Fig. 7. Model suggesting how SHH mediates IRS1 expression during CGNP proliferation. In the absence of SHH, IGF signaling sends survival cues through IRS2 and/or GAB1 and PI-3K signaling (left panel). IRS1 mRNA is present. In the presence of SHH, IRS1 is upregulated by a mechanism that may involve both enhanced translation and protein stabilization. SHH stabilizes IRS1 protein by inhibiting mTOR-mediated activation of S6K, which is known to phosphorylate IRS1 leading to its degradation.