PTEN inhibits adrenomedullin expression and function in brain tumor cells

Adrenomedullin is a vasoactive peptide that is upregulated in higher-grade gliomas and promotes tumor cell proliferation. Since reduced activity of the anti-oncogene PTEN seems to also correlate with higher tumor grade, this suggests an inverse association between PTEN activity and adrenomedullin expression. PC12 pheochromocytoma and human U251 glioma cell lines were stably transfected with human PTEN or control plasmid. Adrenomedullin expression was analyzed using quantitative PCR and Western blotting. A cell proliferation assay was used to assess adrenomedullin effects on U251 cells overexpressing PTEN. PC12 and U251 cells overexpressing PTEN had 17- and 8-fold decreases in adrenomedullin mRNA levels, respectively, compared to control cells. Cellular and secreted adrenomedullin peptide was similarly reduced. Addition of adrenomedullin to medium of controlled cells induced proliferation, as described previously, but U251 cells overexpressing PTEN did not respond to exogenous adrenomedullin. Further exploration revealed that PTEN also inhibits expression of the gliomas receptor for adrenomedullin, which accounts for this effect. These data were all replicated with an inducible PTEN construct confirming that these effects are not exclusively secondary to chronic overexpression. Given the profound effects of adrenomedullin on tumor cells, this is a novel and previously unidentified mechanism by which alterations in PTEN levels or function may influence tumor growth.