P450arom gene expression in peripheral blood lymphocytes: identification of a cryptic splice site for exon-1 after Epstein-Barr virus transformation.

The human aromatase gene (P450arom) is widely expressed, albeit in a tissue-specific manner. In the present study, we measured aromatase activity and investigated the transcribed and translated products of the P450arom gene before and after Epstein-Barr virus (EBV) transformation in peripheral blood lymphocytes (PBLs) from normal individuals. Aromatase activity was determined by [3H]-delta4-androstenedione (A) to [3H]-estrone (E1) conversion. Cellular total RNA and protein lysates were subjected to RT-PCR and Western analysis, respectively. Rapid amplification of cDNA ends (RACE) was used for the detection of novel 5'-untranslated ends of the P450arom mRNA, which were subsequently sequenced and compared to the known transcripts of this gene. In untransformed PBLs, two known variants of exon 1 of the P450arom gene were expressed, corresponding to promoters PI.3 and PII, or 1c and 1d, respectively. In EBV-transformed PBLs, a cryptic splice site was revealed and a new 5'-untranslated product was found. RNase protection assay confirmed that this splice variant is not a RACE artifact. The 53 K P450arom protein was detectable in PBLs both before and after EBV transformation. We conclude that (i) the P450arom mRNA is present in human PBLs and (ii) EBV transformation of the latter leads to novel alternative splicing of the 5' end of this gene.