Abstract 4059: CDK1-dependent hyperphosphorylation of NFIB governs its pro-metastatic function in SCLC

Abstract Small cell lung cancer (SCLC) is a highly aggressive type of lung cancer. Its ability to form a metastatic spread in the early stages of disease accounts for high morbidity rates. Despite initial high rates of response to the most common line of treatment - conventional chemotherapy, majority of SCLC patients suffer from chemoresistant recurrence. Lack of full understanding of molecular basis driving metastasis and resistance are main obstacles in developing more efficient treatments. Several recent studies reported that nuclear factor I/B (NFIB) plays a role in promoting metastasis of SCLC through modulating chromatin accessibility. Moreover, NFIB is frequently found to be overexpressed or amplified in human SCLC and its high levels correlate with poor overall survival. Although oncogenic properties of NFIB have also been reported in studies on melanoma and triple negative breast cancer, other research, involving non-small cell lung cancer, glioblastoma, osteosarcoma and cutaneous squamous cell carcinoma suggest, that NFIB may also function as a tumor suppressor. The nature of this contradictions remains elusive and implies that the function of NFIB might depend on tissue specific regulation, e.g. post-translation modification (PTM). In this study we demonstrate that NFIB undergoes hyperphosphorylation during M-phase. Utilizing kinase specific inhibitors, siRNA and in vitro assays with recombinant proteins, we identified cyclin-dependent kinase 1 (CDK1) as a specific enzyme responsible for phosphorylation of NFIB during M-phase. Using Mass Spectrometry analysis of PTM of NFIB protein, we discovered specific amino acid targets of CDK1 and generated a quadruple NFIB mutant (Ser->Ala) construct, unable to undergo hyperphosphorylation during M-phase. qPCR analysis revealed that expression of phospho-incompetent form of NFIB in human SCLC cell lines resulted in altered expression of EMT-related genes in the fashion similar to NFIB knock-down. Altogether, these results suggest that phosphorylation of NFIB by CDK1 regulates its pro-metastatic function in SCLC. It also underlines the value of further research on targeting phosphorylation state of NFIB in aiding standard chemotherapeutic regimes. Citation Format: Pawel Nowialis, Lina Song, Thi Na Nguyen, Thi Kim Ngan Bui, Wenjing Na, Ryan Clay, Kunyang Li, Lingtao Jin. CDK1-dependent hyperphosphorylation of NFIB governs its pro-metastatic function in SCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4059.