Involvement of protein kinase C in rugulation of histamine H_1 receptor level in U373 astrocytoma cells

Histamine is a mediator of immune hypersensitivity in peripheral tissues and a neurotransmitter in the central nervous system. Astrocytes express histamine H_1 receptors and function as target cells of hisaminergic neurons. H receptors are expressed in U373 astrocytoma cells, and the cells are useful for the study of histamine functions though astrocytes. We observed that up-reguration of H_1 receptors in U373 astrocytoma cells was induced by the treatment of 1 μM phorbol- 12-myristate- 13-acetate (PMA), a protein kinase C (PKC) activator. H_1 receptor level was reached to maximum 20 hours after the treatment of PMA. This upregulation was returned to lower level than the contorol by pretreatment of Ro31-8220, a PKC inhibitor. Furthermore it was observed by RT-PCR that H_1 receptors mRNA expression was suppressed by the treatment of PKC inhibitor, Ro31-8220 or H-7, for 6 hours. On the other hand this suppression was not observed by the treatment of HA1004 which lacks the inhibition of PKC. These results suggest that PKG involves in regulation of H_1 receptor level. Then we identified PKC isozymes expressed in U373 astrocytoma cells by Western blot analysis using antibodies against PKC isozymes. U373 astrocytoma cells revealed to express cPKCs (α and γ), nPKC (ε), aPKCs (ι and λ), and μ type of PKC (now defined protein kinase D).