Detection of P450c17-independent pathways for dehydroepiandrosterone (DHEA) biosynthesis in brain glial tumor cells

Abstract

Dehydroepiandrosterone (D) is biosynthesized in the brain by a pathway different from that existing in the adrenal cortex. C6 rat glioma tumor cells in culture biosynthesize both pregnenolone (P) and D. They possess the mRNA, protein, and side-chain cleavage activity of P450scc. On the other hand, P450c17 was not detected. Adding FeSO₄ to C6 cells increased the synthesis of both P and D. Even in the presence of aminoglutethimide, an inhibitor of P450scc, FeSO₄ increased the synthesis of both steroids, indicating that the Fe²⁺-sensitive process does not involve P450scc. Likewise, the FeSO₄-induced formation of D was not blocked by the P450c17 inhibitor, SU-10603. These results suggest that the FeSO₄-induced synthesis of D as well as of P in C6 cells may be due to the fragmentation of in situ-formed tertiary hydroperoxides. It is likely, however, that the effect of the Fe²⁺ is not limited to this one reaction. When exogenous P was added to C6 microsomes, along with FeSO₄, the amount of D formed was greater than control values, indicating that Fe²⁺ facilitated the conversion of P to D. Unlike the constituents that are converted by Fe²⁺ to P, the precursor of D in C6 cells is not soluble in a 1:1 mixture of ether and ethylacetate. Treatment of C6 cells with KI, NaBH₄, or HIO₄ resulted in an increase in D synthesis. From this it seems clear that a precursor of the D produced in C6 cells is a steroid where both C-17 and C-20 are oxygenated.