Measurement of the Activity of Wildtype and Disease-Causing ALPK1 Mutants in Transfected Cells With a 96-Well Format NF-κB/AP-1 Reporter Assay.

Alpha-protein kinase 1 (ALPK1) is normally activated by bacterial ADP-heptose as part of the innate immune response, leading to the initiation of downstream signalling events that culminate in the activation of transcription factors such as NF-κB and AP-1. In contrast, disease-causing mutations in ALPK1 that cause ROSAH syndrome or spiradenoma allow ALPK1 to be activated in cells in the absence of bacterial infection (i.e., without ADP-heptose). This protocol describes a semi-quantitative reporter assay based on ALPK1 knockout HEK-Blue cells that measures the activity of transfected wildtype and disease-causing forms of ALPK1 by virtue of their ability to activate the transcription factors NF-κB and AP-1. These cells express a synthetic gene encoding alkaline phosphatase under the control of an NF-κB/AP-1-dependent promoter, and consequently, the activation of ALPK1 leads to the production of alkaline phosphatase, which is secreted into the culture media and can be measured colorimetrically at 645 nm after the addition of a detection reagent. Key features • Highly sensitive reporter assay allowing detection of low-level activity arising from ALPK1 mutants • Optimised in 96-well plate format, requiring only 60,000 transfected ALPK1 KO HEK-Blue cells per well • Rapid experimental design, taking only four days from start to finish • Suitable for screening ALPK1 variants of unknown significance in an arrayed 96-well format.