Podoplanin, a novel marker of tumor-initiating cells in human squamous cell carcinoma A431

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Abstract

Squamous cell carcinoma (SCC) is a malignant tumor that shows morphologic and phenotypic similarities to normally differentiated squamous epithelium. Thus, it may be an ideal model for seeking a marker of tumor-initiating cells (TICs) based on their morphology. Using the human SCC cell line A431, we found that, as a paradigm of cancer stem cells: (1) podoplanin+ cells generate both podoplanin+ and podoplanin− cells; (2) podoplanin− cells rarely generate podoplanin+ cells; (3) podoplanin+ cells have higher colony formation efficiency and tumorigenicity than podoplanin− cells; (4) localization and morphology of podoplanin+ cells in a xenografted tumor derived from podoplanin+ cells are similar with those in human oral SCC tissue or normal epithelium. Furthermore, podoplanin+ A431 cells share sonic hedgehog and CD44 expression with stem cells in normal squamous epithelium. Hence, we concluded that podoplanin is a novel marker to enrich TICs with stem-cell-like properties from SCC cell line A431.

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Materials and methods

Culture of A431 cell line. The human squamous cell carcinoma cell line A431 was obtained from RIKEN BioResource Center (Tsukuba, Japan) and cultured in Dulbecco’s modified Eagle’s medium (DMEM, Sigma, St. Louis, MO) containing 10% fetal bovine serum (FBS, Sigma), and 1% penicillin and streptomycin (Sigma) and incubated at 37 °C in an atmosphere containing 5% CO2.

Flow cytometry. Cultured A431 cells were counted and suspended in 100 μl of PBS/2% FBS per 106 cells. The A431 cell suspension was

Identifying a candidate marker for TIC of SCC useful both in vivo and in vitro

Because TICs share expression of some markers with normal stem cells in the same organ [3], [6], [7], [8], [9], we assumed that TICs in SCC shared some marker expressions with normal stem cells in squamous epithelium. We investigated the expression of integrins β1, β4, α6, and of CD44 and podoplanin in normal oral mucosa, in oral SCC, in an A431 xenograft, and in cultured A431. Integrins β1, β4, α6, and CD44 are markers of normal epithelial stem or progenitor cells [10], [11] and podoplanin is

Discussion

We identified podoplanin as a new marker for TIC of SCC. Podoplanin+ A431 cells possessed stem-cell-like properties in vitro because they had the ability to repopulate and to generate a heterogeneous cancer cell population (Fig. 2B–D). Furthermore, we confirmed that podoplanin+ A431 cells had high tumor-initiating potential (Fig. 3A and B) and were capable of recapitulating human SCC (Fig. 3E and F), which is sufficient to consider podoplanin as a TIC marker [6].

We found SHH to be exclusively

Acknowledgments

We thank Hiroko Hashimoto and Mai Okumoto for technical support and Dr. Syuichi Mitsunaga, Takashi Ito and Ayuko Hoshino for their helpful advice. This work was supported in part by a Grant-in-Aid for Cancer Research from the Ministry of Health, Labor and Welfare; a Grant for Scientific Research Expenses for Health Labor and Welfare Programs; the Foundation for the Promotion of Cancer Research, the 3rd-Term Comprehensive 10-Year Strategy for Cancer Control.

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