B76-19 Imp3 and Egfr Silencing Suppress Cigarette Smoke-induced Cyclin D1 Activation in Human Airway Epithelial Cells

Abstract Introduction Cyclin D1 is a proliferation gene that plays a key role in the cell cycle. It helps control cell division, functions as a transcriptional co-regulator, and modulates the expression of genes involved in DNA replication. Specifically, Cyclin D1 phosphorylates the retinoblastoma (Rb) protein to induce cell cycle progression and propel proliferation. IMP3 is an RNA-binding protein involved in post-transcriptional regulation, influencing mRNA stability, localization, and translation. IMP3 stabilizes mRNA transcripts of several oncogenic and cell cycle-related proteins, promoting their translation. Epidermal Growth Factor Receptor (EGFR) is a transmembrane receptor tyrosine kinase that regulates epithelial cell proliferation, differentiation, and survival. Upon ligand binding, EGFR undergoes autophosphorylation and activates downstream signaling cascades, which converge on transcriptional targets including Cyclin D1. In airway epithelial cells, cigarette smoke exposure (CSE) has been shown to increase Cyclin D1 levels, promoting abnormal epithelial proliferation and sustained remodeling responses characteristic of chronic obstructive pulmonary disease (COPD). It remains unclear whether this smoke induced activation of Cyclin D1 is dependent on IMP3 and EGFR. We hypothesized that Cyclin D1 induction under cigarette smoke conditions is dependent on IMP3 and EGFR. Methods Primary human small airway epithelial cells (SAECs) were grown to 65-75% confluency in T-25 flasks. These cells were transfected separately with control, IMP3, and EGFR siRNA using HiPerFect reagent and then treated with 5% CSE for 24 hours. Protein lysates were collected and immunoblots for Cyclin D1, IMP3, EGFR, and GAPDH were conducted. Results The smoke mediated induction of Cyclin D1 protein levels in baseline conditions was suppressed under IMP3 and EGFR knockdown conditions. These findings suggest that IMP3 and EGFR are required for full Cyclin D1 induction in response to cigarette smoke. Conclusions These experiments indicate that IMP3 and EGFR are essential mediators of cigarette smoke induced Cyclin D1 activation in airway epithelial cells. Since Cyclin D1 drives abnormal proliferation and remodeling, targeting IMP3 and EGFR may represent a potential therapeutic strategy to limit proliferation in the diseased state of COPD. This abstract is funded by: NIH