Effects of inhibiting PDK­1 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 3­phosphoinositide­dependent protein kinase­1 (PDK­1) protein is considered the master upstream lipid kinase of the PI3K/AKT cascade. The present study aimed to investigate the role of PDK­1 in the process of mouse osteoblast differentiation in vitro. In the BX­912 group, BX­912, a specific inhibitor of PDK­1, 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 PDK1flox/flox mice were designed and generated, and were used to obtain BMSCsPDK1flox/flox. Subsequently, an adenovirus containing Cre recombinase enzyme (pHBAd­cre­EGFP) was used to disrupt the PDK­1 gene in BMSCsPDK1flox/flox; this served as the pHBAd­cre­EGFP group and the efficiency of the disruption was verified. Western blot analysis demonstrated that the protein expression levels of phosphorylated (p)­PDK1 and p­AKT were gradually increased during the osteoblast differentiation process. Notably, BX­912 treatment and disruption of the PDK­1 gene with pHBAd­cre­EGFP 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 PDK­1 in the pHBAd­cre­EGFP group were significantly downregulated compared with those in the empty vector virus group on days 3­7. The mRNA expression levels of the osteoblast­related genes RUNX2, osteocalcin and collagen I were significantly decreased in the BX­912 and pHBAd­cre­EGFP groups on days 7 and 21 compared with those in the control and empty vector virus groups. Overall, the results indicated that BX­912 and disruption of the PDK­1 gene in vitro significantly inhibited the differentiation and maturation of osteoblasts. These experimental results provided an experimental and theoretical basis for the role of PDK­1 in osteoblasts.

Low expression of PDK1 inhibits renal cell carcinoma cell proliferation, migration, invasion and epithelial mesenchymal transition through inhibition of the PI3K-PDK1-Akt pathway.

As the most commonly occurring form of primary renal tumor, renal cell carcinoma (RCC) is a malignancy accompanied by a high mortality rate. 3-phosphoinositide-dependent protein kinase 1 (PDK1) has been established as a protein target and generated considerable interest in both the pharmaceutical and academia industry. The aim of the current study was to investigate the effect of si-PDK1 on the RCC cell apoptosis, proliferation, migration, invasion and epithelial mesenchymal transition (EMT) in connection with the PI3K-PDK1-Akt pathway. Microarray analysis from the GEO database was adopted to identify differentially expressed genes (DEGs) related to RCC, after which the positive expression of the PDK1 protein in tissue was determined accordingly. The optimal silencing si-RNA was subsequently selected and RCC cell lines 786-O and A498 were selected and transfected with either a si-PDK1 or activator of the PI3K-PDK1-Akt pathway for grouping purposes. The mRNA and protein expressions of PDK1, the PI3K-PDK1-Akt pathway-, EMT- and apoptosis-related genes were then evaluated. The effect of si-PDK1 on cell proliferation, apoptosis, invasion and migration was then analyzed. Through microarray analysis of GSE6344, GSE53757, GSE14762 and GSE781, PDK1 was examined. PDK1 was determined to be highly expressed in RCC tissues. Si-PDK1 exhibited marked reductions in relation to the mRNA and protein expression of PDK1, PI3K, AKT as well as Vimentin while elevated mRNA and protein expressions of E-cadherin were detected, which ultimately suggested that cell migration, proliferation and invasion had been inhibited coupled with enhanced levels of cell apoptosis. While a notable observation was made highlighting that the PI3K-PDK1-Akt pathway antagonized the effect of PDK1 silencing. Taken together, the key observations of this study provide evidence suggesting that high expressions of PDK1 are found in RCC, while highlighting that silencing PDK1 could inhibit RCC cell proliferation, migration, invasion and EMT by repressing the PI3K-PDK1-Akt pathway.

miR-718 is involved in malignancy of papillary thyroid cancer through repression of PDPK1.

BACKGROUND: MicroRNAs bind the 3' untranslated regions (3'-UTRs) of mRNAs and thereby regulate gene expression post-transcriptionally and play an important role in cancer delvelopment. In the present study, we have explored the role of miR-718 in papillary thyroid cancer cell malignancy. MATERIALS/METHODS: Here we examined the miRNA expression in human papillary thyroid cancer by RT-PCR. Luciferase activity, RT-PCR and western blot assays were used to confirmed the target of miRNA. MTT, colony formation, transwell, glucose consumption and lactate production assays were performed to analyze papillary thyroid cancer cell function. Western blot for signaling proteins was used to reveal the mechanism. RESULTS: We first determined that miR-718 mRNA expression levels in PTC samples were reduced. The 3'-UTR of 3-Phosphoinositide Dependent Protein Kinase 1 (PDPK1) was then identified as a target of miR-718. Luciferase assays showed that miR-718 does in fact bind the wild-type PDPK1 3'-UTR. We assessed the effects of miR-718 on p-Akt, Akt, p-mTOR and mTOR expression. We determined that miR-718 negatively regulates their levels, respectively, of Akt-mTOR pathway components. We then assessed the effects of miR-718 on PTC cell behavior. The results revealed that miR-718 negatively regulates PTC cell proliferation, migration, and invasion. In addition, miR-718 was found to inhibit cell glucose metabolism, likely through the Akt-mTOR pathway. Finally, PDPK1 could rescue PTC cell inhibition induced by miR-718. CONCLUSIONS: The present study strongly suggests that miR-718 inhibits PTC cell proliferation, metastasis, and glucose metabolism by negatively regulating the Akt-mTOR signaling pathway.

PDK1 promotes the inflammatory progress of fibroblast-like synoviocytes by phosphorylating RSK2.

This study investigated the role of PDK1 in inflammatory response which is initiated by TNF-α and analyzed the association between PDK1 and RSK2. TNF-α were added into MH7A cells to induce inflammation condition. Through overexpressing or suppressing PDK1 in MH7A cells, the role of PDK1 in cell invasiveness and inflammatory factors was determined. Levels of MMPs protein and inflammatory cytokines were assessed with PDK1 siRNA and TNF-α treatment. Inhibition of RSK2 was used to investigate the function of RSK2 on PDK1-induced inflammation. The phosphorylation of RSK2 was detected when PDK1 was inhibited. Luciferase reporter assay was performed to detect the transcriptional activity of NF-κB. We found highly expressed PDK1 could promote cell invasion and secretion of IL-1ß and IL-6 in MH7A cells. Inhibition of RSK2 reduced the PDK1-induced cell invasion and cytokines secretion in MH7A cells. In response to TNF-α, PDK1 could phosphorylate RSK2 and activated RSK2, then promoting the activation of NF-κB. This may be a possible therapeutic option of rheumatoid arthritis.

MiR-375 promotes redifferentiation of adult human ß cells expanded in vitro.

In-vitro expansion of ß cells from adult human pancreatic islets could provide abundant cells for cell replacement therapy of diabetes. However, proliferation of ß-cell-derived (BCD) cells is associated with dedifferentiation. Here we analyzed changes in microRNAs (miRNAs) during BCD cell dedifferentiation and identified miR-375 as one of the miRNAs greatly downregulated. We hypothesized that restoration of miR-375 expression in expanded BCD cells may contribute to their redifferentiation. Our findings demonstrate that overexpression of miR-375 alone leads to activation of ß-cell gene expression, reduced cell proliferation, and a switch from N-cadherin to E-cadherin expression, which characterizes mesenchymal-epithelial transition. These effects, which are reproducible in cells derived from multiple human donors, are likely mediated by repression of PDPK1 transcripts and indirect downregulation of GSK3 activity. These findings support an important role of miR-375 in regulation of human ß-cell phenotype, and suggest that miR-375 upregulation may facilitate the generation of functional insulin-producing cells following ex-vivo expansion of human islet cells.

Repression of phosphoinositide-dependent protein kinase 1 expression by ciglitazone via Egr-1 represents a new approach for inhibition of lung cancer cell growth.

BACKGROUND: Peroxisome proliferator-activated receptors gamma (PPARγ) ligands have been shown to inhibit the growth of non-small cell lung cancer (NSCLC) cells. However, the mechanisms underlying this effect remain incompletely elucidated. METHODS: Cell proliferation and apoptosis were measured by cell viability, MTT and caspase3/7 activity assays. Phosphorylation/protein expression and gene silence/overexpression of AMPKα, phosphoinositide-dependent protein kinase 1 (PDK1), Egr-1 and PPARγ were performed by Western blot and siRNA/transfection assays. Dual-Luciferase Reporter Kit was used to measure the PPAR response elements (PPRE) reporter and PDK1 promoter activities, and ChIP assay was used to detect the Egr-1 protein binding to the DNA site in the PDK1 gene promoter. RESULTS: We found that ciglitazone, one synthetic PPARγ ligand, inhibited growth and induced apoptosis of NSCLC cells through decreased expression of PDK1, which was not blocked by GW9662 (a specific PPARγ antagonist). Overexpression of PDK1 overcame the effect of ciglitazone on cell growth and caspase 3/7 activity. Ciglitazone increased the phosphorylation of AMPKα and c-Jun N-terminal kinase (JNK), and the inhibitor of AMPK (compound C), but not JNK (SP600125), reversed the effect of ciglitazone on PDK1 protein expression. Ciglitazone reduced PDK1 gene promoter activity, which was not observed in cells exposed to compound C, but not silenced of PPARγ siRNA. Combination of ciglitazone and metformin further reduced PDK1 expression and promoter activity. Furthermore, we showed that ciglitazone induced the protein expression of Egr-1, which was not observed in cells silencing of AMPKα. Moreover, silencing of Egr-1 abrogated the effect of ciglitazone on PDK1 promoter activity and cell growth. On the contrary, overexpression of Egr-1 enhanced the effect of ciglitazone on PDK1 gene promoter activity. ChIP assays demonstrated that ciglitazone induced Egr-1 protein bind to the specific DNA site in the PDK1 gene promoter. CONCLUSION: Collectively, our results demonstrate that ciglitazone inhibits PDK1 expression through AMPKα-mediated induction of Egr-1 and Egr-1 binding to the specific DNA site in the PDK1 gene promoter, which is independent of PPARγ. Activation of AMPKα by metformin enhances the effect of ciglitazone. In turn, this leads to inhibition of NSCLC cell proliferation.