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Antagonistic role of hnRNP A1 and KSRP in the regulation of let-7a biogenesis

Nature Structural & Molecular Biology volume 17, pages 1011–1018 (2010)Cite this article

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Abstract

The pluripotency-promoting proteins Lin28a and Lin28b act as post-transcriptional repressors of let-7 miRNA biogenesis in undifferentiated embryonic stem cells. The levels of mature let-7a differ substantially in cells lacking Lin28 expression, indicating the existence of additional mechanism(s) of post-transcriptional regulation. Here, we present evidence supporting a role for heteronuclear ribonucleoprotein A1 (hnRNP A1) as a negative regulator of let-7a. HnRNP A1 binds the conserved terminal loop of pri-let-7a-1 and inhibits its processing by Drosha. Levels of mature let-7a negatively correlate with hnRNP A1 levels in somatic cell lines. Furthermore, hnRNP A1 depletion increased pri-let-7a-1 processing by cell extracts, whereas its ectopic expression decreased let-7a production in vivo. Finally, hnRNP A1 binding to let-7a interferes with the binding of KSRP, which is known to promote let-7a biogenesis. We propose that hnRNP A1 and KSRP have antagonistic roles in the post-transcriptional regulation of let-7a expression.

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Figure 1: HnRNP A1 specifically binds to the terminal loop of pri-let-7a-1.
Figure 2: Levels of mature let-7a correlate negatively with the levels of hnRNP A1 in human cells.
Figure 3: Ectopic expression of hnRNP A1 in HeLa and Astrocytoma 1321N1 cells reduces the levels of endogenous mature let-7a.
Figure 4: HnRNP A1 negatively regulates the Drosha-mediated processing of let-7a-1.
Figure 5: HnRNP A1 binds and remodels the terminal loop of pri-let-7a-1.
Figure 6: KSRP binds to the terminal loop of pri-let-7a-1.
Figure 7: KSRP and hnRNP A1 compete for binding to the pri-let-7a-1 terminal loop.
Figure 8: Cartoon displaying the antagonism of KSRP and hnRNP A1 in the post-transcriptional regulation of let-7a processing.

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Acknowledgements

We are grateful to N. Hastie and S. Macias for comments and critical reading of the manuscript, H. Kooshapur (Technical University Munich) and M. Sattler (Technical University Munich) for the generous gift of recombinant UP1 protein and D. Black (Univ. of California, Los Angeles) for providing a KSRP expression vector. This work was supported by Core funding from the Medical Research Council and a project grant from the Wellcome Trust, with additional funds from Eurasnet (European Alternative splicing Network-FP6).

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  1. Medical Research Council Human Genetics Unit, Institute of Genetics and Molecular Medicine, Western General Hospital, Edinburgh, UK

    Gracjan Michlewski & Javier F Cáceres

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G.M. and J.F.C. conceived, designed and interpreted the experiments; G.M. performed the experiments and data analysis; J.F.C. supervised the whole project; both authors co-wrote the manuscript.

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Correspondence to Javier F Cáceres.

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Michlewski, G., Cáceres, J. Antagonistic role of hnRNP A1 and KSRP in the regulation of let-7a biogenesis. Nat Struct Mol Biol 17, 1011–1018 (2010). https://doi.org/10.1038/nsmb.1874

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