title: Deregulation of microRNAs Let-7a and miR-21 mediate aberrant STAT3 signaling during human papillomavirus-induced cervical carcinogenesis: role of E6 oncoprotein.
abstract: BACKGROUND
  Aberrantly expressed and constitutively active STAT3 signaling plays a pivotal role in initiation and progression of human papillomavirus-induced cervical carcinogenesis. However, the underlying mechanism(s) responsible for pleiotropic effects of STAT3 signaling is poorly understood. In view of emerging regulatory role of microRNAs, Let-7a and miR-21 that may interact with STAT3 signaling and/or its downstream effectors, present study was designed in HPV16-positive cervical cancer cells to assess the functional contribution of these miRs in STAT3 signaling in cervical cancer.
  
  
  METHODS
  Functional silencing of STAT3 signaling and HPV16 oncoprotein expression in SiHa cells was done by STAT3-specific and 16 E6 siRNAs. Pharmacological intervention of STAT3 was done using specific inhibitors like curcumin and stattic. Loss-of-function study of miR-21 using miR-21 inhibitor and gain-of-function study of let-7a was done using let-7a mimic in SiHa cells.
  
  
  RESULTS
  Functional silencing of STAT3 signaling in SiHa cells by STAT3-specific siRNA resulted in a dose-dependent decrease in cellular miR-21 level. Pharmacological intervention of STAT3 using specific inhibitors like curcumin and Stattic that abrogated STAT3 activation resulted in loss of cellular miR-21 pool. Contrary to this, specific targeting of miR-21 using miR-21 inhibitor resulted in an increased level of PTEN, a negative regulator of STAT3, and reduced active pSTAT3 level. Besides miR-21, restoration of cellular Let-7a using chemically synthesized Let-7a mimic reduced overall STAT3 level. Abrogation of HPV oncoprotein E6 by specific siRNA resulted in increased Let-7a but loss of miR-21 and a correspondingly reduced pSTAT3/STAT3 and elevated the level of cellular PTEN.
  
  
  CONCLUSIONS
  Our results demonstrate existence of a functional loop involving Let-7a, STAT3 and miR-21 which were found potentially regulated by viral oncoprotein E6.
  
  
  CONCLUSIONS
  miR-21 and Let-7a along with STAT3 may prove useful targets for pharmacological intervention for management of cervical cancer.
authors.forename: Gauri
authors.initials: G
authors.lastname: Shishodia
authors.forename: Gaurav
authors.initials: G
authors.lastname: Verma
authors.forename: Yogesh
authors.initials: Y
authors.lastname: Srivastava
authors.forename: Ravi
authors.initials: R
authors.lastname: Mehrotra
authors.forename: Bhudev Chandra
authors.initials: BC
authors.lastname: Das
authors.affiliation: Division of Molecular Oncology, Institute of Cytology and Preventive Oncology, I-7, Sector-39, Noida, Uttar Pradesh 201301, India. bhartiac@icmr.org.in.
authors.forename: Alok Chandra
authors.initials: AC
authors.lastname: Bharti
mesh_terms: D045744:Cell Line, Tumor; D003474:Curcumin / Q000494:pharmacology; D003499:Cyclic S-Oxides / Q000494:pharmacology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D052162:Human papillomavirus 16 / Q000378:metabolism; D006801:Humans; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism; D009856:Oncogene Proteins, Viral / Q000037:antagonists & inhibitors*; D034741:RNA, Small Interfering / Q000378:metabolism; D012097:Repressor Proteins / Q000037:antagonists & inhibitors*; D050796:STAT3 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D002583:Uterine Cervical Neoplasms / Q000235:genetics / Q000378:metabolism / Q000821:virology*
chemical_list: D003499:Cyclic S-Oxides; C068651:E6 protein, Human papillomavirus type 16; C524940:MIRN21 microRNA, human; D035683:MicroRNAs; D009856:Oncogene Proteins, Viral; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C487931:mirnlet7 microRNA, human; C517409:stattic; D003474:Curcumin