenase. Characterization was performed by immunostaining for cytokeratin 5, 6 and 14, smooth muscle actin and vimentin. A semiquantitative technique was applied to determine the degree of mesh coating 5 h and 5 weeks after seeding of fibroblasts. Seven meshes of different mesh types have been tested. Results: Cells with a fibroblast-like morphology have been isolated from vaginal tissue and could be propagated for at least 12 passages, resulting in a total number of 1.2 × 107 cells. Immunostaining showed that cells were positive for the mesenchymal cell marker vimentin and negative for smooth muscle actin, as well as the epithelial cell markers cytokeratin 5, 6 and 14, supporting their classification as fibroblasts. Clear differences in fibroblast colonization between the seven tested mesh types have been observed. Polypropylene mesh Obtape® showed an acceptable covering with fibroblasts. The best coating was obtained for xenograft-based meshes, but under cell-culture conditions the mesh showed signs of decomposition. Conclusion: We have established a technique that allows isolation and propagation of vaginal fibroblasts. The result of vaginal fibroblast colonization of allograft-based meshes strongly depends on the mesh type, whereby the best coating could be achieved for a polypropylene mesh.

Trastuzumab therapy vs tetracycline controlled ERBB2 downregulation: influence on tumour development in an ERBB2-dependent mouse tumour model

Trastuzumab (Herceptin) has improved therapy of breast cancer. Only patients overexpressing ERBB2 are treated with trastuzumab, whereas its use in tumours without ERBB2 expression is useless. This led to the concept that the subgroup of trastuzumab-sensitive tumours is ‘ERBB2-dependent’, meaning that ERBB2 signalling is indispensable for growth of these tumours. We used a mouse model that allows anhydrotetracycline (ATc)-controlled downregulation of ERBB2 in tumour tissue. ERBB2 mRNA and protein expression were downregulated below detection limit leading to a macroscopically complete tumour remission within 14 days. Tumour remission was accompanied by a strong decrease in proliferation, a moderate increase in apoptosis, as well as dephosphorylation of ERK1/2 and AKT/PKB. These data clearly indicate ERBB2 dependence. Therefore, a high sensitivity to trastuzumab may be suspected. Surprisingly, trastuzumab caused a much weaker effect compared to ATc-induced ERBB2 downregulation, although a decrease in ERBB2 membrane localisation was induced. Only a slight decrease in proliferation and a weak transient increase in apoptosis were observed. Interestingly, tumours responded to trastuzumab by a sharp fivefold increase in phosphorylated AKT/PKB as well as a 3.5- and 5.3-fold increase in AKT1 and AKT2 mRNA levels, respectively. In conclusion, ‘ERBB2 dependence’ is not sufficient to define trastuzumab-responsive tumours. The suboptimal effect of trastuzumab compared to the maximally possible effect induced by ATc demonstrates a high potential for improved ERBB2 blocking therapies.

Tracking of human cells in mice

Tracking and tracing of transplanted cells in mice is required in many fields of research. Examples are transplantation of stem cells into organs of mice to study their differentiation capacity and injection of tumor cells to examine metastatic behavior. In the present study we tested the lipid dye CM-DiI and red fluorescent nanoparticles Qdot655 for their applicability in tagging and tracing of human cells in mice. Labeling of different cell types, including MCF-7 human breast cancer cells, human cord blood derived cells, human NeoHep cells and human hepatopancreatic precursor cells, is technically easy and did not compromise further cell culture. After transplantation of CM-DiI or Qdot655 marked cells, red fluorescent structures could be detected already in unprocessed paraffin slices of the studied organs, namely liver, lung, pancreas, kidney, spleen and bone marrow. Next, we examined whether the red fluorescent structures represent the transplanted human cells. For this purpose, we established an in situ hybridization (ISH) technique that allows clear-cut differentiation between human and murine nuclei, based on simultaneous hybridization with human alu and mouse major satellite (mms) probes. We observed a high degree of coincidence between CM-DiI-marked cells and alu positive nuclei. However, also some mms positive cells contained CM-DiI, suggesting phagocytosis of the transplanted CM-DiI-marked cells. The degree of such CM-DiI-positive mouse cells depended on the cell type and route of administration. From a technical point of view it was important that CM-DiI-positive structures in paraffin slices remained fluorescent also after ISH. In contrast, Qdot655 positive structures faded during further staining procedures. In conclusion, marking of cells with CM-DiI or Qdot655 prior to transplantation facilitates recovery of human cells, since a high fraction of positive structures in the host's tissue originate from the transplanted cells. However, CM-DiI or Qdot655 positive staining of individual cells in transplanted tissues is not sufficient to prove their human origin. Additional procedures, such as ISH with alu-probes, are essential, when characterizing individual cells.

Conditional transgenic mouse models: from the basics to genome-wide sets of knockouts and current studies of tissue regeneration

Many mouse models are currently available, providing avenues to elucidate gene function and to recapitulate specific pathological conditions. To a large extent, successful translation of clinical evidence or analytical data into appropriate mouse models is possible through progress in transgenic or gene-targeting technology. Beginning with a review of standard mouse transgenics and conventional gene targeting, this article will move on to discussing the basics of conditional gene expression: the tetracycline (tet)-off and tet-on systems based on the transactivators tet-controlled transactivator (Tta) and reverse tet-on transactivator (rtTA) that allow downregulation or induction of gene expression; Cre or Flp recombinase-mediated modifications, including excision, inversion, insertion and interchromosomal translocation; combination of the tet and Cre systems, permitting inducible knockout, reporter gene activation or activation of point mutations; the avian retroviral system based on delivery of rtTA specifically into cells expressing the avian retroviral receptor, which enables cell type-specific, inducible gene expression; the tamoxifen system, one of the most frequently applied steroid receptor-based systems, allows rapid activation of a fusion protein between the gene of interest and a mutant domain of the estrogen receptor, whereby activation does not depend on transcription; and techniques for cell type-specific ablation. The diphtheria toxin receptor system offers the advantage that it can be combined with the ‘zoo’ of Cre recombinase driver mice. Having described the basics we move on to the cutting edge: generation of genome-wide sets of conditional knockout mice. To this end, large ongoing projects apply two strategies: gene trapping based on random integration of trapping vectors into introns leading to truncation of the transcript, and gene targeting, representing the directed approach using homologous recombination. It can be expected that in the near future genome-wide sets of such mice will be available. Finally, the possibilities of conditional expression systems for investigating gene function in tissue regeneration will be illustrated by examples for neurodegenerative disease, liver regeneration and wound healing of the skin.

Role of urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor type 1 (PAI-1) for prognosis in endometrial cancer

BACKGROUND

Urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor type 1 (PAI-1) contribute to the invasiveness of many carcinomas. Here, we studied a possible association between cytosolic uPA and PA-1 concentrations in tumor tissue with prognosis in patients with endometrial cancer.

METHODS

Cytosolic concentrations of uPA and PAI-1 were determined in 69 primary endothelial adenocarcinomas using an enzyme-linked immunoassay (ELISA). A possible influence of uPA and PAI-1 was studied by multivariate Cox regression adjusting for the established clinical prognostic factors FIGO-stage, grading, depth of invasion, diabetes mellitus and age.

RESULTS

Both uPA (p=0.011) and PAI-1 (p=0.003) were associated with relapse free time using the multivariate proportional hazards model. Association with overall survival was less pronounced with p=0.021 for uPA and p=0.358 for PAI-1. Concentrations of PAI-1 increased with FIGO stage (p=0.003) and with histological grading (p=0.005). Both uPA and PAI-1 concentrations were negatively correlated with estrogen and progesterone receptor levels.

CONCLUSION

The combination of high cytosolic concentrations of uPA (>5 ng/mg total protein) and high PAI-1 (>20 ng/mg total protein) may reveal a group of patients with increased risk of progression.