TISSUE-SPECIFIC STEM CELLS Epithelial Cells Derived from Human Embryonic Stem Cells Display P16INK4A Senescence, Hypermotility, and Differentiation Properties Shared by Many P631 Somatic Cell Types

Human embryonic stem (hES) cells can generate cells expressing p63, K14, and involucrin, which have been pro-posed to be keratinocytes. Although these hES-derived, keratinocyte-like (hESderK) cells form epithelioid colonies when cultured in a fibroblast feeder system optimal for nor-mal tissue-derived keratinocytes, they have a very short replicative lifespan unless engineered to express HPV16 E6E7. We report here that hESderK cells undergo senescence associated with p16INK4A expression, unrelated to telomere status. Transduction to express bmi1, a repressor of the p16INK4A/p14ARF locus, conferred upon hESderK cells and keratinocytes a substantially extended lifespan. When exposed to transforming growth factor beta or to an incompletely processed form of Laminin-332, three lifespan-extended o