CK2 phosphorylates and inhibits TAp73 tumor suppressor function to promote expression of cancer stem cell genes and phenotype in head and neck cancer.
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.
Tumor Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892 ; Orthopaedic Center, Zhujiang Hospital, Southern Medical University, Guangzhou, China.
Hai
H
Lu
Tumor Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892 ; Howard Hughes Medical Institute-NIH Research Scholars Program, Bethesda, MD 20892, USA.
Carol
C
Yan
Tumor Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892.
Xin Xin
XX
Quan
Tumor Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892.
Xinping
X
Yang
Tumor Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892.
Jialing
J
Zhang
Tumor Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892.
Yansong
Y
Bian
Tumor Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892.
Zhong
Z
Chen
Tumor Biology Section, Head and Neck Surgery Branch, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD 20892.
Carter
C
Van Waes
D001562:Benzimidazoles / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D047390:Casein Kinase II / Q000037:antagonists & inhibitors / Q000378:metabolism*; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006258:Head and Neck Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D018398:Homeodomain Proteins / Q000235:genetics; D006801:Humans; D009154:Mutation; D000071317:Nanog Homeobox Protein; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D050814:Octamer Transcription Factor-3 / Q000235:genetics; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000494:pharmacology; D055748:SOXB1 Transcription Factors / Q000235:genetics; D000077195:Squamous Cell Carcinoma of Head and Neck; D013912:Threonine / Q000378:metabolism; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
C492322:2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole; D001562:Benzimidazoles; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D018398:Homeodomain Proteins; C486780:NANOG protein, human; D000071317:Nanog Homeobox Protein; D009687:Nuclear Proteins; D050814:Octamer Transcription Factor-3; C494173:POU5F1 protein, human; D034741:RNA, Small Interfering; C527782:SOX2 protein, human; D055748:SOXB1 Transcription Factors; C495901:TP53 protein, human; C000606460:TP73 protein, human; D000072160:Tumor Protein p73; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D013912:Threonine; D047390:Casein Kinase II
CK2, Casein Kinase 2; CSC, Cancer Stem Cells; DMAT, 2-Dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole; HEKA, Human epidermal keratinocytes; HNSCC, Head and neck squamous cell carcinoma; HOK, Human oral keratinocytes; SP, Side population; TAp73, Transactivating p73; TP53, Transforming Protein p53; UM-SCC, University of Michigan Squamous Cell Carcinoma; mt, Mutant; wt, Wild-type