GAS1 (growth arrest specific 1) is a GPI-anchored plasma membrane protein that functions as a multifaceted regulator of cell proliferation and developmental signaling 1. Its primary function involves blocking cell cycle progression from G0 to S phase, acting as a growth suppressor 1. Mechanistically, GAS1 serves as a co-receptor for Sonic Hedgehog (Shh) signaling, working cooperatively with the Hedgehog receptor Patched 1 to transform HH concentration gradients into morphogenic activity gradients during embryonic development 1. GAS1 also regulates the RET/AKT/mTOR signaling pathway by forming complexes with RET and inhibiting its phosphorylation, thereby suppressing cell survival pathways 2. In disease contexts, GAS1 functions as a tumor suppressor, with its loss promoting cancer stem cell characteristics and chemoresistance in gastric adenocarcinoma 2. GAS1 overexpression induces cell cycle arrest and apoptosis in human gliomas by preventing AKT activation, even in the absence of Shh signaling 3. Additionally, GAS1 is critical for normal tooth development, regulating tooth number and morphology through facilitation of Shh signal transduction 4. The protein is also expressed in senescent fibroblasts associated with aging and cancer progression 5.