G‐protein regulator LGN inhibits the activity of nitric oxide receptor soluble guanylyl cyclase

Abstract

Soluble guanylyl cyclase (sGC) is a heme‐containing enzyme which converts GTP to cGMP. SGC is referred to as nitric oxide (NO) receptor, as it is strongly stimulated by NO. Although the mechanism of sGC activation by NO received a lot of attention, the processes of sGC deactivation are less understood. In this report we demonstrate inhibition of sGC by a LGN‐dependent mechanism. LGN is a known regulator of Gα proteins. We identified LGN as a protein interacting with both α1 and β1 sGC subunits by yeast two‐hybrid screening and by co‐immunoprecipitation of sGC and LGN from BE2 human neuroblastoma cell line. Transient expression of LGN in MDA468 breast cancer cells markedly decreased sGC activity in a gene‐dose dependent fashion. When the effect of purified LGN protein on the activity of purified sGC was tested in vitro, we found no evidence of inhibition, suggesting that LGN does not directly affect sGC function. However, when the same experiment was performed in the lysate of COS7 cell, we observed a marked inhibition of sGC. These data suggest that LGN may function as an adaptor protein for additional cellular factors inhibiting sGC. Since LGN is known to regulate G‐proteins by association with Gα subunit, it may function as an adaptor protein for a complex consisting of sGC, LGN and Gα, thus connecting the NO‐dependent and G‐protein signaling pathways.