EGF-Receptor Related Protein Causes Cell Cycle Arrest and Induces Apoptosis of Colon Cancer Cells In Vitro and In Vivo

Abstract

Background: EGF Receptor Related Protein (ERRP), a recently identified negative regulator of EGF-receptor (EGFR), has been shown to inhibit growth of colon cancer xenograft tumors in SCID mice. However, the mechanisms by which ERRP exerts its anti-tumor properties are poorly understood. The current investigation was undertaken to delineate the inhibitory mechanisms that are triggered by ERRP. Materials and Methods: For in vivo experiments, recombinant ERRP (20 μg/mouse) or an equivalent volume of vehicle was injected (away from the tumor site) every other day for 10 days to SCID mice xenotransplanted with the colon cancer cell line HCT-116. Tumor explants were obtained for further immunohistochemical analysis. For in vitro studies, the HCT-116 cell line was incubated with recombinant ERRP and apoptosis markers and cell cycle changes were evaluated. Results: Recombinant ERRP caused marked inhibition of tumor growth. This was accompanied by increased apoptosis and attenuation of ERK1/2 and Akt activities. Exposure of HCT-116 cells to recombinant ERRP for 24 hours caused apoptosis and cell cycle arrest at G_0/1-phase. Induction of apoptosis was evidenced by increased levels of cleaved caspase-3, PARP proteins and acridine orange staining. Conclusion: Our findings reveal a pro-apoptotic property of ERRP both in vitro and in vivo. We propose that ERRP functions by inhibiting the activation of the EGF-receptor signaling and its downstream effectors such as ERK and Akt kinases, underscoring the potential of ERRP for the treatment of colorectal cancer where the EGF pathway is known to be activated.