An alpha-kinase 2 gene variant disrupts filamentous actin localization in the surface cells of colorectal cancer spheroids

Background/Aim: Alpha-kinase 2 (ALPK2), suggested to be a novel tumour-suppressor gene downregulated by oncogenic KRAS, plays a pivotal role in luminal apoptosis in normal colonic crypts. The aim of this study was to determine the association between ALPK2 germline variants and colorectal cancer. Materials and Methods: Missense single nucleotide variants in the exons of the ALPK2 gene in 2,343 consecutive autopsy cases (1,446 cases with cancer and 897 cases without cancer) were screened using HumanExome BeadChip arrays. To address the functional effect of a missense ALPK2 variant, a 3D floating cell culture was performed using HCT116-derived human colorectal cancer cells stably expressing wild-type (wt) ALPK2 (HCT116-wtALPK2) or amino acid-substituted (sub) ALPK2 (HCT116-subALPK2). Results: We identified that one of the ALPK2 germline variants, rs55674018 (p.Q1853E), was significantly associated with the presence of cancer (adjusted odds ratio(OR)=4.39; 95% confidence interval(CI)=1.31-14.78, p=0.001). The p.Q1853E variant was present in the East Asian population and located in the immunoglobulin-like domain. Notably, the basolateral polarity of actin in the surface of HCT116-wtALPK2 spheroids was more attenuated compared to that of HCT116-subALPK2 spheroids. Furthermore, luminal apoptosis and cell aggregation were promoted by wtALPK2, but not by subALPK2 in 3D culture. Conclusion: The p.Q1853E variant of ALPK2, which had been accumulating in the Japanese population, induced a metastatic phenotype by disrupting ALPK2 function.