α-SMA-Cre-mediated excision of PDK1 reveals an essential role of PDK1 in regulating morphology of cardiomyocyte and tumor progression in tissue microenvironment

Master kinase PDK1 in tumorigenesis

3-phosphoinositide-dependent protein kinase 1 (PDK1) is considered as master kinase regulating AGC kinase family members such as AKT, SGK, PLK, S6K and RSK. Although autophosphorylation regulates PDK1 activity, accumulating evidence suggests that PDK1 is manipulated by many other mechanisms, including S6K-mediated phosphorylation, and the E3 ligase SPOP-mediated ubiquitination and degradation. Dysregulation of these upstream regulators or downstream signals involves in cancer development, as PDK1 regulating cell growth, metastasis, invasion, apoptosis and survival time. Meanwhile, overexpression of PDK1 is also exposed in a plethora of cancers, whereas inhibition of PDK1 reduces cell size and inhibits tumor growth and progression. More importantly, PDK1 also modulates the tumor microenvironments and markedly influences tumor immunotherapies. In summary, we comprehensively summarize the downstream signals, upstream regulators, mouse models, inhibitors, tumor microenvironment and clinical treatments for PDK1, and highlight PDK1 as a potential cancer therapeutic target.

Dioscin ameliorates doxorubicin-induced heart failure via inhibiting autophagy and apoptosis by controlling the PDK1-mediated Akt/mTOR signaling pathway

Heart failure (HF) is a disease with high mortality and morbidity rate. Autophagy is critically implicated in HF progression. The current research was designed to investigate the function of Dioscin on oxidative stress, autophagy, and apoptosis in HF. In this study, doxorubicin (Dox) was employed to induce HF model and HL-1 cell damage model. Echocardiography implied that Dioscin could dramatically relieve heart function in vivo. Western blotting determined that Dioscin treatment reversed the promotive effect of autophagy caused by Dox through modulating levels of key autophagy-associated molecules, including Atg5 and Beclin1. Dioscin also impaired apoptosis by regulating apoptosis-related protein, including Bcl-2 and cleaved caspase-3 following Dox treatment in vivo and in vitro. Furthermore, the impacts of Dioscin were mediated by upregulation of PDK1-mediated Akt/mTOR signaling. The mTOR inhibitor (rapamycin) could counteract the therapeutic impact of Dioscin in vitro. Taken together, Dioscin could relieve cardiac function through blocking apoptosis and autophagy by activating the PDK1-elicited Akt/mTOR pathway.

Activation of long-non-coding RNA NEAT1 sponging microRNA-147 inhibits radiation damage by targeting PDPK1 in troxerutin radioprotection

A better understanding of the molecular mechanism involving the lncRNA-miRNA-mRNA network underlying radiation damage can be beneficial for radioprotection. This study was designed to investigate the potential role of lncRNA NEAT1, miR-147 and Phosphoinositide Dependent Protein Kinase 1 (PDPK1) interaction in radioprotection by troxerutin (TRT). We first demonstrated that NEAT1 sponged miR-147, and PDPK1 mRNA was the primary target of miR-147. In the cells, the NEAT1 and PDPK1 levels were downregulated after the radiation but increased after the treatment with TRT. The miR-147 level was significantly induced by radiation and inhibited by TRT. NEAT1 negatively regulated the expression of miR-147, whereas miR-47 targeted PDPK1 to downregulate its expression. In radioprotection, TRT effectively upregulated NEAT1 to inhibit miR-147 and to upregulate PDPK1. We concluded that TRT could promote radioprotection by stimulating NEAT1 to upregulate PDPK1 expression by suppressing miR-147. NEAT1 could be a critical therapeutic target of radiation damage.

Long noncoding Mirt2 reduces apoptosis to alleviate myocardial infarction through regulation of the miR-764/PDK1 axis

Acute myocardial infarction (AMI) is a common clinical cardiovascular disease, which is the leading cause of death and disability worldwide. Abnormal expression of long noncoding RNAs (lncRNA) is reported to be related to myocardial dysfunctions such as myocardial infarction (MI). In this study, we aimed to investigate the role of lncRNA myocardial infarction-related transcription factors 2 (Mirt2) in AMI and the underlying molecular mechanisms in vivo and in vitro. In vivo AMI model was established by occlusion of the left anterior descending coronary artery. Rats were randomly divided into two groups (five rats per group): the sham group and the AMI group. H9c2 cells were cultured under hypoxia for 4 h and then cultured under normoxia to establish the in vitro hypoxia reoxygenation (H/R) model. Our study shows that the myocardial infarct size and the apoptosis in AMI rats were both significantly increased, indicating that the AMI rat model was successfully established. Additionally, the levels of Mirt2 in AMI rats were increased significantly. Knockdown of Mirt2 by shRNA (shMirt2) had no significant effect on apoptosis and MI in sham rats, but significantly promoted apoptosis and MI in AMI rats. In vitro experiments showed that shMirt2 significantly decreased the level of Mirt2 in H9c2 cells and H9c2 cells treated with H/R. It is worth noting that shMirt2 had no significant effect on H9c2 cells, but significantly increased the levels of oxidative stress markers (malondialdehyde and lactate dehydrogenase), and also increased the number of apoptosis of H/R-treated H9c2 cells. Further mechanistic analysis showed that Mirt2 could protect MI and apoptosis in AMI rats by competitively adsorbing miR-764 and reducing the inhibitory effect of miR-764 on 3-phosphoinositide-dependent kinase 1 (PDK1). More importantly, after overexpression of Mirt2, MI and apoptosis were significantly improved in AMI rats, indicating that Mirt2 showed a protective effect in AMI rats. In summary, these findings suggest that that Mirt2 participated in the regulation of MI through the miR-764/PDK1 axis. Therefore, the current findings provide a theoretical basis for the diagnosis and treatment of clinical MI with changes in Mirt2 levels.

Effects of inhibiting PDK‑1 expression in bone marrow mesenchymal stem cells on osteoblast differentiation in vitro

Osteoblasts are the main functional cells in bone formation, which are responsible for the synthesis, secretion and mineralization of bone matrix. The PI3K/AKT signaling pathway is strongly associated with the differentiation and survival of osteoblasts. The 3-phosphoinositide-dependent protein kinase-1 (PDK-1) protein is considered the master upstream lipid kinase of the PI3K/AKT cascade. The present study aimed to investigate the role of PDK-1 in the process of mouse osteoblast differentiation in vitro. In the BX-912 group, BX-912, a specific inhibitor of PDK-1, was added to osteoblast induction medium (OBM) to treat bone marrow mesenchymal stem cells (BMSCs), whereas the control group was treated with OBM alone. Homozygote PDK1^flox/flox mice were designed and generated, and were used to obtain BMSCs^{PDK1flox/flox}. Subsequently, an adenovirus containing Cre recombinase enzyme (pHBAd-cre-EGFP) was used to disrupt the PDK-1 gene in BMSCs^{PDK1flox/flox}; this served as the pHBAd-cre-EGFP group and the efficiency of the disruption was verified. Western blot analysis demonstrated that the protein expression levels of phosphorylated (p)-PDK1 and p-AKT were gradually increased during the osteoblast differentiation process. Notably, BX-912 treatment and disruption of the PDK-1 gene with pHBAd-cre-EGFP effectively reduced the number of alkaline phosphatase (ALP)-positive cells and the optical density value of ALP activity, as well as the formation of cell mineralization. The mRNA expression levels of PDK-1 in the pHBAd-cre-EGFP group were significantly downregulated compared with those in the empty vector virus group on days 3–7. The mRNA expression levels of the osteoblast-related genes RUNX2, osteocalcin and collagen I were significantly decreased in the BX-912 and pHBAd-cre-EGFP groups on days 7 and 21 compared with those in the control and empty vector virus groups. Overall, the results indicated that BX-912 and disruption of the PDK-1 gene in vitro significantly inhibited the differentiation and maturation of osteoblasts. These experimental results provided an experimental and theoretical basis for the role of PDK-1 in osteoblasts.

Microenvironment in Cardiac Tumor Development: What Lies Beyond the Event Horizon?

Cardiac tumors are found in less than 1% of adult and pediatric autopsies. More than three-fourths of primary cardiac neoplasms are benign, with myxomas and rhabdomyomas being the most common cardiac tumors seen in adults and children, respectively. Primary malignant cardiac tumors are extremely rare, whereas metastatic lesions can be seen in approximately 8% of patients dying from cancer. Attempting to understand why the heart is so resistant to carcinogenesis and which fail-safe mechanisms malfunction when cardiac tumors do develop is particularly challenging considering the rarity of these tumors and the fact that when relevant clinical studies are published, they rarely focus on molecular pathogenesis. Apart from cancer cells, solid tumors are comprised of a concoction of noncancerous cells, and extracellular matrix constituents, which along with pH and oxygen levels jointly constitute the so-called tumor microenvironment (TME). In the present chapter, we explore mechanisms through which TME may influence cardiac carcinogenesis.

A new and important relationship between miRNA-147a and PDPK1 in radiotherapy

It was found that the expression level of miR-147a was significantly increased and the pathway of PI3K/AKT was dramatically inhibited after radiation. In view of the relationship between miRNA and target genes, we put forward the question, what is the relationship between PI3K/AKT and miR-147a? In order to find the answer to the question, we used bioinformatics techniques to analyze the relationship between miR-147 (a or b) and PI3K/AKT signaling pathway. miR-147a overexpression plasmid and PDPK1 3'UTR luciferase reporter gene plasmid were constructed. Dual luciferase reporter gene system validation experiments were carried out on miR-147a and PDPK1 relationship. The verification experiments were also carried out. Bioinformatics analysis showed that there is a miR-147a binding site in the non-coding region (3'UTR) of PDPK1. In the experimental groups transfected with wild type PDPK1 gene of 3'UTR plasmid, the luciferase activity decreased (or increased) significantly in miR-147a (or inhibitor) group compared with miR-NC (or anti-miR-NC); There was no significant difference between the miR-147a group (or inhibitor) and the miR-NC group (or anti-miR-NC) in the transfection of PDPK1-3'UTR-Mut gene vector. PDPK1 was a target gene for direct regulation of miR-147a downstream. Verifying test results showed that the expression of PDPK1 mRNA and protein was reduced after overexpression of miR-147a, which was up-regulated after silencing miR-147a in TC, and V79 cells. These results suggest that miR-147a could be involved in the regulation of PDPK1 transcription by binding to the target site in PDPK1 mRNA 3'UTR, and then regulated AKT.