Numb Isoforms Deregulation in Medulloblastoma and Role of p66 Isoform in Cancer and Neural Stem Cells

Microbiota enterotoxigenic Bacteroides fragilis-secreted BFT-1 promotes breast cancer cell stemness and chemoresistance through its functional receptor NOD1

Tumor-resident microbiota in breast cancer promotes cancer initiation and malignant progression. However, targeting microbiota to improve the effects of breast cancer therapy has not been investigated in detail. Here, we evaluated the microbiota composition of breast tumors and found that enterotoxigenic Bacteroides fragilis (ETBF) was highly enriched in the tumors of patients who did not respond to taxane-based neoadjuvant chemotherapy. ETBF, albeit at low biomass, secreted the toxic protein BFT-1 to promote breast cancer cell stemness and chemoresistance. Mechanistic studies showed that BFT-1 directly bound to NOD1 and stabilized NOD1 protein. NOD1 was highly expressed on ALDH+ breast cancer stem cells (BCSCs) and cooperated with GAK to phosphorylate NUMB and promote its lysosomal degradation, thereby activating the NOTCH1-HEY1 signaling pathway to increase BCSCs. NOD1 inhibition and ETBF clearance increase the chemosensitivity of breast cancer by impairing BCSCs.

Role of PLK1/NUMB/NOTCH in epithelial-mesenchymal transition in human melanoma

Polo-like kinase 1 (PLK1), a serine/threonine kinase, is overexpressed in melanoma and its expression has been associated with poor disease prognosis. PLK1 has been shown to interact with NUMB, a NOTCH antagonist. However, the exact role of PLK1, NUMB, and NOTCH signaling in epithelial-mesenchymal transition (EMT) in melanoma progression is unclear. In this study, Affymetrix microarray analysis was performed to determine differentially expressed genes following shRNA-mediated knockdown of PLK1 in human melanoma cells that showed significant modulations in EMT and metastasis-related genes. Using multiple PLK1-modulated melanoma cell lines, we found that PLK1 is involved in the regulation of cell migration, invasion, and EMT via its kinase activity and NOTCH activation. In vitro kinase assay and mass spectrometry analysis demonstrated a previously unknown PLK1 phosphorylation site (Ser413) on NUMB. Overexpression of non-phosphorylatable (S413A) and phosphomimetic (S413D) mutants of NUMB in melanoma cells implicated the involvement of NUMB-S413 phosphorylation in cell migration and invasion, which was independent of NOTCH activation. To determine the clinical relevance of these findings, immunohistochemistry was performed using melanoma tissue microarray, which indicated a strong positive correlation between PLK1 and N-cadherin, a protein required for successful EMT. These findings were supported by TCGA analysis, where expression of high PLK1 with low NUMB or high NOTCH or N-cadherin showed a significant decrease in survival of melanoma patients. Overall, these results suggest a potential role of PLK1 in EMT, migration, and invasion of melanoma cells. Our findings support the therapeutic targeting of PLK1, NUMB, and NOTCH for melanoma management.

KCTD1 is a new modulator of the KCASH family of Hedgehog suppressors

The Sonic Hedgehog (Hh) signal transduction pathway plays a critical role in many developmental processes and, when deregulated, may contribute to several cancers, including basal cell carcinoma, medulloblastoma, colorectal, prostate, and pancreatic cancer. In recent years, several Hh inhibitors have been developed, mainly acting on the Smo receptor. However, drug resistance due to Smo mutations or non-canonical Hh pathway activation highlights the need to identify further mechanisms of Hh pathway modulation. Among these, deacetylation of the Hh transcription factor Gli1 by the histone deacetylase HDAC1 increases Hh activity. On the other end, the KCASH family of oncosuppressors binds HDAC1, leading to its ubiquitination and subsequent proteasomal degradation, leaving Gli1 acetylated and not active. It was recently demonstrated that the potassium channel containing protein KCTD15 is able to interact with KCASH2 protein and stabilize it, enhancing its effect on HDAC1 and Hh pathway. KCTD15 and KCTD1 proteins share a high homology and are clustered in a specific KCTD subfamily. We characterize here KCTD1 role on the Hh pathway. Therefore, we demonstrated KCTD1 interaction with KCASH1 and KCASH2 proteins, and its role in their stabilization by reducing their ubiquitination and proteasome-mediated degradation. Consequently, KCTD1 expression reduces HDAC1 protein levels and Hh/Gli1 activity, inhibiting Hh dependent cell proliferation in Hh tumour cells. Furthermore, analysis of expression data on publicly available databases indicates that KCTD1 expression is reduced in Hh dependent MB samples, compared to normal cerebella, suggesting that KCTD1 may represent a new putative target for therapeutic approaches against Hh-dependent tumour.

The Multitasker Protein: A Look at the Multiple Capabilities of NUMB

NUMB, a plasma membrane-associated protein originally described in Drosophila, is involved in determining cell function and fate during early stages of development. It is secreted asymmetrically in dividing cells, with one daughter cell inheriting NUMB and the other inheriting its antagonist, NOTCH. NUMB has been proposed as a polarizing agent and has multiple functions, including endocytosis and serving as an adaptor in various cellular pathways such as NOTCH, Hedgehog, and the P53-MDM2 axis. Due to its role in maintaining cellular homeostasis, it has been suggested that NUMB may be involved in various human pathologies such as cancer and Alzheimer's disease. Further research on NUMB could aid in understanding disease mechanisms and advancing the field of personalized medicine and the development of new therapies.

Numb-PRRL promotes TGF-β1- and EGF-induced epithelial-to-mesenchymal transition in pancreatic cancer

Isoform-specific functions of Numb in the development of cancers, especially in the initiation of epithelial-to-mesenchymal transition (EMT) remains controversial. We study the specific function of Numb-PRRL isoform in activated EMT of pancreatic ductal adenocarcinoma (PC), which is distinguished from our previous studies that only focused on the total Numb protein. Numb-PRRL isoform was specifically overexpressed and silenced in PC cells combining with TGF-β1 and EGF stimulus. We systematically explored the potential effect of Numb-PRRL in the activated EMT of PC in vitro and in vivo. The total Numb protein was overexpressed in the normal pancreatic duct and well-differentiated PC by IHC. However, Numb-PRRS isoform but not Numb-PRRL showed dominant expression in PC tissues. Numb-PRRL overexpression promoted TGF-β1-induced EMT in PANC-1 and Miapaca-2 cells. TGF-β1-induced EMT-like cell morphology, cell invasion, and migration were enhanced in Numb-PRRL overexpressing groups following the increase of N-cadherin, Vimentin, Smad2/3, Snail1, Snail2, and cleaved-Notch1 and the decrease of E-cadherin. Numb-PRRL overexpression activated TGFβ1-Smad2/3-Snail1 signaling was significantly reversed by the Notch1 inhibitor RO4929097. Conversely, Numb-PRRL silencing inhibited EGF-induced EMT in AsPC-1 and BxPC-3 cells following the activation of EGFR-ERK/MAPK signaling via phosphorylating EGFR at tyrosine 1045. In vivo, Numb-PRRL overexpression or silencing promoted or inhibited subcutaneous tumor size and distant liver metastases via regulating EMT and Snail signaling, respectively. Numb-PRRL promotes TGF-β1- and EGF-induced EMT in PC by regulating TGF-β1-Smad2/3-Snail and EGF-induced EGFR-ERK/MAPK signaling.

Targeting cancer stem cells in medulloblastoma by inhibiting AMBRA1 dual function in autophagy and STAT3 signalling

Medulloblastoma (MB) is a childhood malignant brain tumour comprising four main subgroups characterized by different genetic alterations and rate of mortality. Among MB subgroups, patients with enhanced levels of the c-MYC oncogene (MB_Group3) have the poorest prognosis. Here we identify a previously unrecognized role of the pro-autophagy factor AMBRA1 in regulating MB. We demonstrate that AMBRA1 expression depends on c-MYC levels and correlates with Group 3 patient poor prognosis; also, knockdown of AMBRA1 reduces MB stem potential, growth and migration of MB_Group3 stem cells. At a molecular level, AMBRA1 mediates these effects by suppressing SOCS3, an inhibitor of STAT3 activation. Importantly, pharmacological inhibition of autophagy profoundly affects both stem and invasion potential of MB_Group3 stem cells, and a combined anti-autophagy and anti-STAT3 approach impacts the MB_Group3 outcome. Taken together, our data support the c-MYC/AMBRA1/STAT3 axis as a strong oncogenic signalling pathway with significance for both patient stratification strategies and targeted treatments of MB_Group3.

RXRα Blocks Nerve Regeneration after Spinal Cord Injury by Targeting p66shc

Nerve regeneration after spinal cord injury is regulated by many factors. Studies have found that the expression of retinoid X receptor α (RXRα) does not change significantly after spinal cord injury but that the distribution of RXRα in cells changes significantly. In undamaged tissues, RXRα is distributed in motor neurons and the cytoplasm of glial cells. RXRα migrates to the nucleus of surviving neurons after injury, indicating that RXRα is involved in the regulation of gene expression after spinal cord injury. p66shc is an important protein that regulates cell senescence and oxidative stress. It can induce the apoptosis and necrosis of many cell types, promoting body aging. The absence of p66shc enhances the resistance of cells to reactive oxygen species (ROS) and thus prolongs life. It has been found that p66shc deletion can promote hippocampal neurogenesis and play a neuroprotective role in mice with multiple sclerosis. To verify the function of RXRα after spinal cord injury, we established a rat T9 spinal cord transection model. After RXRα agonist or antagonist administration, we found that RXRα agonists inhibited nerve regeneration after spinal cord injury, while RXRα antagonists promoted the regeneration of injured neurites and the recovery of motor function in rats. The results showed that RXRα played an impeding role in repair after spinal cord injury. Immunofluorescence staining showed that p66shc expression was upregulated in neurons after spinal cord injury (in vivo and in vitro) and colocalized with RXRα. RXRα overexpression in cultured neurons promoted the expression of p66shc, while RXRα interference inhibited the expression of p66shc. Using a luciferase assay, we found that RXRα could bind to the promoter region of p66shc and regulate the expression of p66shc, thereby regulating nerve regeneration after spinal cord injury. The above results showed that RXRα inhibited nerve regeneration after spinal cord injury by promoting p66shc expression, and interference with RXRα or p66shc promoted functional recovery after spinal cord injury.

KCTD15 inhibits the Hedgehog pathway in Medulloblastoma cells by increasing protein levels of the oncosuppressor KCASH2

Medulloblastoma (MB) is the most common malignant childhood brain tumor. About 30% of all MBs belong to the I molecular subgroup, characterized by constitutive activation of the Sonic Hedgehog (Hh) pathway. The Hh pathway is involved in several fundamental processes during embryogenesis and in adult life and its deregulation may lead to cerebellar tumorigenesis. Indeed, Hh activity must be maintained via a complex network of activating and repressor signals. One of these repressor signals is KCASH2, belonging to the KCASH family of protein, which acts as negative regulators of the Hedgehog signaling pathway during cerebellar development and differentiation. KCASH2 leads HDAC1 to degradation, allowing hyperacetylation and inhibition of transcriptional activity of Gli1, the main effector of the Hh pathway. In turn, the KCASH2 loss leads to persistent Hh activity and eventually tumorigenesis. In order to better characterize the physiologic role and modulation mechanisms of KCASH2, we have searched through a proteomic approach for new KCASH2 interactors, identifying Potassium Channel Tetramerization Domain Containing 15 (KCTD15). KCTD15 is able to directly interact with KCASH2, through its BTB/POZ domain. This interaction leads to increase KCASH2 stability which implies a reduction of the Hh pathway activity and a reduction of Hh-dependent MB cells proliferation. Here we report the identification of KCTD15 as a novel player in the complex network of regulatory proteins, which modulate Hh pathway, this could be a promising new target for therapeutic approach against MB.

Non-canonical Hedgehog Signaling Pathway in Cancer: Activation of GLI Transcription Factors Beyond Smoothened

The Hedgehog-GLI (HH-GLI) pathway is a highly conserved signaling that plays a critical role in controlling cell specification, cell–cell interaction and tissue patterning during embryonic development. Canonical activation of HH-GLI signaling occurs through binding of HH ligands to the twelve-pass transmembrane receptor Patched 1 (PTCH1), which derepresses the seven-pass transmembrane G protein-coupled receptor Smoothened (SMO). Thus, active SMO initiates a complex intracellular cascade that leads to the activation of the three GLI transcription factors, the final effectors of the HH-GLI pathway. Aberrant activation of this signaling has been implicated in a wide variety of tumors, such as those of the brain, skin, breast, gastrointestinal, lung, pancreas, prostate and ovary. In several of these cases, activation of HH-GLI signaling is mediated by overproduction of HH ligands (e.g., prostate cancer), loss-of-function mutations in PTCH1 or gain-of-function mutations in SMO, which occur in the majority of basal cell carcinoma (BCC), SHH-subtype medulloblastoma and rhabdomyosarcoma. Besides the classical canonical ligand-PTCH1-SMO route, mounting evidence points toward additional, non-canonical ways of GLI activation in cancer. By non-canonical we refer to all those mechanisms of activation of the GLI transcription factors occurring independently of SMO. Often, in a given cancer type canonical and non-canonical activation of HH-GLI signaling co-exist, and in some cancer types, more than one mechanism of non-canonical activation may occur. Tumors harboring non-canonical HH-GLI signaling are less sensitive to SMO inhibition, posing a threat for therapeutic efficacy of these antagonists. Here we will review the most recent findings on the involvement of alternative signaling pathways in inducing GLI activity in cancer and stem cells. We will also discuss the rationale of targeting these oncogenic pathways in combination with HH-GLI inhibitors as a promising anti-cancer therapies.

Clobetasol Modulates Adult Neural Stem Cell Growth via Canonical Hedgehog Pathway Activation

Sonic hedgehog (Shh) signaling is a key pathway within the central nervous system (CNS), during both development and adulthood, and its activation via the 7-transmembrane protein Smoothened (Smo) may promote neuroprotection and restoration during neurodegenerative disorders. Shh signaling may also be activated by selected glucocorticoids such as clobetasol, fluocinonide and fluticasone, which therefore act as Smo agonists and hold potential utility for regenerative medicine. However, despite its potential role in neurodegenerative diseases, the impact of Smo-modulation induced by these glucocorticoids on adult neural stem cells (NSCs) and the underlying signaling mechanisms are not yet fully elucidated. The aim of the present study was to evaluate the effects of Smo agonists (i.e., purmorphamine) and antagonists (i.e., cyclopamine) as well as of glucocorticoids (i.e., clobetasol, fluocinonide and fluticasone) on NSCs in terms of proliferation and clonal expansion. Purmorphamine treatment significantly increased NSC proliferation and clonal expansion via GLI-Kruppel family member 1 (Gli1) nuclear translocation and such effects were prevented by cyclopamine co-treatment. Clobetasol treatment exhibited an equivalent pharmacological effect. Moreover, cellular thermal shift assay suggested that clobetasol induces the canonical Smo-dependent activation of Shh signaling, as confirmed by Gli1 nuclear translocation and also by cyclopamine co-treatment, which abolished these effects. Finally, fluocinonide and fluticasone as well as control glucocorticoids (i.e., prednisone, corticosterone and dexamethasone) showed no significant effects on NSCs proliferation and clonal expansion. In conclusion, our data suggest that Shh may represent a druggable target system to drive neuroprotection and promote restorative therapies.