Balancing life with glycoconjugates: monitoring unfolded protein response-mediated anti-angiogenic action of...

Asparagine-linked protein glycosylation is a hallmark for glycoprotein structure and function. Its impairment by tunicamycin [a competitive inhibitor of N-acetylglucosaminyl 1-phosphate transferase (GPT)] has been known to inhibit neo-vascularization (i.e., angiogenesis) in humanized breast tumor due to an induction of ER stress-mediated unfolded protein response (UPR). The studies presented here demonstrate that (i) tunicamycin (i) inhibits capillary endothelial cell proliferation in a dose dependent manner; (ii) treated cells are incapable of forming colonies upon its withdrawal; and (iii) tunicamycin treatment causes nuclear fragmentation. Tunicamycin-induced ER stress-mediated UPR event in these cells was studied with the aid of Raman spectroscopy, in particular, the interpretation of bands at 1672, 1684 and 1694 cm(-1), which are characteristics of proteins and originate from C=O stretching vibrations of mono-substituted amides. In tunicamycin-treated cells these bands decreased in area as follows: at 1672 cm(-1) by 41.85% at 3 h and 55.39% at 12 h; at 1684 cm(-1) by 20.63% at 3 h and 40.08% at 12 h; and also at 1994 cm(-1) by 33.33% at 3 h and 32.92% at 12 h, respectively. Thus, in the presence of tunicamycin, newly synthesized protein chains fail to arrange properly into their final secondary and/or tertiary structures, and the random coils they form had undergone further degradation.