Previously, we have shown that LSD1 overexpression in many different cancer types correlates with a poor clinical outcome. In the present study, we now collected evidence that LSD1 is a crucial factor involved in non-small cell lung cancer initiation, progression, and metastasis.
Histone-modifying repressor and activator complexes are central players of tumour-related gene regulation that leads to cancer specific cell signalling. Lysine-specific demethylase 1 (LSD1/KDM1A) is shown to specifically remove mono- and dimethyl groups from histone H3 at lysine 4 or 9, resulting in gene repression or activation, respectively. Non-small cell lung cancer (NSCLC) is one of the leading causes of deaths worldwide. Our recent studies revealed that LSD1 overexpression is highly associated with NSCLC malignancy (Figure 1).
We measured LSD1 expression on established tissue microarrays (TMAs) comprising a wide panel of lung cancers, all comprehensively characterised for lung cancer relevant genetic alterations by deep sequencing and fluorescence in situ hybridisation. In lung adenocarcinomas (AC) carrying a KRAS mutation, LSD1 expression seemed to be lower than in non-KRAS-mutated tumours (Figure 1). These findings were confirmed by analysis of LSD1 expression in various KRAS-mutated versus wild-type AC cells. In agreement, the anti-proliferative response to LSD1 knockdown (KD) was less efficient in lung cancer cells, harbouring the constitutive active KRAS mutant (A549), in comparison to non-KRAS mutated lung AC cells (PC9) Figure 2).
In addition, extensive chromatin immuneprecipitation followed by whole genome analysis (ChIP-Seq) and expression profiling studies revealed a strong effect of LSD1 on gene expression of lung cancer cells. Hereby, we observed a marked down-regulation of the integrin sets by LSD1 silencing in KRAS-mutated A549 cells (Figure 2). This is of particular interest, because we could show that a non-canonical integrin β3/KRAS/NF-κB signalling pathway, which was recently found to be essential for the maintenance of cancer stem cells and acquisition of Erlotinib drug resistance, was affected by LSD1.
Importantly, LSD1 is suggested to influence lung development by regulating lung-lineage specific transcription factors, such as NKX2.1 and FOXA1. Therefore, we postulate that LSD1 plays a potential role as a switch between maintenance and differentiation of lung progenitor cells. To evaluate the impact of LSD1 in lung cell differentiation processes, we have established the isolation of bronchoalveolar stem cells (BASC) by FACS sorting of CD45, PECAM negative, while EPCAM- and Sca1-positve cell fractions. LSD1 silencing in the characterized BASC fraction, isolated from doxycycline inducible teton shLSD1 mice, showed an altered expression profile of markers, which are involved in BASC and alveolar epithelial AT2 cell development. These findings allow us to hypothesize that LSD1 functions in NSCLC tumour initiation, affecting AT2 cell differentiation, expansion, or their oncogenic susceptibility.
Interestingly, our data on non-small cell lung cancer (NSCLC) mouse models and cell culture systems support recent reports that the histone-modifying machinery is not only crucial for transcriptional regulation, but also for mechanisms involved in DNA repair and in RNA processing. Most notably, the regulation of mRNA alternative splicing is closely linked to the histone-modified regulation of mRNA transcriptional elongation providing first evidence that histone modification also drives oncogenic signalling on the basis of alternative splicing and mRNA export processing. Furthermore, current comprehensive screening of LSD1 interaction partners in non-small cell lung cancer cells revealed cooperative binding to main alternative splicing factors e.g. serine/arginine-rich splicing factors (SRSF) and heterogeneous nuclear ribonucleoproteins (hnRNP). Based on this data, we suggest a main function of LSD1 in triggering the shift from a quiescent to an oncogenic alternatively spliced transcriptome.
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Institute for Pathology
Principal Investigator - A 01
Executive Board Membershow more…
So-Young Lim (PostDoc)
Priya Dalvi (PhD student)
Iris Macheleidt (PhD student)
Hannah Eischeid (technician)