Tumour suppressors: PTEN surprise

Thwarting PTEN Expression by siRNA Augments HL-60 Cell Differentiation to Neutrophil-Like Cells by DMSO and ATRA

Abnormal cell differentiation, in particular suppression of terminal cell differentiation, exists in all tumors. Therapeutic interventions to restore terminal differentiation ("differentiation therapy") are a very attractive way to treat cancer, especially leukemia. A variety of chemicals stimulates differentiation of leukemic cells, such as dimethyl sulfoxide (DMSO) and all-trans retinoic acid (ATRA). Tumor suppressor genes have a vital role in the gateway to terminal cell differentiation. In this study, we inhibited PTEN tumor suppressor gene expression by siRNA to investigate the effect of potentiating cell survival and inhibiting apoptosis on HL-60 cell differentiation by DMSO and ATRA. Our results show that PTEN siRNA increases HL-60 cell differentiation in the presence of DMSO and ATRA. At the same time, the presence of siRNA hampers accumulation of apoptotic cells during incubation. Our study suggests that manipulation of PTEN could hold promise for enhancing efficacy of differentiation therapy of acute myelogenous leukemia.

PTEN-Foxo1 signaling triggers HMGB1-mediated innate immune responses in acute lung injury

PTEN is a multifunctional phosphatase that regulates immune responses through a PI3K/Akt signaling cascade. HMGB1 plays an important role in the initiation of innate immune responses to induce acute lung injury (ALI). This study was designed to investigate the role of PTEN/Foxo1 signaling in the regulation of in vivo and in vitro innate immune responses in ALI. Using a mouse model of ALI, wild-type (WT) and myeloid-specific PTEN knockout (PTEN(M-KO)) mice were instilled with a recombinant HMGB1 (rHMGB1) or PBS. In some experiments, Foxo1 siRNA or non-specific siRNA was injected into mice 6 h prior to rHMGB1 instillation into lung. We found that rHMGB1 treatment in WT mice increased the expression of PTEN, Foxo1, TLR4, and NF-κB in alveolar macrophages from WT mice. However, macrophage-specific PTEN ablation resulted in reduced Foxo1 and TLR4 while increasing β-catenin (Ser552) and Akt (Ser473) phosphorylation in these cells. Knockdown of Foxo1 with siRNA administration in WT mice ameliorated lung injury and inhibited myeloperoxidase activity followed by rHMGB1 treatment, which was accompanied by decreased mRNA expression coding for TNF-α, IL-1β, MIP2, and IP-10. Moreover, Foxo1 knockdown inhibited the expression of TLR4-dependent IRF3 and IFN-β both in vitro and in vivo. These results demonstrate that PTEN/Foxo1 signaling is critical for triggering HMGB1-mediated innate TLR4 activation during ALI. By identifying the molecular signaling pathways within innate immune system, our studies provide the potential therapeutic targets for ALI.

HBx induced expression of alpha fetoprotein drives malignant transformation of liver cells

The development of hepatocellular carcinoma (HCC) is closely related to hepatitis B virus (HBV) infection, and HBV-X protein (HBx) plays a critical role in the malignant transformation of liver cells. HBx stimulates the expression of alpha fetoprotein (AFP) via restraining the transcription activity of P53 in the early stage of HCC genesis. Recently, studies have indicated that HBx preferentially promotes AFP expression during the malignant transformation of hepatic cells, and AFP accelerates the expression of malignant behavior related molecules through activating the phosphatidylinositol-3 kinase (PI3K)/protein kinas A (AKT) signaling pathway. These results suggest that AFP may be an important factor for HBx driven hepatocarcinogenesis. The discovery of novel function of AFP implicates that AFP can be used not only as a tumor marker for HBV-related HCC but also as a target for HCC therapy.

MicroRNA-21 regulates hTERT via PTEN in hypertrophic scar fibroblasts

BACKGROUND

As an important oncogenic miRNA, microRNA-21 (miR-21) is associated with various malignant diseases. However, the precise biological function of miR-21 and its molecular mechanism in hypertrophic scar fibroblast cells has not been fully elucidated.

METHODOLOGY/PRINCIPAL FINDINGS

Quantitative Real-Time PCR (qRT-PCR) analysis revealed significant upregulation of miR-21 in hypertrophic scar fibroblast cells compared with that in normal skin fibroblast cells. The effects of miR-21 were then assessed in MTT and apoptosis assays through in vitro transfection with a miR-21 mimic or inhibitor. Next, PTEN (phosphatase and tensin homologue deleted on chromosome ten) was identified as a target gene of miR-21 in hypertrophic scar fibroblast cells. Furthermore, Western-blot and qRT-PCR analyses revealed that miR-21 increased the expression of human telomerase reverse transcriptase (hTERT) via the PTEN/PI3K/AKT pathway. Introduction of PTEN cDNA led to a remarkable depletion of hTERT and PI3K/AKT at the protein level as well as inhibition of miR-21-induced proliferation. In addition, Western-blot and qRT-PCR analyses confirmed that hTERT was the downstream target of PTEN. Finally, miR-21 and PTEN RNA expression levels in hypertrophic scar tissue samples were examined. Immunohistochemistry assays revealed an inverse correlation between PTEN and hTERT levels in high miR-21 RNA expressing-hypertrophic scar tissues.

CONCLUSIONS/SIGNIFICANCE

These data indicate that miR-21 regulates hTERT expression via the PTEN/PI3K/AKT signaling pathway by directly targeting PTEN, therefore controlling hypertrophic scar fibroblast cell growth. MiR-21 may be a potential novel molecular target for the treatment of hypertrophic scarring.

The PTEN Long N-tail is intrinsically disordered: increased viability for PTEN therapy

Aberrant activation of the PI3K/Akt/mTOR pathway is observed in several cancers and hyper proliferative disorders. PTEN, a tumor suppressor gene, negatively regulates the PI3K/Akt/mTOR pathway. Inhibitors of various components of this pathway are currently being used for cancer therapy. However, the use of these small molecule inhibitors remains limited due to the presence of compensatory feedback loops within the pathway such that inhibition of one oncogenic molecule often results in the activation of another oncogenic molecule resulting in the development of chemoresistance. One novel strategy that has emerged as a means to circumvent the problem of feedback signaling is by activating tumor suppressor genes that abrogate oncogenic pathways and regress tumor growth. In this regard, a newly identified isoform of the PTEN protein shows promise for use in tumors with elevated PI3K/Akt/mTOR signaling. This isoform is a translational variant of PTEN, termed as PTEN Long, and has additional 173 amino acids at its N-terminus (N-173) than normal PTEN. The N-173 region is required for PTEN secretion and transport across the body. Given the potential of this N-173 region to act as a drug delivery system for PTEN, we herein analyze the structural properties of this region. This N-173 tail has a large intrinsically disordered region (IDR) and is composed of highly charged basic residues. Further, the region is enriched in potential linear binding motifs, protein-binding sites and post-translational modifications (PTMs) indicating its probable role in PTEN function and transport across cells. An extensive analysis of this region is warranted to better exploit its structural and biophysical peculiarities to drug discovery and drug delivery applications.

PTEN overexpression improves cisplatin-resistance of human ovarian cancer cells through upregulating KRT10 expression

Multi-drug resistance (MDR) is a common cause of the failure of chemotherapy in ovarian cancer. PTEN, a tumor suppressor gene, has been demonstrated to be able to reverse cisplatin-resistance in ovarian cancer cell line C13K. However, the downstream molecules of PTEN involved in the resistance-reversing effect have not been completely clarified. Therefore, we screened the downstream molecules of PTEN and studied their interactions in C13K ovarian cancer cells using a 3D culture model. Firstly, we constructed an ovarian cancer cell line stably expressing PTEN, C13K/PTEN. MTT assay showed that overexpression of PTEN enhanced the sensitivity of C13K cells to cisplatin, but not to paclitaxel. Then we examined the differently expressed proteins that interacted with PTEN in C13K/PTEN cells with or without cisplatin treatment by co-immunoprecipitation. KRT10 was identified as a differently expressed protein in cisplatin-treated C13K/PTEN cells. Further study confirmed that cisplatin could induce upregulation of KRT10 mRNA and protein in C13K/PTEN cells and there was a directly interaction between KRT10 and PTEN. Forced expression of KRT10 in C13K cells also enhanced cisplatin-induced proliferation inhibition and apoptosis of C13K cells. In addition, KRT10 siRNA blocked cisplatin-induced proliferation inhibition of C13K/PTEN cells. In conclusion, our data demonstrate that KRT10 is a downstream molecule of PTEN which improves cisplatin-resistance of ovarian cancer and forced KRT10 overexpression may also act as a therapeutic method for overcoming MDR in ovarian cancer.