RHOBTB3 Functions As A Tumor Suppressor Through Inhibition Of HIF And Its Signaling Pathway

Under hypoxia treatment or other relative stimulus,cell or tissue would activate HIF(hypoxia-inducible factor)signaling pathway.Previous researches indicate that HIF signaling pathway plays quite an important role in many biological aspects,including development of mammalian embryos,inflammation and tumorigenesis.The heterodimeric transcription factor HIF represents the key mediator of hypoxia response.HIF regulates the expression of over 200 downstream genes,which participate in different cellular process.HIF itself is strictly controlled through regulation of the HIF-a subunit.Through a series of experiments,this thesis firstly proves that RHOBTB3,an atypical member of the Rho superfamily,is a tumor suppressor,and it may function by taking part in the Proline hydroxylation-ubiquitination degradation process of HIF-1? subunit.On the one hand,over-express RHOBTB3 in mammalian cells could strongly inhibits the induction of HIF-1? subuint and HIF-1's downstream genes by hypoxia stimulation.On the other hand,we find that the protein level of HIF-1? subuint is up-regulated in human cells in which RHOBTB3 is knocked-down by shRNA or in Rhobtb3-/-mouse embryonic fibroblasts.So are the mRNA and protein levels of the downstream genes,while RHOBTB3 rescue experiment could restore these phenotypes.Analysis on the collected human RCC(renal cell carcinoma)samples also proves the correlation between RHOBTB3 and HIF signaling pathway.Further study shows that RHOBTB3 could interact with EGLN1 and promote its hydroxylase activity on proline residues of HIF-la subuint,which would recruit the pVHL-dependent ubiquitination-degradation complex,and lead to the proteasomal degradation of HIF-la subuint.