Activin A inhibits the migration of human lung adenocarcinoma A549 cells induced by EGF.

Activin A, a member of the transforming growth factor ß (TGF-ß) superfamily, is involved in tumorigenesis and tumor progression. However, it remains unclear whether activin A can affect the migration of lung adenocarcinoma (LUAD) cells. In this study, the results of differentially expressed genes (DEGs) identification revealed that lung adenocarcinoma tissues exhibited lower expression of activin ßA mRNA, but higher expression of epidermal growth factor (EGF) and MMP9 mRNA compared to nontumor tissues. Moreover, we found that activin A inhibited human LUAD A549 cell proliferation promoted by EGF. Additionally, EGF induced A549 cell migration in microfluidic device, while activin A attenuated EGF actions. Simultaneously, EGF increased the levels of migration-related proteins, but activin A played the opposite role. Furthermore, the study revealed that EGF upregulated the ratio of p-ERK/ERK in A549 cells, which was weakened by activin A, and A549 cell migration regulated by activin A was not related to calcium signaling. In addition, the inhibitory effect of activin A on EGF-induced A549 cell migration was attenuated by the ERK inhibitor FR180204. These findings demonstrate that activin A effectively hinders the migration of A549 cells induced by EGF through ERK1/2 signaling, suggesting that targeting activin A may hold promise in the treatment of EGF-dependent LUAD growth and metastasis.

Activin A plays an essential role in migration and proliferation of hepatic stellate cells via Smad3 and calcium signaling.

Activin A and hepatic stellate cells (HSCs) are involved in tissue repair and fibrosis in liver injury. This study investigated the impact of activin A on HSC activation and migration. A microfluidic D4-chip was used for examining the cell migration of mouse hepatic stellate cell line MHSteC. The analysis of differentially expressed genes revealed that activin ßA (Inhba), activin receptor type 1A (Acvr1a) and type 2A (Acvr2a) mRNAs were more significantly expressed in human HSCs than in the hepatocytes. Moreover, activin A promoted MHSteC proliferation and induced MHSteC migration. Furthermore, the MHSteCs treated with activin A exhibited increased levels of migration-related proteins, N-cadherin, Vimentin, α-SMA, MMP2 and MMP9, but a decreased level of E-cadherin. Additionally, activin A treatment significantly increased the p-Smad3 levels and p-Smad3/Smad3 ratio in the MHSteCs, and the Smad3 inhibitor SIS3 attenuated activin A-induced MHSteC proliferation and migration. Simultaneously, activin A increased the calcium levels in the MHSteCs, and the migratory effects of activin A on MHSteCs were weakened by the intracellular calcium ion-chelating agent BAPTA-AM. These data indicate that activin A can promote MHSteC activation and migration through the canonical Smad3 signaling and calcium signaling.

Application and prospect of microfluidic devices for rapid assay of cell activities in the tumor microenvironment.

The global impact of cancer on human health has raised significant concern. In this context, the tumor microenvironment (TME) plays a pivotal role in the tumorigenesis and malignant progression. In order to enhance the accuracy and efficacy of therapeutic outcomes, there is an imminent requirement for in vitro models that can accurately replicate the intricate characteristics and constituents of TME. Microfluidic devices exhibit notable advantages in investigating the progression and treatment of tumors and have the potential to become a novel methodology for evaluating immune cell activities in TME and assist clinicians in assessing the prognosis of patients. In addition, it shows great advantages compared to traditional cell experiments. Therefore, the review first outlines the applications and advantages of microfluidic chips in facilitating tumor cell culture, constructing TME and investigating immune cell activities. Second, the roles of microfluidic devices in the analysis of circulating tumor cells, tumor prognosis, and drug screening have also been mentioned. Moreover, a forward-looking perspective is discussed, anticipating the widespread clinical adoption of microfluidic devices in the future.

Microfluidic device reveals new insights into impairment of neutrophil transmigration in patients with sepsis.

Neutrophils need to migrate through tight tissue spaces to eliminate pathogens, but their movement is often hindered by their large and stiff nuclei. Neutrophil migration is impaired in sepsis patients, but it is unclear whether this defect is related to the deformability of their nuclei. Herein, we designed microfluidic devices with micron-scale narrow slits to simulate biological barriers. This setup allowed us to observe and record neutrophil movement and nuclear deformation in real-time. We also developed a method for morphological analysis to quantify nucleus deformation in numerous individual cells. Our studies showed that neutrophils from healthy individuals could adjust their nuclear shape to squeeze through these constrictions, whereas those from sepsis patients demonstrated less flexibility. Neutrophils with rigid nuclei struggled to pass through narrow gaps and were more likely to rupture under pressure. These findings suggest that the migration defects of neutrophils observed in sepsis may be attributed to the inability of neutrophils to deform their nuclei, highlighting the crucial role of microfluidic technologies in offering new insights into migration defects under pathological conditions.

Activin A, a Novel Chemokine, Induces Mouse NK Cell Migration via AKT and Calcium Signaling.

Natural killer (NK) cells can migrate quickly to the tumor site to exert cytotoxic effects on tumors, and some chemokines, including CXCL8, CXCL10 or and CXCL12, can regulate the migration of NK cells. Activin A, a member of the transforming growth factor ß (TGF-ß) superfamily, is highly expressed in tumor tissues and involved in tumor development and immune cell activation. In this study, we focus on the effects of activin A on NK cell migration. In vitro, activin A induced NK cell migration and invasion, promoted cell polarization and inhibited cell adhesion. Moreover, activin A increased Ca2+, p-SMAD3 and p-AKT levels in NK cells. An AKT inhibitor and Ca2+ chelator partially blocked activin A-induced NK cell migration. In vivo, exogenous activin A increased tumor-infiltrating NK cells in NS-1 cell solid tumors and inhibited tumor growth, and blocking endogenous activin A with anti-activin A antibody reduced tumor-infiltrating NK cells in 4T-1 cell solid tumors. These results suggest that activin A induces NK cell migration through AKT signaling and calcium signaling and may enhance the antitumor effect of NK cells by increasing tumor-infiltrating NK cells.

Activin A induces apoptosis of human lung adenocarcinoma A549 cells through endoplasmic reticulum stress pathway.

Activin A, a member of the transforming growth factor­ß (TGF­ß) superfamily, has been implicated in the tumorigenesis and progression of various cancers. However, it remains unclear whether activin A induces apoptosis in human lung adenocarcinoma cells through the endoplasmic reticulum (ER) stress pathway. In the present study, BrdU, flow cytometry and western blotting were used to examine cell proliferation, apoptosis and protein expression, respectively. The present study revealed that activin A inhibited human lung adenocarcinoma A549 cell proliferation, induced apoptosis, and upregulated the protein levels of C/EBP homologous protein (CHOP), growth arrest and DNA damage­inducible protein 34 (GADD34), cleaved­caspase­3 and caspase­12. Furthermore, the administration of activin A did not alter the levels of suppressor of mothers against decapentaplegic 3 (Smad3) or phosphorylated (p)­Smad3 proteins, whereas, it significantly elevated the levels of ActRIIA and p­extracellular signal regulated kinase proteins 1 and 2 (ERK1/2) proteins in A549 cells. The apoptotic effects of activin A on A549 cells were attenuated by the ERK inhibitor FR180204, which also downregulated CHOP and caspase­12 protein levels. Additionally, activin A increased intracellular calcium flux in A549 cells, and the calcium ion chelator BAPTA acetoxymethyl ester (BAPTA­AM) inhibited activin A­induced A549 cell apoptosis, whereas the calcium agonist ionomycin significantly increased apoptosis of A549 cells induced by activin A. These findings indicated that the activation of the ER stress pathway resulting in apoptosis of A549 cells triggered by activin A is facilitated by the ActRIIA­ERK1/2 signaling and calcium signaling. The present findings suggest that the agonists of ERK and calcium signaling exhibit promising clinical therapeutic potential for the induction of apoptosis in lung adenocarcinoma.

Follistatin is a crucial chemoattractant for mouse decidualized endometrial stromal cell migration by JNK signalling.

Follistatin (FST) and activin A as gonadal proteins exhibit opposite effects on follicle-stimulating hormone (FSH) release from pituitary gland, and activin A-FST system is involved in regulation of decidualization in reproductive biology. However, the roles of FST and activin A in migration of decidualized endometrial stromal cells are not well characterized. In this study, transwell chambers and microfluidic devices were used to assess the effects of FST and activin A on migration of decidualized mouse endometrial stromal cells (d-MESCs). We found that compared with activin A, FST exerted more significant effects on adhesion, wound healing and migration of d-MESCs. Similar results were also seen in the primary cultured decidual stromal cells (DSCs) from uterus of pregnant mouse. Simultaneously, the results revealed that FST increased calcium influx and upregulated the expression levels of the migration-related proteins MMP9 and Ezrin in d-MESCs. In addition, FST increased the level of phosphorylation of JNK in d-MESCs, and JNK inhibitor AS601245 significantly attenuated FST action on inducing migration of d-MESCs. These data suggest that FST, not activin A in activin A-FST system, is a crucial chemoattractant for migration of d-MESCs by JNK signalling to facilitate the successful uterine decidualization and tissue remodelling during pregnancy.

Follistatin Is a Novel Chemoattractant for Migration and Invasion of Placental Trophoblasts of Mice.

Follistatin (FST) as a gonadal protein is central to the establishment and maintenance of pregnancy. Trophoblasts' migration and invasion into the endometrium are critical events in placental development. This study aimed to elucidate the role of FST in the migration and invasion of placental trophoblasts of mice. We found that FST increased the vitality and proliferation of primary cultured trophoblasts of embryonic day 8.5 (E8.5) mice and promoted wound healing of trophoblasts. Moreover, FST significantly induced migration of trophoblasts in a microfluidic device and increased the number of invasive trophoblasts by Matrigel-coated transwell invasion assay. Being treated with FST, the adhesion of trophoblasts was inhibited, but intracellular calcium flux of trophoblasts was increased. Western blotting results showed that FST had no significant effects on the level of p-Smad3 or the ratio of p-Smad3/Smad3 in trophoblasts. Interestingly, FST elevated the level of p-JNK; the ratio of p-JNK/JNK; and expression of migration-related proteins N-cadherin, vimentin, ezrin and MMP2 in trophoblasts. Additionally, the migration of trophoblasts and expression of N-cadherin, vimentin, and MMP2 in trophoblasts induced by FST were attenuated by JNK inhibitor AS601245. These findings suggest that the elevated FST in pregnancy may act as a chemokine to induce trophoblast migration and invasion through the enhanced JNK signaling to maintain trophoblast function and promote placental development.

Intrachromosomal Looping and Histone K27 Methylation Coordinately Regulates the lncRNA H19-Fetal Mitogen IGF2 Imprinting Cluster in the Decidual Microenvironment of Early Pregnancy.

Recurrent spontaneous abortion (RSA) is a highly heterogeneous complication of pregnancy with the underlying mechanisms remaining uncharacterized. Dysregulated decidualization is a critical contributor to the phenotypic alterations related to pregnancy complications. To understand the molecular factors underlying RSA, we explored the role of longnoncoding RNAs (lncRNAs) in the decidual microenvironment where the crosstalk at the fetal-maternal interface occurs. By exploring RNA-seq data from RSA patients, we identified H19, a noncoding RNA that exhibits maternal monoallelic expression, as one of the most upregulated lncRNAs associated with RSA. The paternally expressed fetal mitogen IGF2, which is reciprocally coregulated with H19 within the same imprinting cluster, was also upregulated. Notably, both genes underwent loss of imprinting, as H19 and IGF2 were actively transcribed from both parental alleles in some decidual tissues. This loss of imprinting in decidual tissues was associated with the loss of the H3K27m3 repressive histone marker in the IGF2 promoter, CpG hypomethylation at the central CTCF binding site in the imprinting control center (ICR), and the loss of CTCF-mediated intrachromosomal looping. These data suggest that dysregulation of the H19/IGF2 imprinting pathway may be an important epigenetic factor in the decidual microenvironment related to poor decidualization.

Activin A is a novel chemoattractant for migration of microglial BV2 cells.

BACKGROUND: Microglia are involved in many neurodegenerative diseases and repairment of traumatic injury to the CNS. Activin A is a neurotrophic and neuroprotective factor that can regulate the activities of macrophages/microglia. However, the effects of activin A on the migration of microglia are still unclear. In this study, the role of activin A in regulation of the microglia migration was investigated with the murine microglial BV2 cell. METHODS: The levels of cytokines were detected by enzyme-linked immunosorbent assay (ELISA). The protein expression was examined by Western blotting. The adhesion of BV2 cells was assayed by real-time cell analysis (RTCA). The migration of BV2 cells was determined by transwell chamber and microfluidics device. Smad3 was overexpressed or knocked down in BV2 cells by transfection of Smad3 or Smad3 shRNA-expressing plasmids. RESULTS: Activin A inhibited the release of nitric oxide (NO) and inflammatory cytokines of TNF-α and IL-6 and the expression of TNF-α and IL-6 mRNA by BV2 cells. In contrast, activin A promoted the production of TGF-ß1. Activin A inhibited adhesion, promoted wound healing and migration which is related to the expression of N-cadherin and E-cadherin expression. Additionally, Smad3 overexpression in BV2 cells decreased the levels of TNF-α and IL-6, and promoted the wound healing, whereas Smad3 knockdown showed the opposite effects. CONCLUSIONS: These findings revealed that activin A regulated the biological behavior of BV2 cells via Smad3 signaling, suggesting that activin A may serve as a potential treatment target for neuroinflammation and glia scar formation in nervous system.

Activin A as a Novel Chemokine Induces Migration of L929 Fibroblasts by ERK Signaling in Microfluidic Devices.

Activin A, a member of the transforming growth factor-beta (TGF-ß) superfamily, contributes to tissue healing and fibrosis. As the innate tissue cells, fibroblasts also play an important role in wound healing and fibrosis. Herein, this study was aimed to investigate how activin A exhibited regulatory effects on adhesion and migration of fibroblasts. We found that activin A induced the migration of fibroblast cell line L929 cells in transwell chamber and microfluidic device. Activin A also promoted L929 cells adhesion, but did not affect L929 cells viability or proliferation. In addition, activin A induced α-SMA expression and TGF-ß1 release, which were factors closely related to tissue fibrosis, but had no effect on IL-6 production, a pro-inflammatory cytokine. Furthermore, activin A elevated calcium levels in L929 cells and increased p-ERK protein levels. Activin A-induced migration of L929 cells was attenuated by ERK inhibitor FR180204. To conclude, these data indicated that activin A as a novel chemokine induced the chemotactic migration of L929 cells via ERK signaling and possessed the pro-fibrosis role. These findings provide a new insight into understanding of activin A in tissue fibrosis.

Activin A impairs ActRIIA+ neutrophil recruitment into infected skin of mice.

Activin A levels are elevated during multiple severe infections and associated with an increased risk of death. However, the role of activin A in bacterial infection is still unclear. Here, we found that activin A levels were increased during S. aureus skin infection in mice. Administration of activin A increased the bacterial burden and promoted the spread of bacteria in vivo. Moreover, activin A inhibited neutrophil chemotaxis to N-formylmethionine-leucyl-phenylalanine via the type IIA activin receptor (ActRIIA) in vitro and impaired ActRIIA+ neutrophil recruitment to infection foci in vivo. Additionally, we identified a novel subpopulation of neutrophils, ActRIIA+ neutrophils, which exhibit superior phagocytic capacity compared to ActRIIA- neutrophils and possess an N2-like immunoregulatory activity via secreting IL-10 and TGF-ß. Taken together, these findings indicate that activin A inhibits the recruitment of ActRIIA+ neutrophils to infected foci, leading to the impairment of bacterial clearance, and thus may hamper early infection control.

Antagonistic effects of activin A and TNF-α on the activation of L929 fibroblast cells via Smad3-independent signaling.

Fibroblasts play an important role in inflammation and tissue fibrosis. Both activin A and TNF-α can activate immune cells, however, the roles and relationship of them in activating fibroblasts in inflammation remain unclear. Here, this study revealed that TNF-α promoted the release of NO and IL-6 by L929 fibroblast cells, but co-treatment with activin A attenuated these effects. In contrast, activin A induced cell migration and increased the production of tissue fibrosis-related TGF-ß1 and fibronectin, while TNF-α inhibited these function changes of L929 cells induced by activin A. Moreover, this study revealed that activin A and TNF-α regulated the activities of L929 cells via ERK1/2/MAPK pathway, rather than Smad3-dependent signaling pathway. Taken together, these data indicate that activin A and TNF-α exert mutually antagonistic effects on regulating fibroblasts activities, and the balance between their action may determine the process and outcome of fibroblasts-mediated inflammation.

circCDYL Acts as a Tumor Suppressor in Triple Negative Breast Cancer by Sponging miR-190a-3p and Upregulating TP53INP1.

BACKGROUND: Breast cancer is the most commonly diagnosed cancer and the leading cause of cancer death among females. Circular RNAs (circRNAs) have been implicated in the initiation and development of cancer. Here, we explored the biological role and regulatory mechanism of circCDYL in breast cancer. MATERIALS AND METHODS: The expression and correlation of circCDYL/miR-190a-3p/TP53INP1 axis in breast cancer tissues and cells were determined by quantitative polymerase chain reaction and Western blot. Cell-counting Kit-8, colony formation, cell migration, and invasion assays were applied to investigate the biological roles of circCDYL in breast cancer development and progression. RESULTS: CircCDYL were down-regulated in breast cancer tissues and cells, the expression of which positively correlated with patients' survival rate. CircCDYL worked as a "sponge," binding to miR-190a-3p directly, which inhibited the expression of miR-190a-3p and relieved the inhibition of tumor suppressor gene TP53INP1. CONCLUSION: CircCDYL promotes apoptosis and inhibits proliferation of the malignant phenotype of breast cancer through regulating miR-190a-3p/TP53INP1 axis, which suggests that circCDYL is a potential therapeutic target for breast cancer.

Inhibitory effect of activin A on IL-9 production by mouse NK cells through Smad3 signaling.

Interleukin-9 (IL-9) is a cytokine secreted by T-helper (Th)9 cells, and activin A can enhance Th9 cell differentiation. However, whether activin A affects IL-9 production by natural killer (NK) cells remains unclear. Herein, we found that not only Th cells, but also CD3-CD49b+NKp46+ NK cells of Balb/c mice produced IL-9. Although activin A promoted IL-9 expression in CD4+ Th cells, it inhibited IL-9 production by CD49b+NKp46+ NK cells in mice. Furthermore, the enzyme-linked immunosorbent assay (ELISA) results showed that mouse NK cells could secrete mature IL-9 protein, and activin A inhibited IL-9 release by NK cells. Additionally, activin A inhibited interferon (IFN)-γ production in splenic NK cells in mice, but promoted IL-2 production, and did not alter the production of IL-10. Western blotting results showed that levels of activin type IIA receptor (ActRIIA), Smad3 and phosphorylated-Smad3 (p-SMAD3) protein increased in activin A-treated splenic NK cells, compared with that in control NK cells. The inhibitory effects of activin A on IL-9 production by NK cells were attenuated in the presence of activin antagonist follistatin (FST) or Smad3 knockdown to NK cells. These data suggest that although activin A up-regulates IL-9 expression in Th cells, it inhibits IL-9 production in NK cells through Smad3 signaling.

Involvement of CHOP in activin A­induced myeloma NS­1 cell apoptosis.

Activin A, a multifunctional cytokine, is a member of transforming growth factor­ß (TGF­ß) superfamily. It is associated with a variety of pathophysiological processes, including inflammation, fibrosis, and tumorigenesis. Chronic or prolonged endoplasmic reticulum (ER) stress can lead to cells apoptosis. However, whether ER stress­related proteins, such as CHOP, GADD34 are involved in activin A­induced myeloma cell apoptosis remains unknown. In the present study, it was revealed that activin A inhibited the proliferation of myeloma cell line NS­1 cells and induced NS­1 cell apoptosis. Activin A upregulated the expression of CHOP, GADD34, caspase­3, and caspase­12. Moreover, both Smad3 and p­Smad3 levels were increased with treatment of activin A. Further studies revealed that the overexpression of activin signaling protein Smad3 in NS­1 cells increased the levels of CHOP, caspase­3, and p­Smad3. These data indicated that the CHOP protein of the ER stress pathway may be involved in activin A­induced NS­1 cell apoptosis, and also indicated the potential therapy of activin A­induced apoptosis via CHOP signaling for multiple myeloma.

Home-Based Computerized Cognitive Training for Postoperative Cognitive Dysfunction After Lung Transplantation in Elderly Population: A Randomized Controlled Trial.

Postoperative cognitive dysfunction is a severe outcome after lung transplantation, especially in the elderly lung transplant recipients. Home-based computerized cognitive training (CCT) is a widely used intervention for cognition improvement, but its efficacy has not been validated in this population. A randomized controlled trial was conducted to analyze the effect of CCT on elderly lung transplant recipients. The participants received either an 8-week CCT intervention or usual care. The changes of cognitive function were assessed between preintervention (T1), postintervention (T2), and 12 weeks postintervention (T3). Among the 46 participants, 91.3% completed the interventions. The CCT group performed better than the control group on Digit-Span Forward Test (T3: p = 0.0044) and Verbal Fluency Test (T3: p = 0.0331), indicating the efficacy of CCT on verbal memory in the elderly lung transplant recipients. Although varied impacts were observed on different cognitive domains, it seems promising to use CCT on the elderly population after lung transplantation.

Profiling the long noncoding RNA interaction network in the regulatory elements of target genes by chromatin in situ reverse transcription sequencing.

Long noncoding RNAs (lncRNAs) can regulate the activity of target genes by participating in the organization of chromatin architecture. We have devised a "chromatin-RNA in situ reverse transcription sequencing" (CRIST-seq) approach to profile the lncRNA interaction network in gene regulatory elements by combining the simplicity of RNA biotin labeling with the specificity of the CRISPR/Cas9 system. Using gene-specific gRNAs, we describe a pluripotency-specific lncRNA interacting network in the promoters of Sox2 and Pou5f1, two critical stem cell factors that are required for the maintenance of pluripotency. The promoter-interacting lncRNAs were specifically activated during reprogramming into pluripotency. Knockdown of these lncRNAs caused the stem cells to exit from pluripotency. In contrast, overexpression of the pluripotency-associated lncRNA activated the promoters of core stem cell factor genes and enhanced fibroblast reprogramming into pluripotency. These CRIST-seq data suggest that the Sox2 and Pou5f1 promoters are organized within a unique lncRNA interaction network that determines the fate of pluripotency during reprogramming. This CRIST approach may be broadly used to map lncRNA interaction networks at target loci across the genome.

Emodin protects against lipopolysaccharide-induced inflammatory injury in HaCaT cells through upregulation of miR-21.

Background/aim: Pressure ulcers are a disastrous health issue in which inflammation is involved. Emodin possesses biological properties in inflammation. Our study investigated functions of emodin in lipopolysaccharide (LPS)-treated HaCaT cells. Methods: LPS was used to induce cell inflammation. MTT and flow cytometry were applied for cell viability and apoptosis assays, respectively. Moreover, apoptotic proteins were detected by western blot. Similarly, inflammatory factors and signalling related proteins were also determined by western blot. Results: Emodin increased cell viability and diminished apoptosis in LPS-treated HaCaT cells. Moreover, cleaved-PARP, cleaved-caspase-3 and cleaved-caspase-9 were all downregulated by emodin. Furthermore, inflammatory factors IL-1ß, IL-6, Cox-2 and iNOS were inhibited by emodin in LPS-treated cells. In addition, emodin decreased phosphorylation of p65 and IκBα and the level of PTEN while enhanced phosphorylation of PI3K and AKT. Importantly, emodin increased expression of miR-21 suppressed by LPS and miR-21 downregulation negated the protective functions of emodin. Conclusions: Emodin promoted cell growth presented by increasing viability and blocking apoptosis process with inflammation inhibition. The protective activity of emodin was mediated by miR-21 up-regulation.

Perspectives of small molecule inhibitors of activin receptor­like kinase in anti­tumor treatment and stem cell differentiation (Review).

Activin receptor­like kinases (ALKs), members of the type I activin receptor family, belong to the serine/threonine kinase receptors of the transforming growth factor­ß (TGF­ß) superfamily. ALKs mediate the roles of activin/TGF­ß in a wide variety of physiological and pathological processes, ranging from cell differentiation and proliferation to apoptosis. For example, the activities of ALKs are associated with an advanced tumor stage in prostate cancer and the chondrogenic differentiation of mesenchymal stem cells. Therefore, potent and selective small molecule inhibitors of ALKs would not only aid in investigating the function of activin/TGF­ß, but also in developing treatments for these diseases via the disruption of activin/TGF­ß. In recent studies, several ALK inhibitors, including LY­2157299, SB­431542 and A­83­01, have been identified and have been confirmed to affect stem cell differentiation and tumor progression in animal models. This review discusses the therapeutic perspective of small molecule inhibitors of ALKs as drug targets in tumor and stem cells.