U-373 MG

Histamine-Induced Upregulation of H1R Gene Expression is Mediated by H1R Activation, and PKCα Is Involved in its Signaling Pathway in U-373 MG Cells

The histamine H1 receptor (H1R) is a histamine target in the nervous system and peripheral tissues. Protein kinase Cδ (PKCδ) signaling plays a role in histamine-induced H1R gene upregulation in HeLa cells. Histamine also upregulates H1R gene expression in U-373 MG cells, but the underlying molecular signaling remains unclear.

Mizuguchi et al. previously reported that histamine upregulates H1R gene expression via H1R activation, and that PKCδ/Hsp90/ERK signaling was involved. In this study, histamine upregulated H1R gene expression in a dose-dependent manner in U-373 MG cells (Fig. 1A). This upregulation was inhibited by the H1R antagonist d-chlorpheniramine but not by H2R, H3R, or H4R antagonists (Fig. 1B). This indicates that histamine-induced H1R gene upregulation in U-373 MG cells is H1R-mediated, similar to HeLa cells. Histamine-induced H1R gene upregulation was suppressed by the pan-PKC inhibitor Ro-31-8220. H1R exists in an equilibrium between active and inactive forms, with constitutive signaling even without histamine. Ro-31-8220 (10 μM) suppressed H1R gene upregulation below control levels, indicating inhibition of H1R's constitutive activity, with PKC signaling as the primary pathway for H1R-activated H1R gene expression in U-373 MG cells. PKCα/βI inhibitor Go6976 also suppressed the histamine-induced H1R gene upregulation. Because 10 μM Go6976 had the same effect as 1 μM, 1 μM is enough to inhibit H1R gene expression. The PKCβ inhibitor Ly333531 (10 μM) showed no inhibition, consistent with the report that U-373 MG cells do not express PKCβ. Therefore, the effect of Go6976 is due to PKCα inhibition. The fact that 10 μM Go6976 could not show further suppression implies that the other PKC isoforms is involved in U-373 MG cells.