Supplementary Material for: The ERBB2 Exonic Variant Pro1170Ala Modulates Mitogen-Activated Protein Kinase Signaling Cascades and Associates with Allergic Asthma

<b><i>Introduction:</i></b> Previous studies have indicated the <i>ERBB2</i> genetic variants in the 17q12 locus might be associated with asthma; however, the functional effects of these variants on asthma risk remain inconclusive. This study aimed to characterize the functional roles of asthma-associated <i>ERBB2</i> single nucleotide polymorphisms (SNPs) in asthma pathogenesis by performing genetic association and functional analysis studies. <b><i>Methods:</i></b> This study belongs to a part of an ongoing Singapore/Malaysia cross-sectional genetics and epidemiological study (SMCSGES). Genotype-phenotype associations were assessed by performing a genotyping assay on <i>n</i> = 4,348 ethnic Chinese individuals from the SMCSGES cohort. The phosphorylation levels of receptors and signaling proteins in the MAPK signaling cascades, including ErbB2, EGFR, and ERK1/2, were compared across the genotypes of asthma-associated SNPs through in vitro and ex vivo approaches. <b><i>Results:</i></b> The <i>ERBB2</i> tag-SNP rs1058808 was significantly associated with allergic asthma, with the allele “G” identified as protective against the disease (adjusted logistic <i>p</i> = 6.56 × 10⁻⁹, OR = 0.625, 95% CI: 0.544–0.718). The allele “G” of rs1058808 resulted in a Pro1170Ala mutation that results in lower phosphorylation levels of ErbB2 in HaCat cells (<i>p</i> &lt; 0.001), whereas the overall <i>ERBB2</i> mRNA expression and the phosphorylation levels of EGFR remained unaffected. In the SMCSGES cohort, individuals carrying the genotype “GG” of rs1058808 had lower phosphorylated ERK1/2 proteins in the MAPK signaling cascade. A lower phosphorylation level of ERK1/2 was also associated with reduced asthma risk. <b><i>Conclusions:</i></b> The present findings highlighted the involvement of a functional exonic variant of <i>ERBB2</i> in asthma development via modulating the MAPK signaling cascade.