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Updated: Dec 26, 2025
Studying TGF-β Signaling and TGF-β-induced Epithelial-to-mesenchymal Transition in Breast Cancer and Normal Cells
Published on: October 27, 2020
PMEPA1/TMEPAI isoforms function via its PY and Smad-interaction motifs for tumorigenic activities of breast cancer
Meidi U Puteri1, Yukihide Watanabe1, Bantari W K Wardhani1,2
1Department of Experimental Pathology, Graduate School of Comprehensive Human Sciences and Faculty of Medicine, University of Tsukuba, Tsukuba, Japan.
Abstract:
PMEPA1 (prostate transmembrane protein, androgen-induced 1)/TMEPAI (transmembrane prostate androgen-induced protein) is highly expressed in diverse cancers, including breast, lung and prostate cancers. It consists of four isoforms with distinct extracellular regions (isoforms a-d). The expression and function of these isoforms are still poorly understood. Hence, we aimed to identify the preferentially expressed isoforms in breast cancer cells and analyze possible differences in tumorigenic functions. In this study, we used 5' Rapid Amplification of cDNA Ends (RACE) and Western blot analyses to identify the mRNA variants and protein isoforms of TMEPAI and found that TMEPAI isoform d as the major isoform expressed by TGF-β stimulation in breast cancer cells. We then generated CRISPR/Cas9-mediated TMEPAI knockout (KO) breast cancer cell lines and used a lentiviral expression system to complement each isoform individually. Although there were no clear functional differences between isoforms, double PPxY (PY) motifs and a Smad-interaction motif (SIM) of TMEPAI were both essential for colony and sphere formation. Collectively, our results provide a novel insight into TMEPAI isoforms in breast cancer cells and showed that coordination between double PY motifs and a SIM of TMEPAI are essential for colony and sphere formation but not for monolayer cell proliferation.
Insights
Transmembrane prostate androgen-induced protein (TMEPAI) isoform d is highly expressed in breast cancer cells. Its double PPxY motifs and Smad-interaction motif are crucial for tumor-like cell growth.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Prostate transmembrane protein, androgen-induced 1 (PMEPA1), also known as transmembrane prostate androgen-induced protein (TMEPAI), is implicated in various cancers.
- TMEPAI exhibits four isoforms (a-d) with distinct extracellular regions, but their expression and functions remain largely uncharacterized.
- Understanding TMEPAI isoform-specific roles is critical for advancing breast cancer research.
Purpose of the Study:
- To identify the predominant TMEPAI isoforms in breast cancer cells.
- To investigate the functional significance of different TMEPAI isoforms in tumorigenesis.
- To elucidate the molecular mechanisms underlying TMEPAI's role in breast cancer progression.
Main Methods:
- Utilized 5' Rapid Amplification of cDNA Ends (RACE) and Western blot analysis to identify TMEPAI mRNA variants and protein isoforms.
- Generated CRISPR/Cas9-mediated TMEPAI knockout (KO) breast cancer cell lines for functional studies.
- Employed a lentiviral expression system to reintroduce individual TMEPAI isoforms into KO cells.
Main Results:
- TMEPAI isoform d was identified as the major isoform expressed in breast cancer cells, particularly upon TGF-β stimulation.
- No significant functional differences were observed between the individual TMEPAI isoforms regarding monolayer cell proliferation.
- Both the double PPxY (PY) motifs and the Smad-interaction motif (SIM) within TMEPAI were found to be essential for colony and sphere formation.
Conclusions:
- TMEPAI isoform d is a key player in TGF-β-stimulated breast cancer cells.
- The tumorigenic functions of TMEPAI, specifically colony and sphere formation, are dependent on the integrity of its double PY motifs and SIM.
- These findings highlight the importance of specific TMEPAI motifs in mediating breast cancer cell growth and provide novel insights into TMEPAI isoform functions.
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