Alternative splicing modulates the expression of many oncogene and tumor-suppressor isoforms. We have tested whether some alternative splicing factors are involved in cancer. We found that the splicing factor SF2/ASF is upregulated in various human tumors, in part due to amplification of its gene, SFRS1. Moreover, slight overexpression of SF2/ASF is sufficient to transform immortal rodent fibroblasts, which form sarcomas in nude mice. We further show that SF2/ASF controls alternative splicing of the tumor suppressor BIN1 and the kinases MNK2 and S6K1. The resulting BIN1 isoforms lack tumor-suppressor activity; an isoform of MNK2 promotes MAP kinase-independent eIF4E phosphorylation; and an unusual oncogenic isoform of S6K1 recapitulates the transforming activity of SF2/ASF. Knockdown of either SF2/ASF or isoform-2 of S6K1 is sufficient to reverse transformation caused by the overexpression of SF2/ASF in vitro and in vivo. Thus, SF2/ASF can act as an oncoprotein and is a potential target for cancer therapy.For about three-quarters of human genes, individual or partial exons can be included in or excluded from different versions of the mature messenger RNA by alternative splicing 1 . Many alternative splicing factors combinatorially affect this process to determine which mRNA isoforms will serve as the templates for protein synthesis in a given cell type, developmental stage or physiological state 2 .SR proteins are a family of RNA-binding proteins that are essential for splicing. They act at multiple steps of spliceosome assembly and function in both constitutive and regulated splicing. Some heterogeneous nuclear ribonucleoprotein (hnRNP) proteins, which rapidly associate with nascent transcripts, have been implicated in the repression of certain alternative splicing events 2 . hnRNP and SR proteins can have antagonistic effects on the alternative splicing of particular exons in several genes 2 . Both types of factor can bind directly to precursor (pre)-mRNA transcripts, eliciting changes in the alternative splicing of various pre-mRNA substrates in a concentration-dependent manner, both in vitro and in transfection experiments 3,4 . Thus, changes in the expression of these proteins can affect the Reprints and permissions information is available online at

The splicing-factor oncoprotein SRSF1 (also known as SF2/ASF) is upregulated in breast cancers. We investigated SRSF1’s ability to transform human and mouse mammary epithelial cells in vivo and in vitro. SRSF1-overexpressing COMMA-1D cells formed tumors, following orthotopic transplantation to reconstitute the mammary gland. In 3-D culture, SRSF1-overexpressing MCF-10A cells formed larger acini than control cells, reflecting increased proliferation and delayed apoptosis during acinar morphogenesis. These effects required the first RNA-recognition motif and nuclear functions of SRSF1. SRSF1 overexpression promoted alternative splicing of BIM and BIN1 isoforms that lack pro-apoptotic functions and contribute to the phenotype. Finally, SRSF1 cooperated specifically with MYC to transform mammary epithelial cells, in part by potentiating eIF4E activation, and these cooperating oncogenes are significantly co-expressed in human breast tumors. Thus, SRSF1 can promote breast cancer, and SRSF1 itself or its downstream effectors may be valuable targets for therapeutics development.

Recent studies revealed a surprising regenerative capacity of insulin-producing β cells in mice, suggesting that regenerative therapy for human diabetes could in principle be achieved. Physiologic β cell regeneration under stressed conditions relies on accelerated proliferation of surviving β cells, but the factors that trigger and control this response remain unclear. Using islet transplantation experiments, we show that β cell mass is controlled systemically rather than by local factors such as tissue damage. Chronic changes in β cell glucose metabolism, rather than blood glucose levels per se, are the main positive regulator of basal and compensatory β cell proliferation in vivo. Intracellularly, genetic and pharmacologic manipulations reveal that glucose induces β cell replication via metabolism by glucokinase, the first step of glycolysis, followed by closure of K(ATP) channels and membrane depolarization. Our data provide a molecular mechanism for homeostatic control of β cell mass by metabolic demand.

Several long noncoding RNAs (lncRNA) are abrogated in cancer but their precise contributions to oncogenesis are still emerging. Here we report that the lncRNA MALAT1 is upregulated in hepatocellular carcinoma (HCC) and acts as a proto-oncogene through Wnt pathway activation and induction of the oncogenic splicing factor SRSF1. Induction of SRSF1 by MALAT1 modulates SRSF1 splicing targets, enhancing the production of anti-apoptotic splicing isoforms and activating the mTOR pathway by modulating the alternative splicing of S6K1. Inhibition of SRSF1 expression or mTOR activity abolishes the oncogenic properties of MALAT1, suggesting that SRSF1 induction and mTOR activation are essential for MALAT1 induced transformation. Our results reveal a mechanism by which lncRNA MALAT1 acts as a proto-oncogene in HCC, modulating oncogenic alternative splicing through SRSF1 upregulation.

The process of alternative splicing is widely misregulated in cancer, but the contribution of splicing regulators to cancer development is largely unknown. In this study, we found that the splicing factor hnRNP A2/B1 is overexpressed in glioblastomas and is correlated with poor prognosis. Conversely, patients who harbor deletions of the HNRNPA2B1 gene show better prognosis than average. Knockdown of hnRNP A2/B1 in glioblastoma cells inhibited tumor formation in mice. In contrast, overexpression of hnRNP A2/B1 in immortal cells led to malignant transformation, suggesting that HNRNPA2B1 is a putative proto-oncogene. We then identified several tumor suppressors and oncogenes that are regulated by HNRNPA2B1, among them are c-FLIP, BIN1, and WWOX, and the proto-oncogene RON. Knockdown of RON inhibited hnRNP A2/B1 mediated transformation, which implied that RON is one of the mediators of HNRNPA2B1 oncogenic activity. Together, our results indicate that HNRNPA2B1 is a novel oncogene in glioblastoma and a potential new target for glioblastoma therapy. Cancer Res; 71(13); 4464-72. Ó2011 AACR.

SF2/ASF is a prototypical SR protein, with important roles in splicing and other aspects of mRNA metabolism. SFRS1 (SF2/ASF) is a potent proto-oncogene with abnormal expression in many tumors. We found that SF2/ASF negatively autoregulates its expression to maintain homeostatic levels. We characterized six SF2/ASF alternatively spliced mRNA isoforms: the major isoform encodes full-length protein, whereas the others are either retained in the nucleus or degraded by NMD. Unproductive splicing accounts for only part of the autoregulation, which occurs primarily at the translational level. The effect is specific to SF2/ASF and requires RRM2. The ultraconserved 3′UTR is necessary and sufficient for downregulation. SF2/ASF overexpression shifts the distribution of target mRNA towards mono-ribosomes, and translational repression is partly independent of Dicer and a 5′ cap. Thus, multiple post-transcriptional and translational mechanisms are involved in fine-tuning the expression of SF2/ASF.

MALAT1 (metastasis associated lung adenocarcinoma transcript1) is a conserved long non-coding RNA, known to regulate gene expression by modulating transcription and post-transcriptional pre-mRNA processing of a large number of genes. MALAT1 expression is deregulated in various tumors, including breast cancer. However, the significance of such abnormal expression is yet to be fully understood. In this study, we demonstrate that regulation of aggressive breast cancer cell traits by MALAT1 is not predicted solely based on an elevated expression level but is context specific. By performing loss- and gain-of-function studies, both under in vitro and in vivo conditions, we demonstrate that MALAT1 facilitates cell proliferation, tumor progression and metastasis of triple-negative breast cancer (TNBC) cells despite having a comparatively lower expression level than ER or HER2-positive breast cancer cells. Furthermore, MALAT1 regulates the expression of several cancer metastasis-related genes, but displays molecular subtype specific correlations with such genes. Assessment of the prognostic significance of MALAT1 in human breast cancer (n=1992) revealed elevated MALAT1 expression was associated with decreased disease-specific survival in ER negative, lymph node negative patients of the HER2 and TNBC molecular subtypes. Multivariable analysis confirmed MALAT1 to have independent prognostic significance in the TNBC lymph node negative patient subset (HR=2.64, 95%CI 1.35 − 5.16, p=0.005). We propose that the functional significance of MALAT1 as a metastasis driver and its potential use as a prognostic marker is most promising for those patients diagnosed with ER negative, lymph node negative breast cancer who might otherwise mistakenly be stratified to have low recurrence risk.

Cancer is a complex disease that involves aberrant gene expression regulation. Discriminating the modified expression patterns driving tumor biology from the many that have no or little contribution is important for understanding cancer molecular basis. Recurrent deregulation patterns observed in multiple cancer types are enriched for such driver events. Here, we studied splicing alterations in hundreds of matched tumor and normal RNA-seq samples of eight solid cancer types. We found hundreds of cassette exons for which splicing was altered in multiple cancer types and identified a set of highly frequent altered splicing events. Specific splicing regulators, including RBFOX2, MBNL1/2 and QKI, appear to account for many splicing alteration events in multiple cancer types. Together, our results provide a first global analysis of regulated splicing alterations in cancer and identify common events with a potential causative role in solid tumor development.