ABSTRACT
Objective To investigate the effects of the rat serum with chronic renal failure (CRF) on ubiquitin-proteasome pathway,histone acetyltransferase p300 and activation of activating transcription factor 4(ATF4) of rat arterial vascular smooth muscle cells(VSMCs) cultured in vitro,and explore the possible mechanism.Methods To establish the rat model of CRF by 5/6 nephrectomy,VSMCs were incubated in the media with the 10％ of CRF serum or control serum in vitro.The mRNA expressions of ubiquitin(Ub),ubiquitin activating enzyme(E1),ubiquitin ligases enzymes (β-transducin repeat containing protein 1,β-TrCP1),p300 and ATF4 in the rat VSMCs were examined by using realtime PCR.Expressions of E1,β-TrCP1,p300 and ATF4 proteins in response to the CRF serum in VSMCs were determined by Western blotting analysis.The enzyme activities of 20S proteasomes in the total protein were examined by using three special fluorogenic peptide substrates.Results The CRF serum significantly promoted the mRNA expressions of Ub,E1,β-TrCP1,p300 and ATF4 in VSMCs in a time dependent manner.Compared with that in control serum group,the mRNA levels of Ub,E1,β-TrCP1,p300 and ATF4 in CRF serum group increased significantly (P ＜ 0.01).The CRF serum also increased the protein expressions of E1,β-TrCP1 and p300 in a time dependent manner.The expression of ATF4 was decreased,but the difference was not significant (P ＞ 0.05).Compared with that in control serum group,the protein expressions of E1,β-TrCP1,p300 and ATF4 in CRF serum group increased significantly (P ＜ 0.01).The activities of 20S proteasomes in the CRF serum group were significantly increased in a time dependent manner.Compared with that in control serum group,the activities of 20S proteasomes in the CRF serum group increased significantly (P ＜ 0.01).Conclusions The serum of CRF rat can effectively active the ubiquitin-proteasome pathway,but ATF4 ubiquitinylated degradation is blocked.The latter may be associated with increased expression of p300.