Expression of the aromatic L-amino acid decarboxylase mRNA in human tumour cell lines of neuroendocrine and neuroectodermal origin.

Neuroendocrine differentiation of lung tumours is characterised by the expression of several neuroendocrine markers and is confined mostly to specific histological subtypes, i.e. small cell carcinomas and carcinoids. One of the markers seen in neuroendocrine tumours, high activity of the aromatic L-amino acid decarboxylase (AADC), is helpful in distinguishing the classic and variant small cell lung tumour subtypes. Here, we have analysed the expression and quantified the level of mRNA coding for AADC in human tumour cell lines by use of the reverse transcription and polymerase chain reaction (RT-PCR). High amounts of mRNA were detected in classic small cell lung carcinomas and a neuroblastoma cell line. Other cell lines (melanomas, non-small cell lung carcinomas and osteosarcoma) also showed AADC expression, but the levels were 2-3 orders lower. Also, the tissue-specific (neuronal versus liver-specific) mRNA type has been estimated. Small cell lung carcinomas, neuroblastoma and melanoma expressed messenger RNA specific for neuronal tissues. Importantly, the non-small cell lung carcinoma cell lines expressed either liver-specific (non-neuronal) mRNA (cell line A549) or predominantly the neuronal (cell line NCI-H520) AADC message. These data indicate that a range of tumour cell lines transcribe the AADC gene and that two distinct types of AADC mRNA which reflect the embryonal (neuronal or non-neuronal) origin of the tumour may be produced in non-small cell lung cancer cells.