Abstract
Human transforming acidic coiled-coil containing protein 3 (TACC3) is a non-motor mitotic spindle protein that plays a critical role during mitosis. However, TACC3 has also been implicated in the regulation of cell growth and differentiation in both normal and malignant cellular contexts. It has been recently shown that TACC3 can interact with various transcription factors/co-factors sequestering them in the cytoplasm and hence preventing their binding to, and activation of gene promoters in the nucleus. Consequently, deregulation of TACC3 is commonly linked to cancer development and increased expression of TACC3 is found in high-grade tumours such as glioblastoma multiforme (GBM), non-small cell lung cancer and invasive breast cancers. We are investigating the role of TACC3 in the initiation and progression of GBM and aim to identify TACC3-dependent gene expression networks and protein interaction partners. Analysis of protein expression in GBM tissue sections revealed a predominantly cytoplasmic localisation of TACC3. This staining pattern was also observed in other cancer tissues (breast, lung and lymphoma) and was in contrast to the low expression of TACC3 observed in non-cancerous tissues. Strikingly the cytoplasmic localisation of TACC3 was also apparent in vitro (patient derived GBM cells) and in vivo (xenograft tumours). We therefore utilised the cell cycle indicator FUCCI to determine the cell cycle phases of our GBM cells with regards to TACC3 expression. Our results indicated that the observed cytoplasmic TACC3 expression pattern arose predominantly during late S and early G2 phase. To gain insight into the role of cytoplasmic TACC3, we carried out gene expression analysis on isolated cell cycle populations from patient-derived GBM cells in the presence or absence of TACC3 targeting shRNAs. Initial principal components and gene set enrichment analysis unveiled key pathways altered in TACC3 knockdown populations relative to controls. Significant transcriptional changes were revealed for S phase and G2 cells in the absence of TACC3, including upregulation of the transcription factor SP1 and alterations in p53 regulated apoptotic pathways, PI3K/Akt and MAPK signalling pathways. Further analysis is ongoing and includes cross-referencing with proteomics data from TACC3 pull-downs and co-immunoprecipitation a studies. Overall, our data indicate a novel cell cycle-dependent regulatory role for cytoplasmic TACC3 in glioma, further supporting the notion of an oncogenic/tumour progression-promoting role of the TACC3 protein.