Exogenous activation of LKB1/AMPK signaling induces G₁ arrest in cells with endogenous LKB1 expression

Immune profiling of premalignant lesions in patients with Peutz-Jeghers syndrome

BACKGROUND

Peutz-Jeghers syndrome (PJS), is a rare autosomal dominant hereditary disease characterized by an elevated risk of various cancers. Serine/Threonine Kinase 11 (STK11) gene is a major tumor suppressor crucial for immune evasion with and beyond tumorigenic cells. It has garnered increasing attention in the realm of oncology treatment, particularly in the context of immunotherapy development.

OBJECTIVE

This study aimed to assess the suitability of polyps obtained from individuals with PJS, resulting from germline STK11 deficiency, for immunotherapy. Additionally, we seek to identify potential shared mechanisms related to immune evasion between PJS polyps and cancers. To achieve this, we examined PJS polyps alongside familial adenomatous polyposis (FAP) and sporadic polyps.

METHODS

Polyps were compared among themselves and with either the paracancerous tissues or colon cancers. Pathological and gene expression profiling approaches were employed to characterize infiltrating immune cells and assess the expression of immune checkpoint genes.

RESULTS

Our findings revealed that PJS polyps exhibited a closer resemblance to cancer tissues than other polyps in terms of their immune microenvironment. Notably, PJS polyps displayed heightened expression of the immune checkpoint gene CD80 and an accumulation of myeloid cells, particularly myeloid-derived suppressor cells (MDSCs).

CONCLUSION

The findings suggest an immunobiological foundation for the increased cancer susceptibility in PJS patients, paving the way for potential immune therapy applications in this population. Furthermore, utilizing PJS as a model may facilitate the exploration of immune evasion mechanisms, benefiting both PJS and cancer patients.

Gradual deterioration of fatty liver disease to liver cancer via inhibition of AMPK signaling pathways involved in energy-dependent disorders, cellular aging, and chronic inflammation

Introduction

Hepatocellular carcinoma (HCC) is the most prevalent primary liver cancer kind. According to recent research, a fatty liver increases the risk of hepatocellular cancer. Nevertheless, the AMPK signaling pathway is crucial. In addition, 5'-AMP-activated protein kinase (AMPK) is strongly linked to alterations in the tumor microenvironment, such as inflammation, hypoxia, and aging. The objective of this study is to evaluate the impact of the AMPK signaling pathway on the progression of fatty liver to HCC.

Methods

In this study, we established a mouse liver cancer model using high-fat diets and nano-nitrosamines (nano-DEN). In addition, we employed a transcriptomic technique to identify all mRNAs detected in liver samples at the 25th weekexpression of proteins linked with the LKB1-AMPK-mTOR signaling pathway, inflammation, aging, and hypoxia was studied in microarrays of liver cancer tissues from mice and humans. These proteins included p-AMPK, LKB1, mTOR, COX-2, β-catenin, HMGB1, p16, and HIF-1α.

Results

Data were collected at different times in the liver as well as in cancerous and paracancerous regions and analyzed by a multispectral imaging system. The results showed that most of the genes in the AMPK signaling pathway were downregulated. Prakk1 expression was upregulated compared to control group but downregulated in the cancerous regions compared to the paracancerous regions. Stk11 expression was downregulated in the cancerous regions. Mtor expression was upregulated in the cancerous regions. During liver cancer formation, deletion of LKB1 in the LKB1-AMPK-mTOR signaling pathway reduces phosphorylation of AMPK. It contributed to the upregulation of mTOR, which further led to the upregulation of HIF1α. In addition, the expression of β-catenin, COX-2, and HMGB1 were upregulated, as well as the expression of p16 was downregulated.

Discussion

These findings suggest that changes in the AMPK signaling pathway exacerbate the deterioration of disrupted energy metabolism, chronic inflammation, hypoxia, and cellular aging in the tumor microenvironment, promoting the development of fatty liver into liver cancer.

Kiss1 Inhibits the Proliferation of Nasopharyngeal Carcinoma Cells Via Activation of the LKB1/AMPK Pathway

Nasopharyngeal carcinoma (NPC) is a cancer that occurs in the nasopharynx. Infinite proliferation and distant metastasis are the main characteristics of NPC cells, and the main reason for the current failure of malignant tumor treatment. In this study, by integrating the immunohistochemical, cell transfection, western blot and real-time reverse transcriptase polymerase chain reaction (RT-PCR) analysis, we observed that the expression of KISS1 and its receptor gene (KISS1R) negatively related with the proliferation of NPC cells. Overexpression of the KISS1 genes in cells reduced cell proliferation, slow down the cell cycle, and increased apoptosis. Additionally, overexpression of these genes significantly increased Liver Kinase B1 (LKB1), phosphorylation of LKB1 and AMPK, indicated by Western blotting. Together, all of these results suggested for the first time that KISS1 and KISS1R suppress the proliferation of NPC cells by activating the LKB1/AMPK pathway, thus revealing a viable indicator for diagnosis of NPC in clinical practice.

Modulating Tumor Microenvironment: A Review on STK11 Immune Properties and Predictive vs Prognostic Role for Non-small-cell Lung Cancer Immunotherapy

OPINION STATEMENT

The quest for immunotherapy (IT) biomarkers is an element of highest clinical interest in both solid and hematologic tumors. In non-small-cell lung cancer (NSCLC) patients, besides PD-L1 expression evaluation with its intrinsic limitations, tissue and circulating parameters, likely portraying the tumor and its stromal/immune counterparts, have been proposed as potential predictors of IT responsiveness. STK11 mutations have been globally labeled as markers of IT resistance. After a thorough literature review, STK11 mutations condition the prognosis of NSCLC patients receiving ICI-containing regimens, implying a relevant biological and clinical significance. On the other hand, waiting for prospective and solid data, the putative negative predictive value of STK11 inactivation towards IT is sustained by less evidence. The physiologic regulation of multiple cellular pathways performed by STK11 likely explains the multifaceted modifications in tumor cells, stroma, and tumor immune microenvironment (TIME) observed in STK11 mutant lung cancer, particularly explored in the molecular subgroup of KRAS co-mutation. IT approaches available thus far in NSCLC, mainly represented by anti-PD-1/PD-L1 inhibitors, are not promising in the case of STK11 inactivation. Perceptive strategies aimed at modulating the TIME, regardless of STK11 status or specifically addressed to STK11-mutated cases, will hopefully provide valid therapeutic options to be adopted in the clinical practice.

Role of next generation sequencing-based liquid biopsy in advanced non-small cell lung cancer patients treated with immune checkpoint inhibitors: impact of STK11, KRAS and TP53 mutations and co-mutations on outcome

BACKGROUND

Characterization of tumor-related genetic alterations is promising for the screening of new predictive markers in non-small cell lung cancer (NSCLC). Aim of the study was to evaluate prognostic and predictive role of most frequent tumor-associated genetic alterations detected in plasma before starting immune checkpoint inhibitors (ICIs).

METHODS

Between January 2017 and October 2019, advanced NSCLC patients were prospectively screened with plasma next-generation sequencing (NGS) while included in two trials: VISION (NCT02864992), using Guardant360^® test, and MAGIC (Monitoring Advanced NSCLC through plasma Genotyping during Immunotherapy: Clinical feasibility and application), using Myriapod NGS-IL 56G Assay. A control group of patients not receiving ICIs was analyzed.

RESULTS

A total of 103 patients receiving ICIs were analyzed: median overall survival (OS) was 20.8 (95% CI: 16.7-24.9) months and median immune-related progression free disease (irPFS) 4.2 (95% CI: 2.3-6.1) months. TP53 mutations in plasma negatively affected OS both in patients treated with ICIs and in control group (P=0.001 and P=0.009), indicating a prognostic role. STK11 mutated patients (n=9) showed a trend for worse OS only if treated with ICIs. The presence of KRAS/STK11 co-mutation and KRAS/STK11/TP53 co-mutation affected OS only in patients treated with ICIs (HR =10.936, 95% CI: 2.337-51.164, P=0.002; HR =17.609, 95% CI: 3.777-82.089, P<0.001, respectively), indicating a predictive role.

CONCLUSIONS

Plasma genotyping demonstrated prognostic value of TP53 mutations and predictive value of KRAS/STK11 and KRAS/STK11/TP53 co-mutations.

AICAR Stimulates the Pluripotency Transcriptional Complex in Embryonic Stem Cells Mediated by PI3K, GSK3β, and β-Catenin

Pluripotent stem cells maintain the property of self-renewal and differentiate into all cell types under clear environments. Though the gene regulatory mechanism for pluripotency has been investigated in recent years, it is still not completely understood. Here, we show several signaling pathways involved in the maintenance of pluripotency. To investigate whether AMPK is involved in maintaining the pluripotency in mouse embryonic stem cells (mESCs) and elucidating the possible molecular mechanisms, implicated D3 and R1/E mESC lines were used in this study. Cells were cultured in the absence or presence of LIF and treated with 1 mM and 0.5 mM 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR), 2 mM metformin, compound C, and the PI3K inhibitor LY294002 for 24, 72, and 120 h. The levels of Nanog, Oct3/4, and REX1 and Brachyury, Notch2, and Gata4 mRNAs and Nanog or OCT3/4 protein levels were analyzed. Alkaline phosphatase and the cellular cycle were determined. The pGSK3β, GSK3β, p-β-catenin, and β-catenin protein levels were also investigated. We found that AMPK activators such as AICAR and metformin increase mRNA expression of pluripotency markers and decrease mRNA expression of differentiation markers in R1/E and D3 ES cells. AICAR increases phosphatase activity and arrests the cellular cycle in the G1 phase in these cells. We describe that AICAR effects were mediated by AMPK activation using a chemical inhibitor or by silencing this gene. AICAR effects were also mediated by PI3K, GSK3β, and β-catenin in R1/E ES cells. According to our findings, we provide a mechanism by which AICAR increases and maintains a pluripotency state through enhanced Nanog expression, involving AMPK/PI3K and p-GSK3β Ser21/9 pathways backing up the AICAR function as a potential target for this drug controlling pluripotency. The highlights of this study are that AICAR (5-aminoimidazole-4-carboxamied-1-b-riboside), an AMP protein kinase (AMPK) activator, blocks the ESC differentiation and AMPK is a key enzyme for pluripotency and shows valuable data to clarify the molecular pluripotency mechanism.

LKB1 and Tumor Metabolism: The Interplay of Immune and Angiogenic Microenvironment in Lung Cancer

Liver kinase B1 (LKB1) is a tumor suppressor gene whose inactivation is frequent in different tumor types, especially in lung adenocarcinoma (about 30% of cases). LKB1 has an essential role in the control of cellular redox homeostasis by regulating ROS production and detoxification. Loss of LKB1 makes the tumor cell more sensitive to oxidative stress and consequently to stress-inducing treatments, such as chemotherapy and radiotherapy. LKB1 loss triggers complex changes in tumor microenvironment, supporting a role in the regulation of angiogenesis and suggesting a potential role in the response to anti-angiogenic treatment. On the other hand, LKB1 deficiency can promote an immunosuppressive microenvironment and may be involved in primary resistance to anti-PD-1/anti-PD-L1, as it has been reported in lung cancer. The aim of this review is to discuss interactions of LKB1 with the tumor microenvironment and the potential applications of this knowledge in predicting response to treatment in lung cancer.

Metformin Counteracts HCC Progression and Metastasis Enhancing KLF6/p21 Expression and Downregulating the IGF Axis

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is the common tumor of the liver. Unfortunately, most HCC seem to be resistant to conventional chemotherapy and radiotherapy. The poor efficacy of antitumor agents is also due, at least in part, to the inefficient drug delivery and metabolism exerted by the steatotic/cirrhotic liver that hosts the tumor. Thus, novel approaches in chemotherapy may be needed to improve the survival rate in patients with HCC. Metformin (METF) has been found to lower HCC risk; however, the mechanisms by which METF performs its anticancer activity are not completely elucidated. Previous studies have showed METF action on growth inhibition in the liver in a dose/time-dependent manner and its antitumor role by targeting multiple pathways. We investigated molecular effects of METF in an in vitro human hepatoma model (HepG2), studying cell cycle regulators, tumorigenesis markers, and insulin-like growth factor (IGF) axis regulation.

MATERIALS AND METHODS

HepG2 cells were treated with METF (400 μM) for 24, 48, and 72 hours. METF action on cell cycle progression and cellular pathways involved in metabolism regulation was evaluated by gene expression analysis, immunofluorescence, and Western blot assay.

RESULTS

By assessing HepG2 cell viability, METF significantly decreased growth cell capacity raising KLF6/p21 protein content. Moreover, METF ameliorated the cancer microenvironment reducing cellular lipid drop accumulation and promoting AMPK activity. The overexpression of IGF-II molecule and the IGF-I receptor that plays a main role in HCC progression was counteracted by METF. Furthermore, the protein content of HCC principal tumor markers, CK19 and OPN, linked to the metastasis process was significantly reduced by METF stimulus.

CONCLUSION

Our data show that METF could suppress HepG2 proliferation, through induction of cell cycle arrest at the G0/G1 phase. In addition, METF effect on the cancer microenvironment and on the IGF axis leads to the development of new METF therapeutic use in HCC treatment.

Liver kinase B1 suppresses growth of lung cancer cells through sonic hedgehog signaling pathway

Lung cancer is one of life-threatening cancers in the worldwide. Liver kinase B1 (LKB1) has been reported to be closely related to cancers; however, the underlying mechanism of LKB1 in lung cancer remains unclear. In our study, a LKB1 specific shRNA was employed to down-regulate LKB1 levels and a LKB1 over-expression plasmid was constructed to up-regulate LKB1 levels. Thereafter, growth of lung cancer cells was assessed by MTT assay and flow cytometry. Effects of LKB1 on the activation of sonic hedgehog (Shh) signaling pathway were detected by Western blot. Effects of LKB1 on lung cancer growth and Shh signaling pathway activation were also assessed in vivo. Our results showed that LKB1 inhibited proliferation of lung cancer cells and induced their apoptosis. Moreover, LKB1 inhibited Shh signaling pathway activation. Our in vivo study also showed that LKB1 inhibited lung cancer growth in vivo and modulated Shh signaling pathway. Treatment with cyclopamine, a Shh signaling pathway inhibitor, reversed the effects of LKB1 silencing and enhanced the effects of LKB1 over-expression. Results of our study demonstrate that LKB1 inhibits lung cancer growth in vitro and in vivo through Shh signaling pathway.

Differentially expressed novel alternatively spliced transcript variant of tumor suppressor Stk11 gene in mouse

Serine/threonine kinase 11 (STK11) is a protein kinase that is encoded by Stk11 gene located on chromosome 19 and 10 in humans and mouse respectively. It acts as a master kinase of adenine monophosphate-activated protein kinase (AMPK) pathway that coordinates the regulation of cellular energy metabolism and cell division. STK11 exerts effect by activating more than 14 kinases including AMPK and AMPK-related kinases. It is also known to regulate cell polarity and acts as tumor suppressor. Alternative splicing of pre-mRNA is a mechanism which results in multiple transcript variants of a single gene. In human, two STK11 isoforms have been reported, an alternatively spliced isoform which has variation at its C-terminal and mostly expressed in testis (LKB1_S). Another isoform exhibiting oncogenic properties lacks few residues at its N-terminal (ΔN-LKB1). In the present study, we report the identification of a new transcript variant Stk11N which is generated through alternative splicing. The new variant was found to have differential and tissue specific expression at Postnatal-7 and adult stages of mouse. As compared to the known variant Stk11C, the conceptually translated amino acid sequences of the new variant differ from exon-E2 onwards. In silico post translational studies of the new and published variant show similarity in some of the properties while differ in properties like nuclear export signals, phosphorylation, glycosylation, etc. Thus, alternative splicing of Stk11 gene generating new variant with heterogeneous properties suggests for complex regulation of these variants in controlling the AMPK pathway and other functions.

PIK3CA mutation sensitizes breast cancer cells to synergistic therapy of PI3K inhibition and AMPK activation

Breast cancer has been emerging as a most common threat among women, thus many efforts were made to find drugs for fighting breast cancer. So far, PI3K (Phosphatidylinositol-4,5-bisphosphate 3-kinase) inhibitors have been believed to be effective drugs until frequent resistance emerged. Recently, PI3K H1047R mutation has been reported to sensitize breast cancer cells to PI3K inhibition by aspirin. Considering aspirin activates AMPK (AMP-activated protein kinase) simultaneously, it is possible that AMPK activators and PI3K inhibitors can synergistically inhibit breast cancers. Here we clearly observed synergistic suppression of cell growth in all three breast cancer cell lines (MCF-7, MDA-MB-361 and HCC38) when co-treating cells with PI3K inhibitor GDC-0941 and AMPK activator AICAR (5-Aminoimidazole-4-carboxamide ribonucleotide). What is more, it is rather remarkable that the synergistic effect was much more dramatic in PIK3CA (PI3K catalytic subunit alpha) mutated (E545K) cells (MCF-7 and MDA-MB-361) than in PIK3CA wild-type cells (HCC38), which implied there is a relationship between PI3K genetic status and the efficacy of combination therapy. By using PIK3CA wild-type isogenic MCF-7 cell line, which exhibited attenuated cell proliferation compared with the parental MCF-7 cell line, we found endogenous reverse mutation of PIK3CA E545K alleles to wild-type sequence in MCF-7 cells dramatically impaired the synergy of PI3Ki&AMPKa (combinatorial PI3K inhibition and AMPK activation). Furthermore, PI3Ki&AMPKa significantly attenuated tumorigenesis of parental MCF-7 cells but not PIK3CA wild-type isogenic MCF-7 cells in tumor xenograft models. Taken together, our results suggest a promising precision therapy of PI3Ki&AMPKa in PIK3CA mutant breast cancers.

MARK2 inhibits the growth of HeLa cells through AMPK and reverses epithelial-mesenchymal transition

Microtubule affinity-regulating kinases (MARKs; MARK1, MARK2, MARK3 and MARK4) act directly downstream of LKB1, the multitasking tumor-suppressor kinase, and thereby mediate its biological effects. Current understanding of the function of MARKs is greatly restricted to regulation of cell polarity. However, whether or how MARKs contribute to cellular growth control remains largely unknown. In the present study, we utilized an inducible lentiviral expression system that allows rapid MARK expression in LKB1-deficient HeLa cells, and characterized additional functions of MARKs: overexpression of MARK2 in HeLa cells resulted in a decrease in cell growth, inhibition of colony formation and arrest in G1 cell cycle phase, with AMPK as the putative downstream effector upregulating the expression of p21 and p16. MARK2 was found to play a role in F-actin reorganization and to contribute to reversal of epithelial‑mesenchymal transition (EMT) as exemplified in the case of HeLa cells that exhibited phenotypic changes, reduced cell migration and invasion. Our findings unveil the coordinated regulation of cell growth and EMT mediated by MARK2, and also provide new insights into the mechanisms underlying the anti-metastatic activity of MARK2.

T cell proliferation and adaptive immune responses are critically regulated by protein phosphatase 4

The clonal expansion of activated T cells is pivotal for the induction of protective immunity. Protein phosphatase 4 (PP4) is a ubiquitously expressed serine/threonine phosphatase with reported functions in thymocyte development and DNA damage responses. However, the role of PP4 in T cell immunity has not been thoroughly investigated. In this report, our data showed that T cell-specific ablation of PP4 resulted in defective adaptive immunity, impaired T cell homeostatic expansion, and inefficient T cell proliferation. This hypo-proliferation was associated with a partial G1-S cell cycle arrest, enhanced transcriptions of CDK inhibitors and elevated activation of AMPK. In addition, resveratrol, a known AMPK activator, induced similar G1-S arrests, while lentivirally-transduced WT or constitutively-active AMPKα1 retarded the proliferation of WT T cells. Further investigations showed that PP4 co-immunoprecipitated with AMPKα1, and the over-expression of PP4 inhibited AMPK phosphorylation, thereby implicating PP4 for the negative regulation of AMPK. In summary, our results indicate that PP4 is an essential modulator for T cell proliferation and immune responses; they further suggest a potential link between PP4 functions, AMPK activation and G1-S arrest in activated T cells.

LKB1 expression reverses the tumorigenicity of L02 cells

The tumor-suppressor liver kinase B1 (LKB1), a highly conserved and ubiquitously expressed protein kinase, plays a critical role in tumorigenesis. In the present study, we revealed that human hepatic L02 cells had severely impaired endogenous LKB1 expression as gauged by western blot, northern blot and RT-PCR analyses. Stable ectopic expression of LKB1 in L02 cells resulted in decreased cell growth, hypophosphorylation of Rb, and marked attenuation of colony formation on soft agar. Inoculation of L02 cells into immunocompromised mice resulted in the development of subcutaneous tumors, which could be completely abrogated by ectopic LKB1 expression. The tumors that formed in the mouse model recapitulated the histopathological features of hepatocellular carcinoma under the microscope. Our results jointly suggest that severely compromised endogenous LKB1 expression in the L02 cell line may confer to L02 cells tumor-initiating capacities in vivo and in vitro, and ectopic LKB1 expression antagonizes the tumorigenic properties of L02 cells. Our findings imply that caution may be needed to interpret the results obtained on the widely used human hepatic L02 cell line. The L02 cell line may be a new model to define the cellular mechanisms of liver transformation, and to unravel the molecular mechanisms underlying the growth suppressive effect of LKB1.

Role of the LKB1/AMPK pathway in tumor invasion and metastasis of cancer cells (Review)

Liver kinase B1 (LKB1), also known as serine/threo-nine kinase 11 (STK11), is a tumor suppressor that is inactivated in Peutz-Jeghers familial cancer syndrome. LKB1 phosphorylates and activates AMP-activated protein kinase (AMPK), which negatively regulates cancer cell proliferation and metabolism. However, recent evidence demonstrates that the LKB1/AMPK pathway is involved in the process of tumor invasion and migration, which is an important hallmark of carcinoma progression to higher pathological grades of malignancy. This review focuses on the function of the LKB1/AMPK pathway in the invasion and migration of cancer cells and provides an overview of therapeutic strategies aimed at this pathway in malignant tumors.

Epithelial morphological reversion drives Profilin-1-induced elevation of p27(kip1) in mesenchymal triple-negative human breast cancer cells through AMP-activated protein kinase activation

Profilin-1 (Pfn1) is an important regulator of actin polymerization that is downregulated in human breast cancer. Previous studies have shown Pfn1 has a tumor-suppressive effect on mesenchymal-like triple-negative breast cancer cells, and Pfn1-induced growth suppression is partly mediated by upregulation of cell-cycle inhibitor p27(kip1) (p27). In this study, we demonstrate that Pfn1 overexpression leads to accumulation of p27 through promoting AMPK activation and AMPK-dependent phosphorylation of p27 on T198 residue, a post-translational modification that leads to increased protein stabilization of p27. This pathway is mediated by Pfn1-induced epithelial morphological reversion of mesenchymal breast cancer through cadherin-mediated restoration of adherens junctions. These findings not only elucidate a potential mechanism of how Pfn1 may inhibit proliferation of mesenchymal breast cancer cells, but also highlight a novel pathway of cadherin-mediated p27 induction and therefore cell-cycle control in cells.

Benzyl isothiocyanate induces apoptosis of hepatocarcinoma cells

AIM: To investigate the influence of benzyl isothiocyanate (BITC) on apoptosis of hepatoma carcinoma cell lines HLE and Bel-7402 in vitro, and to explore the possible mechanism involved.

METHODS: After HLE and Bel-7402 cells were treated with an optimal concentration of BITC for 24 h, cell proliferation was tested by MTT assay, the morphology of apoptotic hepatoma cells was observed after DAPI staining, the enzymatic activity of caspase 3 was assayed using Caspase3 Activity Assay Kit, and expression of caspase 8, caspase 3 and cell cycle related protein cyclin D1 were detected by Western blot.

RESULTS: MTT analysis showed that BITC had an obvious inhibitory effect on the proliferation of hepatoma cells. The growth rates of HLE and Bel-7402 cells treated with 40 µmol/L BITC were 71.56% and 78.09% (P < 0.05 vs control groups), respectively, and the growth rates of HLE and Bel-7402 cells treated with 80 µmol/BITC were 32.91% and 53.06% (P < 0.01 vs control groups), respectively. Hepatoma cells treated with BITC tended to showed characteristic morphological changes of apoptosis. BITC treatment elevated the activity of caspase 3 in hepatoma cells, stimulated the expression of caspase 3 and caspase 8, but inhibited cyclin D1 expression.

CONCLUSION: BITC induces apoptosis of hepatoma cells possibly by activating the caspase signal pathway and inhibiting cell cycle progression.