Soluble and membrane-bound catechol-O-methyltransferase in normal and malignant mammary gland

The levels of 26 kDa-soluble (S) and 30 kDa-membrane-bound (MB) catechol-O- methyltransferase (COMT) polypeptides a ere determined in paired samples fr om normal and neoplastic breast tissue of 32 patients with breast cancer. I mmunohistochemical staining showed that the COMT reaction in normal mammary tissue was restricted to the epithelial cells in the ducti and lobuli, whe reas in the tumors a strong reaction was also seen in the malignant cells. The amounts of COMT proteins in tumors could not be correlated with various clinical or pathological parameters. Quantitative immunoblotting analysis revealed that the total amount of COMT proteins in tumors was more than 50% higher than in respective normal samples in 26 out of 32 patients. Five ca ses showed less than a 50% difference and in one case less COMT was detecte d in the tumor. In most cases the amount of both S- and MB-COMT forms was i ncreased. The average amount of total COMT was 178 +/- 57 pg/mu g total pro tein in normal tissue and 566 +/- 94 pg/mu g total protein in tumor. Respec tive values for S-COMT were 137 +/- 52 pg/mu g total protein in normal tiss ue and 369 +/- 62 pg/mu g total protein in tumor and for MB-COMT 41 +/- 10 and 197 +/- 41 pg/mu g total protein, respectively. Analysis of COMT-specif ic transcripts suggested that the COMT enzyme level in tumors is determined in some cases by transcriptional and in some cases by post-transcriptional mechanisms. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.