Lysocardiolipin acyltransferase regulates NSCLC cell proliferation and migration by modulating mitochondrial dynamics.

Lysocardiolipin acyltransferase (LYCAT), a cardiolipin (CL)-remodeling enzyme, is crucial for maintaining normal mitochondrial function and vascular development. Despite the well-characterized role for LYCAT in the regulation of mitochondrial dynamics, its involvement in lung cancer, if any, remains incompletely understood. In this study, in silico analysis of TCGA lung cancer data sets revealed a significant increase in LYCAT expression, which was later corroborated in human lung cancer tissues and immortalized lung cancer cell lines via indirect immunofluorescence and immunoblotting, respectively. Stable knockdown of LYCAT in NSCLC cell lines not only reduced CL and increased monolyso-CL levels but also reduced in vivo tumor growth, as determined by xenograft studies in athymic nude mice. Furthermore, blocking LYCAT activity using a LYCAT mimetic peptide attenuated cell migration, suggesting a novel role for LYCAT activity in promoting NSCLC. Mechanistically, the pro-proliferative effects of LYCAT were mediated by an increase in mitochondrial fusion and a G1/S cell cycle transition, both of which are linked to increased cell proliferation. Taken together, these results demonstrate a novel role for LYCAT in promoting NSCLC and suggest that targeting LYCAT expression or activity in NSCLC may provide new avenues for the therapeutic treatment of lung cancer.

Orthogonal lipid sensors identify transbilayer asymmetry of plasma membrane cholesterol.

Controlled distribution of lipids across various cell membranes is crucial for cell homeostasis and regulation. We developed an imaging method that allows simultaneous in situ quantification of cholesterol in two leaflets of the plasma membrane (PM) using tunable orthogonal cholesterol sensors. Our imaging revealed marked transbilayer asymmetry of PM cholesterol (TAPMC) in various mammalian cells, with the concentration in the inner leaflet (IPM) being ∼12-fold lower than that in the outer leaflet (OPM). The asymmetry was maintained by active transport of cholesterol from IPM to OPM and its chemical retention at OPM. Furthermore, the increase in the IPM cholesterol level was triggered in a stimulus-specific manner, allowing cholesterol to serve as a signaling lipid. We found excellent correlation between the IPM cholesterol level and cellular Wnt signaling activity, suggesting that TAPMC and stimulus-induced PM cholesterol redistribution are crucial for tight regulation of cellular processes under physiological conditions.

K-homology splicing regulatory protein (KSRP) promotes post-transcriptional destabilization of Spry4 transcripts in non-small cell lung cancer.

AU-rich element-binding proteins (ARE-BPs) offer post-transcriptional regulation of gene expression via physical interaction and recruitment of RNA decay machinery to the AU-rich elements within the 3'-UTR of the target transcripts. However, the role of ARE-BPs in lung cancer remains poorly understood. In this study, we have identified that K-homology splicing regulatory protein (KSRP), an ARE-BP, is robustly up-regulated in human lung cancer. Importantly, Kaplan-Meier survival analysis indicated that elevated KSRP expression was correlated with poor overall survival of lung cancer patients. Furthermore, cigarette smoke, a leading risk factor for lung cancer, was also identified to be an important contributor to increased KSRP expression. Remarkably, silencing of KSRP decreased cell proliferation, reversed anchorage-independent growth, and reduced migration/invasion, suggesting an oncogenic role for KSRP in lung cancer. Finally, we provide mechanistic evidence that KSRP promotes the down-regulation of Spry4 by a previously unidentified mechanism, i.e. post-transcriptional mRNA regulation.

PRMT1 Is a Novel Regulator of Epithelial-Mesenchymal-Transition in Non-small Cell Lung Cancer.

Protein arginine methyl transferase 1 (PRMT1) was shown to be up-regulated in cancers and important for cancer cell proliferation. However, the role of PRMT1 in lung cancer progression and metastasis remains incompletely understood. In the present study, we show that PRMT1 is an important regulator of epithelial-mesenchymal transition (EMT), cancer cell migration, and invasion, which are essential processes during cancer progression, and metastasis. Additionally, we have identified Twist1, a basic helix-loop-helix transcription factor and a well-known E-cadherin repressor, as a novel PRMT1 substrate. Taken together, we show that PRMT1 is a novel regulator of EMT and arginine 34 (Arg-34) methylation of Twist1 as a unique "methyl arginine mark" for active E-cadherin repression. Therefore, targeting PRMT1-mediated Twist1 methylation might represent a novel strategy for developing new anti-invasive/anti-metastatic drugs. Moreover, methylated Twist1 (Arg-34), as such, could also emerge as a potential important biomarker for lung cancer.

Novel Role for γ-Catenin in the Regulation of Cancer Cell Migration via the Induction of Hepatocyte Growth Factor Activator Inhibitor Type 1 (HAI-1).

γ-Catenin (Plakoglobin), a well-described structural protein functioning at the adherens junctions and desmosomes, was shown to be either lost or weakly expressed in non-small cell lung cancer (NSCLC) cells and tumor tissues. However, the tumor suppressive affects of γ-catenin were not fully understood. In this study, we have identified a novel role for the affects of γ-catenin on non-small cell lung cancer (NSCLC) cell migration. Expression of γ-catenin in NSCLC cells resulted in reduced cell migration as determined by both scratch assays and trans-well cell migration assays. Moreover, the affects of γ-catenin on cell migration were observed to be p53-dependent. Mechanistically, the anti-migratory effects seen via γ-catenin were driven by the expression of hepatocyte growth factor activator inhibitor Type I (HAI-1 or SPINT-1), an upstream inhibitor of the c-MET signaling pathway. Furthermore, the re-expression of γ-catenin sensitized NSCLC cells to c-MET inhibitor-mediated growth inhibition. Taken together, we identify γ-catenin as a novel regulator of HAI-1, which is a critical regulator of HGF/c-MET signaling. Therefore, targeting γ-catenin-mediated HAI-1 expression might be a useful strategy to sensitize NSCLC to c-MET inhibitors.

Wnt3a-stimulated LRP6 phosphorylation is dependent upon arginine methylation of G3BP2.

Wnt signaling is initiated upon binding of Wnt proteins to Frizzled proteins and their co-receptors LRP5 and 6. The signal is then propagated to several downstream effectors, mediated by the phosphoprotein scaffold, dishevelled. We report a novel role for arginine methylation in regulating Wnt3a-stimulated LRP6 phosphorylation. G3BP2, a dishevelled-associated protein, is methylated in response to Wnt3a. The Wnt3a-induced LRP6 phosphorylation is attenuated by G3BP2 knockdown, chemical inhibition of methyl transferase activity or expression of methylation-deficient mutants of G3BP2. Arginine methylation of G3BP2 appears to be a Wnt3a-sensitive 'switch' regulating LRP6 phosphorylation and canonical Wnt-ß-catenin signaling.

Arginine methylation of G3BP1 in response to Wnt3a regulates ß-catenin mRNA.

Wnt/ß-catenin signaling is essential for normal mammalian development. Wnt3a activates the Wnt/ß-catenin pathway through stabilization of ß-catenin; a process in which the phosphoprotein Dishevelled figures prominently. Protein arginine methylation in signaling complexes containing Dishevelled was investigated. Mass spectrometry of a prominent arginine-methylated, Dishevelled-associated protein identified the Ras GTPase activating protein-binding protein 1 G3BP1. Stimulation of totipotent mouse embryonic F9 cells with Wnt3a provoked increased methylation of G3BP1. We show that G3BP1 is a novel Ctnnb1 mRNA binding protein. Methylation of G3BP1 constitutes a molecular switch that regulates Ctnnb1 mRNA in response to Wnt3a. Thus, the protein arginine methylation that targets G3BP1 acts as a novel regulator of Ctnnb1 mRNA.

FDA Approval Summary: Amivantamab for the Treatment of Patients with Non-Small Cell Lung Cancer with EGFR Exon 20 Insertion Mutations.

The FDA granted accelerated approval for amivantamab-vmjw (hereafter referred to as amivantamab), a bispecific antibody directed against EGFR and mesenchymal-epithelial transition receptor, on May 21, 2021, for the treatment of adult patients with locally advanced or metastatic non-small cell lung cancer (NSCLC) with EGFR exon 20 insertion mutations whose disease has progressed on or after platinum-based chemotherapy. Approval was based on results of an ongoing, multicenter, nonrandomized, open-label, multicohort clinical trial (CHRYSALIS, NCT02609776), demonstrating a substantial overall response rate (ORR) and durable responses, with an ORR of 40% [95% confidence interval (CI): 29-51] and a median response duration of 11.1 months (95% CI: 6.9-not evaluable). Guardant360 CDx was contemporaneously approved as a companion diagnostic for this indication to identify EGFR exon 20 insertion mutations in plasma specimens. The most notable safety finding was the high incidence (66%) of infusion-related reactions, which is addressed in both the Dosage and Administration and Warnings and Precautions sections of the product label. Other common adverse reactions (occurring in ≥20% of patients) were rash, paronychia, musculoskeletal pain, dyspnea, nausea and vomiting, fatigue, edema, stomatitis, cough, and constipation. The approval of amivantamab was the first approval of a targeted therapy for patients with advanced NSCLC harboring EGFR exon 20 insertion mutations.

FDA Approval Summary: Mobocertinib for Metastatic Non-Small Cell Lung Cancer with EGFR Exon 20 Insertion Mutations.

On September 15, 2021, the FDA granted accelerated approval to mobocertinib (Exkivity, Takeda Pharmaceuticals USA, Inc.) for the treatment of adult patients with locally advanced or metastatic non-small cell lung cancer (NSCLC) with EGFR exon 20 insertion mutations, as detected by an FDA-approved test, whose disease has progressed on or after platinum-based chemotherapy. The approval was based on data from Study AP32788-15-101 (NCT02716116), an international, non-randomized, multi-cohort clinical trial that included patients with locally advanced or metastatic NSCLC with EGFR exon 20 insertion mutations. The overall response rate in 114 patients whose disease had progressed on or after platinum-based chemotherapy was 28% [95% confidence interval (CI), 20%-37%] with a median duration of response of 17.5 months (95% CI, 7.4-20.3). The most common adverse reactions (>20%) were diarrhea, rash, nausea, stomatitis, vomiting, decreased appetite, paronychia, fatigue, dry skin, and musculoskeletal pain. Product labeling includes a Boxed Warning for QTc prolongation and torsades de pointes. This is the first approval of an oral targeted therapy for patients with advanced EGFR exon 20 insertion mutation-positive NSCLC.

Dishevelled-KSRP complex regulates Wnt signaling through post-transcriptional stabilization of beta-catenin mRNA.

Canonical Wnt/beta-catenin signaling is crucial during embryonic development. Upon Wnt stimulation, Dishevelled proteins relay the signal from upstream Frizzled receptors to downstream effectors. By using affinity purification followed by ion-trap mass spectrometry we identified K-homology splicing regulator protein (KSRP) as a novel Dishevelled-interacting protein. We show that KSRP negatively regulates Wnt/beta-catenin signaling at the level of post-transcriptional CTNNB1 (beta-catenin) mRNA stability. Thus, Dishevelled-KSRP complex operates in Wnt regulation of beta-catenin, functioning post-transcriptionally upon CTNNB1 mRNA stability.

PRMT6 Promotes Lung Tumor Progression via the Alternate Activation of Tumor-Associated Macrophages.

Increased expression of protein arginine methyl transferase 6 (PRMT6) correlates with worse prognosis in lung cancer cases. To interrogate the in vivo functions of PRMT6 in lung cancer, we developed a tamoxifen-inducible lung-targeted PRMT6 gain-of-function mouse model, which mimics PRMT6 amplification events in human lung tumors. Lung-targeted overexpression of PRMT6 accelerated cell proliferation de novo and potentiated chemical carcinogen (urethane)-induced lung tumor growth. To explore the molecular mechanism/s by which PRMT6 promotes lung tumor growth, we used proteomics-based approaches and identified interleukin-enhancer binding protein 2 (ILF2) as a novel PRMT6-associated protein. Furthermore, by using a series of in vitro gain-of-function and loss-of-function experiments, we defined a new role for the PRMT6-ILF2 signaling axis in alternate activation of tumor-associated macrophages (TAM). Interestingly, we have also identified macrophage migration inhibitory factor, which has recently been shown to regulate alternate activation of TAMs, as an important downstream target of PRMT6-ILF2 signaling. Collectively, our findings reveal a previously unidentified noncatalytic role for PRMT6 in potentiating lung tumor progression via the alternate activation of TAMs. IMPLICATIONS: This is the first study to demonstrate an in vivo role for PRMT6 in lung tumor progression via the alternate activation of TAMs.

Identification and characterization of surrogate peptide ligand for orphan G protein-coupled receptor mas using phage-displayed peptide library.

In the present study, a phage-displayed random peptide library was used to identify surrogate peptide ligands for orphan GPCR mas. Sequence analysis of the isolated phage clones indicated a selective enrichment of some peptide sequences. Moreover, multiple alignments of the isolated phage clones gave two conserved peptide motifs from which we synthesized peptide MBP7 for further evaluation. Characterization of the representative phage clones and the synthetic peptide MBP7 by immunocytochemistry revealed a strong punctate cell surface staining in CHO cells expressing mas-GFP fusion protein. The isolated phage clones and synthetic peptide MBP7 induced mas internalization in a stable CHO cell clone (MC0M80) over-expressing mas. In addition, MBP7-stimulated phospholipase C activity and intracellular calcium mobilization in these same cells. In summary, we have demonstrated a systematic approach to derive surrogate peptide ligands for orphan GPCRs. With this technique, we have identified two conserved peptide motifs which allow us to identify potential protein partners for mas, and have generated a peptide agonist MBP7 which will be invaluable for functional characterization of the mas oncogene.

In vitro methylation assay to study protein arginine methylation.

Protein arginine methylation is one of the most abundant post-translational modifications in the nucleus. Protein arginine methylation can be identified and/or determined via proteomic approaches, and/or immunoblotting with methyl-arginine specific antibodies. However, these techniques sometimes can be misleading and often provide false positive results. Most importantly, these techniques cannot provide direct evidence in support of the PRMT substrate specificity. In vitro methylation assays, on the other hand, are useful biochemical assays, which are sensitive, and consistently reveal if the identified proteins are indeed PRMT substrates. A typical in vitro methylation assay includes purified, active PRMTs, purified substrate and a radioisotope labeled methyl donor (S-adenosyl-L-[methyl-(3)H] methionine). Here we describe a step-by-step protocol to isolate catalytically active PRMT1, a ubiquitously expressed PRMT family member. The methyl transferase activities of the purified PRMT1 were later tested on Ras-GTPase activating protein binding protein 1 (G3BP1), a known PRMT substrate, in the presence of S-adenosyl-L-[methyl-(3)H] methionine as the methyl donor. This protocol can be employed not only for establishing the methylation status of novel physiological PRMT1 substrates, but also for understanding the basic mechanism of protein arginine methylation.

The soft agar colony formation assay.

Anchorage-independent growth is the ability of transformed cells to grow independently of a solid surface, and is a hallmark of carcinogenesis. The soft agar colony formation assay is a well-established method for characterizing this capability in vitro and is considered to be one of the most stringent tests for malignant transformation in cells. This assay also allows for semi-quantitative evaluation of this capability in response to various treatment conditions. Here, we will demonstrate the soft agar colony formation assay using a murine lung carcinoma cell line, CMT167, to demonstrate the tumor suppressive effects of two members of the Wnt signaling pathway, Wnt7A and Frizzled-9 (Fzd-9). Concurrent overexpression of Wnt7a and Fzd-9 caused an inhibition of colony formation in CMT167 cells. This shows that expression of Wnt7a ligand and its Frizzled-9 receptor is sufficient to suppress tumor growth in a murine lung carcinoma model.

Non-small-cell lung cancer: molecular targeted therapy and personalized medicine - drug resistance, mechanisms, and strategies.

Targeted therapies for cancer bring the hope of specific treatment, providing high efficacy and in some cases lower toxicity than conventional treatment. Although targeted therapeutics have helped immensely in the treatment of several cancers, like chronic myelogenous leukemia, colon cancer, and breast cancer, the benefit of these agents in the treatment of lung cancer remains limited, in part due to the development of drug resistance. In this review, we discuss the mechanisms of drug resistance and the current strategies used to treat lung cancer. A better understanding of these drug-resistance mechanisms could potentially benefit from the development of a more robust personalized medicine approach for the treatment of lung cancer.

hsa-miR29b, a critical downstream target of non-canonical Wnt signaling, plays an anti-proliferative role in non-small cell lung cancer cells via targeting MDM2 expression.

In non-small cell lung cancer cell lines, activation of ß-catenin independent signaling, via Wnt7a/Frizzled9 signaling, leads to reversal of cellular transformation, reduced anchorage-independent growth and induction of epithelial differentiation. miRNA expression profiling on a human lung adenocarcinoma cell line (A549) identified hsa-miR29b as an important downstream target of Wnt7a/Frizzled9 signaling. We show herein that hsa-miR29b expression is lost in non-small cell lung cancer (NSCLC) cell lines and stimulation of ß-catenin independent signaling, via Wnt7a expression, in NSCLC cell lines results in increased expression of hsa-miR29b. Surprisingly, we also identify specific regulation of hsa-miR29b by Wnt7a but not by Wnt3, a ligand for ß-catenin-dependent signaling. Interestingly, knockdown of hsa-miR29b was enough to abrogate the tumor suppressive effects of Wnt7a/Frizzled9 signaling in NSCLC cells, suggesting that hsa-miR29b is an important mediator of ß-catenin independent signaling. Finally, we show for the first time that hsa-miR29b plays an important role as a tumor suppressor in lung cancer by targeting murine double mutant 2 (MDM2), revealing novel nodes for Wnt7a/Frizzled9-mediated regulation of NSCLC cell proliferation.

Heterotrimeric G-protein, Gα16, is a critical downstream effector of non-canonical Wnt signaling and a potent inhibitor of transformed cell growth in non small cell lung cancer.

G-protein-coupled receptors (GPCR) are the largest family of cell surface molecules that play important role/s in a number of biological and pathological processes including cancers. Earlier studies have highlighted the importance of Wnt7a signaling via its cognate receptor Frizzled9, a GPCR, in inhibition of cell proliferation, anchorage-independent growth, and reversal of transformed phenotype in non small cell lung cancer primarily through activation of the tumor suppressor, PPARγ. However, the G-protein effectors that couple to this important tumor suppressor pathway have not been identified, and are of potential therapeutic interest. In this study, by using two independent Wnt7a/Frizzled9-specific read-outs, we identify Gα16 as a novel downstream effector of Wnt7a/Frizzled9 signaling. Interestingly, Gα16 expression is severely down-regulated, both at the messenger RNA levels and protein levels, in many non small cell lung cancer cell lines. Additionally, through gene-specific knock-downs and expression of GTPase-deficient forms (Q212L) of Gα16, we also establish Gα16 as a novel regulator of non small cell lung cancer cell proliferation and anchorage-independent cell growth. Taken together, our data not only establish the importance of Gα16 as a critical downstream effector of the non-canonical Wnt signaling pathway but also as a potential therapeutic target for the treatment of non small cell lung cancer.

Dishevelled3 is a novel arginine methyl transferase substrate.

Dishevelled, a phosphoprotein scaffold, is a central component in all the Wnt-sensitive signaling pathways. In the present study, we report that Dishevelled is post-translationally modified, both in vitro and in vivo, via arginine methylation. We also show protein arginine methyl transferases 1 and 7 as the key enzymes catalyzing Dishevelled methylation. Interestingly, Wnt3a stimulation of F9 teratocarcinoma cells results in reduced Dishevelled methylation. Similarly, the methylation-deficient mutant of Dishevelled, R271K, displayed spontaneous membrane localization and robust activation of Wnt signaling; suggesting that differential methylation of Dishevelled plays an important role in Wnt signaling. Thus arginine methylation is shown to be an important switch in regulation of Dishevelled function and Wnt signaling.

Mitogen-activated protein kinases and Wnt/beta-catenin signaling: Molecular conversations among signaling pathways.

Wnt/beta-catenin canonical pathway is critical for normal embryonic development; mutations and aberrant expression of specific components of this pathway can be oncogenic. Mitogen-activated protein kinase (MAPK) pathways, prominent in intracellular signaling, have been shown to have unique and provocative roles that impact the Wnt/beta-catenin signaling. We discuss recent insights that implicate the three major pathways of the MAPK network, i.e., mediated by p38, c-Jun N-terminal (JNK) kinase and Extra-cellular-Regulated Kinases (ERK) and their downstream signaling elements in Wnt/beta-catenin signaling. Novel "crosstalk" among MAPK and Wnt/beta-catenin canonical signaling pathways is essential. A fuller understanding of how such signaling is integrated during development is a high-value target for future research.

G alpha o mediates WNT-JNK signaling through dishevelled 1 and 3, RhoA family members, and MEKK 1 and 4 in mammalian cells.

In Drosophila, activation of Jun N-terminal Kinase (JNK) mediated by Frizzled and Dishevelled leads to signaling linked to planar cell polarity. A biochemical delineation of WNT-JNK planar cell polarity was sought in mammalian cells, making use of totipotent mouse F9 teratocarcinoma cells that respond to WNT3a via Frizzled-1. The canonical WNT-beta-catenin signaling pathway requires both G alpha o and G alpha q heterotrimeric G-proteins, whereas we show that WNT-JNK signaling requires only G alpha o protein. G alpha o propagates the signal downstream through all three Dishevelled isoforms, as determined by epistasis experiments using the Dishevelled antagonist Dapper1 (DACT1). Suppression of either Dishevelled-1 or Dishevelled-3, but not Dishevelled-2, abolishes WNT3a activation of JNK. Activation of the small GTPases RhoA, Rac1 and Cdc42 operates downstream of Dishevelled, linking to the MEKK 1/MEKK 4-dependent cascade, and on to JNK activation. Chemical inhibitors of JNK (SP600125), but not p38 (SB203580), block WNT3a activation of JNK, whereas both the inhibitors attenuate the WNT3a-beta-catenin pathway. These data reveal both common and unique signaling elements in WNT3a-sensitive pathways, highlighting crosstalk from WNT3a-JNK to WNT3a-beta-catenin signaling.