Importin-11 overexpression promotes the migration, invasion, and progression of bladder cancer associated with the deregulation of CDKN1A and THBS1.

OBJECTIVES: We recently determined that a novel oncogene, IPO11 from 5q12, participates in bladder cancer (BCa) progression. However, the biological function of IPO11 and the molecular mechanisms through which it contributes to BCa progression remain unclear. The aim of this study was to investigate the role of IPO11 in BCa aggressiveness and elucidate the molecular mechanisms underlying its effects in BCa.

MATERIALS AND METHODS: The mRNA expression levels of IPO11 in BIU-87, RT4, UMUC3, EJ, 5637, T24, J82, and HT-1376 cell lines were determined using quantitative real-time polymerase chain reaction. Expression of importin-11 was detected in 134 formalin-fixed and paraffin-embedded (FFPE) BCa tissues and 10 paired nonneoplastic bladder tissue specimens by immunohistochemistry. The copy number of IPO11 was examined in 25 FFPE BCa specimens using fluorescent in situ hybridization. The effects of IPO11 on migration, invasion, and cell proliferation were investigated in EJ and 5637 cell lines using RNA interference. Potential molecular mechanisms were investigated using whole transcriptome sequencing and bioinformatic approaches in EJ cells and IPO11-silenced EJ cells and verified using quantitative real-time polymerase chain reaction.

RESULTS: Endogenous IPO11 mRNA was highly expressed in 6 invasive BCa cell lines (EJ, HT-1376, UMUC3, 5637, J82, and T24) but had a low expression in the noninvasive BCa cell line BIU-87 and the papillary BCa cell line RT4. Immunohistochemical staining revealed that 87 (64.9%) of 134 FFPE BCa tissues displayed importin-11 overexpression. Moreover, importin-11 overexpression was positively associated with increased tumor stages and tumor grades, lymphatic invasion, and lymph node metastasis. Furthermore, importin-11 overexpression was detected in 100% (14/14) of BCa tissues with IPO11 amplification, and IPO11 amplification was not observed in 2 additional BCa tissues with importin-11 overexpression. Small interfering RNA-mediated knockdown of IPO11 is sufficient to inhibit the motility and invasiveness of EJ and 5637 cells. IPO11 knockdown also inhibited cell proliferation in EJ cells, whereas this was not observed in 5637 cells or the in vivo experiments. Using whole transcriptome sequencing, we found that 22 genes (including IPO11) were differentially expressed in IPO11-silenced EJ cells compared with wild-type EJ cells, 4 of which were upregulated, and 18 of which were downregulated. KEGG pathway enrichment analysis of the significantly differentially expressed genes showed that the proteoglycans in cancer pathway (pathway Id: hsa05205) was most significantly enriched among 10 genetically altered pathways and referred to 6 significantly altered genes (CDKN1A, HBEGF, PTK2, THBS1, CCNG2, and EGR1). The next 3 most significantly enriched pathways in order were the p53, ErbB, and BCa pathways. CDKN1A and THBS1 were the most 2 frequently covered genes and were involved in 9 and 6 pathways, respectively. They were also 2 key proteins in the BCa pathway (pathway Id: hsa05219) that were downregulated in IPO11-knockdown EJ cells compared with wild-type EJ cells.

CONCLUSIONS: Importin-11 overexpression can promote BCa cell invasiveness, probably associated with the deregulation of CDKN1A and THBS1 primarily through the activation of the proteoglycans in cancer pathway and the classical BCa pathway. Importin-11 may be a useful target through which the progression of noninvasive BCa to invasive BCa can be blocked.