ADRENOMEDULLIN EXPRESSION IN HUMAN TUMOR-CELL LINES - ITS POTENTIAL ROLE AS AN AUTOCRINE GROWTH-FACTOR

Although adrenomedullin (AM) previously has been identified in human t umors, its role has remained elusive. Analysis by reverse transcriptas e-polymerase chain reaction (RT-PCR) revealed AM mRNA in 18 of 20 huma n normal tissues representing major organs, and 55 of 58 (95%) maligna nt cell lines. Western blot and high performance liquid chromatography analysis showed immunoreactive AM species of 18, 14, and 6 kDa that a re consistent with the precursor, intermediate product, and active pep tide, respectively. Immunohistochemistry and in situ RT-PCR performed on paraffin-embedded tumor cell lines of various tissue origins exhibi ted AM cytoplasmic staining. Neutralizing monoclonal antibody to AM in hibits tumor cell growth in a concentration-dependent manner, an effec t that was reversed with the addition of exogenous AM. Responding tumo r cells were shown to have approximately 50,000 AM receptors per cell by Scatchard analysis with I-125-AM and expressed AM receptor mRNA by RT-PCR. Our data showed 36 of 48 (75%) tumor cell lines expressed AM r eceptor mRNA by RT-PCR assessment, all of them also expressed AM. In t he presence of AM, cAMP levels were shown to increase in tumor cells. Our collective data demonstrate that AM and AM receptor are expressed in numerous human cancer cell lines of diverse origin and constitute a potential autocrine growth mechanism that could drive neoplastic prol iferation.