Unfolded protein response interferes IGF‐1 signaling of capillary endothelial cell survival

Abstract

Angiogenesis is crucial for breast tumor growth and metastasis. Regulated pattern of endothelial cell survival and death play a central role in the timely evolution and regression of angiogenic responses. We have shown that dolichol‐linked oligosaccharide (i.e., LLO) biosynthesis and turnover are required for angiogenesis. Investigating the efficacy of a LLO biosynthetic inhibitor tunicamycin for anti‐angiogenetic breast cancer therapy indicates cell cycle arrest in G1 and induction of apoptosis by unfolded protein response (upr) signaling. This paralleled upregulation of c‐Jun, c‐Myc and down regulation of c‐fos. Upregulated p53 expression indicated failure of cell survival. IGF‐1 (20ng/ml) addition exhibited no change in the cell status as confirmed by down regulation of PI3KR, pAkt and p53(S14). This is supported by down regulation of phospho Akt (473)/Akt (308), GSK3 beta, phosphocaspase‐9, phospho‐Bad and phospho mTOR expression. Changes in NFkB phosphorylation (S14) however remained silent. QRT‐PCR confirmed upregulation of GRP‐78, Bcl‐2, caspase‐3, p53 expression and down regulation of PI3KR following IGF‐1 challenges in tunicamycin treated cells. IGF‐1 signaling triggers glucose uptake for energy metabolism but ATP level could not be raised when tunicamycin was present. This strongly suggested that tunicamycin down regulates the PI3‐K/AKt signaling of cell survival and could help developing glycotherapeutic for treating breast cancer. Supported by NIH/NCRR/RCMI G12‐RR03035 (KB); NIH U54‐CA096297 and Komen for the Cure BCTR06582 (DKB).