In normal cells, activation of the hedgehog signaling pathway begins with the binding of the extracellular hedgehog protein to the membrane receptor Patched. The activation of Patched overcomes the blockage of the membrane receptor Smoothened. Active Smoothened is able to activate Gli2, which translocates into the nucleus, where it induces the expression of CCND1 and other genes activating proliferation.

The hedgehog signaling pathway-Part 2:
The hedgehog signaling pathway-Part 3: