Carcinogenesis Advance Access published online on September 29, 2009
Carcinogenesis, doi:10.1093/carcin/bgp233
HIF-1 is induced via EGFR activation and mediates resistance to anoikis-like cell death under lipid rafts/caveolae-disrupting stress
Division of Translational & Clinical Research II
a Pediatric Oncology Branch
b Specific Organs Cancer Branch, National Cancer Center 809 Madu 1-dong, Ilsan-gu Goyang-si, Gyeonggi-do, 411-769, Korea Tel: 31-920-2415, Fax: 31-920-2468
c Department of Pharmacology, Seoul National University College of Medicine 28 Yongon-dong, Chongno-gu, Seoul 110-779, Korea
Address correspondence to: Yong-Nyun Kim ynk{at}ncc.re.kr
The plasma membrane microdomains, lipid rafts, are involved in regulation of cellular functions such as cell survival and adhesion. Cholesterol is a critical component of lipid rafts in terms of their integrity and functions and rafts disruption by cholesterol depletion can induce detachment-induced cell death. Hypoxia inducible factor-1
(HIF-1) is stabilized in hypoxia and transactivates numerous genes required for cellular adaptation to hypoxia. It is also induced by non-hypoxic stimuli and contributes to cell survival. Because hypoxia inhibits cholesterol synthesis and HIF-1 plays a role in this process, we here explored a possible connection between lipid rafts and HIF-1. We investigated whether HIF-1 is regulated during cholesterol depletion/rafts disruption in A431 cells in normoxic conditions. Methyl-beta cyclodextrin (MβCD), which induces cholesterol depletion, up-regulated HIF-1 even under normoxic conditions and this up-regulation required EGF receptor and ERK1&2 activation, but not Akt activation. MβCD treatment induced HIF-1 up-regulation at both the transcriptional and translational levels, but not at the post-translational levels. In addition, MβCD robustly induced VEGF production and stimulated a HRE-driven luciferase reporter activity under normoxic conditions, indicating that MβCD-induced HIF-1 is functionally activated. Both EGF receptor activity and HIF-1 expression were higher in the attached cells than in the detached cells after MβCD treatment. Furthermore, inhibition of HIF-1 by RNA interference accelerated cell detachment, thus increasing cell death, indicating that HIF-1 expression attenuates MβCD-induced anoikis-like cell death. These data suggest that, depending on cholesterol levels, lipid rafts or membrane fluidity are likely to regulate HIF-1 expression in normoxia by modulating rafts protein activities such as EGF receptor, and this connection between lipid rafts and HIF-1 regulation may provide cell survival under membrane-disturbing stress.
Key Words: lipid rafts • EGFR • HIF-1 • cholesterol • adhesion • anoikis
# These authors contributed equally to this study.
Received March 13, 2009; revised August 18, 2009; accepted September 19, 2009.