Article

Regulation of CD45 Alternative Splicing by Heterogeneous Ribonucleoprotein, hnRNPLL

Department of Pathology, Immune Disease Institute, Harvard Medical School, Boston, MA 02115, USA.
Science (Impact Factor: 31.48). 09/2008; 321(5889):686-91. DOI: 10.1126/science.1157610
Source: PubMed

ABSTRACT The transition from naïve to activated T cells is marked by alternative splicing of pre-mRNA encoding the transmembrane phosphatase
CD45. Using a short hairpin RNA interference screen, we identified heterogeneous ribonucleoprotein L-like (hnRNPLL) as a critical
inducible regulator of CD45 alternative splicing. HnRNPLL was up-regulated in stimulated T cells, bound CD45 transcripts,
and was both necessary and sufficient for CD45 alternative splicing. Depletion or overexpression of hnRNPLL in B and T cell
lines and primary T cells resulted in reciprocal alteration of CD45RA and RO expression. Exon array analysis suggested that
hnRNPLL acts as a global regulator of alternative splicing in activated T cells. Induction of hnRNPLL during hematopoietic
cell activation and differentiation may allow cells to rapidly shift their transcriptomes to favor proliferation and inhibit
cell death.

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    • "Thus, a pre-selection of cells based on their low side scatter (SSC, i.e. their content of organelles capable of scattering the laser light) and their CD45 expression is often employed in multicolour assays. The latter surface marker has served as a model for protein isoforms generation by alternative splicing (Oberdoerffer et al, 2008) and is usually, but by no means always, expressed in decreased amounts on leukaemic cells (Borowitz et al, 1993; Lacombe et al, 1997; Miyachi et al, 1999). As will be seen from Fig 1, the CD45low/SSClow can be an important way of focusing on the AML blasts and has been proven to significantly increase the sensitivity of the MFC approach (Kern et al, 2004). "
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    • "Others have used exon arrays to investigate alternative splicing differences between normal and diseased tissues (Gardina et al. 2006; French et al. 2007), in the presence of a stimulus (McKee et al. 2007), or instances of tissue-specific alternative splicing (Clark et al. 2007). To date, relatively few transcription and/or splicing factors' functions have been investigated by exon array analysis (Hung et al. 2008; Oberdoerffer et al. 2008; Xing et al. 2008; Sun and Li 2009; Warzecha et al. 2009). In the work presented here, Tat-SF1 depletion led to many changes in overall transcript levels, with the overwhelming majority of these genes showing decreased expression. "
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    • "For example, activation through Ras-and protein kinase C-dependent pathways results in altered phosphorylation status of SR proteins leading to changes in activity or subcellular localization (Blaustein et al., 2005; Lynch and Weiss, 2000; Blaustein et al., 2004). More recently, a master regulator of activation-induced splice changes in T cells, hnRNPLL, was identified and found to be necessary for CD45 alternative exon splicing (Oberdoerffer et al., 2008; Topp et al., 2008; Wu et al., 2008). Thus, environmental signals may affect expression, secondary modifications and trafficking of mammalian CD45 splicing regulator proteins or the activity of modulating kinases. "
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