Yan Hong Cui

PTTG1 Oncogene Promotes Tumor Malignancy via Epithelial to Mesenchymal Transition and Expansion of Cancer Stem Cell Population

Background: PTTG1 is an oncogene with its expression levels correlating with tumor development and metastasis. Results: Modulation of PTTG1 expression levels revealed that PTTG1 promotes invasive and migratory properties and expansion of CD44high CD24low cell population via AKT activation in breast cancer cells. Conclusion: PTTG1 induces EMT and promotes cancer stem cells via activation of AKT. Significance: PTTG1 represents a potential target for therapeutic intervention against the spread of breast cancer. The prognosis of breast cancer patients is related to the degree of metastasis. However, the mechanisms by which epithelial tumor cells escape from the primary tumor and colonize at a distant site are not entirely understood. Here, we analyzed expression levels of pituitary tumor-transforming gene-1 (PTTG1), a relatively uncharacterized oncoprotein, in patient-derived breast cancer tissues with corresponding normal breast tissues. We found that PTTG1 is highly expressed in breast cancer patients, compared with normal tissues. Also, PTTG1 expression levels were correlated with the degree of malignancy in breast cancer cell lines; the more migratory and invasive cancer cell lines MDA-MB-231 and BT549 displayed the higher expression levels of PTTG1 than the less migratory and invasive MCF7 and SK-BR3 and normal MCF10A cell lines. By modulating PTTG1 expression levels, we found that PTTG1 enhances the migratory and invasive properties of breast cancer cells by inducing epithelial to mesenchymal transition, as evidenced by altered morphology and epithelial/mesenchymal cell marker expression patterns and up-regulation of the transcription factor Snail. Notably, down-regulation of PTTG1 also suppressed cancer stem cell population in BT549 cells by decreasing self-renewing ability and tumorigenic capacity, accompanying decreasing CD44high CD24low cells and Sox2 expression. Up-regulation of PTTG1 had the opposite effects, increasing sphere-forming ability and Sox2 expression. Importantly, PTTG1-mediated malignant tumor properties were due, at least in part, to activation of AKT, known to be a key regulator of both EMT and stemness in cancer cells. Collectively, these results suggest that PTTG1 may represent a new therapeutic target for malignant breast cancer.

Fractionated radiation-induced nitric oxide promotes expansion of glioma stem-like cells

Glioblastoma remains an incurable brain disease due to the prevalence of its recurrence. Considerable evidence suggests that glioma stem‐like cells are responsible for glioma relapse after treatment, which commonly involves ionizing radiation. Here, we found that fractionated ionizing radiation (2 Gy/day for 3 days) induced glioma stem‐like cell expansion and resistance to anticancer treatment such as cisplatin (50 μM) or taxol (500 nM), or by ionizing radiation (10 Gy) in both glioma cell lines (U87, U373) and patient‐derived glioma cells. Of note, concomitant increase of nitric oxide production occurred with the radiation‐induced increase of the glioma stem‐like cell population through upregulation of inducible nitric oxide synthase (iNOS). In line with this observation, downregulation of iNOS effectively reduced the glioma stem‐like cell population and decreased resistance to anticancer treatment. Collectively, our results suggest that targeting iNOS in combination with ionizing radiation might increase the efficacy of radiotherapy for glioma treatment.

Radiation promotes malignant progression of glioma cells through HIF-1alpha stabilization

Given its contribution to malignant phenotypes of cancer, tumor hypoxia has been considered as a potential therapeutic problem. In the stressful microenvironment condition, hypoxia inducible factor 1 (HIF1) is well known to mediate the transcriptional adaptation of cells to hypoxia and acts as a central player for the process of hypoxia-driven malignant cancer progression. Here, we found that irradiation causes the HIF1α protein to stabilize, even in normoxia condition through activation of p38 MAPK, thereby promoting angiogenesis in tumor microenvironment and infiltrative property of glioma cells. Notably, irradiation reduced hydroxylation of HIF1α through destabilization of prolyl hydroxylases (PHD)-2. Moreover, radiation also decreased the half-life of protein von Hippel-Lindau (pVHL), which is a specific E3 ligase for HIF1α. Of note, inhibition of p38 MAPK attenuated radiation-induced stabilization of HIF1α through destabilization of PHD-2 and pVHL. In agreement with these results, targeting of either p38 MAPK, HIF1α, pVHL or PHD-2 effectively mitigated the radiation-induced tube formation of human brain-derived micro-vessel endothelial cells (HB-MEC) and infiltration of glioma cells. Taken together, our findings suggest that targeting HIF1α in combination with ionizing radiation might increase the efficacy of radiotherapy for glioma treatment.

Radiation promotes invasiveness of non-small-cell lung cancer cells through granulocyte-colony-stimulating factor.

Despite ionizing radiation (IR) is being widely used as a standard treatment for lung cancer, many evidences suggest that IR paradoxically promotes cancer malignancy. However, its molecular mechanisms underlying radiation-induced cancer progression remain obscure. Here, we report that exposure to fractionated radiation (2 Gy per day for 3 days) induces the secretion of granulocyte-colony-stimulating factor (G-CSF) that has been commonly used in cancer therapies to ameliorate neutropenia. Intriguingly, radiation-induced G-CSF promoted the migratory and invasive properties by triggering the epithelial–mesenchymal cell transition (EMT) in non-small-cell lung cancer cells (NSCLCs). By irradiation, G-CSF was upregulated transcriptionally by β-catenin/TCF4 complex that binds to the promoter region of G-CSF as a transcription factor. Importantly, irradiation increased the stability of β-catenin through the activation of PI3K/AKT (phosphatidylinositol 3-kinase/AKT), thereby upregulating the expression of G-CSF. Radiation-induced G-CSF is recognized by G-CSFR and transduced its intracellular signaling JAK/STAT3 (Janus kinase/signal transducers and activators of transcription), thereby triggering EMT program in NSCLCs. Taken together, our findings suggest that the application of G-CSF in cancer therapies to ameliorate neutropenia should be reconsidered owing to its effect on cancer progression, and G-CSF could be a novel therapeutic target to mitigate the harmful effect of radiotherapy for the treatment of NSCLC.

Persistent activation of STAT3 by PIM2‐driven positive feedback loop for epithelial‐mesenchymal transition in breast cancer

Metastasis of breast cancer is promoted by epithelial–mesenchymal transition (EMT). Emerging evidence suggests that STAT3 is a critical signaling node in EMT and is constitutively activated in many carcinomas, including breast cancer. However, its signaling mechanisms underlying persistent activation of STAT3 associated with EMT remain obscure. Here, we report that PIM2 promotes activation of STAT3 through induction of cytokines. Activation of STAT3 caused an increase in PIM2 expression, implicating a positive feedback loop between PIM2 and STAT3. In agreement, targeting of either PIM2, STAT3 or PIM2‐dependent cytokines suppressed EMT‐associated migratory and invasive properties through inhibition of ZEB1. Taken together, our findings identify the signaling mechanisms underlying the persistent activation of STAT3 and the oncogenic role of PIM2 in EMT in breast cancer.

Phloroglucinol suppresses metastatic ability of breast cancer cells by inhibition of epithelial-mesenchymal cell transition.

Metastasis is a challenging clinical problem and the primary cause of death in breast cancer patients. However, there is no therapeutic agent against metastasis of breast cancer cells. Here we report that phloroglucinol, a natural phlorotannin component of brown algae suppresses metastatic ability of breast cancer cells. Treatment with phloroglucinol effectively inhibited mesenchymal phenotypes of basal type breast cancer cells through downregulation of SLUG without causing a cytotoxic effect. Importantly, phloroglucinol decreased SLUG through inhibition of PI3K/AKT and RAS/RAF‐1/ERK signaling. In agreement with in vitro data, phloroglucinol was also effective against in vivo metastasis of breast cancer cells, drastically suppressing their metastatic ability to lungs, and extending the survival time of mice. Collectively, our findings demonstrate a novel anticancer activity of phloroglucinol against metastasis of breast cancer cells, implicating its clinical relevance.

Radiation driven epithelial-mesenchymal transition is mediated by Notch signaling in breast cancer

Epithelial to mesenchymal transition (EMT) is developmental process associated with cancer metastasis. Here, we found that breast carcinoma cells adopt epithelial-to-mesenchymal transition (EMT) in response to fractionated-radiation. Importantly, we show that Notch signaling is highly activated in fractionally-irradiated tumors as compared to non-irradiated tumors that are accompanied by an EMT. Moreover, we uncovered the mechanism of Notch-driven EMT, in which Notch enhanced EMT through IL-6/JAK/STAT3 signaling axis in mammary tumor cells. Collectively, we present converging evidence from our studies that Notch2 is a critical mediator of radiation-induced EMT and responsible for induced malignant tumor growth.

Activation of KRAS promotes the mesenchymal features of basal-type breast cancer

Basal-type breast cancers are among the most aggressive and deadly breast cancer subtypes, displaying a high metastatic ability associated with mesenchymal features. However, the molecular mechanisms underlying the maintenance of mesenchymal phenotypes of basal-type breast cancer cells remain obscure. Here, we report that KRAS is a critical regulator for the maintenance of mesenchymal features in basal-type breast cancer cells. KRAS is preferentially activated in basal-type breast cancer cells as compared with luminal type. By loss and gain of KRAS, we found that KRAS is necessary and sufficient for the maintenance of mesenchymal phenotypes and metastatic ability through SLUG expression. Taken together, this study demonstrates that KRAS is a critical regulator for the metastatic behavior associated with mesenchymal features of breast cancer cells, implicating a novel therapeutic target for basal-type breast cancer.Experimental & Molecular Medicine (2015) 47, e137; doi:10.1038/emm.2014.99; published online 30 January 2015

Radiation promotes malignant phenotypes through SRC in breast cancer cells

Despite the fact that ionizing radiation (IR) is widely used as a standard treatment for breast cancer, much evidence suggests that IR paradoxically promotes cancer malignancy. However, the molecular mechanisms underlying radiation‐induced cancer progression remain obscure. Here, we report that irradiation activates SRC signaling among SRC family kinase proteins, thereby promoting malignant phenotypes such as invasiveness, expansion of the cancer stem‐like cell population, and resistance to anticancer agents in breast cancer cells. Importantly, radiation‐activated SRC induced SLUG expression and caused epithelial–mesenchymal cell transition through phosphatidylinositol 3‐kinase/protein kinase B and p38 MAPK signaling. In agreement, either inhibition of SRC or downstream signaling of p38 MAPK or protein kinase B effectively attenuated radiation‐induced epithelial–mesenchymal cell transition along with an increase in the cancer stem‐like cell population. In addition, downregulation of SRC also abolished radiation‐acquired resistance of breast cancer cells to anticancer agents such as cisplatin, etoposide, paclitaxel, and IR. Taken together, our findings suggest that combining radiotherapy with targeting of SRC might attenuate the harmful effects of radiation and enhance the efficacy of breast cancer treatment.

A novel 2-pyrone derivative, BHP, impedes oncogenic KRAS-driven malignant progression in breast cancer

Elevated KRAS expression has been frequently associated with cancer progression including breast cancer; however, therapeutic approaches targeting KRAS have been widely unsuccessful and KRAS mutant cancers remain unsolved problem in cancer therapy. In this study, we found that a new 2-pyrone derivative, 5-bromo-3-(3-hydroxyprop-1-ynyl)-2H-pyran-2-one (BHP) can block KRAS-driven breast cancer progression. Importantly, treatment with BHP effectively suppressed the migratory and invasive properties along with epithelial-mesenchymal transition (EMT) in MDA-MB231 breast cancer cells that carry oncogenic KRAS and mesenchymal malignant phenotypes. In parallel, BHP also sensitized the cells to anticancer treatment. Consistently, forced-expression of oncogenic KRAS bestowed the migratory and invasive properties, mesenchymal transition and resistance to anticancer treatment into normal human mammalian breast cells MCF10A and relatively non-malignant MCF7 and SK-BR3 breast cancer cells; however, treatment with BHP blocked those KRAS-induced malignant phenotypes. Notably, BHP interfered the interaction of KRAS with Raf-1 in concentration-dependent manner, thereby blocking the downstream effectors of KRAS signaling that is PI3K/AKT and ERK. Taken together, our findings indicate that the BHP, an α-pyrone derivative, suppresses malignant breast cancer progression by targeting of oncogenic KRAS signaling pathways.