Exon-centric regulation of pyruvate kinase M alternative splicing via mutually exclusive exons

Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
Journal of Molecular Cell Biology (Impact Factor: 6.77). 11/2011; 4(2):79-87. DOI: 10.1093/jmcb/mjr030
Source: PubMed


Alternative splicing of the pyruvate kinase M gene (PK-M) can generate the M2 isoform and promote aerobic glycolysis and tumor growth. However, the cancer-specific alternative splicing regulation of PK-M is not completely understood. Here, we demonstrate that PK-M is regulated by reciprocal effects on the mutually exclusive exons 9 and 10, such that exon 9 is repressed and exon 10 is activated in cancer cells. Strikingly, exonic, rather than intronic, cis-elements are key determinants of PK-M splicing isoform ratios. Using a systematic sub-exonic duplication approach, we identify a potent exonic splicing enhancer in exon 10, which differs from its homologous counterpart in exon 9 by only two nucleotides. We identify SRSF3 as one of the cognate factors, and show that this serine/arginine-rich protein activates exon 10 and mediates changes in glucose metabolism. These findings provide mechanistic insights into the complex regulation of alternative splicing of a key regulator of the Warburg effect, and also have implications for other genes with a similar pattern of alternative splicing.

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    • "This mRNA species accounted for $40% of the PKM transcript in Pkm2 D/D tumors (Figure 2H), was identified by sequencing to result from the splicing of exon 8 to exon 11 (Figures S2D, S2F, S2G), and is hereafter referred to as PKM-skip. Splicing of PKM pre-mRNA to produce PKM2 transcript involves repression of exon 9 inclusion and activation of exon 10 inclusion by the binding of specific splicing factors to sequences within the alternatively spliced exons (Clower et al., 2010; David et al., 2010; Wang et al., 2012). Thus, the absence of exon 10 together with repression of exon 9 likely explains the presence of the PKM-skip mRNA species in Pkm2 D/D tumors (Chen et al., 2012). "
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    • "However, independent of their tissue of origin most cancer cells are PKM2 positive. Recent work showed how a mutually exclusive splicing event determines whether PKM2 is expressed and able to promote the Warburg effect.[56] Exon-blockage by heterogeneous nuclear ribonucleoproteins (hnRNPs) (PKM1-specific exon) in combination with serine/arginine-rich splicing factor 3 (SRSF3) binding to an exonic splicing enhancer (PKM2-specific exon), activates PKM1-specific exon exclusion and favors PKM2 production,[5–7] [Figure 1]. "
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