Heterogeneous nuclear ribonucleoprotein M promotes the progression of breast cancer by regulating the axin/ß-catenin signaling pathway.

Despite significant progress in the treatment of breast cancer due to advances in surgery, cytotoxic agents, and endocrine therapy, the prognosis for patients has not improved much. Accumulated evidence indicates that heterogeneous nuclear ribonucleoprotein M (hnRNPM) and Wnt/ß-catenin function as tumor oncogenes in the progression of many cancers. The present study aimed to explore whether HnRNPM/ß-catenin signaling molecules might serve as a genetic target for breast cancer treatment. To shed light on this issue, quantitative real-time polymerase chain reaction (qRT-PCR) detection, Western blotting, and immunohistochemical staining were performed. The hnRNPM is expressed at a much higher level in breast cancer tissues and cell lines than in noncancerous tissues and cell lines. In vitro studies revealed that overexpressed hnRNPM promoted cell proliferation and colony formation but inhibited cell apoptosis. In vivo results demonstrated that upregulation of hnRNPM dramatically increased breast cancer xenograft tumor growth. Western blotting and immunofluorescence studies revealed that hnRNPM markedly activated the Wnt/ß-catenin pathway and catalyzed its translocation from the cytoplasm to the nucleus by targeting axin, a negative regulator of Wnt/ß-catenin signaling in MCF-7 and KPL-4 cells. Elevated levels of c-Myc and cyclin D1 were observed when MCF-7 and KPL-4 cells were transfected with a hnRNPM vector. These findings indicate that the hnRNPM/axin/ß-catenin signaling pathway acts as an oncogenic promoter in the progression of breast cancer, suggesting that hnRNPM may be a potential target for the treatment of this disease.

The Drosophila heterogeneous nuclear ribonucleoprotein M protein, HRP59, regulates alternative splicing and controls the production of its own mRNA.

The Drosophila heterogeneous nuclear ribonucleoprotein M, HRP59, is a nuclear protein that associates co-transcriptionally with pre-mRNA and is necessary for the correct expression of a subset of mRNAs. We show here that the hrp59 pre-mRNA is alternatively spliced to generate two different mRNAs that differ in the presence of exon 3. Exon 3-containing transcripts make up the majority of hrp59 transcripts and encode for the functional protein, HRP59-1. Transcripts that lack exon 3 contain a premature translation termination codon and are targeted to the nonsense mediated decay pathway. We show that exon 3 inclusion is itself inhibited by HRP59 and that changes in the HRP59 protein levels affect the splicing activity of the cell. We propose that the ability of HRP59 to regulate the alternative splicing of its own pre-mRNA serves in a negative feedback loop that controls the levels of the HRP59 protein and maintains the homeostasis of the splicing environment.

Surface expression and CEA binding of hnRNP M4 protein in HT29 colon cancer cells.

Carcinoembryonic antigen (CEA) has been shown to participate in the progression and metastatic growth of colorectal cancer. However, its biological function remains elusive. Recently, we found that CEA protects colon cancer cells from undergoing apoptosis, suggesting a complex role that includes signal transduction activity. Additionally, it was reported that CEA binds to Kupffer cells and macrophages to a membrane-anchored homolog of heterogeneous nuclear protein M4 (hnRNP M4), which subsequently was named CEA-receptor (CEAR). Cytoplasmatic and membranous expression of CEAR in CEA-positive colon cancer tissues prompted us to analyze the CEA-CEAR interaction in HT29 colon cancer cells. Both, CEA and CEAR were found on the cell surface of HT29 cells, as demonstrated by confocal microscopy. Imaging analysis suggested co-localization and, thus, interaction of both molecules. To confirm this observation, immunoprecipitation experiments and Western blot analysis were performed and indicated binding of CEA and CEAR. Immunoprecipitation of CEA resulted in a pull down of CEAR. The pull down of CEAR correlated with the amount of CEA as demonstrated by ribozyme targeting of CEA. Finally, external treatment of HT29 cells with soluble CEA induced tyrosine phosphorylation of CEAR, suggesting a CEA-dependent role of CEAR in signal transduction. Future experiments will elucidate whether the CEA-CEAR interaction is involved in CEA's antiapoptotic role and mediates the prometastatic properties of CEA in colon cancer cells.