MiR-200c suppresses TGF-β signaling and counteracts trastuzumab resistance and metastasis by targeting ZNF217 and ZEB1 in breast cancer

Resistance to trastuzumab and concomitantly distal metastasis are leading causes of mortality in HER2-positive breast cancers, the molecular basis of which remains largely unknown. Here, we generated trastuzumab-resistant breast cancer cells with increased tumorigenicity and invasiveness compared with parental cells, and observed robust epithelial-mesenchymal transition (EMT) and consistently elevated TGF-β signaling in these cells. MiR-200c, which was the most significantly downregulated miRNA in trastuzumab-resistant cells, restored trastuzumab sensitivity and suppressed invasion of breast cancer cells by concurrently targeting ZNF217, a transcriptional activator of TGF-β, and ZEB1, a known mediator of TGF-β signaling. Given the reported backward inhibition of miR-200c by ZEB1, ZNF217 also exerts a feedback suppression of miR-200c via TGF-β/ZEB1 signaling. Restoration of miR-200c, silencing of ZEB1 or ZNF217 or blockade of TGF-β signaling increased trastuzumab sensitivity and suppressed invasiveness of breast cancer cells. Therefore, our study unraveled nested regulatory circuits of miR-200c/ZEB1 and miR-200c/ZNF217/TGF-β/ZEB1 in synergistically promoting trastuzumab resistance and metastasis of breast cancer cells. These findings provide novel insights into the common role of EMT and related molecular machinery in mediating the malignant phenotypes of breast cancers.

Cancer gene therapy targeting cellular apoptosis machinery

The unraveling of cellular apoptosis machinery provides novel targets for cancer treatment, and gene therapy targeting this suicidal system has been corroborated to cause inflammation-free autonomous elimination of neoplastic cells. The apoptotic machinery can be targeted by introduction of a gene encoding an inducer, mediator or executioner of apoptotic cell death or by inhibition of anti-apoptotic gene expression. Strategies targeting cancer cells, which are achieved by selective gene delivery, specific gene expression or secretion of target proteins via genetic modification of autologous cells, dictate the outcome of apoptosis-based cancer gene therapy. Despite so far limited clinical success, gene therapy targeting the apoptotic machinery has great potential to benefit patients with threatening malignancies provided the availability of efficient and specific gene delivery and administration systems.

HER2 interacts with CD44 to up-regulate CXCR4 via epigenetic silencing of microRNA-139 in gastric cancer cells

BACKGROUND & AIMS

Human epidermal growth factor receptor 2 (HER2) (neu/ERBB2) is overexpressed on many types of cancer cells, including gastric cancer cells; HER2 overexpression has been associated with metastasis and poor prognosis. We investigated the mechanisms by which HER2 regulates cell migration and invasion.

METHODS

HER2 expression or activity was reduced in gastric cancer cell lines using small interfering RNAs or the monoclonal antibody, trastuzumab. We identified proteins that interact with HER2 or microRNAs (miRNAs) involved in HER2 signaling. We used various software programs to identify miRNAs that regulate factors in the HER2 signaling pathway. We analyzed expression patterns of these miRNAs in gastric cancer cell lines and tumor samples from patients.

RESULTS

We found that CD44 binds directly to HER2, which up-regulates the expression of metastasis-associated protein-1, induces deacetylation of histone H3 lysine 9, and suppresses transcription of microRNA139 (miR-139) to inhibit expression of its target gene, C-X-C chemokine receptor type 4 (CXCR4). Knockdown of HER2 and CD44 reduced invasive activity of cultured gastric cancer cells and suppressed tumor growth in nude mice. Lymph node metastasis was associated with high levels of HER2, CD44, and CXCR4, and reduced levels of miR-139 in human metastatic gastric tumors. Cultures of different types of metastatic cancer cells with histone deacetylase inhibitors and/or DNA methyltransferase resulted in up-regulation of miR-139.

CONCLUSIONS

HER2 interaction with CD44 up-regulates CXCR4 by inhibiting expression of miR-139, at the epigenetic level, in gastric cancer cells. These findings indicate how HER2 signaling might promote gastric tumor progression and metastasis.

Estrogen-induced dimerization and activation of ERα-fused caspase-8: artificial reversal of the estrogenic hormone effect in carcinogenesis

The cascade of caspase processing and activation is the core of apoptotic cell signaling. Initiator caspases are activated by adaptor-mediated clustering, which allows the intermolecular autoprocessing of the zymogens in close proximity. Caspase-8, the prototypical initiator critically involved in apoptosis induced by varied extrinsic stimuli, is physiologically recruited via a classical FasL/Fas/FADD pathway. Meanwhile, artificial models of caspase-8 activation have been proposed via inducible dimerization of a heterologous domain fused to the zymogen. Here, we describe the generation of a chimeric protein of caspase-8 and the ligand-binding domain (LBD) of estrogen receptor α (ERα), which dimerizes and undergoes autocleavage upon engagement by the ligand, estradiol. Breast cancer cells expressing this fusion protein exhibit apoptotic cell death in vitro and suppressed tumor growth in xenograft nude mice models in response to the administration of estrogen. Thus, the suicidal caspase-8/ERα-LBD protein, which reverses the mitogenic effects of estrogens, has potential to provide novel approaches to treating estrogen-dependent and -independent breast cancers.

PTEN suppression promotes neurite development exclusively in differentiating PC12 cells via PI3-kinase and MAP kinase signaling

As a dual-specificity phosphatase catalyzing the dephosphorylation of phosphatidylinositols and protein substrates, PTEN is critically involved in the nervous system development. However, the regulatory role of PTEN in neurite outgrowth is still controversial, and the downstream signaling events remain elusive. Here, we show that PTEN knockdown promoted the proliferation and survival but not the neurite outgrowth of rat pheochromocytoma PC12 cells when exposed to nerve growth factor (NGF). In contrast, selective PTEN silencing in differentiating PC12 cells that express nestin significantly facilitated neurite elongation. Elevated Akt and Erk1/2 phosphorylation was involved in accelerated NGF-induced neurite development of PC12 cells following PTEN knockdown. Discriminated roles of the lipid phosphatase and protein phosphatase activities of PTEN in neurite development, as well as the detailed molecular profiles affected by these phosphatase activities, were defined by restored expression of a lipid phosphatase-deficient PTEN mutant following endogenous PTEN silencing in PC12 cells. Our study suggests an overall inhibitory effect of PTEN in neurite development reconciled by a probably indispensable role of this phosphatase in the initiation of PC12 cell differentiation.