Rab coupling protein mediated endosomal recycling of N-cadherin influences cell motility

A systematic computational analysis of the endosomal recycling pathway in glioblastoma

Glioblastoma (GBM) is the most common and aggressive brain cancer in adults. The standard treatment is brutal and has changed little in 20 years, and more than 85% of patients will die within two years of their diagnosis. There is thus an urgent need to identify new drug targets and develop novel therapeutic strategies to increase survival and improve quality of life. Using publicly available genomics, transcriptomics and proteomics datasets, we compared the expression of endosomal recycling pathway regulators in non-tumour brain tissue with their expression in GBM. We found that key regulators of this pathway are dysregulated in GBM and their expression levels can be linked to survival outcomes. Further analysis of the differentially expressed endosomal recycling regulators allowed us to generate an 8-gene prognostic signature that can distinguish low-risk from high-risk GBM and potentially identify tumours that may benefit from treatment with endosomal recycling inhibitors. This study presents the first systematic analysis of the endosomal recycling pathway in glioblastoma and suggests it could be a promising target for the development of novel therapies and therapeutic strategies to improve outcomes for patients.

Endosomal recycling inhibitors downregulate estrogen receptor-alpha and synergise with endocrine therapies

PURPOSE

Breast cancer (BC) accounts for roughly 30% of new cancers diagnosed in women each year; thus, this cancer type represents a substantial burden for people and health care systems. Despite the existence of effective therapies to treat BC, drug resistance remains a problem and is a major cause of treatment failure. Therefore, new drugs and treatment regimens are urgently required to overcome resistance. Recent research indicates that inhibition of the endosomal recycling pathway, an intracellular membrane trafficking pathway that returns endocytosed proteins back to the plasma membrane, may be a promising strategy to downregulate clinically relevant cell surface proteins such as HER2 and HER3, and to overcome drug resistance.

METHODS

To investigate the molecular mechanism of action of an endosomal recycling inhibitor (ERI) called primaquine, we performed a reverse-phase protein array (RPPA) assay using a HER2-positive breast cancer cell line. The RPPA findings were confirmed by Western blot and RT-qPCR in several BC cell lines. Novel drug combinations were tested by MTT cell viability and clonogenic assays.

RESULTS

Among the signalling molecules downregulated by ERIs were estrogen receptor-alpha (ER-α) and androgen receptor. We confirmed this finding in other breast cancer cell lines and show that downregulation occurs at the transcriptional level. We also found that ERIs synergise with tamoxifen, a standard-of-care therapy for breast cancer.

DISCUSSION

Our data suggest that combining ERIs with hormone receptor antagonists may enhance their efficacy and reduce the emergence of drug resistance.

YAP1 controls the N-cadherin-mediated tumor-stroma interaction in melanoma progression

The hallmark of epithelial-to-mesenchymal transition (EMT) is the switch from epithelial cadherin (E-cadherin) to neural cadherin (N-cadherin), allowing melanoma cells to form a homotypic N-cadherin-mediated adhesion with stromal fibroblasts. However, how cadherin switching is initiated, maintained, and regulated in melanoma remains elusive. Here, we report a novel mechanism underlying cadherin switching in melanoma cells that is regulated by stromal Yes-associated protein 1 (YAP1) signaling. The progression of a BRAF-mutant mouse melanoma was suppressed in vivo upon YAP1 ablation in cancer-associated fibroblasts (CAFs). On the contrary, overexpressing YAP1 in CAFs accelerated melanoma development. By RNA-Seq, N-cadherin was identified as a major downstream effector of YAP1 signaling in CAFs. YAP1 silencing reduced N-cadherin expression in CAFs, leading to the downregulation of N-cadherin in neighboring melanoma cells. N-cadherin ablation inhibited the PI3K-AKT signaling pathway in melanoma cells and melanoma cell proliferation. The findings suggest that YAP1 depletion in CAFs induces the downregulation of p-AKT signaling in melanoma cells through the N-cadherin-mediated interaction between melanoma cells and CAFs. The data underscore an important role of CAFs in regulating N-cadherin-mediated adhesion and signaling in melanoma and highlight that disentangling cadherin-mediated cell-cell interactions can potentially disrupt tumor-stroma interactions and reverse the tumor cell invasive phenotype.

Endosomal recycling inhibitors downregulate the androgen receptor and synergise with enzalutamide

Prostate cancer is the second most frequent cancer diagnosed in men, and accounts for one-fifth of cancer associated deaths worldwide. Despite the availability of effective prostate cancer therapies, if it is not cured by radical local treatment, progression to drug resistant metastatic prostate cancer is inevitable. Therefore, new drugs and treatment regimens are urgently required to overcome resistance. We have recently published research demonstrating that targeting the endosomal recycling pathway, a membrane transport pathway that recycles internalised cell surface proteins back to the plasma membrane, may be a novel means to downregulate clinically relevant cell surface proteins and potentially overcome drug resistance. A reverse phase protein array (RPPA) assay of breast cancer cells treated with an endosomal recycling inhibitor identified the androgen receptor (AR) as one of the top downregulated proteins. We confirmed that endosomal recycling inhibitors also downregulated AR in prostate cancer cells and show that this occurs at the transcriptional level. We also found that endosomal recycling inhibitors synergise with enzalutamide, a standard-of-care therapy for prostate cancer. Our data suggest that combining recycling inhibitors with hormone receptor antagonists may enhance their efficacy and reduce the emergence of drug resistance.

YAP1 controls the N-cadherin-mediated tumor-stroma interaction in melanoma progression

Epithelial-to-mesenchymal transition (EMT) is crucial for melanoma cells to escape keratinocyte control, invade underlying dermal tissues, and metastasize to distant organs. The hallmark of EMT is the switch from epithelial cadherin (E-cadherin) to neural cadherin (N-cadherin), allowing melanoma cells to form a homotypic N-cadherin-mediated adhesion with stromal fibroblasts. However, how "cadherin switching" is initiated, maintained, and regulated in melanoma remains unknown. Here, we show that upon Yes-associated protein 1 (YAP1) ablation in cancer-associated fibroblasts (CAFs), the progression of a BRAF-mutant mouse melanoma was significantly suppressed in vivo, and overexpressing YAP1 in CAFs accelerated melanoma growth. CAFs require the YAP1 function to proliferate, migrate, remodel the cytoskeletal machinery and matrix, and promote cancer cell invasion. By RNA-Seq, N-cadherin was identified as a major downstream effector of YAP1 signaling in CAFs. YAP1 silencing led to N-cadherin downregulation in CAFs, which subsequently induced the downregulation of N-cadherin in neighboring melanoma cells. N-cadherin downregulation inhibited the PI3K-AKT signaling pathway in melanoma cells and suppressed melanoma growth in vivo, supporting the role of N-cadherin as an adhesive and signaling molecule in melanoma cells. This finding suggests that YAP1 depletion in CAFs induces the downregulation of p-AKT signaling in melanoma cells through the N-cadherin-mediated interaction between melanoma cells and CAFs. Importantly, our data underscore that CAFs can regulate N-cadherin-mediated interactions with melanoma cells. Thus, disentangling cadherin-mediated cell-cell interactions can potentially disrupt tumor-stroma interactions and reverse the tumor cell invasive phenotype.

The small GTPase ARF3 controls invasion modality and metastasis by regulating N-cadherin levels

ARF GTPases are central regulators of membrane trafficking that control local membrane identity and remodeling facilitating vesicle formation. Unraveling their function is complicated by the overlapping association of ARFs with guanine nucleotide exchange factors (GEFs), GTPase-activating proteins (GAPs), and numerous interactors. Through a functional genomic screen of three-dimensional (3D) prostate cancer cell behavior, we explore the contribution of ARF GTPases, GEFs, GAPs, and interactors to collective invasion. This revealed that ARF3 GTPase regulates the modality of invasion, acting as a switch between leader cell-led chains of invasion or collective sheet movement. Functionally, the ability of ARF3 to control invasion modality is dependent on association and subsequent control of turnover of N-cadherin. In vivo, ARF3 levels acted as a rheostat for metastasis from intraprostatic tumor transplants and ARF3/N-cadherin expression can be used to identify prostate cancer patients with metastatic, poor-outcome disease. Our analysis defines a unique function for the ARF3 GTPase in controlling how cells collectively organize during invasion and metastasis.

TP53 mutations upregulate RCP expression via Sp1/3 to drive lung cancer progression

Mutant p53 (mtp53) can exert cancer-promoting activities via "gain-of-function", which has become a popular research target. Although lots of researchers focus on the tumor-suppressor role for p53, the regulation of mutant p53 remains unknown. Here, we report a mechanism by which mtp53 regulate the transcription of Rab coupling protein (RCP) to influence lung cancer behavior. First, we show that RCP is specifically expressed at high levels in lung cancer tissues and cells, and RCP knockout suppresses tumor growth and metastasis. Further mass spectrometry and functional analysis identify that Sp1, Sp3 and Stat3 are the transcriptional activators of RCP. Moreover, p53 is involved in modulating RCP expression in an Sp1/3 dependent manner. Mechanistically, in contrast to wild-type p53 suppression of RCP transcription by decreasing Sp1/3 proteins, TP53 mutations have changed on Sp1/3 expression via "loss-of-function". Surprisingly, the DNA contact mutants of p53 further robustly enhance their binding ability with Sp1/3 to drive RCP expression through the "gain-of-function" activity. Collectively, we reveal a mechanism by which p53 regulating the transcription of RCP to influence lung cancer progression, which provides new insights for treating p53 mutant lung cancer.

Inhibition of the endosomal recycling pathway downregulates HER2 activation and overcomes resistance to tyrosine kinase inhibitors in HER2-positive breast cancer

The development of HER2-targeted therapies has led to a dramatic improvement in outcomes for breast cancer patients. However, nearly all patients with metastatic HER2-positive breast cancer will eventually progress on these therapies due to innate or acquired resistance. Recent evidence suggests that the endosomal recycling of HER2 plays an important role in regulating its oncogenic signalling. Here we report that the expression of Rab coupling protein (RCP), a key regulator of endosomal recycling, positively correlates with that of HER2 and HER3 in breast tumours, and high RCP expression is predictive of poor relapse-free and overall survival in patients with HER2-amplified breast cancer. Chemical and genetic inhibition of endosomal recycling leads to a reduction in the total cellular levels of HER2 and HER3 and inhibits the activation of their downstream signalling pathways. We find that HER2 and HER3 that have been internalised from the plasma membrane are diverted to lysosomes for degradation when endosomal recycling is blocked. Primaquine (PQ), a small molecule inhibitor of the endosomal recycling pathway, synergises with HER2-targeting tyrosine kinase inhibitors and overcomes innate and acquired resistance to these TKIs. Moreover, TKI-induced drug tolerant persister cells are vulnerable to endosomal recycling inhibitors. These findings suggest that inhibition of endosomal recycling represents a promising therapeutic strategy for treating drug resistant HER2-positive breast cancer.

Glypican 4 regulates planar cell polarity of endoderm cells by controlling the localization of Cadherin 2

Noncanonical Wnt/planar cell polarity (Wnt/PCP) signaling has been implicated in endoderm morphogenesis. However, the underlying cellular and molecular mechanisms of this process are unclear. We found that, during convergence and extension (C&E) in zebrafish, gut endodermal cells are polarized mediolaterally, with GFP-Vangl2 enriched at the anterior edges. Endoderm cell polarity is lost and intercalation is impaired in the absence of glypican 4 (gpc4), a heparan-sulfate proteoglycan that promotes Wnt/PCP signaling, suggesting that this signaling is required for endodermal cell polarity. Live imaging revealed that endoderm C&E is accomplished by polarized cell protrusions and junction remodeling, which are impaired in gpc4-deficient endodermal cells. Furthermore, in the absence of gpc4, Cadherin 2 expression on the endodermal cell surface is increased as a result of impaired Rab5c-mediated endocytosis, which partially accounts for the endodermal defects in these mutants. These findings indicate that Gpc4 regulates endodermal planar cell polarity during endoderm C&E by influencing the localization of Cadherin 2. Thus, our study uncovers a new mechanism by which Gpc4 regulates planar cell polarity and reveals the role of Wnt/PCP signaling in endoderm morphogenesis.

Rab11-FIP1 mediates epithelial-mesenchymal transition and invasion in esophageal cancer

Esophageal squamous cell carcinoma (ESCC) is the most common subtype of esophageal cancer worldwide. The most commonly mutated gene in ESCC is TP53. Using a combinatorial genetic and carcinogenic approach, we generate a novel mouse model of ESCC expressing either mutant or null p53 and show that mutant p53 exhibits enhanced tumorigenic properties and displays a distinct genomic profile. Through RNA-seq analysis, we identify several endocytic recycling genes, including Rab Coupling Protein (Rab11-FIP1), which are significantly downregulated in mutant p53 tumor cells. In 3-dimensional (3D) organoid models, genetic knockdown of Rab11-FIP1 results in increased organoid size. Loss of Rab11-FIP1 increases tumor cell invasion in part through mutant p53 but also in an independent manner. Furthermore, loss of Rab11-FIP1 in human ESCC cell lines decreases E-cadherin expression and increases mesenchymal lineage-specific markers, suggesting induction of epithelial-mesenchymal transition (EMT). Rab11-FIP1 regulates EMT through direct inhibition of Zeb1, a key EMT transcriptional factor. Our novel findings reveal that Rab11-FIP1 regulates organoid formation, tumor cell invasion, and EMT.

Integrin linked kinase regulates endosomal recycling of N-cadherin in melanoma cells

Malignant transformation is characterized by a phenotype "switch" from E- to N-cadherin - a major hallmark of epithelial to mesenchymal transition (EMT). The increased expression of N-cadherin is commonly followed by a growing capacity for migration as well as resistance to apoptosis. Integrin Linked Kinase (ILK) is a key molecule involved in EMT and progression of cancer cells. ILK is known as a major signaling mediator involved in cadherin switch, but the specific mechanism through which ILK modulates N-cadherin expression is still not clear. Studies were carried out on human melanoma WM793 and 1205Lu cell lines. Expression of proteins was analyzed using PCR and Western Blot; siRNA transfection was done for ILK. Analysis of cell signaling pathways was monitored with phospho-specific antibodies. Subcellular localization of protein was studied using the ProteoExtract Subcellular Kit and Western blot analysis. Our data show that ILK knockdown by siRNA did suppress N-cadherin expression in melanoma, but only at the protein level. The ILK silencing-induced decrease of N-cadherin membranous expression in melanoma highlights the likely crucial role of ILK in the coordination of membrane trafficking through alteration of Rab expression. It is essential to understand the molecular mechanism of increased N-cadherin expression in cancer to possibly use it in the search of new therapeutic targets.

Vesicle trafficking pathways that direct cell migration in 3D matrices and in vivo

Cell migration is a vital process in development and disease, and while the mechanisms that control motility are relatively well understood on two-dimensional surfaces, the control of cell migration in three dimensions (3D) and in vivo has only recently begun to be understood. Vesicle trafficking pathways have emerged as a key regulatory element in migration and invasion, with the endocytosis and recycling of cell surface cargos, including growth factor and chemokine receptors, adhesion receptors and membrane-associated proteases, being of major importance. We highlight recent advances in our understanding of how endocytic trafficking controls the availability and local activity of these cargoes to influence the movement of cells in 3D matrix and in developing organisms. In particular, we discuss how endocytic trafficking of different receptor classes spatially restricts signals and activity, usually to the leading edge of invasive cells.

Rab11 family expression in the human placenta: Localization at the maternal-fetal interface

Rab proteins are a family of small GTPases involved in a variety of cellular processes. The Rab11 subfamily in particular directs key steps of intracellular functions involving vesicle trafficking of the endosomal recycling pathway. This Rab subfamily works through a series of effector proteins including the Rab11-FIPs (Rab11 Family-Interacting Proteins). While the Rab11 subfamily has been well characterized at the cellular level, its function within human organ systems is still being explored. In an effort to further study these proteins, we conducted a preliminary investigation of a subgroup of endosomal Rab proteins in a range of human cell lines by Western blotting. The results from this analysis indicated that Rab11a, Rab11c(Rab25) and Rab14 were expressed in a wide range of cell lines, including the human placental trophoblastic BeWo cell line. These findings encouraged us to further analyse the localization of these Rabs and their common effector protein, the Rab Coupling Protein (RCP), by immunofluorescence microscopy and to extend this work to normal human placental tissue. The placenta is a highly active exchange interface, facilitating transfer between mother and fetus during pregnancy. As Rab11 proteins are closely involved in transcytosis we hypothesized that the placenta would be an interesting human tissue model system for Rab investigation. By immunofluorescence microscopy, Rab11a, Rab11c(Rab25), Rab14 as well as their common FIP effector RCP showed prominent expression in the placental cell lines. We also identified the expression of these proteins in human placental lysates by Western blot analysis. Further, via fluorescent immunohistochemistry, we noted abundant localization of these proteins within key functional areas of primary human placental tissues, namely the outer syncytial layer of placental villous tissue and the endothelia of fetal blood vessels. Overall these findings highlight the expression of the Rab11 family within the human placenta, with novel localization at the maternal-fetal interface.