Functional expression of serotonin 5-HT7 receptor in human glioblastoma cell lines

Abstract

Serotonin 5‐HT7 receptors are present in astrocytes. Understanding their role in this type of cell would greatly benefit from the identification of astroglial cell lines expressing this receptor type. The aim of the present study was to assess the expression of native 5‐HT7 receptors and 5‐HT7 receptor mRNA in a number of human glioblastoma cell lines, by means of cAMP measurements, Western blot analysis and reverse transcriptase–polymerase chain reaction (RT–PCR) analysis. 5‐Hydroxytryptamine (5‐HT), 5‐carboxamidotryptamine (5‐CT), 5‐methoxytryptamine (5‐MeOT) and 8‐hydroxy‐2‐(di‐n‐propylamino)tetralin (8‐OH‐DPAT) induced concentration‐dependent stimulations of cAMP accumulation in the human glioblastoma cell lines, U‐373 MG, U‐138 MG, U‐87 MG, DBTRG‐05MG, T98G, H4, CCF‐STTG1 and Hs 683. The rank order of potency was 5‐CT>5‐HT=5‐MeOT≫8‐OH‐DPAT. The effect of 5‐CT was inhibited in a concentration‐dependent manner by the selective 5‐HT7 receptor antagonist SB‐269970 in all human glioblastoma cells. Schild analyses yielded slope factors close to unity (0.89–1.13) and pA2 values of 8.69–9.05. Western blot analysis revealed the presence of immunoreactive bands corresponding to the human 5‐HT7 receptor in extracts of all human glioblastoma cell lines. The presence of the three splice variants of the 5‐HT7 receptor (5‐HT7(a/b/d)) was visualized by RT–PCR analysis with specific primers in all human glioblastoma cell lines. In conclusion, human glioblastoma cell lines express functional 5‐HT7 receptors and the three splice variants of the corresponding mRNA. These cell lines could serve as model systems of native 5‐HT7 receptors in glial cells to investigate their putative role in processes like release of neurotrophic factors or inflammatory cytokines.