THE EXPRESSION OF A NOVEL CA2+ CAM STIMULATED ADENYLYL-CYCLASE ACTIVITY IN THE NEUROBLASTOMA CELL-LINE LAN-1 IS REGULATED BY CELL-DENSITY/

In the human neuroblastoma cell line Lan-1, the mRNA encoding the Ca2/calmodulin (CaM) sensitive adenylyl cyclase type-1 (AC-I) was detecte d by reverse transcription-polymerase chain reaction (RT-PCR) as well as by Northern blotting. However, neither Ca2+/CaM stimulated AC activ ity was found nor could AC-1 type protein be detected by a specific an tibody (anti-1C1). In contrast, when cells were grown to high cell den sity, Ca2+/CaM stimulated AC-activity could be indeed found in membran es. The large increase in activity was paralleled by the appearance of a 110 kDa protein detected by the monoclonal AC antibody BBC-2. At th e same time a 150 kDa adenylyl cyclase species present in growing cell s was absent. The 110 kDa protein co-migrated with bovine AC-1 and was slightly larger than the human AC-1. Unexpectedly, however, the antib ody anti-1C1 was not able to precipitate the newly induced Lan-1 AC. I n addition, no increase in type-1 AC mRNA could be detected either by PCR or by Northern blotting. Treatment of Lan-1 cells with 10 mu M ret inoic acid for 7 days caused growth arrest and morphological different iation of the cells, yet the induction of the Ca2+/CaM-stimulated AC a ctivity was much lower than in the dense grown control cultures. It is concluded that the Ca2+/CaM-activated AC of M(r) 110 kDa in Lan-1 cel ls is not related to the previously known Ca2+/CaM stimulated AC isofo rms, and might thus represent a novel AC.