Meizhi Wang

Activation of the human histamine H2 receptor is linked to cell proliferation and c-fos gene transcription

We examined whether histamine could regulate cell proliferation and expression of the early response gene c- fos in HEK-293 cells stably transfected with the human H2receptor (HEK-H2). Histamine stimulated [3H]thymidine incorporation [50% effective concentration (EC50) = 3.6 × 10-6 M] in HEK-H2 cells in a cimetidine-sensitive manner and increased c- fos mRNA in a time-dependent fashion, reaching maximal induction after 30 min. Histamine induced luciferase activity in HEK-H2cells transiently transfected with a construct containing the luciferase reporter gene ( Luc) coupled to the serum response element (SRE) of the c- fos gene promoter (EC50 = 1.5 × 10-6 M) or a plasmid containing the SRE core fragment (bases -320 to -298). The protein kinase C (PKC) inhibitor staurosporine and long-term pretreatment of HEK cells with phorbol ester inhibited the effect of histamine on PKC activation, SRE- Lucactivity, and [3H]thymidine incorporation. We have demonstrated that activation of the human H2 receptor can lead to induction of c- fos gene transcription and cell proliferation through a PKC-dependent mechanism.

The human histamine H2 receptor regulates c-jun and c-fos in a differential manner

Previously, we demonstrated that activation of the human H(2) receptor (hH(2)R) leads to an increase in c-fos transcription and cell proliferation. The purpose of these studies was to examine whether hH(2)R regulates c-jun expression and, if so, explore the mechanisms by which it does so. Histamine induced an increase in c-jun mRNA in human embryonic kidney cells stably transfected with the hH(2)R (maximal effect: 554.6 +/- 86.8% of control). The protein kinase C (PKC) inhibitors staurosporine (10(-6) M) and GF-109203X (10(-6) M) significantly inhibited histamine-stimulated c-fos mRNA while not altering c-jun expression. The protein kinase A (PKA) pathway inhibitors Rp-cAMP and protein kinase inhibitor did not affect the action of histamine on c-jun or c-fos mRNA. Histamine (10(-4) M) stimulated extracellularly regulated kinase 2 tyrosine phosphorylation. The specific inhibitor of the mitogen-activated protein (MAP) kinase pathway, PD-98059 (5 x 10(-5) M), significantly inhibited histamine-induced c-fos and c-jun mRNA. Of interest, the p70 S6 kinase inhibitor rapamycin (10(-6) M) but not wortmannin decreased histamine-stimulated c-jun mRNA by 58.5 +/- 12% (mean +/- SE, n = 4) while not significantly altering c-fos message. Histamine (10(-4) M) also led to an approximately 4.5-fold increase in Jun NH(2)-terminal kinase activity in a PKC-, PKA-, and MAP kinase-independent but rapamycin-sensitive manner. Our findings suggest that histamine stimulates both c-fos and c-jun mRNA in a differential manner. PKC is involved in histamine-mediated c-fos activation, whereas p70 S6 kinase is important for linkage of this receptor to c-jun.