CD44 splice isoform switching in human and mouse epithelium is essential for epithelial-mesenchymal transition and breast cancer progression
Rhonda L. Brown, … , Jing Yang, Chonghui Cheng
Rhonda L. Brown, … , Jing Yang, Chonghui Cheng
Published March 1, 2011; First published February 14, 2011
Citation Information: J Clin Invest. 2011;121(3):1064-1074. https://doi.org/10.1172/JCI44540.
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Research Article Oncology

CD44 splice isoform switching in human and mouse epithelium is essential for epithelial-mesenchymal transition and breast cancer progression

Abstract

Epithelial-mesenchymal transition (EMT) is a tightly regulated process that is critical for embryogenesis but is abnormally activated during cancer metastasis and recurrence. Here we show that a switch in CD44 alternative splicing is required for EMT. Using both in vitro and in vivo systems, we have demonstrated a shift in CD44 expression from variant isoforms (CD44v) to the standard isoform (CD44s) during EMT. This isoform switch to CD44s was essential for cells to undergo EMT and was required for the formation of breast tumors that display EMT characteristics in mice. Mechanistically, the splicing factor epithelial splicing regulatory protein 1 (ESRP1) controlled the CD44 isoform switch and was critical for regulating the EMT phenotype. Additionally, the CD44s isoform activated Akt signaling, providing a mechanistic link to a key pathway that drives EMT. Finally, CD44s expression was upregulated in high-grade human breast tumors and was correlated with the level of the mesenchymal marker N-cadherin in these tumors. Together, our data suggest that regulation of CD44 alternative splicing causally contributes to EMT and breast cancer progression.

Authors

Rhonda L. Brown, Lauren M. Reinke, Marin S. Damerow, Denise Perez, Lewis A. Chodosh, Jing Yang, Chonghui Cheng

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Figure 1

Switch in CD44 isoform expression during EMT.

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Switch in CD44 isoform expression during EMT. (A) Immunoblot analysis of...
(A) Immunoblot analysis of CD44 isoforms during tamoxifen-induced (TAM-induced) EMT in HMLE cells expressing Twist-ER (HMLE/Twist-ER). The CD44 antibody recognizes CD44v and CD44s isoforms, although with conceivably higher affinity for CD44s. Immunoblots of EMT markers E-cadherin and N-cadherin confirm that these cells undergo EMT. (B) qRT-PCR analysis of levels of CD44 isoforms using primers that specifically detect either CD44s or CD44v containing variable exons v5 and v6 (v5/6). Relative expression levels of CD44s or CD44v5/6 in TAM-treated cells were normalized to untreated cells at each time point, and the results are shown relative to day 0. Error bars indicate SD; n = 4. (C) Relative mRNA levels of all CD44 isoforms in TAM-treated cells were normalized to untreated cells at each time point, and results are shown relative to day 0. Error bars indicate SD; n = 4. (D) Immunoblot analysis of CD44 isoforms during EMT induced by tamoxifen-mediated Snail-ER translocation to the nucleus in HMLE/Snail-ER cells (left), TGF-β (5 ng/ml) treatment in HMLE cells (middle), or Twist expression in MDCK cells (right). Immunoblots of EMT markers E-cadherin and N-cadherin confirm that these cells undergo EMT.