Understanding the biology of an ADCK4-NUMBL fusion in lung adenocarcinoma aggressiveness

Lung malignancies are the leading cause of cancer death. We have identified an ADCK4-NUMBL cis-SAGe fusion transcript by screening a cohort of lung adenocarcinoma patients known to lack typical oncogenic drivers. Cis-splicing between adjacent genes (cis-SAGe) is an understudied biological mechanism associated with an increase in genomic complexity. We find that the ADCK4-NUMBL fusion transcript is detectable in normal immortalized lung epithelial cells and at various levels in seven lung cancer cell lines evaluated. Likewise, measurement of the ADCK4-NUMBL Exon 14-Exon 2 transcripts in RNA derived from tumors from patients with lung adenocarcinoma revealed significant variation. A cohort of 193 lung adenocarcinoma patients was divided into high and low ADCK4-NUMBL expression groups, and overall survival comparisons were made. Kaplan- Meier analysis revealed that patients with high RNA expression (above the median) of ADCK4-NUMBL have diminished overall survival (Log-rank p <0.001) compared to patients with low expression. ADCK4-NUMBL levels were elevated in self-identified Black patients (p = 0.01), in smokers (p = 0.03), and in patients with KRAS mutations (p <0.04). No differences in ADCK4-NUMBL expression were observed when comparing patients by sex, age, stage, or body mass index. NUMBL immunoprecipitation, gel electrophoresis, and mass spectrometry analysis support the conclusion that the endogenous ADCK4-NUMBL transcript produces a protein product. Enforced expression of the ADCK4-NUMBL Exon 14-Exon 2 protein in A549 cells results in accelerated cell proliferation. These preliminary findings lead us to hypothesize that the ADCK4-NUMBL transcript produces an oncogenic protein that contributes significantly to lung cancer aggressiveness in a subset of lung cancer patients. In this pilot study, we propose the following exploratory aims to probe deeper into this general hypothesis and generate a strong premise for a future R01 application.