Stem cells are characterized by longevity, self-renewal throughout the lifetime of a tissue or organism and the ability to generate all lineages of a tissue. Pathways involved in stem cell function are commonly dysregulated in cancer. Emerging evidence in leukemias and epithelial cancers suggests that tumors can be maintained by self-renewing cancer stem cells (CSCs), defined functionally by their ability to regenerate tumors. Delineating mechanisms that regulate self-renewal in human CSCs are essential to design new therapeutic strategies to combat cancer.
We have developed an in vivo tissue-regeneration model of primary human prostate cancer and identified two distinct populations of CSCs that can self-renew and serially propagate tumors. Both CSC subsets express the transmembrane protein Trop2. We have previously shown that Trop2 is a marker and a new regulator of stem/progenitor activity in the prostate. Trop2 controls self-renewal, proliferation and tissue hyperplasia through two cleavage products—intracellular domain (ICD) and extracellular domain (ECD) generated by regulated intramembrane proteolysis (RIP). RIP of Trop2 is carried out by TACE metalloprotease and gamma-secretase complex.
We have also demonstrated that cleaved Trop2 ICD is found in human prostate cancer but not in the cancer-adjacent benign tissue, suggesting a role for Trop2 cleavage in tumorigenesis. So far we generated seventeen antibodies against Trop2. Currently we are testing the inhibitory effect of the antibodies on Trop2 cleavage and activation. Blocking Trop2 signaling will be an effective strategy to prevent disease progression not only in the prostate but also in other epithelial cancers.