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TISSUE-SPECIFIC STEM CELLS

Survivin Identifies Keratinocyte Stem Cells and Is Downregulated by Anti-ß1 Integrin During Anoikis

Department of Medicine, Institute of Dermatology, University of Modena and Reggio Emilia, Modena, Italy

Key Words. Survivin • Stem cells • Anoikis • Keratinocytes

Correspondence: Carlo Pincelli, M.D., Institute of Dermatology, University of Modena and Reggio Emilia, Via del Pozzo, 71, 41100 Modena, Italy. Telephone: +39 059 4222931; Fax: +39 059 4224271; e-mail: carlo{at}unimo.it

Received March 21, 2006; accepted for publication September 20, 2006.
First published online in STEM CELLS EXPRESS   September 28, 2006.



Survivin belongs to the family of inhibitor of apoptosis proteins and is involved in regulation of cell death as well as cell division. Here, we show that wild-type (WT) survivin is expressed in a subpopulation of basal keratinocytes in normal human skin at the cytoplasmic level. WT survivin is highly expressed in keratinocyte stem cells (KSCs), whereas its mRNA level decreases in transit amplifying (TA) cells and disappears in postmitotic (PM) cells. Likewise, WT survivin protein is expressed in KSCs, almost undetectable in TA cells, and absent in PM cells. Real time polymerase chain reaction demonstrates that the putative antiapoptotic isoforms survivin-2B and survivin-Ex3 are expressed at the highest levels in KSCs, whereas they tend to decrease in TA cells and disappear in PM cells. On the contrary, the putative proapoptotic variants of survivin, survivin-3B, and survivin-2 tend to be high in PM and TA cells and are almost absent in KSCs. By confocal microscopy, survivin is predominantly expressed at the nuclear level in KSCs, which proliferate significantly better than TA cells, which, in turn, express mostly cytosolic WT survivin. Blocking ß1 integrin signal downregulates WT survivin mRNA and protein expression and induces apoptosis (anoikis) in KSCs. On the other hand, inhibition of ß1 integrin upregulates mRNA expression of survivin-2. Taken together, these results indicate that survivin identifies human KSCs. Expression of nuclear survivin could reflect the different behavior between KSCs in vitro and in vivo, in terms of proliferation. Finally, survivin could be part of the "niche" protection by preventing anoikis in KSCs.