Improved Therapeutic Effect of Puerarin-Encapsulated PEG-PLGA Nanoparticle on an In Vitro Cerebral Infarction Model

This study was to explore the therapeutic effect and mechanism of puerarin (PUE) combined with PEGylated nanoparticles on a rat cerebral infarction cell model. In this context, PEG-PLGA/PUE nanoparticles were prepared by the thin-film hydration method, and the toxicity of PEG-PLGA/PUE nanoparticles to brain capillary endothelial cell (BCEC) was detected by MTT. The BCEC/TF cell model was obtained by induction of BCEC cells with TNF-α. The BCEC/TF cell model was identified by immunofluorescence; the protein expression was detected by western blotting; the expression level of miR-424 in cells was measured by RT-qPCR; the targeting relationship between miR-424 and PDCD4 was confirmed by dual-luciferase reporter assay. We found that PEG-PLGA/PUE nanoparticles prepared by the thin-film hydration method had uniform particle size, regular shape, and good stability and were not toxic to cells. The vWF was widely expressed in the cytoplasm in BCECs. The BCEC/TF cell model was obtained after TNF-α treatment, and tissue factor (TF) was widely expressed on the cell membrane of BCEC/TF cells. Furthermore, it was observed that the PEG-PLGA/PUE nanoparticles showed better therapeutic effect on the BCEC/TF cell model than PUE. PEG-PLGA/PUE nanoparticles and PUE inhibited the expression of PDCD4 protein by increasing the expression of miR-424 in BCEC/TF cells. In summary, the therapeutic effect of PEG-PLGA/PUE nanoparticles on the in vitro cell model of cerebral infarction is better than that of PUE. Moreover, PEG-PLGA/PUE inhibits the expression of PDCD4 protein by lowering the expression level of miR-424 in cells, thereby reducing the hazard of cerebral infarction.

Degradation of the Tumor Suppressor PDCD4 Is Impaired by the Suppression of p62/SQSTM1 and Autophagy

PDCD4 (programmed cell death 4) is a tumor suppressor that plays a crucial role in multiple cellular functions, such as the control of protein synthesis and transcriptional control of some genes, the inhibition of cancer invasion and metastasis. The expression of this protein is controlled by synthesis, such as via transcription and translation, and degradation by the ubiquitin-proteasome system. The mitogens, known as tumor promotors, EGF (epidermal growth factor) and TPA (12-O-tetradecanoylphorbol-13-acetate) stimulate the degradation of PDCD4 protein. However, the whole picture of PDCD4 degradation mechanisms is still unclear, we therefore investigated the relationship between PDCD4 and autophagy. The proteasome inhibitor MG132 and the autophagy inhibitor bafilomycin A1 were found to upregulate the PDCD4 levels. PDCD4 protein levels increased synergistically in the presence of both inhibitors. Knockdown of p62/SQSTM1 (sequestosome-1), a polyubiquitin binding partner, also upregulated the PDCD4 levels. P62 and LC3 (microtubule-associated protein 1A/1B-light chain 3)-II were co-immunoprecipitated by an anti-PDCD4 antibody. Colocalization particles of PDCD4, p62 and the autophagosome marker LC3 were observed and the colocalization areas increased in the presence of autophagy and/or proteasome inhibitor(s) in Huh7 cells. In ATG (autophagy related) 5-deficient Huh7 cells in which autophagy was impaired, the PDCD4 levels were increased at the basal levels and upregulated in the presence of autophagy inhibitors. Based on the above findings, we concluded that after phosphorylation in the degron and ubiquitination, PDCD4 is degraded by both the proteasome and autophagy systems.

Control Mechanisms of the Tumor Suppressor PDCD4: Expression and Functions

PDCD4 is a novel tumor suppressor to show multi-functions inhibiting cell growth, tumor invasion, metastasis, and inducing apoptosis. PDCD4 protein binds to the translation initiation factor eIF4A, some transcription factors, and many other factors and modulates the function of the binding partners. PDCD4 downregulation stimulates and PDCD4 upregulation inhibits the TPA-induced transformation of cells. However, PDCD4 gene mutations have not been found in tumor cells but gene expression was post transcriptionally downregulated by micro environmental factors such as growth factors and interleukins. In this review, we focus on the suppression mechanisms of PDCD4 protein that is induced by the tumor promotors EGF and TPA, and in the inflammatory conditions. PDCD4-protein is phosphorylated at 2 serines in the SCFβTRCP ubiquitin ligase binding sequences via EGF and/or TPA induced signaling pathway, ubiquitinated, by the ubiquitin ligase and degraded in the proteasome system. The PDCD4 protein synthesis is inhibited by microRNAs including miR21.

The expression and clinical significance of PDCD4 and Her-2 in human gastric cancer

To investigate the correlation and clinical significance between programmed cell death factor 4 (PDCD4) and epidermal growth factor receptor 2 (Her-2) expressions and clinicopathological parameters in patients with gastric cancer, a total of 65 cases of gastric cancer and the corresponding normal mucosa with PDCD4 and Her-2 protein expressions were detected by SP immunohistochemical staining, and 50 cases of gastric cancer and the corresponding normal mucosa with PDCD4 and Her-2 protein expression quantities were detected by Western blot, in order to analyze the relationship between the positive expressions of PDCD4 and Her-2 protein and the clinicopathological features of patients with gastric cancer. The results showed that the positive rate of PDCD4 protein expression in gastric cancer tissues was 7.7%, which was significantly lower than that in the corresponding normal tissues, that is, 77.5% ( P < 0.05); the positive rate of Her-2 expression was 41.5%, which was significantly higher than that of the corresponding normal tissues, which is 2.5% ( P < 0.05). The Western blot test showed that the expression of PDCD4 protein in gastric cancer was 0.3105 ± 0.0073, which was significantly lower than that in the corresponding normal tissues, that is, 0.9428 ± 0.0127 ( P < 0.05); the expression level of Her-2 protein in gastric cancer tissues was 0.9428 ± 0.0127, which was significantly higher than that of the corresponding normal mucosa, which is 0.2054 ± 0.0264 ( P < 0.05). The positive expressions of PDCD4 (5/65) and Her-2 (27/65) were significantly correlated with the differentiation degrees and TNM stages of gastric cancer ( P < 0.05). However, no significant correlation can be observed from Table 2 ( P > 0.05), regarding sex, age, tumor size, and lymph node metastasis. Our research claimed that PDCD4 and Her-2 may play an important role in the invasion and metastasis of gastric cancer, which has a negative correlation with biological behaviors of gastric cancer. The low expression of PDCD4 and the high expression of Her-2 in gastric cancer may promote the occurrence and progression of cancer. The PDCD4 and Her-2 test can be used as an index to evaluate the malignant biological behaviors of gastric cancer and prognosis, and provide a theoretical basis for targeted therapy.

A microRNA expression signature of osteoclastogenesis

MicroRNAs (miRs) are small noncoding RNAs that principally function in the spatiotemporal regulation of protein translation in animal cells. Although emerging evidence suggests that some miRs play important roles in osteoblastogenesis and skeletal homeostasis, much less is known in osteoclastogenesis. Here, we show that receptor activator of nuclear factor κB ligand (RANKL)–induced osteoclastogenesis is mediated by miR-21. MiR-21 was identified as an miR expression signature of RANKL-induced osteoclastogenesis that down-regulates programmed cell death 4 (PDCD4) protein levels. Diminished PDCD4 removes a repression from c-Fos, a critical transcription factor for osteoclastogenesis and osteoclast-specific downstream target genes. In addition, RANKL-induced c-Fos up-regulates miR-21 gene expression. Bone marrow–derived monocyte/macrophage precursors deficient of DiGeorge syndrome critical region gene 8, an RNA binding protein associated with miR biogenesis, and Dicer, an endoribonuclease in the RNaseIII family associated with miR biogenesis, possessed significantly decreased miR-21 levels and increased PDCD4 protein levels so that RANKL-induced osteoclastogenesis was impaired in those cells. However, forced expression of miR-21 rescued osteoclast development because of down-regulation of PDCD4 protein expression levels. Thus, our studies provide a new molecular mechanism, including a positive feedback loop of c-Fos/miR-21/PDCD4, regulating osteoclastogenesis.