title: A protein-based set of reference markers for liver tissues and hepatocellular carcinoma.
abstract: BACKGROUND
  During the last decade, investigations have focused on revealing genes or proteins that are involved in HCC carcinogenesis using either genetic or proteomic techniques. However, these studies are overshadowed by a lack of good internal reference standards. The need to identify "housekeeping" markers, whose expression is stable in various experimental and clinical conditions, is therefore of the utmost clinical relevance in quantitative studies. This is the first study employed 2-DE analysis to screen for potential reference markers and aims to correlate the abundance of these proteins with their level of transcript expression.
  
  
  METHODS
  A Chinese cohort of 224 liver tissues samples (105 cancerous, 103 non-tumourous cirrhotic, and 16 normal) was profiled using 2-DE analysis. Expression of the potential reference markers was confirmed by western blot, immunohistochemistry and real-time quantitative PCR. geNorm algorithm was employed for gene stability measure of the identified reference markers.
  
  
  RESULTS
  The expression levels of three protein markers beta-actin (ACTB), heat shock protein 60 (HSP60), and protein disulphide isomerase (PDI) were found to be stable using p-values (p > 0.99) as a ranking tool in all 224 human liver tissues examined by 2-DE analysis. Of high importance, ACTB and HSP 60 were successfully validated at both protein and mRNA levels in human hepatic tissues by western blot, immunohistochemistry and real-time quantitative PCR. In addition, no significant correlation of these markers with any clinicopathological features of HCC and cirrhosis was found. Gene stability measure of these two markers with other conventionally applied housekeeping genes was assessed by the geNorm algorithm, which ranked ACTB and HSP60 as the most stable genes among this cohort of clinical samples.
  
  
  CONCLUSIONS
  Our findings identified 2 reference markers that exhibited stable expression across human liver tissues with different conditions thus should be regarded as reliable reference moieties for normalisation of gene and protein expression in clinical research employing human hepatic tissues.
authors.affiliation: Department of Surgery, LKS Faculty of Medicine, Jockey Club Clinical Research Centre, The University of Hong Kong, Pokfulam, Hong Kong. h0594109@hkusua.hku.hk
authors.forename: Stella
authors.initials: S
authors.lastname: Sun
authors.forename: Xin
authors.initials: X
authors.lastname: Yi
authors.forename: Ronnie Tp
authors.initials: RT
authors.lastname: Poon
authors.forename: Chun
authors.initials: C
authors.lastname: Yeung
authors.forename: Philip J R
authors.initials: PJ
authors.lastname: Day
authors.forename: John M
authors.initials: JM
authors.lastname: Luk
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism*; D018834:Chaperonin 60 / Q000235:genetics / Q000378:metabolism*; D015331:Cohort Studies; D015180:Electrophoresis, Gel, Two-Dimensional / Q000379:methods / Q000592:standards*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism*; D040901:Proteomics / Q000379:methods / Q000592:standards*; D012015:Reference Standards
chemical_list: D000199:Actins; D018834:Chaperonin 60