The COPD GWAS gene ADGRG6 instructs function and injury response in human iPSC-derived type II alveolar epithelial cells

Emphysema and chronic obstructive pulmonary disease (COPD) most commonly result from the effects of environmental exposures in genetically susceptible individuals. Genome-wide association studies have implicated ADGRG6 in COPD and reduced lung function, and a limited number of studies have examined the role of ADGRG6 in cells representative of the airway. However, the ADGRG6 locus is also associated with DLCO/VA, an indicator of gas exchange efficiency and alveolar function. Here, we sought to evaluate the mechanistic contributions of ADGRG6 to homeostatic function and disease in type 2 alveolar epithelial cells. We applied an inducible CRISPR interference (CRISPRi) human induced pluripotent stem cell (iPSC) platform to explore ADGRG6 function in iPSC-derived AT2s (iAT2s). We demonstrate that ADGRG6 exerts pleiotropic effects on iAT2s including regulation of focal adhesions, cytoskeleton, tight junctions, and proliferation. Moreover, we find that ADGRG6 knockdown in cigarette smoke-exposed iAT2s alters cellular responses to injury, downregulating apical complexes in favor of proliferation. Our work functionally characterizes the COPD GWAS gene ADGRG6 in human alveolar epithelium.

Noncoding SNP at rs1663689 represses ADGRG6 via interchromosomal interaction and reduces lung cancer progression

A previous genome-wide association study (GWAS) revealed an association of the noncoding SNP rs1663689 with susceptibility to lung cancer in the Chinese population. However, the underlying mechanism is unknown. In this study, using allele-specific 4C-seq in heterozygous lung cancer cells combined with epigenetic information from CRISPR/Cas9-edited cell lines, we show that the rs1663689 C/C variant represses the expression of ADGRG6, a gene located on a separate chromosome, through an interchromosomal interaction of the rs1663689 bearing region with the ADGRG6 promoter. This reduces downstream cAMP-PKA signaling and subsequently tumor growth both in vitro and in xenograft models. Using patient-derived organoids, we show that rs1663689 T/T-but not C/C-bearing lung tumors are sensitive to the PKA inhibitor H89, potentially informing therapeutic strategies. Our study identifies a genetic variant-mediated interchromosomal interaction underlying ADGRG6 regulation and suggests that targeting the cAMP-PKA signaling pathway may be beneficial in lung cancer patients bearing the homozygous risk genotype at rs1663689.

Collagen VI Is a Gi-Biased Ligand of the Adhesion GPCR GPR126/ADGRG6

GPR126/ADGRG6, a member of the adhesion G-protein-coupled receptor family, balances cell differentiation and proliferation through fine-tuning of intracellular cAMP levels, which is achieved through coupling to Gs and Gi proteins. While GPR126-mediated cAMP increase has been proven to be essential for differentiation of Schwann cells, adipocytes and osteoblasts, Gi-signaling of the receptor was found to propagate breast cancer cell proliferation. Extracellular ligands or mechanical forces can modulate GPR126 activity but require an intact encrypted agonist sequence, coined the Stachel. Even though coupling to Gi can be seen for constitutively active truncated receptor versions of GPR126 as well as with a peptide agonist derived from the Stachel sequence, all known N-terminal modulators have so far only been shown to modulate Gs coupling. Here, we identified collagen VI as the first extracellular matrix ligand of GPR126 that induces Gi signaling at the receptor, which shows that N-terminal binding partners can mediate selective G protein signaling cascades that are masked by fully active truncated receptor variants.

Detection of the ADGRG6 hotspot mutations in urine for bladder cancer early screening by ARMS-qPCR

BACKGROUND

In bladder cancer, recurrent ADGRG6 enhancer hotspot mutations (chr. 6: 142,706,206 G>A, chr. 6:142,706,209 C>T) were reported at a high mutation rate of approximately 50%. Thus, ADGRG6 enhancer mutation status might be a candidate for diagnostic biomarker.

METHODS

To improve test efficacy, an amplification refractory mutation system combined with quantitative real-time PCR (ARMS-qPCR) assay was developed to detect the ADGRG6 mutations in a patient as a clinical diagnostic test. To validate the performance of the ARMS-qPCR assay, artificial plasmids, cell DNA reference standard were used as templates, respectively. To test the clinical diagnostic ability, we detected the cell free DNA (cfDNA) and sediment DNA (sDNA) of 30 bladder cancer patients' urine by ARMS-qPCR comparing with Sanger sequencing, followed by the droplet digital PCR to confirm the results. We also tested the urine of 100 healthy individuals and 90 patients whose diagnoses urinary tract infections or urinary stones but not bladder cancer.

RESULTS

Sensitivity of 100% and specificity of 96.7% were achieved when the mutation rate of the artificial plasmid was 1%, and sensitivity of 96.7% and specificity of 100% were achieved when the mutation frequency of the reference standard was 0.5%. Sanger sequencing and ARMS-qPCR both detected 30 cases of bladder cancer with 93.3% agreement. For the remaining unmatched sites, ARMS-qPCR results were consistent with droplet digital PCR. Among 100 healthy individuals, three of them carried hotspot mutations by way of ARMS-qPCR. Of 90 patients with urinary tract infections or urinary stones, no mutations were found by ARMS-qPCR. Based on clinical detection, the ARMS-qPCR assay's sensitivity is 83.3%, specificity is 98.4%.

CONCLUSION

We here present a novel urine test for ADGRG6 hotspot mutations with high accuracy and sensitivity, which may potentially serve as a rapid and non-invasive tool for bladder cancer early screening and follow-up relapse monitoring.