Signaling complexes and protein-protein interactions involved in the activation of the Ras and phosphatidylinositol 3-kinase pathways by the c-Ret receptor tyrosine kinase

RET overexpression leads to increased brain metastatic competency in luminal breast cancer

BACKGROUND

Breast cancer brain metastasis is a rising occurrence, necessitating a better understanding of the mechanisms involved for effective management. Breast cancer brain metastases diverge notably from the primary tumor, with gains in kinase and concomitant losses of steroid signaling observed. In this study, we explored the role of the kinase receptor RET in promoting breast cancer brain metastases and provide a rationale for targeting this receptor.

METHODS

RET expression was characterized in a cohort of patients with primary and brain metastatic tumors. RET functionality was assessed using pharmacological inhibition and gene silencing in patient-derived brain metastatic tumor explants and in vivo models, organoid models, and brain organotypic cultures. RNA sequencing was used to uncover novel brain metastatic relevant RET mechanisms of action.

RESULTS

A statistically significant enrichment of RET in brain metastases was observed in estrogen receptor-positive breast cancer, where it played a role in promoting cancer cell adhesion, survival, and outgrowth in the brain. In vivo, RET overexpression enhanced brain metastatic competency in patient-derived models. At a mechanistic level, RET overexpression was found to enhance the activation of gene programs involved in cell adhesion, requiring EGFR cooperation to deliver a pro-brain metastatic phenotype.

CONCLUSION

Our results illustrate, for the first time, the role of RET in regulating colonization and outgrowth of breast cancer brain metastasis and provide data to support the use of RET inhibitors in the management strategy for patients with breast cancer brain metastases.

CCDC6-RET fusion protein regulates Ras/MAPK signaling through the fusion- GRB2-SHC1 signal niche

Rearranged during transfection (RET) rearrangement oncoprotein-mediated Ras/MAPK signaling cascade is constitutively activated in cancers. Here, we demonstrate a unique signal niche. The niche is a ternary complex based on the chimeric RET liquid-liquid phase separation. The complex comprises the rearranged kinase (RET fusion); the adaptor (GRB2), and the effector (SHC1). Together, they orchestrate the Ras/MAPK signal cascade, which is dependent on tyrosine kinase. CCDC6-RET fusion undergoes LLPS requiring its kinase domain and its fusion partner. The CCDC6-RET fusion LLPS promotes the autophosphorylation of RET fusion, with enhanced kinase activity, which is necessary for the formation of the signaling niche. Within the signal niche, the interactions among the constituent components are reinforced, and the signal transduction efficiency is amplified. The specific RET fusion-related signal niche elucidates the mechanism of the constitutive activation of the Ras/MAPK signaling pathway. Beyond just focusing on RET fusion itself, exploration of the ternary complex potentially unveils a promising avenue for devising therapeutic strategies aimed at treating RET fusion-driven diseases.

Genetic diagnosis in acromegaly and gigantism: From research to clinical practice

It is usually considered that only 5% of all pituitary neuroendocrine tumours are due to inheritable causes. Since this estimate was reported, however, multiple genetic defects driving syndromic and nonsyndromic somatotrophinomas have been unveiled. This heterogeneous genetic background results in overlapping phenotypes of GH excess. Genetic tests should be part of the approach to patients with acromegaly and gigantism because they can refine the clinical diagnoses, opening the possibility to tailor the clinical conduct to each patient. Even more, genetic testing and clinical screening of at-risk individuals have a positive impact on disease outcomes, by allowing for the timely detection and treatment of somatotrophinomas at early stages. Future research should focus on determining the actual frequency of novel genetic drivers of somatotrophinomas in the general population, developing up-to-date disease-specific multi-gene panels for clinical use, and finding strategies to improve access to modern genetic testing worldwide.

Comprehensive molecular analysis identifies RET alterations association with response of ICIs in multi-immunotherapy cohorts

BACKGROUND

The RET gene, which is frequently mutated across many types of cancer, has been proven to be critically involved in tumorigenesis and tumour development; however, its prediction of the therapeutic efficacy of immune checkpoint inhibitor (ICI) therapy remains to be elucidated. The present research aims to investigate the association between RET mutations and the efficiency of ICI therapy.

METHOD

We analysed the role of RET mutations in predicting the prognosis of patients receiving ICIs therapy in the discovery cohort and validated it in the validation cohort. Then, multi-omics data from TCGA pan-cancer cohort was employed to propose the association between RET mutations and tumour inflamed anti-tumour immune response and tumour antigenicity.

RESULTS

Our study revealed that among 606 cases and across five types of cancer, RET mutation was associated with better clinical outcomes for ICIs therapy, including elevated response rate, longer progression-free survival PFS, and longer overall survival OS. Multivariate analysis showed that RET mutation could independently predict the prognosis of patients treated with ICIs, after adjusting cancer types. The predictive value of RET status for the OS of patients treated with ICIs immunotherapy was further validated in the validation cohort (n = 1,409). Subgroup analysis suggested that only the monotherapy group showed significant differences in OS(P < 0.05) and PFS(P < 0.05) between RET-wildtype tumours and RET-mutant tumours. Multi-omics data analysis revealed potential anti-tumour immunity mechanisms of RET mutations, suggesting that RET-mutant tumours have enhanced immunogenicity, higher expression of immune checkpoints and chemokines, and higher immune cell infiltration than those observed in RET-wildtype tumours; thus, potentially indicating a more favourable response to immunotherapy.

CONCLUSIONS

RET mutation may be a predictive biomarker of enhanced response to ICIs therapy. Extensive investigation of the underlying molecular mechanisms and prospective studies are needed in the future.

TMEM127 suppresses tumor development by promoting RET ubiquitination, positioning, and degradation

The TMEM127 gene encodes a transmembrane protein of poorly known function that is mutated in pheochromocytomas, neural crest-derived tumors of adrenomedullary cells. Here, we report that, at single-nucleus resolution, TMEM127-mutant tumors share precursor cells and transcription regulatory elements with pheochromocytomas carrying mutations of the tyrosine kinase receptor RET. Additionally, TMEM127-mutant pheochromocytomas, human cells, and mouse knockout models of TMEM127 accumulate RET and increase its signaling. TMEM127 contributes to RET cellular positioning, trafficking, and lysosome-mediated degradation. Mechanistically, TMEM127 binds to RET and recruits the NEDD4 E3 ubiquitin ligase for RET ubiquitination and degradation via TMEM127 C-terminal PxxY motifs. Lastly, increased cell proliferation and tumor burden after TMEM127 loss can be reversed by selective RET inhibitors in vitro and in vivo. Our results define TMEM127 as a component of the ubiquitin system and identify aberrant RET stabilization as a likely mechanism through which TMEM127 loss-of-function mutations cause pheochromocytoma.

A network map of GDNF/RET signaling pathway in physiological and pathological conditions

Glial cell line-derived neurotrophic factor (GDNF) signals through a multi-component receptor system predominantly consisting of glycosyl-phosphatidylinositol-anchored GDNF family receptor alpha-1 (GFRα1) and the Rearranged during transfection (RET) receptor tyrosine kinase. GDNF/RET signaling is vital to the central and peripheral nervous system, kidney morphogenesis, and spermatogenesis. In addition, the dysregulation of the GDNF/RET signaling has been implicated in the pathogenesis of cancers. Despite the extensive research on GDNF/RET signaling, a molecular network of reactions induced by GDNF reported across the published literature. However, a comprehensive GDNF/RET pathway resource is currently unavailable. We describe an integrated signaling pathway reaction map of GDNF/RET consisting of 1151 molecular reactions. These include information pertaining to 52 molecular association events, 70 enzyme catalysis events, 36 activation/inhibition events, 22 translocation events, 856 gene regulation events, and 115 protein-level expression events induced by GDNF in diverse cell types. We developed a comprehensive GDNF/RET signaling network map based on these molecular reactions. The pathway map was made accessible through WikiPathways database ( https://www.wikipathways.org/index.php/Pathway:WP5143 ). Biocuration and development of gene regulatory network map of GDNF/RET signaling pathway.

Deep learning-based network pharmacology for exploring the mechanism of licorice for the treatment of COVID-19

Licorice, a traditional Chinese medicine, has been widely used for the treatment of COVID-19, but all active compounds and corresponding targets are still not clear. Therefore, this study proposed a deep learning-based network pharmacology approach to identify more potential active compounds and targets of licorice. 4 compounds (quercetin, naringenin, liquiritigenin, and licoisoflavanone), 2 targets (SYK and JAK2) and the relevant pathways (P53, cAMP, and NF-kB) were predicted, which were confirmed by previous studies to be associated with SARS-CoV-2-infection. In addition, 2 new active compounds (glabrone and vestitol) and 2 new targets (PTEN and MAP3K8) were further validated by molecular docking and molecular dynamics simulations (simultaneous molecular dynamics), as well as the results showed that these active compounds bound well to COVID-19 related targets, including the main protease (Mpro), the spike protein (S-protein) and the angiotensin-converting enzyme 2 (ACE2). Overall, in this study, glabrone and vestitol from licorice were found to inhibit viral replication by inhibiting the activation of Mpro, S-protein and ACE2; related compounds in licorice may reduce the inflammatory response and inhibit apoptosis by acting on PTEN and MAP3K8. Therefore, licorice has been proposed as an effective candidate for the treatment of COVID-19 through PTEN, MAP3K8, Mpro, S-protein and ACE2.

RET signaling in breast cancer therapeutic resistance and metastasis

RET, a single-pass receptor tyrosine kinase encoded on human chromosome 10, is well known to the field of developmental biology for its role in the ontogenesis of the central and enteric nervous systems and the kidney. In adults, RET alterations have been characterized as drivers of non-small cell lung cancer and multiple neuroendocrine neoplasms. In breast cancer, RET signaling networks have been shown to influence diverse functions including tumor development, metastasis, and therapeutic resistance. While RET is known to drive the development and progression of multiple solid tumors, therapeutic agents selectively targeting RET are relatively new, though multiple multi-kinase inhibitors have shown promise as RET inhibitors in the past; further, RET has been historically neglected as a potential therapeutic co-target in endocrine-refractory breast cancers despite mounting evidence for a key pathologic role and repeated description of a bi-directional relationship with the estrogen receptor, the principal driver of most breast tumors. Additionally, the recent discovery of RET enrichment in breast cancer brain metastases suggests a role for RET inhibition specific to advanced disease. This review assesses the status of research on RET in breast cancer and evaluates the therapeutic potential of RET-selective kinase inhibitors across major breast cancer subtypes.

Loss of non-motor kinesin KIF26A causes congenital brain malformations via dysregulated neuronal migration and axonal growth as well as apoptosis

Kinesins are canonical molecular motors but can also function as modulators of intracellular signaling. KIF26A, an unconventional kinesin that lacks motor activity, inhibits growth-factor-receptor-bound protein 2 (GRB2)- and focal adhesion kinase (FAK)-dependent signal transduction, but its functions in the brain have not been characterized. We report a patient cohort with biallelic loss-of-function variants in KIF26A, exhibiting a spectrum of congenital brain malformations. In the developing brain, KIF26A is preferentially expressed during early- and mid-gestation in excitatory neurons. Combining mice and human iPSC-derived organoid models, we discovered that loss of KIF26A causes excitatory neuron-specific defects in radial migration, localization, dendritic and axonal growth, and apoptosis, offering a convincing explanation of the disease etiology in patients. Single-cell RNA sequencing in KIF26A knockout organoids revealed transcriptional changes in MAPK, MYC, and E2F pathways. Our findings illustrate the pathogenesis of KIF26A loss-of-function variants and identify the surprising versatility of this non-motor kinesin.

Super-enhancer-controlled positive feedback loop BRD4/ERα-RET-ERα promotes ERα-positive breast cancer

Estrogen and estrogen receptor alpha (ERα)-induced gene transcription is tightly associated with ERα-positive breast carcinogenesis. ERα-occupied enhancers, particularly super-enhancers, have been suggested to play a vital role in regulating such transcriptional events. However, the landscape of ERα-occupied super-enhancers (ERSEs) as well as key ERα-induced target genes associated with ERSEs remain to be fully characterized. Here, we defined the landscape of ERSEs in ERα-positive breast cancer cell lines, and demonstrated that bromodomain protein BRD4 is a master regulator of the transcriptional activation of ERSEs and cognate ERα target genes. RET, a member of the tyrosine protein kinase family of proteins, was identified to be a key ERα target gene of BRD4-regulated ERSEs, which, in turn, is vital for ERα-induced gene transcriptional activation and malignant phenotypes through activating the RAS/RAF/MEK2/ERK/p90RSK/ERα phosphorylation cascade. Combination therapy with BRD4 and RET inhibitors exhibited additive effects on suppressing ERα-positive breast cancer both in vitro and in vivo, comparable with that of standard endocrine therapy tamoxifen. Furthermore, combination therapy re-sensitized a tamoxifen-resistant ERα-positive breast cancer cell line to tamoxifen treatment. Taken together, our data uncovered the critical role of a super-enhancer-associated positive feedback loop constituting BRD4/ERα–RET–ERα in ERα-positive breast cancer, and suggested that targeting components in this loop would provide a new therapeutic avenue for treating ERα-positive breast cancer in the clinic.

A RET::GRB2 fusion in pheochromocytoma defies the classic paradigm of RET oncogenic fusions

The RET kinase receptor is a target of mutations in neural crest tumors, including pheochromocytomas, and of oncogenic fusions in epithelial cancers. We report a RET::GRB2 fusion in a pheochromocytoma in which RET, functioning as the upstream partner, retains its kinase domain but loses critical C-terminal motifs and is fused to GRB2, a physiological RET interacting protein. RET::GRB2 is an oncogenic driver that leads to constitutive, ligand-independent RET signaling; has transforming capability dependent on RET catalytic function; and is sensitive to RET inhibitors. These observations highlight a new driver event in pheochromocytomas potentially amenable for RET-driven therapy.

Predictive molecular pathology in metastatic thyroid cancer: the role of RET fusions

BACKGROUND

Rearranged during transfection (RET) gene fusions are detected in 10-20% of thyroid cancer patients. Recently, RET fusion-positive metastatic thyroid cancers have attracted much attention owing to the FDA approval of two highly selective anti-RET tyrosine kinase inhibitors, namely, selpercatinib, and pralsetinib.

AREAS COVERED

This review summarizes the available evidence on the biological and predictive role of RET gene fusions in thyroid carcinoma patients and the latest screening assays currently used to detect these genomic alterations in histological and cytological specimens.

EXPERT OPINION

Management of advanced thyroid carcinoma has significantly evolved over the last decade thanks to the approval of three multikinase inhibitors, i.e. sorafenib, lenvatinib, cabozantinib, and of two selective RET-tyrosine inhibitors, i.e. selpercatinib and pralsetinib. In this setting, the detection of RET-fusions in advanced thyroid cancer specimens through the use of next-generation sequencing has become a commonly used strategy in clinical practice to select the best treatment options.

Gab2 deficiency prevents Flt3-ITD driven acute myeloid leukemia in vivo

Internal tandem duplications (ITD) of the FMS-like tyrosine kinase 3 (FLT3) predict poor prognosis in acute myeloid leukemia (AML) and often co-exist with inactivating DNMT3A mutations. In vitro studies implicated Grb2-associated binder 2 (GAB2) as FLT3-ITD effector. Utilizing a Flt3-ITD knock-in, Dnmt3a haploinsufficient mouse model, we demonstrate that Gab2 is essential for the development of Flt3-ITD driven AML in vivo, as Gab2 deficient mice displayed prolonged survival, presented with attenuated liver and spleen pathology and reduced blast counts. Furthermore, leukemic bone marrow from Gab2 deficient mice exhibited reduced colony-forming unit capacity and increased FLT3 inhibitor sensitivity. Using transcriptomics, we identify the genes encoding for Axl and the Ret co-receptor Gfra2 as targets of the Flt3-ITD/Gab2/Stat5 axis. We propose a pathomechanism in which Gab2 increases signaling of these receptors by inducing their expression and by serving as downstream effector. Thereby, Gab2 promotes AML aggressiveness and drug resistance as it incorporates these receptor tyrosine kinases into the Flt3-ITD signaling network. Consequently, our data identify GAB2 as a promising biomarker and therapeutic target in human AML.

Precision therapy for RET-altered cancers with RET inhibitors

Rearranged during transfection (RET) is involved in the physiological development of some organ systems. Activating RET alterations via either gene fusions or point mutations are potent oncogenic drivers in non-small cell lung cancer, thyroid cancer, and in multiple diverse cancers. RET-altered cancers were initially treated with multikinase inhibitors (MKIs). The efficacy of MKIs was modest at the expense of notable toxicities from their off-target activity. Recently, highly potent and RET-specific inhibitors selpercatinib and pralsetinib were successfully translated to the clinic and FDA approved. We summarize the current state-of-the-art therapeutics with preclinical and clinical insights of these novel RET inhibitors, acquired resistance mechanisms, and future outlooks.

Long-term exposure to GDNF induces dephosphorylation of Ret, AKT, and ERK1/2, and is ineffective at protecting midbrain dopaminergic neurons in cellular models of Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) promotes differentiation, proliferation, and survival in different cell types, including dopaminergic neurons. Thus, GDNF has been proposed as a promising neuroprotective therapy in Parkinson's disease. Although findings from cellular and animal models of Parkinson's disease were encouraging, results emerging from clinical trials were not as good as expected, probably due to the inappropriate administration protocols. Despite the growing information on GDNF action mechanisms, many aspects of its pharmacological effects are still unclear and data from different studies are still contradictory. Considering that GDNF action mechanisms are mediated by its receptor tyrosine kinase Ret, which activates PI3K/AKT and MAPK/ERK signaling pathways, we aimed to investigate Ret activation and its effect over both signaling pathways in midbrain cell cultures treated with GDNF at different doses (0.3, 1, and 10 ng/ml) and times (15 min, 24 h, 24 h (7 days), and 7 continuous days). The results showed that short-term or acute (15 min, 24 h, and 24 h (7 days)) GDNF treatment in rat midbrain neurons increases Tyrosine hydroxylase (TH) expression and the phosphorylation levels of Ret (Tyr 1062), AKT (Ser 473), ERK1/2 (Thr202/Tyr204), S6 (Ser 235/236), and GSK3-β (Ser 9). However, the phosphorylation level of these kinases, TH expression, and dopamine uptake, decreased below basal levels after long-term or prolonged treatment with 1 and 10 ng/ml GDNF (7 continuous days). Our data suggest that long-term GDNF treatment inactivates the receptor by an unknown mechanism, affecting its neuroprotective capacity against degeneration caused by 6-OHDA or rotenone, while short-term exposure to GDNF promoted dopaminergic cell survival. These findings highlight the need to find new and more effective long-acting therapeutic approaches for disorders in which GDNF plays a beneficial role, including Parkinson's disease. In this regard, it is necessary to propose new GDNF treatment guidelines to regulate and control its long-term expression levels and optimize the clinical use of this trophic factor in patients with Parkinson's disease.

Targeting Rearranged during Transfection in Cancer: A Perspective on Small-Molecule Inhibitors and Their Clinical Development

Rearranged during transfection (RET) is a receptor tyrosine kinase essential for the normal development and maturation of a diverse range of tissues. Aberrant RET signaling in cancers, due to RET mutations, gene fusions, and overexpression, results in the activation of downstream pathways promoting survival, growth, and metastasis. Pharmacological manipulation of RET is effective in treating RET-driven cancers, and efforts toward developing RET-specific therapies have increased over the last 5 years. In 2020, RET-selective inhibitors pralsetinib and selpercatinib achieved clinical approval, which marked the first approvals for kinase inhibitors specifically developed to target the RET oncoprotein. This Perspective discusses current development and clinical applications for RET precision medicine by providing an overview of the incremental improvement of kinase inhibitors for use in RET-driven malignancies.

Advances in Lung Cancer Driver Genes Associated With Brain Metastasis

Brain metastasis, one of the common complications of lung cancer, is an important cause of death in patients with advanced cancer, despite progress in treatment strategies. Lung cancers with positive driver genes have higher incidence and risk of brain metastases, suggesting that driver events associated with these genes might be biomarkers to detect and prevent disease progression. Common lung cancer driver genes mainly encode receptor tyrosine kinases (RTKs), which are important internal signal molecules that interact with external signals. RTKs and their downstream signal pathways are crucial for tumor cell survival, invasion, and colonization in the brain. In addition, new tumor driver genes, which also encode important molecules closely related to the RTK signaling pathway, have been found to be closely related to the brain metastases of lung cancer. In this article, we reviewed the relationship between lung cancer driver genes and brain metastasis, and summarized the mechanism of driver gene-associated pathways in brain metastasis. By understanding the molecular characteristics during brain metastasis, we can better stratify lung cancer patients and alert those at high risk of brain metastasis, which helps to promote individual therapy for lung cancer.

The Role of Neurotrophic Factors in Pathophysiology of Major Depressive Disorder

According to the neurotrophic hypothesis of major depressive disorder (MDD), impairment in growth factor signaling might be associated with the pathology of this illness. Current evidence demonstrates that impaired neuroplasticity induced by alterations of neurotrophic growth factors and related signaling pathways may be underlying to the pathophysiology of MDD. Brain-derived neurotrophic factor (BDNF) is the most studied neurotrophic factor involved in the neurobiology of MDD. Nevertheless, developing evidence has implicated other neurotrophic factors, including neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), nerve growth factor (NGF), vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF), glial cell-derived neurotrophic factor (GDNF), and fibroblast growth factor (FGF) in the MDD pathophysiology. Here, we summarize the current literature on the involvement of neurotrophic factors and related signaling pathways in the pathophysiology of MDD.

RET isoforms contribute differentially to invasive processes in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a therapeutically challenging disease with poor survival rates, owing to late diagnosis and early dissemination. These tumors frequently undergo perineural invasion, spreading along nerves regionally and to distant sites. The RET receptor tyrosine kinase is implicated in increased aggressiveness, local invasion, and metastasis in multiple cancers, including PDAC. RET mediates directional motility and invasion towards sources of its neurotrophic factor ligands, suggesting that it may enhance perineural invasion of tumor cells towards nerves. RET is expressed as two main isoforms, RET9 and RET51, which differ in their protein interactions and oncogenic potentials, however, the contributions of RET isoforms to neural invasion have not been investigated. In this study, we generated total RET and isoform-specific knockdown PDAC cell lines and assessed the contributions of RET isoforms to PDAC invasive spread. Our data show that RET activity induces cell polarization and actin remodeling through activation of CDC42 and RHOA GTPases to promote directional motility in PDAC cells. Further, we show that RET interacts with the adaptor protein TKS5 to induce invadopodia formation, enhance matrix degradation and promote tumor cell invasion through a SRC and GRB2-dependent mechanism. Finally, we show that RET51 is the predominant isoform contributing to these RET-mediated invasive processes in PDAC. Together, our work suggests that RET expression in pancreatic cancers may enhance tumor aggressiveness by promoting perineural invasion, and that RET expression may be a valuable marker of invasiveness, and a potential therapeutic target in the treatment of these cancers.

1,25(OH)2D3 Alleviates Aβ(25-35)-Induced Tau Hyperphosphorylation, Excessive Reactive Oxygen Species, and Apoptosis Through Interplay with Glial Cell Line-Derived Neurotrophic Factor Signaling in SH-SY5Y Cells

Amyloid beta (Aβ) accumulation in the brain is one of the major pathological features of Alzheimer's disease. The active form of vitamin D (1,25(OH)₂D₃), which acts via its nuclear hormone receptor, vitamin D receptor (VDR), has been implicated in the treatment of Aβ pathology, and is thus considered as a neuroprotective agent. However, its underlying molecular mechanisms of action are not yet fully understood. Here, we aim to investigate whether the molecular mechanisms of 1,25(OH)₂D₃ in ameliorating Aβ toxicity involve an interplay of glial cell line-derived neurotrophic factor (GDNF)-signaling in SH-SY5Y cells. Cells were treated with Aβ(25-35) as the source of toxicity, followed by the addition of 1,25(OH)₂D₃ with or without the GDNF inhibitor, heparinase III. The results show that 1,25(OH)₂D₃ modulated Aβ-induced reactive oxygen species, apoptosis, and tau protein hyperphosphorylation in SH-SY5Y cells. Additionally, 1,25(OH)₂D₃ restored the decreasing GDNF and the inhibited phosphorylation of the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (Akt)/glycogen synthase kinase-3β (GSK-3β) protein expressions. In the presence of heparinase III, these damaging effects evoked by Aβ were not abolished by 1,25(OH)₂D_3. It appears 1,25(OH)₂D₃ is beneficial for the alleviation of Aβ neurotoxicity, and it might elicit its neuroprotection against Aβ neurotoxicity through an interplay with GDNF-signaling.

State-of-the-Art Strategies for Targeting RET-Dependent Cancers

Activating receptor tyrosine kinase RET (rarranged during transfection) gene alterations have been identified as oncogenic in multiple malignancies. RET gene rearrangements retaining the kinase domain are oncogenic drivers in papillary thyroid cancer, non-small-cell lung cancer, and multiple other cancers. Activating RET mutations are associated with different phenotypes of multiple endocrine neoplasia type 2 as well as sporadic medullary thyroid cancer. RET is thus an attractive therapeutic target in patients with oncogenic RET alterations. Multikinase inhibitors with RET inhibitor activity, such as cabozantinib and vandetanib, have been explored in the clinic for tumors with activating RET gene alterations with modest clinical efficacy. As a result of the nonselective nature of these multikinase inhibitors, patients had off-target adverse effects, such as hypertension, rash, and diarrhea. This resulted in a narrow therapeutic index of these drugs, limiting ability to dose for clinically effective RET inhibition. In contrast, the recent discovery and clinical validation of highly potent selective RET inhibitors (pralsetinib, selpercatinib) demonstrating improved efficacy and a more favorable toxicity profile are poised to alter the landscape of RET-dependent cancers. These drugs appear to have broad activity across tumors with activating RET alterations. The mechanisms of resistance to these next-generation highly selective RET inhibitors is an area of active research. This review summarizes the current understanding of RET alterations and the state-of-the-art treatment strategies in RET-dependent cancers.

PTPRA Phosphatase Regulates GDNF-Dependent RET Signaling and Inhibits the RET Mutant MEN2A Oncogenic Potential

The RET proto-oncogene encodes receptor tyrosine kinase, expressed primarily in tissues of neural crest origin. De-regulation of RET signaling is implicated in several human cancers. Recent phosphatome interactome analysis identified PTPRA interacting with the neurotrophic factor (GDNF)-dependent RET-Ras-MAPK signaling-axis. Here, by identifying comprehensive interactomes of PTPRA and RET, we reveal their close physical and functional association. The PTPRA directly interacts with RET, and using the phosphoproteomic approach, we identify RET as a direct dephosphorylation substrate of PTPRA both in vivo and in vitro. The protein phosphatase domain-1 is indispensable for the PTPRA inhibitory role on RET activity and downstream Ras-MAPK signaling, whereas domain-2 has only minor effect. Furthermore, PTPRA also regulates the RET oncogenic mutant variant MEN2A activity and invasion capacity, whereas the MEN2B is insensitive to PTPRA. In sum, we discern PTPRA as a novel regulator of RET signaling in both health and cancer.

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PTPRA inhibits ligand (GDNF-GFRα1)-mediated RET activity on Ras-MAPK signaling axis

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PTPRA dephosphorylate RET on key functional phosphotyrosine sites

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PTPRA catalytic (PTPase) domain 1 regulates RET-driven signaling

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PTPRA suppresses RET oncogenic mutant MEN2A in both Ras-MAPK and cell invasion models

RET fusions in solid tumors

The RET proto-oncogene has been well-studied. RET is involved in many different physiological and developmental functions. When altered, RET mutations influence disease in a variety of organ systems from Hirschsprung's disease and multiple endocrine neoplasia 2 (MEN2) to papillary thyroid carcinoma (PTC) and non-small cell lung cancer (NSCLC). Changes in RET expression have been discovered in 30-70% of invasive breast cancers and 50-60% of pancreatic ductal adenocarcinomas in addition to colorectal adenocarcinoma, melanoma, small cell lung cancer, neuroblastoma, and small intestine neuroendocrine tumors. RET mutations have been associated with tumor proliferation, invasion, and migration. RET fusions or rearrangements are somatic juxtapositions of 5' sequences from other genes with 3' RET sequences encoding tyrosine kinase. RET rearrangements occur in approximately 2.5-73% of sporadic PTC and 1-3% of NSCLC patients. The most common RET fusions are CDCC6-RET and NCOA4-RET in PTC and KIF5B-RET in NSCLC. Tyrosine kinase inhibitors are drugs that target kinases such as RET in RET-driven (RET-mutation or RET-fusion-positive) disease. Multikinase inhibitors (MKI) target various kinases and other receptors. Several MKIs are FDA-approved for cancer therapy (sunitinib, sorafenib, vandetanib, cabozantinib, regorafenib, ponatinib, lenvatinib, alectinib) and non-oncologic disease (nintedanib). Selective RET inhibitor drugs LOXO-292 (selpercatinib) and BLU-667 (pralsetinib) are also undergoing phase I/II and I clinical trials, respectively, with preliminary results demonstrating partial response and low incidence of serious adverse events. RET fusions provide a viable therapeutic target for oncologic treatment, and further study is warranted into the prevalence and pathogenesis of RET fusions as well as development of current and new tyrosine kinase inhibitors.

Therapies targeting the signal pathways of pheochromocytoma and paraganglioma

Pheochromocytoma and paraganglioma (PCC/PGL) are rare tumors that originate from adrenal or extra-adrenal chromaffin cells. A significant clinical manifestation of PCC/PGL is that the tumors release a large number of catecholamines continuously or intermittently, causing persistent or paroxysmal hypertension and multiple organ functions and metabolic disorders. Though majority of the tumors are non-metastatic, about 10% are metastatic tumors. Others even have estimated that the rate of metastasis may be as high as 26%. The disease is most common in individuals ranging from 20 to 50 years old and the age of onset strongly depends on the genetic background: patients with germline mutations in susceptible genes have an earlier presentation. Besides, there are no significant differences in the incidence between men and women. At present, traditional treatments, such as surgical treatment, radionuclide therapy, and chemotherapy are still prior choices. However, they all have several deficiencies so that the effects are not extremely significant. Contemporary studies have shown that hypoxia-associated signal pathway, associated with the cluster 1 genes of PCC/PGL, and increased kinase signal pathways, associated with the cluster 2 genes of PCC/PGL, are the two major pathways involving the molecular pathogenesis of PCC/PGL, indicating that PCC/PGL can be treated with targeted therapies in emerging trends. This article reviews the progress of molecular-targeted therapies for PCC/PGL.

Global phosphoproteomic analysis identifies SRMS-regulated secondary signaling intermediates

Background

The non-receptor tyrosine kinase, SRMS (Src-related kinase lacking C-terminal regulatory tyrosine and N-terminal myristoylation sites) is a member of the BRK family kinases (BFKs) which represents an evolutionarily conserved relative of the Src family kinases (SFKs). Tyrosine kinases are known to regulate a number of cellular processes and pathways via phosphorylating substrate proteins directly and/or by partaking in signaling cross-talks leading to the indirect modulation of various signaling intermediates. In a previous study, we profiled the tyrosine-phosphoproteome of SRMS and identified multiple candidate substrates of the kinase. The broader cellular signaling intermediates of SRMS are unknown.

Methods

In order to uncover the broader SRMS-regulated phosphoproteome and identify the SRMS-regulated indirect signaling intermediates, we performed label-free global phosphoproteomics analysis on cells expressing wild-type SRMS. Using computational database searching and bioinformatics analyses we characterized the dataset.

Results

Our analyses identified 60 hyperphosphorylated (phosphoserine/phosphothreonine) proteins mapped from 140 hyperphosphorylated peptides. Bioinfomatics analyses identified a number of significantly enriched biological and cellular processes among which DNA repair pathways were found to be upregulated while apoptotic pathways were found to be downregulated. Analyses of motifs derived from the upregulated phosphosites identified Casein kinase 2 alpha (CK2α) as one of the major potential kinases contributing to the SRMS-dependent indirect regulation of signaling intermediates.

Conclusions

Overall, our phosphoproteomics analyses identified serine/threonine phosphorylation dynamics as important secondary events of the SRMS-regulated phosphoproteome with implications in the regulation of cellular and biological processes.

Electronic supplementary material

The online version of this article (10.1186/s12953-018-0143-7) contains supplementary material, which is available to authorized users.

GFRA1: A Novel Molecular Target for the Prevention of Osteosarcoma Chemoresistance

The glycosylphosphatidylinositol-linked GDNF (glial cell derived neurotrophic factor) receptor alpha (GFRA), a coreceptor that recognizes the GDNF family of ligands, has a crucial role in the development and maintenance of the nervous system. Of the four identified GFRA isoforms, GFRA1 specifically recognizes GDNF and is involved in the regulation of proliferation, differentiation, and migration of neuronal cells. GFRA1 has also been implicated in cancer cell progression and metastasis. Recent findings show that GFRA1 can contribute to the development of chemoresistance in osteosarcoma. GFRA1 expression was induced following treatment of osteosarcoma cells with the popular anticancer drug, cisplatin and induction of GFRA1 expression significantly suppressed apoptosis mediated by cisplatin in osteosarcoma cells. GFRA1 expression promotes autophagy by activating the SRC-AMPK signaling axis following cisplatin treatment, resulting in enhanced osteosarcoma cell survival. GFRA1-induced autophagy promoted tumor growth in mouse xenograft models, suggesting a novel function of GFRA1 in osteosarcoma chemoresistance.

Overexpression of TFEB Drives a Pleiotropic Neurotrophic Effect and Prevents Parkinson's Disease-Related Neurodegeneration

The possible implication of transcription factor EB (TFEB) as a therapeutic target in Parkinson's disease has gained momentum since it was discovered that TFEB controls lysosomal biogenesis and autophagy and that its activation might counteract lysosomal impairment and protein aggregation. However, the majority of putative direct targets of TFEB described to date is linked to a range of biological processes that are not related to the lysosomal-autophagic system. Here, we assessed the effect of overexpressing TFEB with an adeno-associated viral vector in mouse substantia nigra dopaminergic neurons. We demonstrate that TFEB overexpression drives a previously unknown bona fide neurotrophic effect, giving rise to cell growth, higher tyrosine hydroxylase levels, and increased dopamine release in the striatum. TFEB overexpression induces the activation of the mitogen-activated protein kinase 1/3 (MAPK1/3) and AKT pro-survival pathways, phosphorylation of mTORC1 effectors 4E-binding protein 1 (4E-BP1) and S6 kinase B1 (S6K1), and increased protein synthesis. We show that TFEB overexpression prevents dopaminergic cell loss and counteracts atrophy and the associated protein synthesis decline in the MPTP mouse model of Parkinson's disease. Our results suggest that increasing TFEB activity might prevent neuronal death and restore neuronal function in Parkinson's disease and other neurodegenerative diseases through different mechanisms.

Glial cell-derived neurotrophic factor alleviates sepsis-induced neuromuscular dysfunction by decreasing the expression of γ- and α7-nicotinic acetylcholine receptors in an experimental rat model of neuromyopathy

Sepsis-induced neuromuscular dysfunction results from up-regulation of the expression of γ- and α7-nicotinic acetylcholine receptors (nAChR). Although glial cell derived neurotrophic factor (GDNF) has been implicated in repairing and supporting neurons, little is known about the effects of GDNF on demyelination of nerves in sepsis. In this study, we tested the hypothesis that GDNF could alleviate sepsis-induced neuromuscular dysfunction by decreasing the expression of γ- and α7-nAChR in an experimental rat model of neuromyopathy. Rats were randomly divided into a sham group and a sepsis group. Levels of inflammatory factors, muscle function, and nicotinic acetylcholine receptors were tested in rats after cecal ligation and puncture (CLP). At 24 h after CLP, GDNF was injected around the sciatic nerve of sepsis rats, cytokines were detected by enzyme-linked immunosorbent assay (ELISA), and immunofluorescence staining was used to detect the expression of nAChRs. GDNF and its downstream effector (Erk1/2 and GFR-α), neuregulin-1 (NRG-1) and γ- and α7-nAChR were measured using Western blot analysis. The expression of GDNF reached a minimum at 24 h after CLP. Compared with the sham group, the release of cytokines and the expression of γ- and α7-nAChR were significantly increased in the sepsis group. The administration of GDNF significantly alleviated sepsis-induced neuromuscular dysfunction, as well as reducing the expression of γ- and α7-nAChR. In addition, the expression of Erk1/2, GFR-α, NRG-1 were significantly increased after GDNF treatment. GDNF administration may improve patient outcomes by reducing the demyelination of nerves and the expression of γ- and α7-nAChR.

Resistance to RET-Inhibition in RET-Rearranged NSCLC Is Mediated By Reactivation of RAS/MAPK Signaling

Oncogenic rearrangements in RET are present in 1%-2% of lung adenocarcinoma patients. Ponatinib is a multi-kinase inhibitor with low-nanomolar potency against the RET kinase domain. Here, we demonstrate that ponatinib exhibits potent antiproliferative activity in RET fusion-positive LC-2/ad lung adenocarcinoma cells and inhibits phosphorylation of the RET fusion protein and signaling through ERK1/2 and AKT. Using distinct dose escalation strategies, two ponatinib-resistant LC-2/ad cell lines, PR1 and PR2, were derived. PR1 and PR2 cell lines retained expression, but not phosphorylation of the RET fusion and lacked evidence of a resistance mutation in the RET kinase domain. Both resistant lines retained activation of the MAPK pathway. Next-generation RNA sequencing revealed an oncogenic NRAS p.Q61K mutation in the PR1 cell. PR1 cell proliferation was preferentially sensitive to siRNA knockdown of NRAS compared with knockdown of RET, more sensitive to MEK inhibition than the parental line, and NRAS dependence was maintained in the absence of chronic RET inhibition. Expression of NRAS p.Q61K in RET fusion expressing TPC1 cells conferred resistance to ponatinib. PR2 cells exhibited increased expression of EGFR and AXL. EGFR inhibition decreased cell proliferation and phosphorylation of ERK1/2 and AKT in PR2 cells, but not LC-2/ad cells. Although AXL inhibition enhanced PR2 sensitivity to afatinib, it was unable to decrease cell proliferation by itself. Thus, EGFR and AXL cooperatively rescued signaling from RET inhibition in the PR2 cells. Collectively, these findings demonstrate that resistance to ponatinib in RET-rearranged lung adenocarcinoma is mediated by bypass signaling mechanisms that result in restored RAS/MAPK activation. Mol Cancer Ther; 16(8); 1623-33. ©2017 AACR.

Precision medicine in pheochromocytoma and paraganglioma: current and future concepts

Pheochromocytoma and paraganglioma (PPGL) are rare diseases but are also amongst the most characterized tumour types. Hence, patients with PPGL have greatly benefited from precision medicine for more than two decades. According to current molecular biology and genetics-based taxonomy, PPGL can be divided into three different clusters characterized by: Krebs cycle reprogramming with oncometabolite accumulation or depletion (group 1a); activation of the (pseudo)hypoxia signalling pathway with increased tumour cell proliferation, invasiveness and migration (group 1b); and aberrant kinase signalling causing a pro-mitogenic and anti-apoptotic state (group 2). Categorization into these clusters is highly dependent on mutation subtypes. At least 12 different syndromes with distinct genetic causes, phenotypes and outcomes have been described. Genetic screening tests have a documented benefit, as different PPGL syndromes require specific approaches for optimal diagnosis and localization of various syndrome-related tumours. Genotype-tailored treatment options, follow-up and preventive care are being investigated. Future new developments in precision medicine for PPGL will mainly focus on further identification of driver mechanisms behind both disease initiation and malignant progression. Identification of novel druggable targets and prospective validation of treatment options are eagerly awaited. To achieve these goals, we predict that collaborative large-scale studies will be needed: Pheochromocytoma may provide an example for developing precision medicine in orphan diseases that could ultimately aid in similar efforts for other rare conditions.

Ret function in muscle stem cells points to tyrosine kinase inhibitor therapy for facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) involves sporadic expression of DUX4, which inhibits myogenesis and is pro-apoptotic. To identify target genes, we over-expressed DUX4 in myoblasts and found that the receptor tyrosine kinase Ret was significantly up-regulated, suggesting a role in FSHD. RET is dynamically expressed during myogenic progression in mouse and human myoblasts. Constitutive expression of either RET9 or RET51 increased myoblast proliferation, whereas siRNA-mediated knockdown of Ret induced myogenic differentiation. Suppressing RET activity using Sunitinib, a clinically-approved tyrosine kinase inhibitor, rescued differentiation in both DUX4-expressing murine myoblasts and in FSHD patient-derived myoblasts. Importantly, Sunitinib also increased engraftment and differentiation of FSHD myoblasts in regenerating mouse muscle. Thus, DUX4-mediated activation of Ret prevents myogenic differentiation and could contribute to FSHD pathology by preventing satellite cell-mediated repair. Rescue of DUX4-induced pathology by Sunitinib highlights the therapeutic potential of tyrosine kinase inhibitors for treatment of FSHD.

DOI:http://dx.doi.org/10.7554/eLife.11405.001

Neurotrophin Signaling and Stem Cells-Implications for Neurodegenerative Diseases and Stem Cell Therapy

Neurotrophins (NTs) are members of a neuronal growth factor protein family whose action is mediated by the tropomyosin receptor kinase (TRK) receptor family receptors and the p75 NT receptor (p75NTR), a member of the tumor necrosis factor (TNF) receptor family. Although NTs were first discovered in neurons, recent studies have suggested that NTs and their receptors are expressed in various types of stem cells mediating pivotal signaling events in stem cell biology. The concept of stem cell therapy has already attracted much attention as a potential strategy for the treatment of neurodegenerative diseases (NDs). Strikingly, NTs, proNTs, and their receptors are gaining interest as key regulators of stem cells differentiation, survival, self-renewal, plasticity, and migration. In this review, we elaborate the recent progress in understanding of NTs and their action on various stem cells. First, we provide current knowledge of NTs, proNTs, and their receptor isoforms and signaling pathways. Subsequently, we describe recent advances in the understanding of NT activities in various stem cells and their role in NDs, particularly Alzheimer's disease (AD) and Parkinson's disease (PD). Finally, we compile the implications of NTs and stem cells from a clinical perspective and discuss the challenges with regard to transplantation therapy for treatment of AD and PD.

Trophic factors for Parkinson's disease: To live or let die

Trophic factors show great promise in laboratory studies as potential therapies for PD. However, multiple double-blind, clinical trials have failed to show benefits in comparison to a placebo control. This article will review the scientific rationale for testing trophic factors in PD, the results of the different clinical trials that have been performed to date, and the possible explanations for these failed outcomes. We will also consider future directions and the likelihood that trophic factors will become a viable therapy for patients with PD.

Exon Skipping in the RET Gene Encodes Novel Isoforms That Differentially Regulate RET Protein Signal Transduction

Rearranged during transfection (RET), a receptor tyrosine kinase that is activated by the glial cell line-derived neurotrophic factor family ligands (GFLs), plays a crucial role in the development and function of the nervous system and additionally is required for kidney development and spermatogenesis. RET encodes a transmembrane receptor that is 20 exons long and produces two known protein isoforms differing in C-terminal amino acid composition, referred to as RET9 and RET51. Studies of human pheochromocytomas identified two additional novel transcripts involving the skipping of exon 3 or exons 3, 4, and 5 and are referred to as RET(Δ) (E3) and RET(Δ) (E345), respectively. Here we report the presence of Ret(Δ) (E3) and Ret(Δ) (E345) in zebrafish, mice, and rats and show that these transcripts are dynamically expressed throughout development of the CNS, peripheral nervous system, and kidneys. We further explore the biochemical properties of these isoforms, demonstrating that, like full-length RET, RET(ΔE3) and RET(ΔE345) are trafficked to the cell surface, interact with all four GFRα co-receptors, and have the ability to heterodimerize with full-length RET. Signaling experiments indicate that RET(ΔE3) is phosphorylated in a similar manner to full-length RET. RET(ΔE345), in contrast, displays higher baseline autophosphorylation, specifically on the catalytic tyrosine, Tyr(905), and also on one of the most important signaling residues, Tyr(1062) These data provide the first evidence for a physiologic role of these isoforms in RET pathway function.

Brain ischemia downregulates the neuroprotective GDNF-Ret signaling by a calpain-dependent mechanism in cultured hippocampal neurons

The glial cell line-derived neurotrophic factor (GDNF) has an important role in neuronal survival through binding to the GFRα1 (GDNF family receptor alpha-1) receptor and activation of the receptor tyrosine kinase Ret. Transient brain ischemia alters the expression of the GDNF signaling machinery but whether the GDNF receptor proteins are also affected, and the functional consequences, have not been investigated. We found that excitotoxic stimulation of cultured hippocampal neurons leads to a calpain-dependent downregulation of the long isoform of Ret (Ret51), but no changes were observed for Ret9 or GFRα1 under the same conditions. Cleavage of Ret51 by calpains was selectively mediated by activation of the extrasynaptic pool of N-methyl-d-aspartate receptors and leads to the formation of a stable cleavage product. Calpain-mediated cleavage of Ret51 was also observed in hippocampal neurons subjected to transient oxygen and glucose deprivation (OGD), a model of global brain ischemia, as well as in the ischemic region in the cerebral cortex of mice exposed to transient middle cerebral artery occlusion. Although the reduction of Ret51 protein levels decreased the total GDNF-induced receptor activity (as determined by assessing total phospho-Ret51 protein levels) and their downstream signaling activity, the remaining receptors still showed an increase in phosphorylation after incubation of hippocampal neurons with GDNF. Furthermore, GDNF protected hippocampal neurons when present before, during or after OGD, and the effects under the latter conditions were more significant in neurons transfected with human Ret51. These results indicate that the loss of Ret51 in brain ischemia partially impairs the neuroprotective effects of GDNF.

Overexpression of genes involved in miRNA biogenesis in medullary thyroid carcinomas with RET mutation

Abnormal expression of non-coding micro RNA (miRNA) has been described in medullary thyroid carcinoma (MTC). Expression of genes encoding factors involved in miRNA biogenesis results often deregulated in human cancer and correlates with aggressive clinical behavior. In this study, expression of four genes involved in miRNA biogenesis (DICER, DROSHA, DCGR8, and XPO5) was investigated in 54 specimens of MTC. Among them, 33 and 13 harbored RET and RAS mutations, respectively. DICER, DGCR8, and XPO5 mRNA levels were significantly overexpressed in MTC harboring RET mutations, in particular, in the presence of RET634 mutation. When MTCs with RET and RAS mutations were compared, only DGCR8 displayed a significant difference, while MTCs with RAS mutations did not show significant differences with respect to non-mutated tumors. We then attempted to correlate expression of miRNA biogenesis genes with tumor aggressiveness. According to the TNM status, MTCs were divided in two groups and compared (N0 M0 vs. N1 and/or M1): for all four genes no significant difference was detected. Cell line experiments, in which expression of a RET mutation is silenced by siRNA, suggest the existence of a causal relationship between RET mutation and overexpression of DICER, DGCR8, and XPO5 genes. These findings demonstrate that RET- but not RAS-driven tumorigenic alterations include abnormalities in the expression of some important genes involved in miRNA biogenesis that could represent new potential markers for targeted therapies in the treatment of RET-mutated MTCs aimed to restore the normal miRNA expression profile.

The genetics and epigenetics of kidney development

The development of the mammalian kidney has been studied at the genetic, biochemical, and cell biological level for more than 40 years. As such, detailed mechanisms governing early patterning, cell lineages, and inductive interactions have been well described. How genes interact to specify the renal epithelial cells of the nephrons and how this specification is relevant to maintaining normal renal function is discussed. Implicit in the development of the kidney are epigenetic mechanisms that mark renal cell types and connect certain developmental regulatory factors to chromatin modifications that control gene expression patterns and cellular physiology. In adults, such regulatory factors and their epigenetic pathways may function in regeneration and may be disturbed in disease processes.

Mechanisms of RET signaling in cancer: current and future implications for targeted therapy

De-regulation of RET signaling by oncogenic mutation, gene rearrangement, overexpression or transcriptional up-regulation is implicated in several human cancers of neuroendocrine and epithelial origin (thyroid, breast, lung). Understanding how RET signaling mechanisms associated with these oncogenic events are deregulated, and their impact in the biological processes driving tumor formation and progression, as well as response to treatment, will be crucial to find and develop better targeted therapeutic strategies. In this review we emphasie the distinct mechanisms of RET signaling in cancer and summarise current knowledge on small molecule inhibitors targeting the tyrosine kinase domain of RET as therapeutic drugs in RET-positive cancers.

Renin-angiotensin system in ureteric bud branching morphogenesis: implications for kidney disease

Failure of normal branching morphogenesis of the ureteric bud (UB), a key ontogenic process that controls organogenesis of the metanephric kidney, leads to congenital anomalies of the kidney and urinary tract (CAKUT), the leading cause of end-stage kidney disease in children. Recent studies have revealed a central role of the renin-angiotensin system (RAS), the cardinal regulator of blood pressure and fluid/electrolyte homeostasis, in the control of normal kidney development. Mice or humans with mutations in the RAS genes exhibit a spectrum of CAKUT which includes renal medullary hypoplasia, hydronephrosis, renal hypodysplasia, duplicated renal collecting system and renal tubular dysgenesis. Emerging evidence indicates that severe hypoplasia of the inner medulla and papilla observed in angiotensinogen (Agt)- or angiotensin (Ang) II AT 1 receptor (AT 1 R)-deficient mice is due to aberrant UB branching morphogenesis resulting from disrupted RAS signaling. Lack of the prorenin receptor (PRR) in the UB in mice causes reduced UB branching, resulting in decreased nephron endowment, marked kidney hypoplasia, urinary concentrating and acidification defects. This review provides a mechanistic rational supporting the hypothesis that aberrant signaling of the intrarenal RAS during distinct stages of metanephric kidney development contributes to the pathogenesis of the broad phenotypic spectrum of CAKUT. As aberrant RAS signaling impairs normal renal development, these findings advocate caution for the use of RAS inhibitors in early infancy and further underscore a need to avoid their use during pregnancy and to identify the types of molecular processes that can be targeted for clinical intervention.

RET revisited: expanding the oncogenic portfolio

The RET receptor tyrosine kinase is crucial for normal development but also contributes to pathologies that reflect both the loss and the gain of RET function. Activation of RET occurs via oncogenic mutations in familial and sporadic cancers - most notably, those of the thyroid and the lung. RET has also recently been implicated in the progression of breast and pancreatic tumours, among others, which makes it an attractive target for small-molecule kinase inhibitors as therapeutics. However, the complex roles of RET in homeostasis and survival of neural lineages and in tumour-associated inflammation might also suggest potential long-term pitfalls of broadly targeting RET.