CAMK2D isoform 15 facilitates gefitinib resistance <italic>via</italic> AKT phosphorylation in lung adenocarcinoma

Objective: Acquired resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) is a major challenge in the treatment of lung adenocarcinoma (LUAD). Our previous study demonstrated that EGFR signaling activates calcium/calmodulin-dependent protein kinase 2 (CAMK2). However, the relationship between this mechanism and TKI resistance has not been fully elucidated. Methods: In this study the role of calcium/calmodulin-dependent protein kinase IIδ (CAMK2D) splice variants in gefitinib resistance was investigated using clinical specimens and chronically TKI-exposed cell lines. The biological effects of CAMK2D isoform 15 were evaluated using in vitro assays and in vivo xenograft models. In addition, integrative multi-omics analysis was applied to identify potential upstream regulators of CAMK2D splicing 15. Results: Analysis of clinical samples and cell models revealed that CAMK2D overexpression, particularly isoform 15 containing exon 7, was strongly associated with resistance to EGFR-TKIs. Upregulation of isoform 15 enhanced gefitinib resistance, while knockdown of isoform 15 restored drug sensitivity in vitro. Upregulation of isoform 15 significantly increased tumor growth in xenograft models. Mechanistically, isoform 15 directly interacted with AKT and promoted phosphorylation of AKT at Thr308, thereby activating anti-apoptotic signaling. Multi-omics analysis further identified small nuclear ribonucleoprotein polypeptide A1 (SNRPA1) as a key upstream splicing regulator. Downregulation of SNRPA1 promoted isoform 15 expression and induced a high-resistance phenotype. Conclusions: Our findings revealed a novel mechanism underlying EGFR-TKI resistance in which SNRPA1-controlled alternative splicing drives the expression of CAMK2D isoform 15, leading to activation of AKT signaling and gefitinib resistance. These results identified CAMK2D isoform 15 as a potential prognostic biomarker and therapeutic target, providing a rationale for splicing-directed strategies to overcome EGFR-TKI resistance in LUAD.