Cytoplasmic PML function in TGF-β signalling


Transforming growth factor β (TGF-β) is a pluripotent cytokine that controls key tumour suppressive functions1,2,3, but cancer cells are often unresponsive to it1,4. The promyelocytic leukaemia (PML) tumour suppressor of acute promyelocytic leukaemia (APL) accumulates in the PML nuclear body, but cytoplasmic PML isoforms of unknown function have also been described5,6. Here we show that cytoplasmic Pml is an essential modulator of TGF-β signalling. Pml-null primary cells are resistant to TGF-β-dependent growth arrest, induction of cellular senescence and apoptosis. These cells also have impaired phosphorylation and nuclear translocation of the TGF-β signalling proteins Smad2 and Smad3, as well as impaired induction of TGF-β target genes. Expression of cytoplasmic Pml is induced by TGF-β. Furthermore, cytoplasmic PML physically interacts with Smad2/3 and SARA (Smad anchor for receptor activation) and is required for association of Smad2/3 with SARA and for the accumulation of SARA and TGF-β receptor in the early endosome. The PML–RARα oncoprotein of APL can antagonize cytoplasmic PML function and APL cells have defects in TGF-β signalling similar to those observed in Pml-null cells. Our findings identify cytoplasmic PML as a critical TGF-β regulator, and further implicate deregulated TGF-β signalling in cancer pathogenesis.

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Figure 1: Pml is essential for TGF-β1 transcriptional and biological functions.
Figure 4: Aberrant TGF-β1 signalling in APL.
Figure 2: cPML interacts physically and functionally with Smad2/3 and SARA.
Figure 3: PML is required for TβRI/II and SARA localization in the early endosome.


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We are grateful to C. Chang, K. S. Chang, H. Y. Kang, Y. B. Kang, S. W. Lowe, P. G. Pelicci, M. Reiss, T. Sollner and J. L. Wrana for reagents and advice. Special thanks to all the members of the Pandolfi laboratory for comments and discussion. We also thank T. Merghoub and I. Guernah for technical help, R. Hobbs and L. DiSantis for critical reading and preparation of the manuscript. This work was supported by National Institutes of Health grants to P.P.P.

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Correspondence to Pier Paolo Pandolfi.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Methods (DOC 20 kb)

Supplementary Figure Legends (DOC 24 kb)

Supplementary Figure 1

cPML is induced by TGF-β1 and exhibits a punctate cytoplasmic localization pattern. (PPT 790 kb)

Supplementary Figure 2

Role of cPml in TGF-β1 signal transduction. (PPT 1480 kb)

Supplementary Figure 3

Determination of the cPML and Smad3 regions required for their physical interaction. (PPT 407 kb)

Supplementary Figure 4

cPML, SARA, and Smad3 colocalize in cytoplasmic region. (PPT 1186 kb)

Supplementary Figure 5

Colocalization of Smad3 and SARA is impaired in Pml-/- MEFs. (PPT 222 kb)

Supplementary Figure 6

Localization of endogenous TbRI to the early endosome is impaired in Pml-/- MEFs. (PPT 763 kb)

Supplementary Figure 7

Endogenous cPml colocalizes with EEA1. (PPT 354 kb)

Supplementary Figure 8

cPML interacts with TβRI and TβRII. (PPT 196 kb)

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