Downregulation of LKB1 suppresses Stat3 activity to promote the proliferation of esophageal carcinoma cells

STK11 loss leads to YAP1-mediated transcriptional activation in human KRAS-driven lung adenocarcinoma cell lines

Serine Threonine Kinase 11 (STK11) loss of function (LoF) correlates with anti-PD-1 therapy resistance in patients with KRAS-driven lung adenocarcinoma (LUAD). The molecular mechanisms governing this observation remain unclear and represent a critical outstanding question in the field of lung oncology. As an initial approach to understand this phenomenon, we knocked-out (KO) STK11 in multiple KRAS-driven, STK11-competent human LUAD cell lines and performed whole transcriptome analyses to identify STK11-loss-dependent differential gene expression. Subsequent pathway enrichment studies highlighted activation of the HIPPO/YAP1 signaling axis, along with the induction of numerous tumor-intrinsic cytokines. To validate that YAP1-mediated transcriptional activation occurs in response to STK11 loss, we pursued YAP1 perturbation as a strategy to restore an STK11-competent gene expression profile in STK11-KO LUAD cell lines. Together, our data link STK11 loss with YAP1-mediated transcriptional activation, including the upregulation of immune-evasion promoting cytokines IL-6, CXCL8 and CXCL2. Further, our results raise the intriguing possibility that YAP1 antagonism may represent a therapeutic approach to counter anti-PD-1 therapy resistance in STK11-null, KRAS-driven LUADs by modulating tumor-intrinsic gene expression to promote a "hot" tumor immune microenvironment.

Role of Protein Kinases in Hedgehog Pathway Control and Implications for Cancer Therapy

Hedgehog (HH) signaling is an evolutionarily conserved pathway that is crucial for growth and tissue patterning during embryonic development. It is mostly quiescent in the adult, where it regulates tissue homeostasis and stem cell behavior. Aberrant reactivation of HH signaling has been associated to several types of cancer, including those in the skin, brain, prostate, breast and hematological malignancies. Activation of the canonical HH signaling is triggered by binding of HH ligand to the twelve-transmembrane protein PATCHED. The binding releases the inhibition of the seven-transmembrane protein SMOOTHENED (SMO), leading to its phosphorylation and activation. Hence, SMO activates the transcriptional effectors of the HH signaling, that belong to the GLI family of transcription factors, acting through a not completely elucidated intracellular signaling cascade. Work from the last few years has shown that protein kinases phosphorylate several core components of the HH signaling, including SMO and the three GLI proteins, acting as powerful regulatory mechanisms to fine tune HH signaling activities. In this review, we will focus on the mechanistic influence of protein kinases on HH signaling transduction. We will also discuss the functional consequences of this regulation and the possible implications for cancer therapy.

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.

Down-regulation of STAT3 induces the apoptosis and G1 cell cycle arrest in esophageal carcinoma ECA109 cells

Background

Signal transducer and activator of transcription 3 (STAT3) is persistently activated in a wide variety of epithelial cancers. Aberrant activity of STAT3 correlates with tumor growth, invasion and metastasis, which makes it a potential therapeutic target of cancer. To explore the biological role of STAT3 in esophageal cancer, we used small hairpin RNA to knockdown the expression of the STAT3 gene in the esophageal carcinoma ECA109 cell line and the cell apoptosis, cell cycle and cell migration were investigated.

Methods

The cell apoptosis was tested using DNA ladder, mitochondrial membrane potential assay, TUNEL assay, annexin V-PI staining. Cell cycle phases were estimated using flow cytometry analysis. The mRNA and proteins related to apoptosis and cell cycle were examined by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot, respectively. And cell migration was investigated by in vitro Transwell assay. The data were analyzed with two-sample Student’s t test and ANOVA followed by the LSD post hoc test.

Results

Our results showed that knockdown of STAT3 in ECA109 cells induced noticeable apoptotic morphological changes like cell shrinkage, apoptotic vacuoles, membrane blebbing time-dependently. In addition, DNA ladder, TUNEL assay, Annexin V-PI staining and declined level of cleaved Caspase-3 indicated that down-regulation of STAT3 could induce apoptosis in ECA109 cells. Flow cytometry analysis displayed the induction of G1-phase cell cycle arrest of ECA109 cells by STAT3 decreasing, consistent with the descend of c-Myc and cyclin D1 in protein levels. Furthermore, STAT3 knockdown suppressed the expression of matrix metalloproteinases-9, sushi domain containing 2 and urokinase plasminogen activator in ECA109 cells and inhibited cell migration ability.

Conclusions

Knockdown of STAT3 could induce the apoptosis and G1 cell cycle arrest in esophageal carcinoma ECA109 cells, and inhibit the migration ability of cells as well.

LKB1 inactivation occurs in a subset of esophageal adenocarcinomas and is sufficient to drive tumor cell proliferation

BACKGROUND

The incidence of esophageal adenocarcinoma (EAC) has increased over the last several decades. Apart from mutations in TP53 gene, there are little data on genetic drivers of EAC. Liver kinase B1 (LKB1) has emerged as a multifunctional tumor suppressor regulating cell growth, differentiation, and metabolism. Somatic inactivation of LKB1 has been described in several tumor types; however, whether LKB1 inactivation has a role in EAC is unknown. Here we analyzed patient tumors to assess the prevalence of LKB1 loss in EAC.

METHODS

Chromosomal deletion and expression of LKB1 in EAC were investigated using publicly available genomic data. Protein expression was assessed by immunohistochemistry (IHC) analysis for LKB1 in a tissue microarray (TMA) containing esophageal tumor specimens, including EAC. LKB1 was suppressed in EAC cells to determine the effects on cell growth in vitro.

RESULTS

Analysis of EAC data in The Cancer Genome Atlas dataset revealed significant deletion of chromosome 19p13.3, containing the LKB1 gene locus. Single copy loss (shallow deletion) of LKB1 was present in 58% of EAC samples. Expression of LKB1 was significantly lower in EAC tumors compared with normal esophagus. IHC analysis showed reduced LKB1 protein expression in EAC. Suppression of LKB1 was sufficient to enhance EAC cell growth in vitro.

CONCLUSIONS

Our data suggest that inactivation of LKB1 frequently occurs in EAC. Based on the reported oncogenic effects of LKB1 inactivation, our data indicate that LKB1 loss may play a significant role in EAC tumorigenesis, and point to the need for future studies.

Synergistic effects of eukaryotic co-expression plasmid-based STAT3-specific siRNA and LKB1 on ovarian cancer in vitro and in vivo

The signal transducer and activator of transcription 3 (STAT3) are ideal targets for ovarian cancer. Previous studies showed that downregulation of STAT3 using specific short hairpin RNAs (shRNA) can significantly reduce ovarian tumor growth. However, RNA interference does not fully ablate target gene expression due to idiosyncrasies associated with shRNAs and their targets. To enhance the therapeutic efficacy of STAT3-specific shRNA, we employed a combinatorial expression of STAT3-specific shRNA and liver kinase B1 (LKB1), a tumor suppressor. Thus, the LKB1 coding sequences and STAT3-specific shRNAs were constructed in a eukaryotic co-expression plasmid pCDNA3.1, and then transfected into ovarian cancer cells to evaluate the synergistic effects of this combination on anticancer activity and explore the relevant molecular mechanisms. Co-expression of STAT3‑specific siRNA and LKB1 (pSi-STAT3-LKB1) synergistically inhibited ovarian cancer cell growth, invasion and migration, induced cell apoptosis and arrested the cell cycle in vitro when compared with monotherapy. The results showed that the co-expression of plasmid pSi-STAT3-LKB1 inserted subcutaneously into ovarian tumor xenograft resulted in more significant inhibition of tumor growth. Further study showed that the synergistic anti-ovarian cancer effects of the co-expression of STAT3-specific siRNA and LKB1 may be associated with the upregulation of p-p53, p21 and downregulation of survivin, BCL-2 and cyclin D1. Results of the present study suggested that combined therapy with eukaryotic co-expression of the plasmid‑carrying STAT3-specific siRNA and LKB1 is a novel and efficient treatment strategy for human ovarian cancer.