Jianliang Xu, Sophia Beng Hui Lim, Mei Yong Ng, Safiah Mohamed Ali, Kausalya PJ, Vachiranee Limviphuvadh°, Sebastian Maurer-Stroh° and Walter Hunziker
Epithelial Cell Biology Laboratory, Institute of Molecular and Cell Biology (IMCB) and
° Bioinformatics Institute (BII), Agency for Science Technology and Research (A*STAR), Singapore
Published in Stem Cells on July 10, 2012
ZO-1/Tjp1 is a cytosolic adaptor that links tight junction (TJ) transmembrane proteins to the actin cytoskeleton and has also been implicated in regulating cell proliferation and differentiation by interacting with transcriptional regulators and signaling proteins. To explore possible roles for ZO-1 in mESCs, we inactivated the ZO-1 locus by homologous recombination. The lack of ZO-1 was found to affect mESC self-renewal and differentiation in the presence of LIF/Bmp4 or following removal of the growth factors. Our data suggest that ZO-1 suppresses Stat3 and Smad1/5/8 activities and sustains Erk activity to promote mESC differentiation. Interestingly, Smad2, critical for human but not mouse ESC self-renewal, was hyperactivated in ZO-1-/- mESCs and RhoA protein levels were concomitantly enhanced, suggesting attenuation of the non-canonical Tgfβ/Activin/Nodal pathway that mediates ubiquitination and degradation of RhoA via the TJ proteins Occludin, Par6 and Smurf1, and activation of the canonical Smad2 dependent pathway. Furthermore, Bmp4 induced differentiation of mESCs in the absence of LIF was suppressed in ZO-1-/- mESCs, but differentiation along the neural or cardiac lineages were not disturbed. These findings reveal novel roles for ZO-1 in mESC self-renewal, pluripotency and differentiation by influencing several signaling networks that regulate these processes. Possible implications for the differing relevance of Smad2 in mouse and human ESC self-renewal and how ZO-1 may connect to the different pathways are discussed.
Figure Legend: Effects of inactivating ZO-1 and possible connections on signaling pathways involved in mESC self-renewal and differentiation. The diagram shows the ZO-1 deletion pathway map and connections that may play a role. Key proteins are indicated by gene symbol in green boxes, the deleted ZO-1 in a red box. Effects or actions established in this study are indicated by red lines. Relevant previously known direct interactions as cited in the main text are shown as solid black lines, whereas indirect effects are represented by dashed lines. This pathway map was created with the help of KEGG, GeneMANIA and STRING.
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