Abstract 1300: Far upstream element binding proteins (FBP)-1 and FBP-2 in non-small cell lung cancer: Key factors regulating tumor cell proliferation, migration, and invasion

Abstract

Abstract The far upstream element (FUSE)-binding proteins (FBP)- 1, FBP-2, and FBP-3 represent a family of single-strand nucleic acid binding factors, regulating transcriptional as well as post-transcriptional processes. Elevated expression and pro-tumorigenic functions of all FBPs have been described for human liver cancer [1, 2]. First data indicated that FBP-1 affects microtubule dynamics through regulating MT-destabilizing factors in non-small cell lung cancer (NSCLC) [3], however, comprehensive studies analyzing the expression and functional relevance of all FBPs in NSCLCs are missing so far. In order to define the expression of FBPs in lung cancer, FBP-transcript and protein levels were analysed in primary human NSCLC tissue samples. Semiquantitative real-time PCR as well as Tissue-Micro-Array (TMA) analyses revealed an elevated expression of FBP-1 and FBP-2 in most NSCLC tissue samples (>60%) in comparison to non-tumorous specimens. Interestingly, nuclear accumulation of FBP-1 significantly correlated with FBP-2 expression (r=0.33; p<0.01), suggesting common regulatory mechanisms. In vitro, transient inhibition of FBP-1 by gene-specific siRNAs in NSCLC cell lines (Calu-6) was associated with decreased tumor cell viability (-76%; MTT assay), proliferation (-83%; BrdU assay), and increased apoptosis (2.8-fold; Nicoletti FACS assay). In contrast, inhibition of FBP-2 reduced cell viability of Calu-1 cells (-32%; MTT assay) but predominantly reduced tumor cell migration (-62%; two-dimensional scratch assay) as well as tumor cell invasion (-81%; sprouting assay) in all analyzed NSCLC cell lines (Calu-1, Calu-6, and A549), suggesting that both FBP isoforms facilitate partly distinct tumor-supporting effects. Surprisingly, efficient single-gene inhibition of FBP-1 or FBP-2 in A549 cells did not affect tumor cell viability. In contrast, the concomitant knock down of both FBP isoforms resulted in significantly decreased cell viability (-69%), suggesting that some FBP family members may compensate the loss of other members. Actually, FBP-2 negatively regulates FBP-1 expression in A549 cells, resulting in increased FBP-1 transcript and protein levels after FBP-2 inhibition. Therefore, functional compensation prevents A549 cells from anti-tumorigenic effects after FBP-2 knock down. In summary, this study provides evidence that coordinated overexpression of FBP-1 and FBP-2 is a frequent event in NSCLCs and that both factors are support tumor growth and NSCLC cell dissemination. Interestingly, partial functional redundance and mutual negative regulation of FBPs indicate that these factors may fine-tune the oncogenic behavior of NSCLC cells.