Abstract
The understanding of the anatomy and development of fetal and adult hair follicles and the molecular study of the major embryonic pathways that regulate the hair follicle have led to exciting discoveries concerning the development of basal cell carcinoma (BCC). These studies have shed light on the major roles of Sonic hedgehog (Shh) signaling and its interactions with the insulin-like growth factor (IGF) axis in BCC development. New work, for example, explores a link between Shh signaling and IGF binding protein-2 (IGFBP-2) in the hair follicle as it transforms into BCC. IGFBP-2 was overexpressed in specific hair follicle cells of mice with ectopically activated Shh signaling [keratin 14 (K14)-Cre: patched homologue 1 (Cre: Ptch1)(lox/lox) mice]. Ptch1 deletion resulted in both an expansion of the stem cell niche and inhibition of cell differentiation. In transformed hair follicles, IGFBP-2 mediates epidermal progenitor cell expansion. Evidence also indicated that IGFBP-2 is expressed in human BCC.