Production and secretion of adrenomedullin by cultured choroid plexus carcinoma cells

Adrenomedullin is a potent vasodilator peptide that was originally isolated from pheochromocytoma. The production and secretion of adrenomedullin by cultured choroid plexus carcinoma cells were studied by radioimmunoassay and northern blot hybridization. Choroid plexus carcinoma is a rare malignant tumor derived from the epithelium of the choroid plexus. Immunoreactive adrenomedullin was detected in the conditioned medium of choroid plexus carcinoma cells (40.8 ± 7.5 fmol/10⁵ cells/24 h: mean ± SEM, n = 5). Reverse-phase HPLC of the conditioned medium showed one major peak of the immunoreactive peptide eluting in the position of synthetic human adrenomedullin and two smaller peaks eluting earlier. Addition of interleukin-1β (10 ng/ml) alone or in combination with three cytokines, interferon-γ (100 U/ml), tumor necrosis factor-α (20 ng/ml), and interleukin-1β (10 ng/ml), caused significant increases in the immunoreactive adrenomedullin concentrations in the medium (~175 and 293% of the control level, respectively). Northern blot analysis showed the expression of 1.6-kb adrenomedullin mRNA in the total RNA sample prepared from cultured choroid plexus carcinoma cells. Treatment with either interleukin-1β or the combination of three cytokines caused significant increases in levels of adrenomedullin mRNA in parallel with those in immunoreactive adrenomedullin concentrations in the conditioned medium. These findings raise a possibility that adrenomedullin is secreted from the choroid plexus and has physiological roles in the CNS via the CSF. In addition, adrenomedullin secreted from choroid plexus carcinoma may be related to the pathophysiology of the tumor.