IGF2BP1/IMP1 Deletion Enhances a Facultative Stem Cell State via Regulation of MAP1LC3B.

BACKGROUND & AIMS: The intestinal epithelium interfaces with a diverse milieu of luminal contents while maintaining robust digestive and barrier functions. Facultative intestinal stem cells are cells that survive tissue injury and divide to re-establish the epithelium. Prior studies have shown autophagic state as functional marker of facultative intestinal stem cells, but regulatory mechanisms are not known. The current study evaluated a post-transcriptional regulation of autophagy as an important factor for facultative stem cell state and tissue regeneration. METHODS: We evaluated stem cell composition, autophagic vesicle content, organoid formation, and in vivo regeneration in mice with intestinal epithelial deletion of the RNA binding protein IGF2 messenger RNA binding protein 1 (IMP1). The contribution of autophagy to resulting in vitro and in vivo phenotypes was evaluated via genetic inactivation of Atg7. Molecular analyses of IMP1 modulation of autophagy at the protein and transcript localization levels were performed using IMP1 mutant studies and single-molecule fluorescent in situ hybridization. RESULTS: Epithelial Imp1 deletion reduced leucine rich repeat containing G protein coupled receptor 5 cell frequency but enhanced both organoid formation efficiency and in vivo regeneration after irradiation. We confirmed prior studies showing increased autophagy with IMP1 deletion. Deletion of Atg7 reversed the enhanced regeneration observed with Imp1 deletion. IMP1 deletion or mutation of IMP1 phosphorylation sites enhanced expression of essential autophagy protein microtubule-associated protein 1 light chain 3ß. Furthermore, immunofluorescence imaging coupled with single-molecule fluorescent in situ hybridization showed IMP1 colocalization with MAP1LC3B transcripts at homeostasis. Stress induction led to decreased colocalization. CONCLUSIONS: Depletion of IMP1 enhances autophagy, which promotes intestinal regeneration via expansion of facultative intestinal stem cells.

RASopathy mutations open new insights into the mechanism of BRAF activation.

Spencer-Smith et al. (2022)1 investigate multiple functions of the BRAF cysteine-rich domain (CRD), finding distinct classes of RASopathy-associated BRAF mutations and unique features among RAF paralogs that may contribute to the spectrum of mutations observed in disease.

Oxidation state-specific fluorescent copper sensors reveal oncogene-driven redox changes that regulate labile copper(II) pools.

Copper is an essential metal nutrient for life that often relies on redox cycling between Cu(I) and Cu(II) oxidation states to fulfill its physiological roles, but alterations in cellular redox status can lead to imbalances in copper homeostasis that contribute to cancer and other metalloplasias with metal-dependent disease vulnerabilities. Copper-responsive fluorescent probes offer powerful tools to study labile copper pools, but most of these reagents target Cu(I), with limited methods for monitoring Cu(II) owing to its potent fluorescence quenching properties. Here, we report an activity-based sensing strategy for turn-on, oxidation state-specific detection of Cu(II) through metal-directed acyl imidazole chemistry. Cu(II) binding to a metal and oxidation state-specific receptor that accommodates the harder Lewis acidity of Cu(II) relative to Cu(I) activates the pendant dye for reaction with proximal biological nucleophiles and concomitant metal ion release, thus avoiding fluorescence quenching. Copper-directed acyl imidazole 649 for Cu(II) (CD649.2) provides foundational information on the existence and regulation of labile Cu(II) pools, including identifying divalent metal transporter 1 (DMT1) as a Cu(II) importer, labile Cu(II) increases in response to oxidative stress induced by depleting total glutathione levels, and reciprocal increases in labile Cu(II) accompanied by decreases in labile Cu(I) induced by oncogenic mutations that promote oxidative stress.

Copper Modulates the Catalytic Activity of Protein Kinase CK2.

Casein kinase 2 (CK2) is an evolutionarily conserved serine/threonine kinase implicated in a wide range of cellular functions and known to be dysregulated in various diseases such as cancer. Compared to most other kinases, CK2 exhibits several unusual properties, including dual co-substrate specificity and a high degree of promiscuity with hundreds of substrates described to date. Most paradoxical, however, is its apparent constitutive activity: no definitive mode of catalytic regulation has thus far been identified. Here we demonstrate that copper enhances the enzymatic activity of CK2 both in vitro and in vivo. We show that copper binds directly to CK2, and we identify specific residues in the catalytic subunit of the enzyme that are critical for copper-binding. We further demonstrate that increased levels of intracellular copper result in enhanced CK2 kinase activity, while decreased copper import results in reduced CK2 activity. Taken together, these findings establish CK2 as a copper-regulated kinase and indicate that copper is a key modulator of CK2-dependent signaling pathways.

Direct anabolic metabolism of three-carbon propionate to a six-carbon metabolite occurs in vivo across tissues and species.

Anabolic metabolism of carbon in mammals is mediated via the one- and two-carbon carriers S-adenosyl methionine and acetyl-coenzyme A. In contrast, anabolic metabolism of three-carbon units via propionate has not been shown to extensively occur. Mammals are primarily thought to oxidize the three-carbon short chain fatty acid propionate by shunting propionyl-CoA to succinyl-CoA for entry into the TCA cycle. Here, we found that this may not be absolute as, in mammals, one nonoxidative fate of propionyl-CoA is to condense to two three-carbon units into a six-carbon trans-2-methyl-2-pentenoyl-CoA (2M2PE-CoA). We confirmed this reaction pathway using purified protein extracts provided limited substrates and verified the product via LC-MS using a synthetic standard. In whole-body in vivo stable isotope tracing following infusion of 13C-labeled valine at steady state, 2M2PE-CoA was found to form via propionyl-CoA in multiple murine tissues, including heart, kidney, and to a lesser degree, in brown adipose tissue, liver, and tibialis anterior muscle. Using ex vivo isotope tracing, we found that 2M2PE-CoA also formed in human myocardial tissue incubated with propionate to a limited extent. While the complete enzymology of this pathway remains to be elucidated, these results confirm the in vivo existence of at least one anabolic three- to six-carbon reaction conserved in humans and mice that utilizes propionate.

Cuproptosis: Cellular and molecular mechanisms underlying copper-induced cell death.

Tsvetkov et al. (2022) discovered a new form of cell death triggered by targeted accumulation of Cu in mitochondria that drives lipoylated TCA cycle enzyme aggregation via direct Cu binding.

The transcription factor PAX8 promotes angiogenesis in ovarian cancer through interaction with SOX17.

PAX8 is a master transcription factor that is essential during embryogenesis and promotes neoplastic growth. It is expressed by the secretory cells lining the female reproductive tract, and its deletion during development results in atresia of reproductive tract organs. Nearly all ovarian carcinomas express PAX8, and its knockdown results in apoptosis of ovarian cancer cells. To explore the role of PAX8 in these tissues, we purified the PAX8 protein complex from nonmalignant fallopian tube cells and high-grade serous ovarian carcinoma cell lines. We found that PAX8 was a member of a large chromatin remodeling complex and preferentially interacted with SOX17, another developmental transcription factor. Depleting either PAX8 or SOX17 from cancer cells altered the expression of factors involved in angiogenesis and functionally disrupted tubule and capillary formation in cell culture and mouse models. PAX8 and SOX17 in ovarian cancer cells promoted the secretion of angiogenic factors by suppressing the expression of SERPINE1, which encodes a proteinase inhibitor with antiangiogenic effects. The findings reveal a non-cell-autonomous function of these transcription factors in regulating angiogenesis in ovarian cancer.

Understanding and drugging RAS: 40†years to break the tip of the iceberg.

Several cancers and rare genetic diseases are caused by dysregulation in the RAS signaling pathway. RAS proteins serve as molecular switches that regulate pathways involved in cellular growth, differentiation and survival. These pathways have been an intense area of investigation for four decades, since the initial identification of somatic RAS mutations linked to human cancers. In the past few years, inhibitors against several RAS effectors, as well as direct inhibitors of the K-RAS mutant G12C, have been developed. This Special Issue in DMM includes original Research articles on RAS-driven cancers and RASopathies. The articles provide insights into mechanisms and biomarkers, and evaluate therapeutic targets. Several articles also present new disease models, whereas others describe technologies or approaches to evaluate the function of RAS in vivo. The collection also includes a series of Review articles on RAS biology and translational aspects of defining and treating RAS-driven diseases. In this Editorial, we summarize this collection and discuss the potential impact of the articles within this evolving area of research. We also identify areas of growth and possible future developments.

BRAFV600E-Driven Lung Adenocarcinoma Requires Copper to Sustain Autophagic Signaling and Processing.

The transition metal copper (Cu) is an essential micronutrient required for development and proliferation, but the molecular mechanisms by which Cu contributes to these processes is not fully understood. Although traditionally studied as a static cofactor critical for the function of Cu-dependent enzymes, an expanding role for Cu is emerging to include its novel function as a dynamic mediator of signaling processes through the direct control of protein kinase activity. We now appreciate that Cu directly binds to and influences MEK1/2 and ULK1/2 kinase activity, and show here that reductions in MAPK and autophagic signaling are associated with dampened growth and survival of oncogenic BRAF-driven lung adenocarcinoma cells upon loss of Ctr1. Efficient autophagy, clonogenic survival, and tumorigenesis of BRAF-mutant cells required ULK1 Cu-binding. Although treatment with canonical MAPK inhibitors resulted in the upregulation of protective autophagy, mechanistically, the Cu chelator tetrathiomolybdate (TTM) was sufficient to target both autophagic and MAPK signaling as a means to blunt BRAF-driven tumorigenic properties. These findings support leveraging Cu chelation with TTM as an alternative therapeutic strategy to impair autophagy and MAPK signaling. As traditional MAPK monotherapies initiate autophagy signaling and promote cancer cell survival. IMPLICATIONS: We establish that copper chelation therapy inhibits both autophagy and MAPK signaling in BRAFV600E-driven lung adenocarcinoma, thus overcoming the upregulation of protective autophagy elicited by canonical MAPK pathway inhibitors.

Loss of p19Arf promotes fibroblast survival during leucine deprivation.

Fibroblasts are quiescent and tumor suppressive in nature but become activated in wound healing and cancer. The response of fibroblasts to cellular stress has not been extensively investigated, however the p53 tumor suppressor has been shown to be activated in fibroblasts during nutrient deprivation. Since the p19 Alternative reading frame (p19Arf) tumor suppressor is a key regulator of p53 activation during oncogenic stress, we investigated the role of p19Arf in fibroblasts during nutrient deprivation. Here, we show that prolonged leucine deprivation results in increased expression and nuclear localization of p19Arf, triggering apoptosis in primary murine adult lung fibroblasts (ALFs). In contrast, the absence of p19Arf during long-term leucine deprivation resulted in increased ALF proliferation, migration and survival through upregulation of the Integrated Stress Response pathway and increased autophagic flux. Our data implicates a new role for p19Arf in response to nutrient deprivation. This article has an associated First Person interview with the first author of the paper.

Connecting copper and cancer: from transition metal signalling to metalloplasia.

Copper is an essential nutrient whose redox properties make it both beneficial and toxic to the cell. Recent progress in studying transition metal signalling has forged new links between researchers of different disciplines that can help translate basic research in the chemistry and biology of copper into clinical therapies and diagnostics to exploit copper-dependent disease vulnerabilities. This concept is particularly relevant in cancer, as tumour growth and metastasis have a heightened requirement for this metal nutrient. Indeed, the traditional view of copper as solely an active site metabolic cofactor has been challenged by emerging evidence that copper is also a dynamic signalling metal and metalloallosteric regulator, such as for copper-dependent phosphodiesterase 3B (PDE3B) in lipolysis, mitogen-activated protein kinase kinase 1 (MEK1) and MEK2 in cell growth and proliferation and the kinases ULK1 and ULK2 in autophagy. In this Perspective, we summarize our current understanding of the connection between copper and cancer and explore how challenges in the field could be addressed by using the framework of cuproplasia, which is defined as regulated copper-dependent cell proliferation and is a representative example of a broad range of metalloplasias. Cuproplasia is linked to a diverse array of cellular processes, including mitochondrial respiration, antioxidant defence, redox signalling, kinase signalling, autophagy and protein quality control. Identifying and characterizing new modes of copper-dependent signalling offers translational opportunities that leverage disease vulnerabilities to this metal nutrient.

The copper chaperone CCS facilitates copper binding to MEK1/2 to promote kinase activation.

Normal physiology relies on the precise coordination of intracellular signaling pathways that respond to nutrient availability to balance cell growth and cell death. The canonical mitogen-activated protein kinase pathway consists of the RAF-MEK-ERK signaling cascade and represents one of the most well-defined axes within eukaryotic cells to promote cell proliferation, which underscores its frequent mutational activation in human cancers. Our recent studies illuminated a function for the redox-active micronutrient copper (Cu) as an intracellular mediator of signaling by connecting Cu to the amplitude of mitogen-activated protein kinase signaling via a direct interaction between Cu and the kinases MEK1 and MEK2. Given the large quantities of molecules such as glutathione and metallothionein that limit cellular toxicity from free Cu ions, evolutionarily conserved Cu chaperones facilitate efficient delivery of Cu to cuproenzymes. Thus, a dedicated cellular delivery mechanism of Cu to MEK1/2 likely exists. Using surface plasmon resonance and proximity-dependent biotin ligase studies, we report here that the Cu chaperone for superoxide dismutase (CCS) selectively bound to and facilitated Cu transfer to MEK1. Mutants of CCS that disrupt Cu(I) acquisition and exchange or a CCS small-molecule inhibitor were used and resulted in reduced Cu-stimulated MEK1 kinase activity. Our findings indicate that the Cu chaperone CCS provides fidelity within a complex biological system to achieve appropriate installation of Cu within the MEK1 kinase active site that in turn modulates kinase activity and supports the development of novel MEK1/2 inhibitors that target the Cu structural interface or blunt dedicated Cu delivery mechanisms via CCS.

Copper biology.

Metals are vital for life as they are necessary for essential biological processes. Traditionally, metals are categorized as either dynamic signals or static cofactors. Redox-inactive metals such as calcium (Ca), potassium (K), sodium (Na), and zinc (Zn) signal through large fluctuations in their metal-ion pools. In contrast, redox-active transition metals such as copper (Cu) and iron (Fe) drive catalysis and are largely characterized as static cofactors that must be buried and protected within the active sites of proteins, due to their ability to generate damaging reactive-oxygen species through Fenton chemistry. Cu has largely been studied as a static cofactor in fundamental processes from cellular respiration to pigmentation, working through cytochrome c oxidase and tyrosinase, respectively. However, within the last decade, a new paradigm in nutrient sensing and protein regulation - termed 'metalloallostery' - has emerged, expanding the repertoire of Cu beyond the catalytic proteins to dynamic signaling molecules essential for cellular processes that impact normal physiology and disease states. In this Primer we introduce both the 'traditional' and emerging roles for Cu in biology and the many ways in which Cu intersects with human health.

Altered copper homeostasis underlies sensitivity of hepatocellular carcinoma to copper chelation.

Hepatocellular carcinoma (HCC), the most common primary liver cancer, of which ∼800 000 new cases will be diagnosed worldwide this year, portends a five-year survival rate of merely 17% in patients with unresectable disease. This dismal prognosis is due, at least in part, from the late stage of diagnosis and the limited efficacy of systemic therapies. As a result, there is an urgent need to identify risk factors that contribute to HCC initiation and provide targetable vulnerabilities to improve patient survival. While myriad risk factors are known, elevated copper (Cu) levels in HCC patients and the incidence of hepatobiliary malignancies in Wilson disease patients, which exhibit hereditary liver Cu overload, suggests the possibility that metal accumulation promotes malignant transformation. Here we found that expression of the Cu transporter genes ATP7A, ATP7B, SLC31A1, and SLC31A2 was significantly altered in liver cancer samples and were associated with elevated Cu levels in liver cancer tissue and cells. Further analysis of genomic copy number data revealed that alterations in Cu transporter gene loci correlate with poorer survival in HCC patients. Genetic loss of the Cu importer SLC31A1 (CTR1) or pharmacologic suppression of Cu decreased the viability, clonogenic survival, and anchorage-independent growth of human HCC cell lines. Mechanistically, CTR1 knockdown or Cu chelation decreased glycolytic gene expression and downstream metabolite utilization and as a result forestalled tumor cell survival after exposure to hypoxia, which mimics oxygen deprivation elicited by transarterial embolization, a standard-of-care therapy used for patients with unresectable HCC. Taken together, these findings established an association between altered Cu homeostasis and HCC and suggest that limiting Cu bioavailability may provide a new treatment strategy for HCC by restricting the metabolic reprogramming necessary for cancer cell survival.

The Race toward Equity: Increasing Racial Diversity in Cancer Research and Cancer Care.

Cancer research and cancer care require deliberate attention to racial diversity. Here we comment on the ongoing issues of diversity and racism in cancer research.

Copper is an essential regulator of the autophagic kinases ULK1/2 to drive lung adenocarcinoma.

Although the transition metal copper (Cu) is an essential nutrient that is conventionally viewed as a static cofactor within enzyme active sites, a non-traditional role for Cu as a modulator of kinase signalling is emerging. Here, we found that Cu is required for the activity of the autophagic kinases ULK1 and ULK2 (ULK1/2) through a direct Cu-ULK1/2 interaction. Genetic loss of the Cu transporter Ctr1 or mutations in ULK1 that disrupt the binding of Cu reduced ULK1/2-dependent signalling and the formation of autophagosome complexes. Increased levels of intracellular Cu are associated with starvation-induced autophagy and are sufficient to enhance ULK1 kinase activity and, in turn, autophagic flux. The growth and survival of lung tumours driven by KRASG12D is diminished in the absence of Ctr1, is dependent on ULK1 Cu binding and is associated with reduced levels of autophagy and signalling. These findings suggest a molecular basis for exploiting Cu-chelation therapy to prevent autophagy signalling to limit proliferation and improve patient survival in cancer.

Inhibition of BCL2 Family Members Increases the Efficacy of Copper Chelation in BRAFV600E-Driven Melanoma.

The principal unmet need in BRAFV600E-positive melanoma is lack of an adequate therapeutic strategy capable of overcoming resistance to clinically approved targeted therapies against oncogenic BRAF and/or the downstream MEK1/2 kinases. We previously discovered that copper (Cu) is required for MEK1 and MEK2 activity through a direct Cu-MEK1/2 interaction. Repurposing the clinical Cu chelator tetrathiomolybdate (TTM) is supported by efficacy in BRAFV600E-driven melanoma models, due in part to inhibition of MEK1/2 kinase activity. However, the antineoplastic activity of Cu chelators is cytostatic. Here, we performed high-throughput small-molecule screens to identify bioactive compounds that synergize with TTM in BRAFV600E-driven melanoma cells. Genetic perturbation or pharmacologic inhibition of specific members of the BCL2 family of antiapoptotic proteins (BCL-W, BCL-XL, and MCL1) selectively reduced cell viability when combined with a Cu chelator and induced CASPASE-dependent cell death. Further, in BRAFV600E-positive melanoma cells evolved to be resistant to BRAF and/or MEK1/2 inhibitors, combined treatment with TTM and the clinically evaluated BCL2 inhibitor, ABT-263, restored tumor growth suppression and induced apoptosis. These findings further support Cu chelation as a therapeutic strategy to target oncogene-dependent tumor cell growth and survival by enhancing Cu chelator efficacy with chemical inducers of apoptosis, especially in the context of refractory or relapsed BRAFV600E-driven melanoma. SIGNIFICANCE: This study unveils a novel collateral drug sensitivity elicited by combining copper chelators and BH3 mimetics for treatment of BRAFV600E mutation-positive melanoma.

Evaluation of copper chaperone ATOX1 as prognostic biomarker in breast cancer.

Copper is involved in different hallmarks of cancer, including metastasis, but responsible copper-binding proteins and pathways are not clear. The copper chaperone ATOX1 was recently shown to play a role in breast cancer cell migration, which is a key step in metastasis. Since most cancer-related deaths are due to metastasis, we hypothesized that ATOX1 mRNA expression may be associated with breast cancer disease progression and thus, a prognostic biomarker in breast cancer. We therefore studied the association of ATOX1 expression levels with clinicopathological parameters and survival for 1904 breast cancer patients using the METABRIC data set. Our results indicate ATOX1 expression levels as a potential prognostic biomarker for ER-positive subtypes and early stages of breast cancer. Pre-clinical studies and clinical trials are desired to identify the molecular roles of ATOX1 in these conditions.

CDK7 Inhibition Suppresses Castration-Resistant Prostate Cancer through MED1 Inactivation.

Metastatic castration-resistant prostate cancer (CRPC) is a fatal disease, primarily resulting from the transcriptional addiction driven by androgen receptor (AR). First-line CRPC treatments typically target AR signaling, but are rapidly bypassed, resulting in only a modest survival benefit with antiandrogens. Therapeutic approaches that more effectively block the AR-transcriptional axis are urgently needed. Here, we investigated the molecular mechanism underlying the association between the transcriptional coactivator MED1 and AR as a vulnerability in AR-driven CRPC. MED1 undergoes CDK7-dependent phosphorylation at T1457 and physically engages AR at superenhancer sites, and is essential for AR-mediated transcription. In addition, a CDK7-specific inhibitor, THZ1, blunts AR-dependent neoplastic growth by blocking AR/MED1 corecruitment genome-wide, as well as reverses the hyperphosphorylated MED1-associated enzalutamide-resistant phenotype. In vivo, THZ1 induces tumor regression of AR-amplified human CRPC in a xenograft mouse model. Together, we demonstrate that CDK7 inhibition selectively targets MED1-mediated, AR-dependent oncogenic transcriptional amplification, thus representing a potential new approach for the treatment of CRPC. SIGNIFICANCE: Potent inhibition of AR signaling is critical to treat CRPC. This study uncovers a driver role for CDK7 in regulating AR-mediated transcription through phosphorylation of MED1, thus revealing a therapeutically targetable potential vulnerability in AR-addicted CRPC.See related commentary by Russo et al., p. 1490.This article is highlighted in the In This Issue feature, p. 1469.