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Expression of transcription factor AP-2 in colorectal adenomas and adenocarcinomas; comparison of immunohistochemistry and in situ hybridisation
  1. K M Ropponen1,
  2. J K Kellokoski1,3,
  3. R T Pirinen1,
  4. K I Moisio1,
  5. M J Eskelinen2,
  6. E M Alhava2,
  7. V-M Kosma1
  1. 1Department of Pathology and Forensic Medicine, University of Kuopio, PO Box 1627, FIN 70211, Kuopio University Hospital, Kuopio, Finland
  2. 2Department of Surgery, University of Kuopio
  3. 3Departments of Oral and Maxillofacial Unit and Oncology, Kuopio University Hospital
  1. Dr Kosma VeliMatti.Kosma{at}


Aims—To investigate whether the three different AP-2 isoforms are expressed differently in colorectal adenomas and carcinomas.

Methods—The study comprised 43 randomly selected patients diagnosed and treated at Kuopio University Hospital in 1996 for colorectal adenocarcinoma (n = 30) and colorectal adenoma (n = 13). The expression of AP-2α, AP-2β, and AP-2γ was analysed by immunohistochemistry (IHC) and the mRNA status of AP-2α was determined by in situ hybridisation (ISH) and confirmed by reverse transcription polymerase chain reaction (RT-PCR). AP-2 expression patterns were correlated with clinicopathological variables.

Results—In adenomas and carcinomas, AP-2β cytoplasmic positivity was higher than that of AP-2α or AP-2γ. AP-2α expression was reduced in advanced Dukes's stage carcinomas. In high grade carcinomas, both AP-2α and AP-2γ expression was reduced. ISH demonstrated increased AP-2α values in high grade carcinomas. Seven of 30 carcinoma specimens displayed a moderate or strong mRNA signal, despite being negative for AP-2α protein. RT-PCR from AP-2α mRNA and protein positive tumours confirmed that the positive signal in ISH originated from the exon 2 of TFAP2A.

Conclusions—AP-2α was reduced in advanced Dukes's stage adenocarcinomas. Together with reduced AP-2γ expression in high grade carcinomas, this might contribute to tumour progression. The discrepancy between mRNA and protein expression suggests that post-transcriptional regulatory mechanisms might modify the availability of functional AP-2α protein in colorectal carcinoma.

  • AP-2 proteins
  • immunohistochemistry
  • in situ hybridisation
  • colorectal neoplasms

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