Rab25-Mediated EGFR Recycling Causes Tumor Acquired Radioresistance

The protease ADAMTS5 controls ovarian cancer cell invasion, downstream of Rab25

Ovarian cancer is the 3rd most common gynaecological malignancy worldwide, with a 5-year survival rate of < 30% in the presence of metastasis. Metastatic progression is characterised by extensive remodelling of the extracellular matrix, primarily mediated by secreted proteases, including members of the 'a disintegrin and metalloprotease with thrombospondin motif' (ADAMTS) family. In particular, ADAMTS5 has been reported to be upregulated in ovarian malignant tumours compared to borderline and benign lesions, suggesting it might play a role in metastatic progression. Furthermore, it has been suggested that Rab25, a small GTPase of the Ras family, might upregulate ADAMTS5 expression in ovarian cancer cells. Here we demonstrated that Rab25 promotes ADAMTS5 expression through the activation of the nuclear factor κB (NF-κB) signalling pathway. Furthermore, ADAMTS5 was necessary and sufficient to stimulate ovarian cancer cell migration through complex fibroblast-secreted matrices, while selective ADAMTS5 inhibition prevented ovarian cancer spheroid invasion in 3D systems. Finally, in ovarian cancer patients, high ADAMTS5 expression correlated with poor prognosis. Altogether, these data identify ADAMTS5 as a novel regulator of ovarian cancer cell migration and invasion, suggesting it might represent a previously undescribed therapeutic target to prevent ovarian cancer metastasis.

Modulation of tumor inflammatory signaling and drug sensitivity by CMTM4

Although inflammation has been widely associated with cancer development, how it affects the outcomes of immunotherapy and chemotherapy remains incompletely understood. Here, we show that CKLF-like MARVEL transmembrane domain-containing member 4 (CMTM4) is highly expressed in multiple human and murine cancer types including Lewis lung carcinoma, triple-negative mammary cancer and melanoma. In lung carcinoma, loss of CMTM4 significantly reduces tumor growth and impairs NF-κB, mTOR, and PI3K/Akt pathway activation. Furthermore, we demonstrate that CMTM4 can regulate epidermal growth factor (EGF) signaling post-translationally by promoting EGFR recycling and preventing its Rab-dependent degradation. Consequently, CMTM4 knockout sensitizes human lung tumor cells to EGFR inhibitors. In addition, CMTM4 knockout tumors stimulated with EGF show a decreased ability to produce inflammatory cytokines including granulocyte colony-stimulating factor (G-CSF), leading to decreased recruitment of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) and therefore establishing a less suppressive tumor immune environment in both lung and mammary cancers. We also present evidence indicating that CMTM4-targeting siRNA-loaded liposomes reduce lung tumor growth in vivo and prolong animal survival. Knockout of CMTM4 enhances immune checkpoint blockade or chemotherapy to further reduce lung tumor growth. These data suggest that CMTM4 represents a novel target for the inhibition of tumor inflammation, and improvement of the immune response and tumor drug sensitivity.

Insights into the role of derailed endocytic trafficking pathway in cancer: From the perspective of cancer hallmarks

The endocytic trafficking pathway is a highly organized cellular program responsible for the regulation of membrane components and uptake of extracellular substances. Molecules internalized into the cell through endocytosis will be sorted for degradation or recycled back to membrane, which is determined by a series of sorting events. Many receptors, enzymes, and transporters on the membrane are strictly regulated by endocytic trafficking process, and thus the endocytic pathway has a profound effect on cellular homeostasis. However, the endocytic trafficking process is typically dysregulated in cancers, which leads to the aberrant retention of receptor tyrosine kinases and immunosuppressive molecules on cell membrane, the loss of adhesion protein, as well as excessive uptake of nutrients. Therefore, hijacking endocytic trafficking pathway is an important approach for tumor cells to obtain advantages of proliferation and invasion, and to evade immune attack. Here, we summarize how dysregulated endocytic trafficking process triggers tumorigenesis and progression from the perspective of several typical cancer hallmarks. The impact of endocytic trafficking pathway to cancer therapy efficacy is also discussed.

Rab25 suppresses colon cancer cell invasion through upregulating claudin‑7 expression

Ras‑related protein 25 (Rab25) is a member of small GTPase and is implicated in cancer cell progression of various types of cancer. Growing evidence suggests the context‑dependent role of Rab25 in cancer invasiveness. Claudin‑7 is a tight junction protein and has been known to suppress cancer cell invasion. Although Rab25 was reported to repress cancer aggressiveness through recycling β1 integrin to the plasma membrane, the detailed underlying mechanism remains to be elucidated. The present study identified the critical role of claudin‑7 in Rab25‑induced suppression of colon cancer invasion. 3D Matrigel system and modified Boyden chamber analysis showed that enforced expression of Rab25 attenuated colon cancer cell invasion. In addition, Rab25 inactivated epidermal growth factor receptor (EGFR) and increased E‑cadherin expression. Unexpectedly, it was observed that Rab25 induces claudin‑7 expression through protein stabilization. In addition, ectopic claudin‑7 expression reduced EGFR activity and Snail expression as well as colon cancer cell invasion. However, silencing of claudin‑7 expression reversed the tumor suppressive role of Rab25, thereby increasing colon cancer cell invasiveness. Collectively, the present data indicated that Rab25 inactivates EGFR and colon cancer cell invasion by upregulating claudin‑7 expression.

New Directions for Advanced Targeting Strategies of EGFR Signaling in Cancer

Epidermal growth factor (EGF)-EGF receptor (EGFR) signaling studies paved the way for a basic understanding of growth factor and oncogene signaling pathways and the development of tyrosine kinase inhibitors (TKIs). Due to resistance mutations and the activation of alternative pathways when cancer cells escape TKIs, highly diverse cell populations form in recurrent tumors through mechanisms that have not yet been fully elucidated. In this review, we summarize recent advances in EGFR basic research on signaling networks and intracellular trafficking that may clarify the novel mechanisms of inhibitor resistance, discuss recent clinical developments in EGFR-targeted cancer therapy, and offer novel strategies for cancer drug development.

Cezanne promoted autophagy through PIK3C3 stabilization and PIK3C2A transcription in lung adenocarcinoma

Osimertinib is a promising approved third-generation epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) for treating patients with lung adenocarcinoma (LUAD) harboring EGFR-activating mutations, however, almost all patients develop resistance to Osimertinib eventually limiting the long-term efficacy. Autophagy is a vital cellular recycling process promoting Osimertinib resistance. Identifying accurate and efficient autophagy-regulatory factors is of great significance in reducing Osimertinib resistance. This study identified Cezanne, a member of the ovarian tumor protease (OTU)-deubiquitinating family, as an autophagy regulator. Cezanne was highly expressed in Osimertinib-resistant cells, and Cezanne overexpression promoted Osimertinib resistance, while chloroquine (CQ), an autophagy inhibitor, reverted this process. In the Cezanne-overexpressing cells, autophagy was activated even in the absence of autophagy inducers rapamycin and Earle's Balanced Salt Solution (EBSS). Further study showed that Cezanne stabilized PIK3C3 by deubiquitinating K48-linked ubiquitination at Lysine 322. Surprisingly, as a compensatory mechanism of PI3P generation, PIK3C2A was shown to be upregulated by Cezanne by promoting its transcription in a POLR2A-dependent way. Based on these results, Cezanne also accelerates EGFR recycling which may explain the mechanism mediating Cezanne expression and Osimertinib resistance. In conclusion, this study establishes a new model connecting Cezanne, autophagy, and Osimertinib resistance, opening new avenues to explore the effect of Cezanne and autophagy in LUAD.

An integrated mechanistic and data-driven computational model predicts cell responses to high- and low-affinity EGFR ligands

The biophysical properties of ligand binding heavily influence the ability of receptors to specify cell fates. Understanding the rules by which ligand binding kinetics impact cell phenotype is challenging, however, because of the coupled information transfers that occur from receptors to downstream signaling effectors and from effectors to phenotypes. Here, we address that issue by developing an integrated mechanistic and data-driven computational modeling platform to predict cell responses to different ligands for the epidermal growth factor receptor (EGFR). Experimental data for model training and validation were generated using MCF7 human breast cancer cells treated with the high- and low-affinity ligands epidermal growth factor (EGF) and epiregulin (EREG), respectively. The integrated model captures the unintuitive, concentration-dependent abilities of EGF and EREG to drive signals and phenotypes differently, even at similar levels of receptor occupancy. For example, the model correctly predicts the dominance of EREG over EGF in driving a cell differentiation phenotype through AKT signaling at intermediate and saturating ligand concentrations and the ability of EGF and EREG to drive a broadly concentration-sensitive migration phenotype through cooperative ERK and AKT signaling. Parameter sensitivity analysis identifies EGFR endocytosis, which is differentially regulated by EGF and EREG, as one of the most important determinants of the alternative phenotypes driven by different ligands. The integrated model provides a new platform to predict how phenotypes are controlled by the earliest biophysical rate processes in signal transduction and may eventually be leveraged to understand receptor signaling system performance depends on cell context.

One-sentence summary

Integrated kinetic and data-driven EGFR signaling model identifies the specific signaling mechanisms that dictate cell responses to EGFR activation by different ligands.

Sialylation of EGFR by ST6GAL1 induces receptor activation and modulates trafficking dynamics

Aberrant glycosylation is a hallmark of a cancer cell. One prevalent alteration is an enrichment in α2,6-linked sialylation of N-glycosylated proteins, a modification directed by the ST6GAL1 sialyltransferase. ST6GAL1 is upregulated in many malignancies including ovarian cancer. Prior studies have shown that the addition of α2,6 sialic acid to the Epidermal Growth Factor Receptor (EGFR) activates this receptor, although the mechanism was largely unknown. To investigate the role of ST6GAL1 in EGFR activation, ST6GAL1 was overexpressed in the OV4 ovarian cancer line, which lacks endogenous ST6GAL1, or knocked down in the OVCAR-3 and OVCAR-5 ovarian cancer lines, which have robust ST6GAL1 expression. Cells with high expression of ST6GAL1 displayed increased activation of EGFR and its downstream signaling targets, AKT and NFκB. Using biochemical and microscopy approaches, including Total Internal Reflection Fluorescence (TIRF) microscopy, we determined that the α2,6 sialylation of EGFR promoted its dimerization and higher order oligomerization. Additionally, ST6GAL1 activity was found to modulate EGFR trafficking dynamics following EGF-induced receptor activation. Specifically, EGFR sialylation enhanced receptor recycling to the cell surface following activation while simultaneously inhibiting lysosomal degradation. 3D widefield deconvolution microscopy confirmed that in cells with high ST6GAL1 expression, EGFR exhibited greater co-localization with Rab11 recycling endosomes and reduced co-localization with LAMP1-positive lysosomes. Collectively, our findings highlight a novel mechanism by which α2,6 sialylation promotes EGFR signaling by facilitating receptor oligomerization and recycling.

PKCα is a Potentially Useful Marker for Planning Individualized Radiotherapy for Nasopharyngeal Carcinoma

Purpose

To examine the expression of protein kinase C alpha (PKCα) in nasopharyngeal carcinoma (NPC) and determine its relationship to the radio-sensitivity of NPC in order to evaluate its potential as a molecular marker for the guidance of individualized radiation therapy for NPC.

Materials and Methods

PKCα expression levels were detected in tumor samples from patients and in NPC cell lines with varying degrees of radio-sensitivity. A survival analysis was performed to analyze the association of PKCα expression with the 5-year overall survival (OS), progression-free survival (PFS), locoregional recurrence-free survival (LRFS), and distant metastasis-free survival (DMFS) in patients. In vitro and in vivo experiments using NPC cell lines were performed to study the effects of down-regulation of PKCα by short hairpin RNA treatment on the radio-sensitivity of NPC.

Results

PKCα expression was up-regulated in the well-differentiated NPC tissues of patients and in the more radio-resistant NPC cell lines. Moreover, high PKCα expression was associated with a worse 5-year PFS and LRFS of patients. shRNA-mediated knockdown of PKCα led to an increase in the sensitivity of NPC cells to radiation therapy, both in vitro as cultured cells and in vivo as tumor xenografts.

Conclusion

The elevated expression of PKCα in NPC and its association with patient PFS indicates that PKCα is a potential molecular marker for guiding precision radiotherapy in NPC patients. Also, the increased radiosensitivity of NPC cells after loss of PKCα identifies PKCα as a promising therapeutic target for enhancing the radio-sensitivity of NPC.

RAB11-Mediated Trafficking and Human Cancers: An Updated Review

Simple Summary

The small GTPase RAB11 is a master regulator of both vesicular trafficking and membrane dynamic defining the surface proteome of cellular membranes. As a consequence, the alteration of RAB11 activity induces changes in both the sensory and the transduction apparatuses of cancer cells leading to tumor progression and invasion. Here, we show that this strictly depends on RAB11′s ability to control the sorting of signaling receptors from endosomes. Therefore, RAB11 is a potential therapeutic target over which to develop future therapies aimed at dampening the acquisition of aggressive traits by cancer cells.

Abstract

Many disorders block and subvert basic cellular processes in order to boost their progression. One protein family that is prone to be altered in human cancers is the small GTPase RAB11 family, the master regulator of vesicular trafficking. RAB11 isoforms function as membrane organizers connecting the transport of cargoes towards the plasma membrane with the assembly of autophagic precursors and the generation of cellular protrusions. These processes dramatically impact normal cell physiology and their alteration significantly affects the survival, progression and metastatization as well as the accumulation of toxic materials of cancer cells. In this review, we discuss biological mechanisms ensuring cargo recognition and sorting through a RAB11-dependent pathway, a prerequisite to understand the effect of RAB11 alterations in human cancers.

Cancer-driving mutations and variants of components of the membrane trafficking core machinery

The core machinery for vesicular membrane trafficking broadly comprises of coat proteins, RABs, tethering complexes and SNAREs. As cellular membrane traffic modulates key processes of mitogenic signaling, cell migration, cell death and autophagy, its dysregulation could potentially results in increased cell proliferation and survival, or enhanced migration and invasion. Changes in the levels of some components of the core machinery of vesicular membrane trafficking, likely due to gene amplifications and/or alterations in epigenetic factors (such as DNA methylation and micro RNA) have been extensively associated with human cancers. Here, we provide an overview of association of membrane trafficking with cancer, with a focus on mutations and variants of coat proteins, RABs, tethering complex components and SNAREs that have been uncovered in human cancer cells/tissues. The major cellular and molecular cancer-driving or suppression mechanisms associated with these components of the core membrane trafficking machinery shall be discussed.