Label-Free Investigations on the G Protein Dependent Signaling Pathways of Histamine Receptors

G protein activation represents an early key event in the complex GPCR signal transduction process and is usually studied by label-dependent methods targeting specific molecular events. However, the constrained environment of such "invasive" techniques could interfere with biological processes. Although histamine receptors (HRs) represent (evolving) drug targets, their signal transduction is not fully understood. To address this issue, we established a non-invasive dynamic mass redistribution (DMR) assay for the human HRs expressed in HEK cells, showing excellent signal-to-background ratios above 100 for histamine (HIS) and higher than 24 for inverse agonists with pEC values consistent with literature. Taking advantage of the integrative nature of the DMR assay, the involvement of endogenous Gα, Gα, Gα and Gβγ proteins was explored, pursuing a two-pronged approach, namely that of classical pharmacology (G protein modulators) and that of molecular biology (Gα knock-out HEK cells). We showed that signal transduction of hHRs occurred mainly, but not exclusively, via their canonical Gα proteins. For example, in addition to Gα, the Gα protein was proven to contribute to the DMR response of hHRs. Moreover, the Gα was identified to be involved in the hHR mediated signaling pathway. These results are considered as a basis for future investigations on the (patho)physiological role and the pharmacological potential of HRs.