LINE-1 Transcript Heterogeneity in Non-Small Cell Lung Cancers Is Driven by Host Genomic Context and Conserved Functional Hotspots

Background: Long INterspersed Element-1 (LINE-1) retrotransposons comprise 17–20% of the human genome. These retroelements are normally silenced early in embryonic development through epigenetic mechanisms and reawakened during oncogenesis, leading to transcriptional dysregulation, genomic instability, and immune evasion. Methods: In the present study, we categorized LINE-1 transcripts across 121 non-small cell lung cancer (NSCLC) cell lines from the Cancer Cell Line Encyclopedia (CCLE) by subfamily, length, orientation, chromosomal origin, and distribution. In addition, high-prevalence insertions were mapped to nearby genes to assess potential functional interactions. Results: LINE-1 transcript abundance and length in NSCLC were dominated by evolutionarily young subfamilies, particularly L1HS and L1PA2 through L1PA5. Chromosomal patterns were conserved across NSCLC subtypes, with modest enrichment of L1HS activity on Chromosome 4 and the X Chromosome. The lung squamous cell carcinoma (LSQCC) subtype exhibited the highest total levels of L1HS expression relative to other NSCLC subtypes. Race modestly influenced LINE-1 transcript abundance, with cell lines derived from self-identified African American individuals showing elevated overall LINE-1 and L1HS expression. Age showed a weak positive correlation with total LINE-1 abundance. Integrative analysis revealed recurrent hotspots at 22q12.1 and 20p11.21 that were transcriptionally active across subtypes and coincided with previously reported intact LINE-1 elements active in epithelial cancers. Recurrent insertions were located near cancer-associated genes, including RB1, NEDD4, FTO, LAMA2, NOD1, and KCNB2, implicating LINE-1 activity in cis-regulatory remodeling of oncogenic pathways. Conclusions: Together, these findings indicate that LINE-1 transcript heterogeneity in NSCLC is shaped by host genomic architecture and conserved functional hotspots, providing new insights into the mechanisms of genetic and epigenetic dysregulation associated with LINE-1 retroelements.