Figure 4.

Caspase function in tissue regeneration and tumor cell proliferation. Activation of caspase-3 and -7 during radiotherapy or during tissue injury causes cleavage and activation of iPLA₂. This results in AA synthesis and subsequent PGE₂ activation. The secreted PGE₂ promotes proliferation in surrounding tumor cells by activation of Wnt/β-catenin signaling. This facilitates tumor cell repopulation and acts as a limiting factor of effective therapy. Shedding of microparticles by apoptosing cells (pancreatic beta cells) stimulates proliferation/differentiation of neighboring cells through activation of regenerating (reg) genes. PGE₂ also interacts with Wnt signaling pathway to regulate stem cell/progenitor formation and function. iPLA₂, calcium-independent phospholipase A2; AA, arachidonic acid; PGE₂, prostaglandin E2; HSC, hematopoietic stem cells