Activation of the tumour suppressor kinase LKB1 by the STE20-like pseudokinase STRAD

LKB1 biology: assessing the therapeutic relevancy of LKB1 inhibitors

Liver Kinase B1 (LKB1), encoded by Serine-Threonine Kinase 11 (STK11), is a master kinase that regulates cell migration, polarity, proliferation, and metabolism through downstream adenosine monophosphate-activated protein kinase (AMPK) and AMPK-related kinase signalling. Since genetic screens identified STK11 mutations in Peutz-Jeghers Syndrome, STK11 mutants have been implicated in tumourigenesis labelling it as a tumour suppressor. In support of this, several compounds reduce tumour burden through upregulating LKB1 signalling, and LKB1-AMPK agonists are cytotoxic to tumour cells. However, in certain contexts, its role in cancer is paradoxical as LKB1 promotes tumour cell survival by mediating resistance against metabolic and oxidative stressors. LKB1 deficiency has also enhanced the selectivity and cytotoxicity of several cancer therapies. Taken together, there is a need to develop LKB1-specific pharmacological compounds, but prior to developing LKB1 inhibitors, further work is needed to understand LKB1 activity and regulation. However, investigating LKB1 activity is strenuous as cell/tissue type, mutations to the LKB1 signalling pathway, STE-20-related kinase adaptor protein (STRAD) binding, Mouse protein 25-STRAD binding, splicing variants, nucleocytoplasmic shuttling, post-translational modifications, and kinase conformation impact the functional status of LKB1. For these reasons, guidelines to standardize experimental strategies to study LKB1 activity, associate proteins, spliced isoforms, post-translational modifications, and regulation are of upmost importance to the development of LKB1-specific therapies. Therefore, to assess the therapeutic relevancy of LKB1 inhibitors, this review summarizes the importance of LKB1 in cell physiology, highlights contributors to LKB1 activation, and outlines the benefits and risks associated with targeting LKB1.

PyLKB1 regulates glucose transport via activating PyAMPKα in Yesso Scallop Patinopecten yessoensis under high temperature stress

Liver kinase B1 (LKB1) is a classical serine/threonine protein kinase and plays an important role in maintaining energy homeostasis through phosphorylate AMP-activated protein kinase α subunit (AMPKα). In this study, a homologous molecule of LKB1 with a typical serine/threonine kinase domain and two nuclear localization sequences (NLSs) was identified in Yesso Scallop Patinopecten yessoensis (PyLKB1). The mRNA transcripts of PyLKB1 were found to be expressed in haemocytes and all the examined tissues, including gill, mantle, gonad, adductor muscle and hepatopancreas, with the highest expression level in hepatopancreas. PyLKB1 was mainly located in cytoplasm and nucleus of scallop haemocytes. At 3 h after high temperature stress treatment (25 °C), the mRNA transcripts of PyLKB1, PyAMPKα, and PyGLUT1 in hepatopancreas, the phosphorylation level of PyAMPKα at Thr170 in hepatopancreas, the positive fluorescence signals of PyLKB1 in haemocytes, glucose analogue 2-NBDG content in haemocytes, and glucose content in hepatopancreas, haemocytes and serum all increased significantly (p < 0.05) compared to blank group (15 °C). However, there was no significant difference at the protein level of PyLKB1 and PyAMPKα. After PyLKB1 was knockdown by siRNA, the mRNA expression level of PyGLUT1, and the glucose content in hepatopancreas and serum were significantly down-regulated (p < 0.05) compared with the negative control group receiving an injection of siRNA-NC. However, there were no significant difference in PyGLUT1 expression, glucose content and glucose analogue 2-NBDG content in haemocytes. These results collectively suggested that PyLKB1-PyAMPKα pathway was activated to promote glucose transport by regulating PyGLUT1 in response to high temperature stress. These results would be helpful for understanding the function of PyLKB1-PyAMPKα pathway in regulating glucose metabolism and maintaining energy homeostasis under high temperature stress in scallops.

TBC1D23 mediates Golgi-specific LKB1 signaling

Liver kinase B1 (LKB1), an evolutionarily conserved serine/threonine kinase, is a master regulator of the AMPK subfamily and controls cellular events such as polarity, proliferation, and energy homeostasis. Functions and mechanisms of the LKB1-AMPK axis at specific subcellular compartments, such as lysosome and mitochondria, have been established. AMPK is known to be activated at the Golgi; however, functions and regulatory mechanisms of the LKB1-AMPK axis at the Golgi apparatus remain elusive. Here, we show that TBC1D23, a Golgi-localized protein that is frequently mutated in the neurodevelopment disorder pontocerebellar hypoplasia (PCH), is specifically required for the LKB1 signaling at the Golgi. TBC1D23 directly interacts with LKB1 and recruits LKB1 to Golgi, promoting Golgi-specific activation of AMPK upon energy stress. Notably, Golgi-targeted expression of LKB1 rescues TBC1D23 deficiency in zebrafish models. Furthermore, the loss of LKB1 causes neurodevelopmental abnormalities in zebrafish, which partially recapitulates defects in TBC1D23-deficient zebrafish, and LKB1 sustains normal neuronal development via TBC1D23 interaction. Our study uncovers a regulatory mechanism of the LKB1 signaling, and reveals that a disrupted Golgi-LKB1 signaling underlies the pathogenesis of PCH.

Extracellular Vesicles in Transplantation: Friend or Foe

The long-term function of transplanted organs, even under immunosuppression, is hindered by rejection, especially chronic rejection. Chronic rejection occurs more frequently after lung transplantation, termed chronic lung allograft dysfunction (CLAD), than after transplantation of other solid organs. Pulmonary infection is a known risk factor for CLAD, as transplanted lungs are constantly exposed to the external environment; however, the mechanisms by which respiratory infections lead to CLAD are poorly understood. The role of extracellular vesicles (EVs) in transplantation remains largely unknown. Current evidence suggests that EVs released from transplanted organs can serve as friend and foe. EVs carry not only major histocompatibility complex antigens but also tissue-restricted self-antigens and various transcription factors, costimulatory molecules, and microRNAs capable of regulating alloimmune responses. EVs play an important role in antigen presentation by direct, indirect, and semidirect pathways in which CD8 and CD4 cells can be activated. During viral infections, exosomes (small EVs <200 nm in diameter) can express viral antigens and regulate immune responses. Circulating exosomes may also be a viable biomarker for other diseases and rejection after organ transplantation. Bioengineering the surface of exosomes has been proposed as a tool for targeted delivery of drugs and personalized medicine. This review focuses on recent studies demonstrating the role of EVs with a focus on exosomes and their dual role (immune activation or tolerance induction) after organ transplantation, more specifically, lung transplantation.

The LKB1-TSSK1B axis controls YAP phosphorylation to regulate the Hippo-YAP pathway

The Hippo pathway's main effector, Yes-associated protein (YAP), plays a crucial role in tumorigenesis as a transcriptional coactivator. YAP's phosphorylation by core upstream components of the Hippo pathway, such as mammalian Ste20 kinase 1/2 (MST1/2), mitogen-activated protein kinase kinase kinase kinases (MAP4Ks), and their substrate, large tumor suppressor 1/2 (LATS1/2), influences YAP's subcellular localization, stability, and transcriptional activity. However, recent research suggests the existence of alternative pathways that phosphorylate YAP, independent of these core upstream Hippo pathway components, raising questions about additional means to inactivate YAP. In this study, we present evidence demonstrating that TSSK1B, a calcium/calmodulin-dependent protein kinase (CAMK) superfamily member, is a negative regulator of YAP, suppressing cellular proliferation and oncogenic transformation. Mechanistically, TSSK1B inhibits YAP through two distinct pathways. Firstly, the LKB1-TSSK1B axis directly phosphorylates YAP at Ser94, inhibiting the YAP-TEAD complex's formation and suppressing its target genes' expression. Secondly, the TSSK1B-LATS1/2 axis inhibits YAP via phosphorylation at Ser127. Our findings reveal the involvement of TSSK1B-mediated molecular mechanisms in the Hippo-YAP pathway, emphasizing the importance of multilevel regulation in critical cellular decision-making processes.

Josephin domain containing 2 (JOSD2) promotes lung cancer by inhibiting LKB1 (Liver kinase B1) activity

Non-small cell lung cancer (NSCLC) ranks as one of the leading causes of cancer-related deaths worldwide. Despite the prominence and effectiveness of kinase-target therapies in NSCLC treatment, these drugs are suitable for and beneficial to a mere ~30% of NSCLC patients. Consequently, the need for novel strategies addressing NSCLC remains pressing. Deubiquitinases (DUBs), a group of diverse enzymes with well-defined catalytic sites that are frequently overactivated in cancers and associated with tumorigenesis and regarded as promising therapeutic targets. Nevertheless, the mechanisms by which DUBs promote NSCLC remain poorly understood. Through a global analysis of the 97 DUBs' contribution to NSCLC survival possibilities using The Cancer Genome Atlas (TCGA) database, we found that high expression of Josephin Domain-containing protein 2 (JOSD2) predicted the poor prognosis of patients. Depletion of JOSD2 significantly impeded NSCLC growth in both cell/patient-derived xenografts in vivo. Mechanically, we found that JOSD2 restricts the kinase activity of LKB1, an important tumor suppressor generally inactivated in NSCLC, by removing K6-linked polyubiquitination, an action vital for maintaining the integrity of the LKB1-STRAD-MO25 complex. Notably, we identified the first small-molecule inhibitor of JOSD2, and observed that its pharmacological inhibition significantly arrested NSCLC proliferation in vitro/in vivo. Our findings highlight the vital role of JOSD2 in hindering LKB1 activity, underscoring the therapeutic potential of targeting JOSD2 in NSCLC, especially in those with inactivated LKB1, and presenting its inhibitors as a promising strategy for NSCLC treatment.

Ulk4 promotes Shh signaling by regulating Stk36 ciliary localization and Gli2 phosphorylation

The Hedgehog (Hh) family of secreted proteins governs embryonic development and adult tissue homeostasis through the Gli family of transcription factors. Gli is thought to be activated at the tip of primary cilium, but the underlying mechanism has remained poorly understood. Here, we show that Unc-51-like kinase 4 (Ulk4), a pseudokinase and a member of the Ulk kinase family, acts in conjunction with another Ulk family member Stk36 to promote Gli2 phosphorylation and Hh pathway activation. Ulk4 interacts with Stk36 through its N-terminal region containing the pseudokinase domain and with Gli2 via its regulatory domain to bridge the kinase and substrate. Although dispensable for Hh-induced Stk36 kinase activation, Ulk4 is essential for Stk36 ciliary tip localization, Gli2 phosphorylation, and activation. In response to Hh, both Ulk4 and Stk36 colocalize with Gli2 at ciliary tip, and Ulk4 and Stk36 depend on each other for their ciliary tip accumulation. We further show that ciliary localization of Ulk4 depends on Stk36 kinase activity and phosphorylation of Ulk4 on Thr1023, and that ciliary tip accumulation of Ulk4 is essential for its function in the Hh pathway. Taken together, our results suggest that Ulk4 regulates Hh signaling by promoting Stk36-mediated Gli2 phosphorylation and activation at ciliary tip.

RBM4 dictates ESCC cell fate switch from cellular senescence to glutamine-addiction survival through inhibiting LKB1-AMPK-axis

Cellular senescence provides a protective barrier against tumorigenesis in precancerous or normal tissues upon distinct stressors. However, the detailed mechanisms by which tumor cells evade premature senescence to malignant progression remain largely elusive. Here we reported that RBM4 adversely impacted cellular senescence to favor glutamine-dependent survival of esophageal squamous cell carcinoma (ESCC) cells by dictating the activity of LKB1, a critical governor of cancer metabolism. The level of RBM4 was specifically elevated in ESCC compared to normal tissues, and RBM4 overexpression promoted the malignant phenotype. RBM4 contributed to overcome H-RAS- or doxorubicin-induced senescence, while its depletion caused P27-dependent senescence and proliferation arrest by activating LKB1-AMPK-mTOR cascade. Mechanistically, RBM4 competitively bound LKB1 to disrupt the LKB1/STRAD/MO25 heterotrimeric complex, subsequently recruiting the E3 ligase TRIM26 to LKB1, promoting LKB1 ubiquitination and degradation in nucleus. Therefore, such molecular process leads to bypassing senescence and sustaining cell proliferation through the activation of glutamine metabolism. Clinically, the ESCC patients with high RBM4 and low LKB1 have significantly worse overall survival than those with low RBM4 and high LKB1. The RBM4 high/LKB1 low expression confers increased sensitivity of ESCC cells to glutaminase inhibitor CB-839, providing a novel insight into mechanisms underlying the glutamine-dependency to improve the efficacy of glutamine inhibitors in ESCC therapeutics.

LKB1 Signaling and Patient Survival Outcomes in Hepatocellular Carcinoma

The liver is a major organ that is involved in essential biological functions such as digestion, nutrient storage, and detoxification. Furthermore, it is one of the most metabolically active organs with active roles in regulating carbohydrate, protein, and lipid metabolism. Hepatocellular carcinoma is a cancer of the liver that is associated in settings of chronic inflammation such as viral hepatitis, repeated toxin exposure, and fatty liver disease. Furthermore, liver cancer is the most common cause of death associated with cirrhosis and is the 3^rd leading cause of global cancer deaths. LKB1 signaling has been demonstrated to play a role in regulating cellular metabolism under normal and nutrient deficient conditions. Furthermore, LKB1 signaling has been found to be involved in many cancers with most reports identifying LKB1 to have a tumor suppressive role. In this review, we use the KMPlotter database to correlate RNA levels of LKB1 signaling genes and hepatocellular carcinoma patient survival outcomes with the hopes of identifying potential biomarkers clinical usage. Based on our results STRADß, CAB39L, AMPKα, MARK2, SIK1, SIK2, BRSK1, BRSK2, and SNRK expression has a statistically significant impact on patient survival.

Downregulation of a tumor suppressor gene LKB1 in lung transplantation as a biomarker for chronic murine lung allograft rejection

BACKGROUND

We recently demonstrated decreased tumor suppressor gene liver kinase B1 (LKB1) level in lung transplant recipients diagnosed with bronchiolitis obliterans syndrome. STE20-related adaptor alpha (STRADα) functions as a pseudokinase that binds and regulates LKB1 activity.

METHODS

A murine model of chronic lung allograft rejection in which a single lung from a B6D2F1 mouse was orthotopically transplanted into a DBA/2J mouse was employed. We examined the effect of LKB1 knockdown using CRISPR-CAS9 in vitro culture system.

RESULTS

Significant downregulation of LKB1 and STRADα expression was found in donor lung compared to recipient lung. STRADα knockdown significantly inhibited LKB1, pAMPK expression but induced phosphorylated mammalian target of rapamycin (mTOR), fibronectin, and Collagen-I, expression in BEAS-2B cells. LKB1 overexpression decreased fibronectin, Collagen-I, and phosphorylated mTOR expression in A549 cells.

CONCLUSIONS

We demonstrated that downregulation of LKB1-STRADα pathway accompanied with increased fibrosis, results in development of chronic rejection following murine lung transplantation.

Lanthanum Chloride Induces Axon Abnormality Through LKB1-MARK2 and LKB1-STK25-GM130 Signaling Pathways

Lanthanum (La) is a natural rare-earth element that can damage the central nervous system and impair learning and memory. However, its neurotoxic mechanism remains unclear. In this study, adult female rats were divided into 4 groups and given distilled water solution containing 0%, 0.125%, 0.25%, and 0.5% LaCl₃, respectively, and this was done from conception to the end of the location. Their offspring rats were used to establish animal models to investigate LaCl₃ neurotoxicity. Primary neurons cultured in vitro were treated with LaCl₃ and infected with LKB1 overexpression lentivirus. The results showed that LaCl₃ exposure resulted in abnormal axons in the hippocampus and primary cultured neurons. LaCl₃ reduced the expression of LKB1, p-LKB1, STRAD and MO25 proteins, and directly or indirectly affected the expression of LKB1, leading to decreased activity of LKB1-MARK2 and LKB1-STK25-GM130 pathways. This study indicated that LaCl₃ exposure could interfere with the normal effects of LKB1 in the brain and downregulate LKB1-MARK2 and LKB1-STK25-GM130 signaling pathways, resulting in abnormal axon in offspring rats.

6-Gingerol Ameliorates Hepatic Steatosis, Inflammation and Oxidative Stress in High-Fat Diet-Fed Mice through Activating LKB1/AMPK Signaling

6-Gingerol, one of the major pharmacologically active ingredients extracted from ginger, has been reported experimentally to exert hepatic protection in non-alcoholic fatty liver disease (NAFLD). However, the molecular mechanism remains largely elusive. RNA sequencing indicated the significant involvement of the AMPK signaling pathway in 6-gingerol-induced alleviation of NAFLD in vivo. Given the significance of the LKB1/AMPK pathway in metabolic homeostasis, this study aims to investigate its role in 6-gingerol-induced mitigation on NAFLD. Our study showed that 6-gingerol ameliorated hepatic steatosis, inflammation and oxidative stress in vivo and in vitro. Further experiment validation suggested that 6-gingerol activated an LKB1/AMPK pathway cascade in vivo and in vitro. Co-immunoprecipitation analysis demonstrated that the 6-gingerol-elicited activation of an LKB1/AMPK pathway cascade was related to the enhanced stability of the LKB1/STRAD/MO25 complex. Furthermore, radicicol, an LKB1 destabilizer, inhibited the activating effect of 6-gingerol on an LKB1/AMPK pathway cascade via destabilizing LKB1/STRAD/MO25 complex stability in vitro, thus reversing the 6-gingerol-elicited ameliorative effect. In addition, molecular docking analysis further predicated the binding pockets of LKB1 necessary for binding with 6-gingerol. In conclusion, our results indicate that 6-gingerol plays an important role in regulating the stability of the LKB1/STRAD/MO25 complex and the activation of LKB1, which might weigh heavily in the 6-gingerol alleviation of NAFLD.

Posttranslational regulation of liver kinase B1 (LKB1) in human cancer

Liver kinase B1 (LKB1) is a serine-threonine kinase that participates in multiple cellular and biological processes, including energy metabolism, cell polarity, cell proliferation, cell migration, and many others. LKB1 is initially identified as a germline-mutated causative gene in Peutz-Jeghers syndrome (PJS) and is commonly regarded as a tumor suppressor due to frequent inactivation in a variety of cancers. LKB1 directly binds and activates its downstream kinases including the AMP-activated protein kinase (AMPK) and AMPK-related kinases by phosphorylation, which has been intensively investigated for the past decades. An increasing number of studies has uncovered the posttranslational modifications (PTMs) of LKB1 and consequent changes in its localization, activity, and interaction with substrates. The alteration in LKB1 function as a consequence of genetic mutations and aberrant upstream signaling regulation leads to tumor development and progression. Here, we review current knowledge about the mechanism of LKB1 in cancer and the contributions of PTMs, such as phosphorylation, ubiquitination, SUMOylation, acetylation, prenylation, and others, to the regulation of LKB1 function, offering new insights into the therapeutic strategies in cancer.

Ethylene-triggered subcellular trafficking of CTR1 enhances the response to ethylene gas

The phytohormone ethylene controls plant growth and stress responses. Ethylene-exposed dark-grown Arabidopsis seedlings exhibit dramatic growth reduction, yet the seedlings rapidly return to the basal growth rate when ethylene gas is removed. However, the underlying mechanism governing this acclimation of dark-grown seedlings to ethylene remains enigmatic. Here, we report that ethylene triggers the translocation of the Raf-like protein kinase CONSTITUTIVE TRIPLE RESPONSE1 (CTR1), a negative regulator of ethylene signaling, from the endoplasmic reticulum to the nucleus. Nuclear-localized CTR1 stabilizes the ETHYLENE-INSENSITIVE3 (EIN3) transcription factor by interacting with and inhibiting EIN3-BINDING F-box (EBF) proteins, thus enhancing the ethylene response and delaying growth recovery. Furthermore, Arabidopsis plants with enhanced nuclear-localized CTR1 exhibited improved tolerance to drought and salinity stress. These findings uncover a mechanism of the ethylene signaling pathway that links the spatiotemporal dynamics of cellular signaling components to physiological responses.

RanBP1 plays an essential role in directed migration of neural crest cells during development

Collective cell migration is essential for embryonic development, tissue regeneration and repair, and has been implicated in pathological conditions such as cancer metastasis. It is, in part, directed by external cues that promote front-to-rear polarity in individual cells. However, our understanding of the pathways that underpin the directional movement of cells in response to external cues remains incomplete. To examine this issue we made use of neural crest cells (NC), which migrate as a collective during development to generate vital structures including bones and cartilage. Using a candidate approach, we found an essential role for Ran-binding protein 1 (RanBP1), a key effector of the nucleocytoplasmic transport pathway, in enabling directed migration of these cells. Our results indicate that RanBP1 is required for establishing front-to-rear polarity, so that NCs are able to chemotax. Moreover, our work suggests that RanBP1 function in chemotaxis involves the polarity kinase LKB1/PAR4. We envisage that regulated nuclear export of LKB1 through Ran/RanBP1 is a key regulatory step required for establishing front-to-rear polarity and thus chemotaxis, during NC collective migration.

Substrate recognition by Arg/Pro-rich insert domain in calcium/calmodulin-dependent protein kinase kinase for target protein kinases

Calcium/calmodulin-dependent protein kinase kinases (CaMKKs) activate CaMKI, CaMKIV, protein kinase B/Akt, and AMP-activated protein kinase (AMPK) by phosphorylating Thr residues in activation loops to mediate various Ca²⁺ -signaling pathways. Mammalian cells expressing CaMKKα and CaMKKβ lacking Arg/Pro-rich insert domain (RP-domain) sequences showed impaired phosphorylation of AMPKα, CaMKIα, and CaMKIV, whereas the autophosphorylation activities of CaMKK mutants remained intact and were similar to those of wild-type CaMKKs. Liver kinase B1 (LKB1, an AMPK kinase) complexed with STRAD and MO25 and was unable to phosphorylate CaMKIα and CaMKIV; however, mutant LKB1 with the RP-domain sequences of CaMKKα and CaMKKβ inserted between kinase subdomains II and III acquired CaMKIα and CaMKIV phosphorylating activity in vitro and in transfected cultured cells. Furthermore, ionomycin-induced phosphorylation of hemagglutinin (HA)-CaMKIα at Thr177, HA-CaMKIV at Thr196, and HA-AMPKα at Thr172 in transfected cells was significantly suppressed by cotransfection of kinase-dead mutants of CaMKK isoforms, but these dominant-negative effects were abrogated with RP-deletion mutants, suggesting that sequestration of substrate kinases by loss-of-function CaMKK mutants requires the RP-domain. This was confirmed by pulldown experiments that showed that dominant-negative mutants of CaMKKα and CaMKKβ interact with target kinases but not RP-deletion mutants. Taken together, these results clearly indicate that both CaMKK isoforms require the RP-domain to recognize downstream kinases to interact with and phosphorylate Thr residues in their activation loops. Thus, the RP-domain may be a promising target for specific CaMKK inhibitors.

Liver Kinase B1 Functions as a Regulator for Neural Development and a Therapeutic Target for Neural Repair

The liver kinase B1 (LKB1), also known as serine/threonine kinase 11 (STK11) and Par-4 in C. elegans, has been identified as a master kinase of AMPKs and AMPK-related kinases. LKB1 plays a crucial role in cell growth, metabolism, polarity, and tumor suppression. By interacting with the downstream signals of SAD, NUAK, MARK, and other kinases, LKB1 is critical to regulating neuronal polarization and axon branching during development. It also regulates Schwann cell function and the myelination of peripheral axons. Regulating LKB1 activity has become an attractive strategy for repairing an injured nervous system. LKB1 upregulation enhances the regenerative capacity of adult CNS neurons and the recovery of locomotor function in adult rodents with CNS axon injury. Here, we update the major cellular and molecular mechanisms of LKB1 in regulating neuronal polarization and neural development, and the implications thereof for promoting neural repair, axon regeneration, and functional recovery in adult mammals.

The Distinct Roles of LKB1 and AMPK in p53-Dependent Apoptosis Induced by Cisplatin

Liver kinase B1 (LKB1) is a serine/threonine protein kinase that acts as a key tumor suppressor protein by activating its downstream kinases, such as AMP-activated protein kinase (AMPK). However, the regulatory actions of LKB1 and AMPK on DNA damage response (DDR) remain to be explored. In this study, we investigated the function of LKB1 in DDR induced by cisplatin, a representative DNA-damaging agent, and found that LKB1 stabilizes and activates p53 through the c-Jun N-terminal kinase (JNK) pathway, which promotes cisplatin-induced apoptosis in human fibrosarcoma cell line HT1080. On the other hand, we found that AMPKα1 and α2 double knockout (DKO) cells showed enhanced stabilization of p53 and increased susceptibility to apoptosis induced by cisplatin, suggesting that AMPK negatively regulates cisplatin-induced apoptosis. Moreover, the additional stabilization of p53 and subsequent apoptosis in AMPK DKO cells were clearly canceled by the treatment with the antioxidants, raising the possibility that AMPK suppresses the p53 activation mediated by oxidative stress. Thus, our findings unexpectedly demonstrate the reciprocal regulation of p53 by LKB1 and AMPK in DDR, which provides insights into the molecular mechanisms of DDR.

LKB1: An emerging therapeutic target for cardiovascular diseases

Cardiovascular diseases (CVDs) are currently the most common cause of morbidity and mortality worldwide. Experimental studies suggest that liver kinase B1 (LKB1) plays an important role in the heart. Several studies have shown that cardiomyocyte-specific LKB1 deletion leads to hypertrophic cardiomyopathy, left ventricular contractile dysfunction, and an increased risk of atrial fibrillation. In addition, the cardioprotective effects of several medicines and natural compounds, including metformin, empagliflozin, bexarotene, and resveratrol, have been reported to be associated with LKB1 activity. LKB1 limits the size of the damaged myocardial area by modifying cellular metabolism, enhancing the antioxidant system, suppressing hypertrophic signals, and inducing mild autophagy, which are all primarily mediated by the AMP-activated protein kinase (AMPK) energy sensor. LKB1 also improves myocardial efficiency by modulating the function of contractile proteins, regulating the expression of electrical channels, and increasing vascular dilatation. Considering these properties, stimulation of LKB1 signaling offers a promising approach in the prevention and treatment of heart diseases.

Will We Unlock the Benefit of Metformin for Patients with Lung Cancer? Lessons from Current Evidence and New Hypotheses

Metformin has been under basic and clinical study as an oncological repurposing pharmacological agent for several years, stemming from observational studies which consistently evidenced that subjects who were treated with metformin had a reduced risk for development of cancer throughout their lives, as well as improved survival outcomes when diagnosed with neoplastic diseases. As a result, several basic science studies have attempted to dissect the relationship between metformin’s metabolic mechanism of action and antineoplastic cellular signaling pathways. Evidence in this regard was compelling enough that a myriad of randomized clinical trials was planned and conducted in order to establish the effect of metformin treatment for patients with diverse neoplasms, including lung cancer. As with most novel antineoplastic agents, early results from these studies have been mostly discouraging, though a recent analysis that incorporated body mass index may provide significant information regarding which patient subgroups might derive the most benefit from the addition of metformin to their anticancer treatment. Much in line with the current pipeline for anticancer agents, it appears that the benefit of metformin may be circumscribed to a specific patient subgroup. If so, addition of metformin to antineoplastic agents could prove one of the most cost-effective interventions proposed in the context of precision oncology. Currently published reviews mostly rely on a widely questioned mechanism of action by metformin, which fails to consider the differential effects of the drug in lean vs. obese subjects. In this review, we analyze the pre-clinical and clinical information available to date regarding the use of metformin in various subtypes of lung cancer and, further, we present evidence as to the differential metabolic effects of metformin in lean and obese subjects where, paradoxically, the obese subjects have reported more benefit with the addition of metformin treatment. The novel mechanisms of action described for this biguanide may explain the different results observed in clinical trials published in the last decade. Lastly, we present novel hypothesis regarding potential biomarkers to identify who might reap benefit from this intervention, including the role of prolyl hydroxylase domain 3 (PHD3) expression to modify metabolic phenotypes in malignant diseases.

Translation initiation factor eIF3a regulates glucose metabolism and cell proliferation via promoting small GTPase Rheb synthesis and AMPK activation

Eukaryotic translation initiation factor 3 subunit A (eIF3a), the largest subunit of the eIF3 complex, has been shown to be overexpressed in malignant cancer cells, potentially making it a proto-oncogene. eIF3a overexpression can drive cancer cell proliferation but contributes to better prognosis. While its contribution to prognosis was previously shown to be due to its function in suppressing synthesis of DNA damage repair proteins, it remains unclear how eIF3a regulates cancer cell proliferation. In this study, we show using genetic approaches that eIF3a controls cell proliferation by regulating glucose metabolism via the phosphorylation and activation of AMP-activated protein kinase alpha (AMPKα) at Thr¹⁷² in its kinase activation loop. We demonstrate that eIF3a regulates AMPK activation mainly by controlling synthesis of the small GTPase Rheb, largely independent of the well-known AMPK upstream liver kinase B1 and Ca²⁺/calmodulin-dependent protein kinase kinase 2, and also independent of mammalian target of rapamycin signaling and glucose levels. Our findings suggest that glucose metabolism in and proliferation of cancer cells may be translationally regulated via a novel eIF3a–Rheb–AMPK signaling axis.

The Tumor Suppressor Kinase LKB1: Metabolic Nexus

Liver kinase B1 (LKB1) is a multitasking tumor suppressor kinase that is implicated in multiple malignancies such as lung, gastrointestinal, pancreatic, and breast. LKB1 was first identified as the gene responsible for Peutz-Jeghers syndrome (PJS) characterized by hamartomatous polyps and oral mucotaneous pigmentation. LKB1 functions to activate AMP-activated protein kinase (AMPK) during energy stress to shift metabolic processes from active anabolic pathways to active catabolic pathways to generate ATP. Genetic loss or inactivation of LKB1 promotes metabolic reprogramming and metabolic adaptations of cancer cells that fuel increased growth and division rates. As a result, LKB1 loss is associated with increased aggressiveness and treatment options for patients with LKB1 mutant tumors are limited. Recently, there has been new insights into the role LKB1 has on metabolic regulation and the identification of potential vulnerabilities in LKB1 mutant tumors. In this review, we discuss the tumor suppressive role of LKB1 and the impact LKB1 loss has on metabolic reprograming in cancer cells, with a focus on lung cancer. We also discuss potential therapeutic avenues to treat malignancies associated with LKB1 loss by targeting aberrant metabolic pathways associated with LKB1 loss.

The miR-26 family regulates early B cell development and transformation

MiRNAs are small noncoding RNAs that promote the sequence-specific repression of their respective target genes, thereby regulating diverse physiological as well as pathological processes. Here, we identify a novel role of the miR-26 family in early B cell development. We show that enhanced expression of miR-26 family members potently blocks the pre-B to immature B cell transition, promotes pre-B cell expansion and eventually enables growth factor independency. Mechanistically, this is at least partially mediated by direct repression of the tumor-suppressor Pten, which consequently enhances PI3K-AKT signaling. Conversely, limiting miR-26 activity in a more physiological loss-of-function approach counteracts proliferation and enhances pre-B cell differentiation in vitro as well as in vivo. We therefore postulate a rheostat-like role for the miR-26 family in progenitor B cells, with an increase in mature miR-26 levels signaling cell expansion, and facilitating pre-B to the immature B cell progression when reduced.

Elevated expression of sepiapterin reductase, regulator of G protein signaling 1, hypothetical protein CXorf58 homolog, and zinc finger and BTB domain-containing protein 21 isoform X2 is associated with progression of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers associated with high mortality rate. Understanding of events leading to HCC pathophysiology is essential for its better management. We earlier reported development of a novel rodent model by administrating chemical carcinogens, DEN, and 2-AAF for study of HCC at very early stage. 2D-Electrophoresis analysis of total serum proteins identified several differentially expressed proteins in animals undergoing tumorigenesis. MALDI-TOF-MS/MS analyses were performed to characterize the differentially expressed proteins. Further real-time PCR analyses were taken place to quantify the transcript expression for the identified proteins at HCC initiation and tumor stages. Considering protein-protein interactions among the experimentally identified proteins and their interacting neighbors, a protein network has been analyzed that provided further insight into molecular events taking place during HCC development. Histological changes confirmed HCC initiation and hepatotumorigenesis at 1 and 4 months post carcinogen treatment, respectively. Four differentially expressed proteins were identified which were further characterized as regulator of G protein signaling 1 (RGS1), sepiapterin reductase (SPR), similar to zinc finger and BTB domain-containing protein 21 isoform X2 (ZNF295), and a hypothetical protein CXorf58 homolog. Quantification of transcripts for these proteins revealed elevation in their expression both at initiation and tumorigenesis stages. The study deciphers the regulatory role of these proteins during HCC progression.

Characterization of a novel mesophilic CTP-dependent riboflavin kinase and rational engineering to create its thermostable homologs

Flavins play a central role in metabolism as molecules that catalyze a wide range of redox reactions in living organisms. Several variations in flavin biosynthesis exist among the domains of life, and their analysis has revealed many new structural and mechanistic insights till date. The cytidine triphosphate (CTP)-dependent riboflavin kinase in archaea is one such example - unlike most kinases that use adenosine triphosphate, archaeal riboflavin kinases utilize CTP to phosphorylate riboflavin and produce flavin mononucleotide. In this study, we present the characterization of a new mesophilic archaeal CTP-utilizing riboflavin kinase homolog from Methanococcus maripaludis (MmpRibK), which is linked closely in sequence to the previously characterized thermophilic Methanocaldococcus jannaschii homolog. We reconstitute the activity of MmpRibK, determine its kinetic parameters and molecular factors that contribute to its unique properties, and finally establish the residues that improve its thermostability using computation and a series of experiments.  Our work advances the molecular understanding of flavin biosynthesis in archaea by the characterization of the first mesophilic CTP-dependent riboflavin kinase. Finally, it validates the role of salt bridges and rigidifying amino acid residues in imparting thermostability to this unique structural fold that characterizes archaeal riboflavin kinase enzymes, with implications in enzyme engineering and biotechnological applications.

No Tumor Suppressor Role for LKB1 in Prostate Cancer

To elucidate the pathogenesis of prostate diseases, following in silico analysis, the LKB1 gene was selected for further investigation. The LKB1 gene has been associated with poor prognosis and is frequently mutated in different types of cancers. In this study, 50 benign prostatic hyperplasia (BPH) and 57 prostate cancer (PCa) tissues, including matched normal tissue for the patients, were analyzed by qRT-PCR and DNA sequencing for LKB1 expression and the mutation profile, respectively. Expression of LKB1 was increased in 60.7% of the PCa tissues compared with noncancerous tissue samples (p ≤ 0.001). However, LKB1 expression was lower when compared with normal tissues in BPH (p = 0.920). Four coding sequence alterations were detected in BPH. Three silent mutations were located in codons 9, 32, and 275 and a missense mutation was observed in codon 384. Six alterations were identified in the intronic regions of the LKB1 gene in both PCa and BPH. Five mutations were observed in both patient groups. A new alteration in intron 6 was observed in a patient with PCa. The LKB1 gene may be associated with benign transformations rather than the tumors in prostate pathogenesis when its expression and mutation status are considered. However, the mechanism of LKB1 in PCa needs further studies.

Resveratrol-induced Sirt1 phosphorylation by LKB1 mediates mitochondrial metabolism

The NAD⁺-dependent deacetylase Sirt1 has been implicated in the prevention of many age-related diseases, including cancer, type 2 diabetes, and cardiovascular disease. Resveratrol, a plant polyphenol, exhibits antiaging, antitumor, and vascular protection effects by activating Sirt1. However, the molecular mechanism of Sirt1 activation as induced by resveratrol remains unclear. By knockdown/rescue experiments, fluorometric Sirt1 activity assay, immunoprecipitation, and pull-down assays, we identify here that the tumor suppressor LKB1 (liver kinase B1) as a direct activator of Sirt1 elicited by resveratrol. Resveratrol promotes the binding between LKB1 and Sirt1, which we first reported, and this binding leads to LKB1-mediated phosphorylation of Sirt1 at three different serine residues in the C terminus of Sirt1. Mechanistically, LKB1-mediated phosphorylation increases intramolecular interactions in Sirt1, such as the binding of the C terminus to the deacetylase core domain, thereby eliminating DBC1 (Deleted in Breast Cancer 1, Sirt1 endogenous inhibitor) inhibition and promoting Sirt1–substrate interaction. Functionally, LKB1-dependent Sirt1 activation increases mitochondrial biogenesis and respiration through deacetylation and activation of the transcriptional coactivator PGC-1α. These results identify Sirt1 as a context-dependent target of LKB1 and suggest that a resveratrol-stimulated LKB1-Sirt1 pathway plays a vital role in mitochondrial metabolism, a key physiological process that contributes to numerous age-related diseases.

Targeting mTOR and Glycolysis in HER2-Positive Breast Cancer

Up to one third of all breast cancers are classified as the aggressive HER2-positive subtype, which is associated with a higher risk of recurrence compared to HER2-negative breast cancers. The HER2 hyperactivity associated with this subtype drives tumor growth by up-regulation of mechanistic target of rapamycin (mTOR) pathway activity and a metabolic shift to glycolysis. Although inhibitors targeting the HER2 receptor have been successful in treating HER2-positive breast cancer, anti-HER2 therapy is associated with a high risk of recurrence and drug resistance due to stimulation of the PI3K-Akt-mTOR signaling pathway and glycolysis. Combination therapies against HER2 with inhibition of mTOR improve clinical outcomes compared to HER2 inhibition alone. Here, we review the role of the HER2 receptor, mTOR pathway, and glycolysis in HER2-positive breast cancer, along with signaling mechanisms and the efficacy of treatment strategies of HER2-positive breast cancer.

Parental energy-sensing pathways control intergenerational offspring sex determination in the nematode Auanema freiburgensis

BACKGROUND

Environmental stimuli experienced by the parental generation influence the phenotype of subsequent generations (Demoinet et al., Proc Natl Acad Sci U S A 114:E2689-E2698, 2017; Burton et al., Nat Cell Biol 19:252-257, 2017; Agrawal et al., Nature 401:60-63, 1999). The effects of these stimuli on the parental generation may be passed through the germline, but the mechanisms at the basis of this non-Mendelian type of inheritance, their level of conservation, how they lead to adaptive vs non-adaptive, and intergenerational vs transgenerational inheritance are poorly understood. Here we show that modulation of nutrient-sensing pathways in the parental generation of the nematode Auanema freiburgensis regulates phenotypic plasticity of its offspring.

RESULTS

In response to con-specific pheromones indicative of stress, AMP-activated protein kinase (AMPK), mechanistic target of rapamycin complex 1 (mTORC1), and insulin signaling regulate stress resistance and sex determination across one generation, and these effects can be mimicked by pathway modulators. The effectors of these pathways are closely associated with the chromatin, and their regulation affects the chromatin acetylation status in the germline.

CONCLUSION

These results suggest that highly conserved metabolic sensors regulate phenotypic plasticity through regulation of subcellular localization of their effectors, leading to changes in chromatin acetylation and epigenetic status of the germline.

Tankyrases as modulators of pro-tumoral functions: molecular insights and therapeutic opportunities

Tankyrase 1 (TNKS1) and tankyrase 2 (TNKS2) are two homologous proteins that are gaining increasing importance due to their implication in multiple pathways and diseases such as cancer. TNKS1/2 interact with a large variety of substrates through the ankyrin (ANK) domain, which recognizes a sequence present in all the substrates of tankyrase, called Tankyrase Binding Motif (TBM). One of the main functions of tankyrases is the regulation of protein stability through the process of PARylation-dependent ubiquitination (PARdU). Nonetheless, there are other functions less studied that are also essential in order to understand the role of tankyrases in many pathways. In this review, we concentrate in different tankyrase substrates and we analyze in depth the biological consequences derived of their interaction with TNKS1/2. We also examine the concept of both canonical and non-canonical TBMs and finally, we focus on the information about the role of TNKS1/2 in different tumor context, along with the benefits and limitations of the current TNKS inhibitors targeting the catalytic PARP domain and the novel strategies to develop inhibitors against the ankyrin domain. Available data indicates the need for further deepening in the knowledge of tankyrases to elucidate and improve the current view of the role of these PARP family members and get inhibitors with a better therapeutic and safety profile.

STRADA-mutant human cortical organoids model megalencephaly and exhibit delayed neuronal differentiation

Genetic diseases involving overactivation of the mechanistic target of rapamycin (mTOR) pathway, so-called "mTORopathies," often manifest with malformations of cortical development (MCDs), epilepsy, and cognitive impairment. How mTOR pathway hyperactivation results in abnormal human cortical development is poorly understood. To study the effect of mTOR hyperactivity on early stages of cortical development, we focused on Pretzel Syndrome (polyhydramnios, megalencephaly, symptomatic epilepsy; PMSE syndrome), a rare mTORopathy caused by homozygous germline mutations in the STRADA gene. We developed a human cortical organoid (hCO) model of PMSE and examined morphology and size for the first 2 weeks of organoid growth, and cell type composition at weeks 2, 8, and 12 of differentiation. In the second week, PMSE hCOs enlarged more rapidly than controls and displayed an abnormal Wnt pathway-dependent increase in neural rosette structures. PMSE hCOs also exhibited delayed neurogenesis, decreased subventricular zone progenitors, increased proliferation and cell death, and an abnormal architecture of primary cilia. At week 8, PMSE hCOs had fewer deep layer neurons. By week 12, neurogenesis recovered in PMSE organoids, but they displayed increased outer radial glia, a cell type thought to contribute to the expansion of the human cerebral cortex. Together, these findings suggest that megalencephaly in PMSE arises from the expansion of neural stem cells in early corticogenesis and potentially also from increased outer radial glial at later gestational stages. The delayed neuronal differentiation in PMSE organoids demonstrates the important role the mTOR pathway plays in the maintenance and expansion of the stem cell pool.

AMPKα-like proteins as LKB1 downstream targets in cell physiology and cancer

One of the key events in cancer development is the ability of tumor cells to overcome nutrient deprivation and hypoxia. Among proteins performing metabolic adaptation to the various cellular nutrient conditions, liver kinase B 1 (LKB1) and its main downstream target adenosine monophosphate (AMP)-activated protein kinase α (AMPKα) are important sensors of energy requirements within the cell. Although LKB1 was originally described as a tumor suppressor, given its role in metabolism, it potentially acts as a double-edged sword. AMPKα, a master regulator of cell energy demands, is activated when ATP level drops under a certain threshold, responding accordingly through its downstream targets. Twelve downstream kinase targets of LKB1 have been described as AMPKα-like proteins. This group is comprised of novel (nua) kinase family (NUAK) kinases (NUAK1 and 2) linked to cell cycle progression and ultraviolet (UV)-damage; microtubule affinity regulating kinases (MARKs) (MARK1, MARK2, MARK3, and MARK4) that are involved in cell polarity; salt inducible kinases (SIK) (SIK1, SIK2, also known as Qin-induced kinase or QIK and SIK3) that are implicated in cell metabolism and adipose tissue development and mitotic regulation; maternal embryonic leuzine zipper kinase (MELK) that regulate oocyte maturation; and finally brain selective kinases (BRSKs) (BRSK1 and 2), which have been mainly characterized in the brain due to their role in neuronal polarization. Thus, many efforts have been made in order to harness LKB1 kinase and its downstream targets as a possible therapeutic hub in tumor development and propagation. In this review, we describe LKB1 and its downstream target AMPK summarize major functions of various AMPK-like proteins, while focusing on biological functions of BRSK1 and 2 in different models.

Cloning and prokaryotic expression of the chicken liver kinase B1 (LKB1) and its localization in liver, heart and hypothalamus

Liver kinase B1 (LKB1) is a member of the serine/threonine kinase family, which plays an indispensable role in the organism of animals. In the current study, the chicken LKB1 protein gene was amplified by PCR based on the primers and cDNA templates. Then, the cloning vector was constructed and the target gene was cloned. After that, the target gene was inserted into the expression vector to construct the recombinant plasmid. The recombinant plasmid was transformed into BL21 (DE3) host cells and the LKB1 recombinant proteins were successfully expressed by using Isopropyl-β-D-thiogalactopyranoside (IPTG). Finally, purified LKB1 proteins were used as antigen and the rabbit-derived antiserums were collected. The antiserum titer determined by ELISA was not less than 1:128000. The results of Western blot suggested that the polyclonal antibody is highly specific to chicken LKB1 protein. Immunofluorescence indicated that the LKB1 protein is mainly expressed in the cytoplasm of liver, heart and hypothalamus cells of chicken. Our study showed that the LKB1 polyclonal antibodies produced by this method are effective and can be used to further study the role of LKB1 in the pathogenesis of chicken disease.

Activation of LKB1 rescues 3T3-L1 adipocytes from senescence induced by Sirt1 knock-down: a pivotal role of LKB1 in cellular aging

Previous reports have shown that excess calorie intake promotes p53 dependent senescence in mouse adipose tissues. The objective of the current study was to address the mechanism underlying this observation, i.e. adipocyte aging. Using cultured 3T3-L1 cells, we investigated the involvement of energy regulators Sirt1, AMPK, and LKB1 in senescence. Fifteen days post differentiation, Sirt1 knock-down increased senescence-associated beta-galactosidase (SA-β-Gal) staining by 20-40% (p<0.05, n=12) and both cyclin kinase inhibitor p21^Cip and chemokine receptor IL8Rb expression by 2-4 fold. ATP and expression of mitochondria Complex 1 were also reduced by 30% and 50%, respectively (p<0.05, n=4). Such energy depletion may have caused the observed increase in AMPK activity, despite LKB1 activity downregulation. This association between Sirt1 and LKB1 activity was confirmed in vivo in mouse adipose tissue. Upregulation of LKB1 activity by expression of the Sirt1-insensitive LKB1-K48R mutant in 3T3-L1 cells completely prevented the senescence-associated changes of Sirt1 knock-down. In addition, cellular senescence, which also occurs in cultured primary human aortic endothelial cells, was largely prevented by ectopic expression of LKB1. These results suggest that LKB1 plays a pivotal role in cellular senescence occurring in adipocytes and other cell types.

Insight on Transcriptional Regulation of the Energy Sensing AMPK and Biosynthetic mTOR Pathway Genes

The Adenosine Monophosphate-activated Protein Kinase (AMPK) and the Mechanistic Target of Rapamycin (mTOR) are two evolutionarily conserved kinases that together regulate nearly every aspect of cellular and systemic metabolism. These two kinases sense cellular energy and nutrient levels that in turn are determined by environmental nutrient availability. Because AMPK and mTOR are kinases, the large majority of studies remained focused on downstream substrate phosphorylation by these two proteins, and how AMPK and mTOR regulate signaling and metabolism in normal and disease physiology through phosphorylation of their substrates. Compared to the wealth of information known about the signaling and metabolic pathways modulated by these two kinases, much less is known about how the transcription of AMPK and mTOR pathway genes themselves are regulated, and the extent to which AMPK and mTOR regulate gene expression to cause durable changes in phenotype. Acute modification of cellular systems can be achieved through phosphorylation, however, induction of chronic changes requires modulation of gene expression. In this review we will assemble evidence from published studies on transcriptional regulation by AMPK and mTOR and discuss about the putative transcription factors that regulate expression of AMPK and mTOR complex genes.

LKB1 inactivation leads to centromere defects and genome instability via p53-dependent upregulation of survivin

Inactivating mutations in the liver kinase B1 (LKB1) tumor suppressor gene underlie Peutz-Jeghers syndrome (PJS) and occur frequently in various human cancers. We previously showed that LKB1 regulates centrosome duplication via PLK1. Here, we report that LKB1 further helps to maintain genomic stability through negative regulation of survivin, a member of the chromosomal passenger complex (CPC) that mediates CPC targeting to the centromere. We found that loss of LKB1 led to accumulation of misaligned and lagging chromosomes at metaphase and anaphase and increased the appearance of multi- and micro-nucleated cells. Ectopic LKB1 expression reduced these features and improved mitotic fidelity in LKB1-deficient cells. Through pharmacological and genetic manipulations, we showed that LKB1-mediated repression of survivin is independent of AMPK, but requires p53. Consistent with the key influence of LKB1 on survivin expression, immunohistochemical analysis indicated that survivin is highly expressed in intestinal polyps from a PJS patient. Lastly, we reaffirm a potential therapeutic avenue to treat LKB1-mutated tumors by demonstrating the increased sensitivity to survivin inhibitors of LKB1-deficient cells.

Novel insights into adiponectin action in breast cancer: Evidence of its mechanistic effects mediated by ERα expression

This review describes the multifaceted effects of adiponectin on breast cancer cell signalling, tumour metabolism, and microenvironment. It is largely documented that low adiponectin levels are associated with an increased risk of breast cancer. However, it needs to be still clarified what are the extents of the decrease of local/intra-tumoural adiponectin concentrations, which promote breast tumour malignancy. Most of the anti-proliferative and pro-apoptotic effects induced by adiponectin have been obtained in breast cancer cells not expressing estrogen receptor alpha (ERα). Here, we will highlight recent findings demonstrating the mechanistic effects through which adiponectin is able to fuel genomic and non-genomic estrogen signalling, inhibiting LKB1/AMPK/mTOR/S6K pathway and switching energy balance. Therefore, it emerges that the reduced adiponectin levels in patients with obesity work to sustain tumour growth and progression in ERα-positive breast cancer cells. All this may contribute to remove the misleading paradigm that adiponectin univocally inhibits breast cancer cell growth and progression independently on ERα status. The latter concept, here clearly provided by pre-clinical studies, may have translational relevance adopting adiponectin as a potential therapeutic tool. Indeed, the interfering role of ERα on adiponectin action addresses how a separate assessment of adiponectin treatment needs to be considered in novel therapeutic strategies for ERα-positive and ERα-negative breast cancer.

Sevoflurane Postconditioning Reduces Hypoxia-Reoxygenation Injury in H9C2 Embryonic Rat Cardiomyocytes and Targets the STRADA Gene by Upregulating microRNA-107

BACKGROUND Sevoflurane as a widely used inhalational general anesthetic that also has a cardioprotective role in hypoxia-reoxygenation (H/R) injury. This study aimed to investigate the effects of microRNA-107 (miR-107) on sevoflurane postconditioning (SpostC) in H9C2 embryonic rat cardiomyocytes and to use bioinformatics analysis to identify the molecular basis of cardioprotection from sevoflurane in human cardiac tissue. MATERIAL AND METHODS The STRADA gene was identified from the Gene Expression Omnibus (GEO) database. H9C2 embryonic rat cardiomyocytes were cultured with sevoflurane. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot were used to measure the mRNA expression and protein expression of STRADA and miR-107 in H9C2 cells. TargetScanHuman version 7.2 was used to identify the target gene of miR-107 and to predict the STRADA 3'-UTR binding site of miR-107. The dual-luciferase reporter assay measured the relative luciferase activity. The cell proliferation rate and cell apoptosis were measured using the MTT assay and flow cytometry, respectively. RESULTS H/R injury in H9C2 cells following SpostC resulted in increased expression of miR-107 and reduced expression of STRADA. Specific binding of miR-107 was identified to STRADA 3'-UTR. Upregulation of the miR-107 in SpostC H/R injured H9C2 cells promoted cell proliferation, reduced cell apoptosis, and downregulating the protein expression of caspase-3. STRADA overexpression reduced the effects of a miR-107 mimic on SpostC. CONCLUSIONS SpostC reduced H/R injury in H9C2 embryonic rat cardiomyocytes by targeting the STRADA gene and by upregulating the expression of microRNA-107.

SNRK: a metabolic regulator with multifaceted role in development and disease

Sucrose nonfermenting 1-related kinase (SNRK) is a serine/threonine kinase and a member of the adenosine monophosphate (AMP)-activated protein kinase (AMPK) family that is involved in the metabolic regulatory mechanisms in various cell types. SNRK is an important mediator in maintaining cellular metabolic homeostasis. In this review, we discuss the role of SNRK in metabolic tissues where it is expressed, including heart and adipose tissue. We discuss its role in regulating inflammation in these tissues and the pathways associated with regulating inflammation. We also discuss SNRK's role in vascular development and the processes associated with it. Finally, we review SNRK's potential as a target in various metabolic dysfunction-associated diseases such as cardiovascular diseases, diabetes, obesity, and cancer. This comprehensive review on SNRK suggests that it has therapeutic value in the suppression of inflammation in cardiac and adipose tissue.

Anti-inflammatory Property of AMP-activated Protein Kinase

BACKGROUND

One of the many debated topics in inflammation research is whether this scenario is really an accelerated form of human wound healing and immunityboosting or a push towards autoimmune diseases. The answer requires a better understanding of the normal inflammatory process, including the molecular pathology underlying the possible outcomes. Exciting recent investigations regarding severe human inflammatory disorders and autoimmune conditions have implicated molecular changes that are also linked to normal immunity, such as triggering factors, switching on and off, the influence of other diseases and faulty stem cell homeostasis, in disease progression and development.

METHODS

We gathered around and collected recent online researches on immunity, inflammation, inflammatory disorders and AMPK. We basically searched PubMed, Scopus and Google Scholar to assemble the studies which were published since 2010.

RESULTS

Our findings suggested that inflammation and related disorders are on the verge and interfere in the treatment of other diseases. AMPK serves as a key component that prevents various kinds of inflammatory signaling. In addition, our table and hypothetical figures may open a new door in inflammation research, which could be a greater therapeutic target for controlling diabetes, obesity, insulin resistance and preventing autoimmune diseases.

CONCLUSION

The relationship between immunity and inflammation becomes easily apparent. Yet, the essence of inflammation turns out to be so startling that the theory may not be instantly established and many possible arguments are raised for its clearance. However, this study might be able to reveal some possible approaches where AMPK can reduce or prevent inflammatory disorders.

The LKB1-SIK Pathway Controls Dendrite Self-Avoidance in Purkinje Cells

Strictly controlled dendrite patterning underlies precise neural connection. Dendrite self-avoidance is a crucial system preventing self-crossing and clumping of dendrites. Although many cell-surface molecules that regulate self-avoidance have been identified, the signaling pathway that orchestrates it remains poorly understood, particularly in mammals. Here, we demonstrate that the LKB1-SIK kinase pathway plays a pivotal role in the self-avoidance of Purkinje cell (PC) dendrites by ensuring dendritic localization of Robo2, a regulator of self-avoidance. LKB1 is activated in developing PCs, and PC-specific deletion of LKB1 severely disrupts the self-avoidance of PC dendrites without affecting gross morphology. SIK1 and SIK2, downstream kinases of LKB1, mediate LKB1-dependent dendrite self-avoidance. Furthermore, loss of LKB1 leads to significantly decreased Robo2 levels in the dendrite but not in the cell body. Finally, restoration of dendritic Robo2 level via overexpression largely rescues the self-avoidance defect in LKB1-deficient PCs. These findings reveal an LKB1-pathway-mediated developmental program that establishes dendrite self-avoidance.

Tankyrase disrupts metabolic homeostasis and promotes tumorigenesis by inhibiting LKB1-AMPK signalling

The LKB1/AMPK pathway plays a major role in cellular homeostasis and tumor suppression. Down-regulation of LKB1/AMPK occurs in several human cancers and has been implicated in metabolic diseases. However, the precise upstream regulation of LKB1-AMPK pathway is largely unknown. Here, we report that AMPK activation by LKB1 is regulated by tankyrases. Tankyrases interact with and ribosylate LKB1, promoting its K63-linked ubiquitination by an E3 ligase RNF146, which blocks LKB1/STRAD/MO25 complex formation and LKB1 activation. LKB1 activation by tankyrase inhibitors induces AMPK activation and suppresses tumorigenesis. Similarly, the tankyrase inhibitor G007-LK effectively regulates liver metabolism and glycemic control in diabetic mice in a LKB1-dependent manner. In patients with lung cancer, tankyrase levels negatively correlate with p-AMPK levels and poor survival. Taken together, these findings suggest that tankyrase and RNF146 are major up-stream regulators of LKB1-AMPK pathway and provide another focus for cancer and metabolic disease therapies.

LKB1 specifies neural crest cell fates through pyruvate-alanine cycling

Metabolic processes underlying the development of the neural crest, an embryonic population of multipotent migratory cells, are poorly understood. Here, we report that conditional ablation of the Lkb1 tumor suppressor kinase in mouse neural crest stem cells led to intestinal pseudo-obstruction and hind limb paralysis. This phenotype originated from a postnatal degeneration of the enteric nervous ganglia and from a defective differentiation of Schwann cells. Metabolomic profiling revealed that pyruvate-alanine conversion is enhanced in the absence of Lkb1. Mechanistically, inhibition of alanine transaminases restored glial differentiation in an mTOR-dependent manner, while increased alanine level directly inhibited the glial commitment of neural crest cells. Treatment with the metabolic modulator AICAR suppressed mTOR signaling and prevented Schwann cell and enteric defects of Lkb1 mutant mice. These data uncover a link between pyruvate-alanine cycling and the specification of glial cell fate with potential implications in the understanding of the molecular pathogenesis of neural crest diseases.

FBXO22 mediates polyubiquitination and inactivation of LKB1 to promote lung cancer cell growth

Liver kinase B1 (LKB1) regulates both cell growth and energy metabolism. Inactivated mutations of LKB1, observed in 20–30% of nonsmall cell lung cancers (NSCLC), contribute significantly to lung cancer malignancy progression. However, the upstream signalings regulating LKB1 activity remain incompletely understood. Here, we present evidence that FBXO22 interacts with and promotes polyubiquitination of LKB1. More intriguingly, FBXO22 mediates Lys-63-linked LKB1 polyubiquitination and inhibits kinase activity of LKB1. Furthermore, over-expression of FBXO22 promotes NSCLC cell growth through inhibiting LKB1-AMPK-mTOR signaling in vitro and in vivo. Clinically, FBXO22 is highly expressed in human lung adenocarcinoma and high FBXO22 expression predicts significant poor prognosis. Our study provides new insights into the upstream regulation of LKB1 activation and identifies FBXO22 as a potential therapeutic target for lung cancer treatment.

Post-translational modifiers of liver kinase B1/serine/threonine kinase 11 in hepatocellular carcinoma

Liver kinase B1 (LKB1) also referred to as serine/threonine kinase 11 (STK11) encodes a 50 kDa evolutionary conserved serine/threonine kinase that is ubiquitously expressed in adult and fetal tissues. LKB1 is a master kinase known to phosphorylate and activate several kinases including AMP-activated protein kinase, a crucial cellular energy sensor. LKB1 shows pleiotropic activity playing diverse roles in multiple processes, including cell polarity and other processes relevant in cancer pathology, such as energy metabolism, proliferation and apoptosis. In spite of the fact that LKB1 is often considered a tumor suppressor in a wide variety of organs, in the last years, several studies have shown that LKB1 is unexpectedly high in hepatocellular carcinoma (HCC), the most common type of primary liver cancer. Post-translational modifications of LKB1 are potentially relevant in HCC. Herein, we provide a comprehensive revision of post-translational modifications of LKB1 in HCC and how they modulate LKB1 function by different mechanisms such as regulation of its activity, localization or stability. Overall, the signature post-translational modifications of LKB1 in HCC appear to play an important role in the rather unique role of LKB1 as an oncogenic driver in liver cancer and may provide an alternative valuable therapeutic approach to regulate LKB1 expression and/or activity in HCC.

Point your SmartPhone at the code above. If you have a QR code reader the video abstract will appear. Or use:

https://youtu.be/YCfD3s4OVcQ

Pathogenesis, diagnosis, and treatment of Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS), an autosomal dominant inherited disease, is caused by germinal mutations of the STK11. It is characterized by gastrointestinal hamartomas, mucocutaneous pigmentation and increased cancer risk. Germline mutations in STK11 cause a harmful effect on cell apoptosis, G1 arrest, and cell polarization, which leads to polyp formation and cancer occurrence. Balloon-assisted enteroscopy is widely used in removal of PJS polyps in the small bowel and it is proved to be safe and effective. We suggest to screen polyps and cancer in PJS patients, which seems to benefit these patients in the long run.

An exploration of genotype-phenotype link between Peutz-Jeghers syndrome and STK11: a review

Peutz-Jeghers Syndrome (PJS) is an autosomal dominant hereditary polyposis syndrome. Clinical features include hamartomatous polyps, mucocutaneous pigmentation and an increased predisposition towards developing malignancy. Variants in STK11, a tumour suppressor gene, located on Chromosome 19, predispose to PJS. Peutz-Jeghers Syndrome is associated with increased rates of malignancy, particularly gastrointestinal. However, PJS is also associated with increased gynaecological, testicular and thyroid papillary malignancy. Truncating variants in STK11 are thought to predispose to a more severe phenotype. Phenotype severity is based on earlier onset of gastrointestinal pathology arising from the polyps, such as intussusception or earlier onset malignancy. Missense variants are generally considered less severe than truncating variants. There remain a large number of variants of undetermined significance. Studies have attempted to correlate the location of variants with impact on protein structure and overall severity of the PJS phenotype. The results from these cohort studies have consistently found a non-random distribution of variants. Nevertheless, a consensus on phenotype severity based on variant location is yet to be established. A centralised database that collates all known variants would facilitate the interpretation of these variants, best under the governance of an international disease-specific organisation (InSiGHT). In particular, it could help explore the significance of variants based on their type or location. Understanding the genotype-phenotype link between STK11 variants and PJS could allow more personalised care for PJS patients and their families via appropriate risk stratification and personalised and targeted cancer screening.

MIR-1265 regulates cellular proliferation and apoptosis by targeting calcium binding protein 39 in gastric cancer and, thereby, impairing oncogenic autophagy

Increasing evidence indicates that microRNAs (miRNAs) play an important role in various tumors by regulating downstream target genes and diverse signaling pathways. Herein, we confirmed miR-1265 expression in gastric cancer (GC) using the Cancer Genome Atlas (TCGA) database and assessed the level of miR-1265 expression in clinical specimens and cell lines. We found that miR-1265 expression was negatively correlated with tumor size. Further functional analysis revealed that miR-1265 suppresses cellular proliferation and autophagy while inducing apoptosis in GC cells. A luciferase reporter assay was used to identify an miR-1265 targeted gene, calcium binding protein 39 (CAB39), which is an essential upstream regulator in the AMPK-mTOR signaling pathway. Upregulation or downregulation of CAB39 expression reversed the effects of miR-1265 overexpression or inhibition, respectively. Notably, the knockdown of autophagy-related gene 12 (ATG12) impaired the effects of miR-1265 inhibition or CAB39 overexpression in GC. MiR-1265 also suppressed the growth of GC cells in vivo and that of human gastric organoids. Altogether, our results show that miR-1265 suppresses GC progression and oncogenic autophagy by reducing CAB39 expression and regulating the AMPK-mTOR signaling pathway. Therefore, miR-1265 may represent a potential therapeutic target for GC.