GLI1 and neoplasm: NRP2 maintains the tumour initiating cell compartment by stimulating α6β1 integrin, FAK-mediated activation of Ras signalling and consequent induction of the zinc finger transcription factor and Hedgehog effector GLI1, which in turn induces the stem cell factor BMI1 (Lobo et al, 2007), enhances NRP2 expression and α6β1 function, thus establishing a positive autocrine loop.