Inhibition of CK2α Down-Regulates Hedgehog/Gli Signaling Leading to a Reduction of a Stem-Like Side Population in Human Lung Cancer Cells

Thoracic Oncology Laboratory, Department of Surgery, Helen Diller Family Comprehensive Cancer Center, University of California San Francisco, San Francisco, California, United States of America.
PLoS ONE (Impact Factor: 3.23). 06/2012; 7(6):e38996. DOI: 10.1371/journal.pone.0038996
Source: PubMed


Protein kinase CK2 is frequently elevated in a variety of human cancers. The Hedgehog (Hh) signaling pathway has been implicated in stem cell maintenance, and its aberrant activation has been indicated in several types of cancer, including lung cancer. In this study, we show that CK2 is positively involved in Hh/Gli signaling in lung cancer cell lines A549 and H1299. First, we found a correlation between CK2α and Gli1 mRNA levels in 100 primary lung cancer tissues. Down-regulation of Gli1 expression and transcriptional activity were demonstrated after the silencing of CK2α in lung cancer cells. In addition, CK2α siRNA down-regulated the expression of Hh target genes. Furthermore, two small-molecule CK2α inhibitors led to a dose-dependent inhibition of Gli1 expression and transcriptional activity in lung cancer cells. Reversely, forced over-expression of CK2α resulted in an increase both in Gli1 expression and transcriptional activity in A549 cells. Finally, the inhibition of Hh/Gli by CK2α siRNA led to a reduction of a cancer stem cell-like side population that shows higher ABCG2 expression level. Thus, we report that the inhibition of CK2α down-regulates Hh/Gli signaling and subsequently reduces stem-like side population in human lung cancer cells.

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Available from: Jian-Hua Mao, Aug 28, 2014
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    • "Prior studies suggest that CK2 may modulate the CSC phenotype through a variety of transcriptional mechanisms. A recent study demonstrates that CK2α is associated with Hedgehog (Hh)-Gli1 and Notch1 pathway transcription factors in lung cancers, where knockdown of CK2α reduced Hh/Gli1 and Notch1 signaling and the stem-like side population [28] [29]. Knockout of the regulatory CK2β subunit in mice inhibited transcription factor Olig2, embryonic neural stem cell proliferation, and oligodendrocyte development [30]. "
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    ABSTRACT: Cancer stem cells (CSC) and genes have been linked to cancer development and therapeutic resistance, but the signaling mechanisms regulating CSC genes and phenotype are incompletely understood. CK2 has emerged as a key signal serine/threonine kinase that modulates diverse signal cascades regulating cell fate and growth. We previously showed that CK2 is often aberrantly expressed and activated in head and neck squamous cell carcinomas (HNSCC), concomitantly with mutant (mt) tumor suppressor TP53, and inactivation of its family member, TAp73. Unexpectedly, we observed that classical stem cell genes Nanog, Sox2, and Oct4, are overexpressed in HNSCC with inactivated TAp73 and mtTP53. However, the potential relationship between CK2, TAp73 inactivation, and CSC phenotype is unknown. We reveal that inhibition of CK2 by pharmacologic inhibitors or siRNA inhibits the expression of CSC genes and side population (SP), while enhancing TAp73 mRNA and protein expression. Conversely, CK2 inhibitor attenuation of CSC protein expression and the SP by was abrogated by TAp73 siRNA. Bioinformatic analysis uncovered a single predicted CK2 threonine phosphorylation site (T27) within the N-terminal transactivation domain of TAp73. Nuclear CK2 and TAp73 interaction, confirmed by co-immunoprecipitation, was attenuated by CK2 inhibitor, or a T27A point-mutation of this predicted CK2 threonine phospho-acceptor site of TAp73. Further, T27A mutation attenuated phosphorylation, while enhancing TAp73 function in repressing CSC gene expression and SP cells. A new CK2 inhibitor, CX-4945, inhibited CSC related SP cells, clonogenic survival, and spheroid formation. Our study unveils a novel regulatory mechanism whereby aberrant CK2 signaling inhibits TAp73 to promote the expression of CSC genes and phenotype.
    Neoplasia (New York, N.Y.) 10/2014; 16(10):789–800. DOI:10.1016/j.neo.2014.08.014 · 4.25 Impact Factor
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    • "Zhang et al. (2012) expanded on Jia et al's discovery and determined that CK2 can regulate the stem-like side population in human lung cancer cells. Zhang et al. discovered that inhibition of CK2α using small molecule inhibitors or siRNAs reduced expression of Gli1 mRNA and protein, and also decreased Gli1 transcriptional activity (Zhang et al., 2012). In addition, decreasing CK2α expression altered ABCG2 expression which consistently led to a reduction in the cancer stem cell-like side population in the lung cancer cells. "
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    ABSTRACT: Casein kinase 2 (CK2) is an oncogenic protein kinase which contributes to tumor development, proliferation, and suppression of apoptosis in multiple cancer types. The mechanism by which CK2 expression and activity leads to tumorigenesis in glioblastoma (GBM), a stage IV primary brain tumor, is being studied. Recent studies demonstrate that CK2 plays an important role in GBM formation and growth through the inhibition of tumor suppressors and activation of oncogenes. In addition, intriguing new reports indicate that CK2 may regulate GBM formation in a novel manner; CK2 may play a critical role in cancer stem cell (CSC) maintenance. Since glial CSCs have the ability to self-renew and initiate tumor growth, new treatments which target these CSCs are needed to treat this fatal disease. Inhibition of CK2 is potentially a novel method to inhibit GBM growth and reoccurrence by targeting the glial CSCs. A new, orally available, selective CK2 inhibitor, CX-4945 has had promising results when tested in cancer cell lines, in vivo xenograft models, and human clinical trials. The development of CK2 targeted inhibitors, starting with CX-4945, may lead to a new class of more effective cancer therapies.
    Journal of molecular and genetic medicine: an international journal of biomedical research 12/2013; 8(1). DOI:10.4172/1747-0862.1000094
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    • "Cancer stem-like side population (SP) cells have been successfully identified in a wide range of solid tumors, including breast cancer [1], [2], hepatocellular carcinoma [3]–[7], lung cancer [8], [9], gastrointestinal cancer [10]–[12], prostate cancer [13], gallbladder cancer [14], ovarian cancer [15], endometrial cancer [16], pancreatic cancer [17], [18], urological cancer [19], [20], glioblastoma [21], melanoma [22], osteosarcoma [23], [24], mesenchymal neoplasms [25], nasopharyngeal cancer [26], oral cancer [27], [28], and other head and neck cancers [29], [30]. However, most of these investigations have been performed using established cancer cell lines. "
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    ABSTRACT: Cancer stem-like side population (SP) cells have been identified in many solid tumors; however, most of these investigations are performed using established cancer cell lines. Cancer cells in tumor tissue containing fibroblasts and many other types of cells are much more complex than any cancer cell line. Although SP cells were identified in the laryngeal squamous cell carcinoma (LSCC) cell line Hep-2 in our pilot study, it is unknown whether the LSCC tissue contains SP cells. In this study, LSCC cells (LSCCs) were primary cultured and purified from a surgically resected LSCC specimen derived from a well-differentiated epiglottic neoplasm of a Chinese male. This was followed by the verification of epithelium-specific characteristics, such as ultrastructure and biomarkers. A distinct SP subpopulation (4.45±1.07%) was isolated by Hoechst 33342 efflux analysis from cultured LSCCs by using a flow cytometer. Cancer stem cell (CSC)-associated assays, including expression of self-renewal and CSC marker genes, proliferation, differentiation, spheroid formation, chemotherapy resistance, and tumorigenicity were then conducted between SP and non-SP (NSP) LSCCs. In vitro and in vivo assays revealed that SP cells manifested preferential expression of self-renewal and CSC marker genes, higher capacity for proliferation, differentiation, and spheroid formation; enhanced resistance to chemotherapy; and greater xenograft tumorigenicity in immunodeficient mice compared with NSP cells. These findings suggest that the primary cultured and purified LSCCs contain cancer stem-like SP cells, which may serve as a valuable model for CSC research in LSCC.
    PLoS ONE 06/2013; 8(6):e65750. DOI:10.1371/journal.pone.0065750 · 3.23 Impact Factor
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