miR-520b Regulates Migration of Breast Cancer Cells by Targeting Hepatitis B X-interacting Protein and Interleukin-8

Abstract

MicroRNAs play important roles in tumor metastasis. Recently, we reported that the level of miR-520b is inversely related to the metastatic potential of breast cancer cells. In this study, we investigated the role of miR-520b in breast cancer cell migration. We found that miR-520b suppressed the migration of breast cancer cells with high metastatic potential, including MDA-MB-231 and LM-MCF-7 cells, although the inhibition of miR-520b enhanced the migration of low metastatic potential MCF-7 cells. We further discovered that miR-520b directly targets the 3-untranslated region (3UTR) of either hepatitis B X-interacting protein (HBXIP) or interleukin-8 (IL-8), which has been reported to contribute to cell migration. Surprisingly, tissue array assays showed that 75% (38:49) and 94% (36:38) of breast cancer tissues and metastatic lymph tissues, respectively, were positive for HBXIP expression. Moreover, overexpression of HBXIP was able to promote the migration of MCF-7 cells. Interestingly, HBXIP was able to regulate IL-8 transcription by NF-B, suggesting that the two target genes of miR-520b are functionally connected. In addition, we found that miR-520b could indirectly regulate IL-8 transcription by targeting HBXIP. Thus, we conclude that miR-520b is involved in regulating breast cancer cell migration by targeting HBXIP and IL-8 via a network in which HBXIP promotes migration by stimulating NF-B-mediated IL-8 expression. These studies point to HBXIP as a potential therapeutic target for breast cancer. MicroRNAs (miRNAs)3 are a class of small noncoding RNAs that act as post-transcriptional regulators of gene expression. It is currently estimated that the human genome may contain at least 700 miRNAs (1, 2). Emerging evidence has demonstrated that miRNAs can function as oncogenes or tumor suppressors involved in neoplasm development, progression, diagnosis, and prognostication (3, 4). It was recently reported that miRNAs are mutated or differentially expressed in breast cancer, with profound positive or negative effects on breast cancer cell migration. For instance, miR-10b is highly expressed in human and mouse metastatic breast cancer cell lines and positively regulates cell migration (5), and MiR-27b stimulates cell migration by targeting ST14 (6). Let-7g targets collagen type I ␣2 and inhibits cell migration in hepatocellular carcinoma (7). Although a large number of miRNAs have been identified to date, their roles in breast cancer cell migration and the underlying mechanisms of this regulation remain to be determined.Hepatitis B X-interacting protein (HBXIP) was originally identified by its interaction with the C terminus of the hepatitis B virus X protein (8). It forms a complex with survivin, leading to the suppression of apoptosis initiated through the mitochondrial cytochrome c pathway (9). HBXIP was shown to interact with the hSuv3 protein, which encodes an NTP-dependent DNA/RNA DEXH box helicase predominantly localized in mitochondria (10). Furthermore, HBXIP also plays a critical role in mitosis, serving ...

The Nuclear Import of Oncoprotein Hepatitis B X-interacting Protein Depends on Interacting with c-Fos and Phosphorylation of Both Proteins in Breast Cancer Cells

“…But, HBXIP is undetectable in normal breast tissues (6). Our recent data have shown that HBXIP acts as a novel transcriptional coactivator to promote proliferation and migration of breast cancer cells (8 -11).…”

“…ATM phosphorylates Snail, an epithelial mesenchymal transition marker, suggesting that the ATM-Snail pathway promotes tumor metastasis (48). We have demonstrated that HBXIP promotes migration of breast cancer cells (6,8 required for its nuclear import. In this study, we validated that the three phosphorylation sites of HBXIP could be phosphorylated in our system.…”

“…Plasmids and siRNAs-pCMV-3V-c-Fos, pCMV-4A-c-Fos, and full-length HBXIP constructs were previously described (6,27,28). To identify the corresponding domain that activates c-Fos, full-length HBXIP was divided into 4 fragments, including amino acids 1-82, 83-173, 83-144, and 145-173.…”

“…Wound Healing Assay-Wound healing assay for migration analysis was performed as described previously (6).…”

“…We previously demonstrated that HBXIP was a novel important oncoprotein in the development of cancer. HBXIP was overexpressed in clinical breast cancer tissues and could promote proliferation and migration through NF-B, MAPK/ERK, or PI3K/AKT pathways in breast cancer cells (6,7). Recently, we have discovered that HBXIP acts as a novel oncogenic coactivator of transcription factors, such as STAT4, SP1, E2F1, and TFIID to transactivate S100A4, LMO4, Skp2, and Lin28B in promotion of growth and migration of breast cancer cells (8 -11).…”