Heme: a determinant of life and death in renal tubular epithelial cells.
Heme oxygenase-1 (HO-1) and p21 influence cell fate, and genetic HO-1 overexpression upregulates p21 and confers resistance to apoptosis. The present study examined the effects of heme, a metabolite incriminated in renal injury, on sensitivity to apoptosis and cell growth in conjunction with cellular expression of HO-1 and p21. Immortalized rat proximal tubular epithelial cells (IRPTCs) were exposed to hemin (10 microM) in serum-deplete media (0.1% FBS) and in standard cell culture media (5.0% FBS). In the presence of 0.1% FBS media, hemin induced p21 through an HO-dependent, p53-independent mechanism; certain products of HO activity (iron and carbon monoxide), but not others (ferritin, apoferritin, bilirubin), recapitulated these inductive effects on p21 expression. Along with this inductive effect on HO-1 and p21, hemin worsened apoptosis, the latter exacerbated by the inhibition of HO activity and loss of p21 expression. In IRPTCs maintained in 5% FBS, hemin induced HO-dependent p21 expression, provoked cell cycle arrest, and inhibited cell growth without inducing apoptosis; this inhibitory effect of hemin on cell growth was blocked by the concomitant inhibition of HO activity and loss of p21 expression. We conclude that hemin is a potent HO-dependent inducer of p21 and that hemin increases the sensitivity to apoptosis in serum-deplete conditions and decreases cell growth in serum-replete conditions; inhibiting HO activity and concomitantly ablating p21 expression exacerbate apoptosis and reverse the growth-inhibitory actions of hemin. We suggest that these effects of heme may influence the nature of, and recovery from, ischemic and nephrotoxic insults to the kidney.
Gonzalez-Michaca
Luis
L
Division of Nephrology, Mayo Clinic Foundation, Rochester, Minnesota 55905, USA.
Farrugia
Gianrico
G
Croatt
Anthony J
AJ
Alam
Jawed
J
Nath
Karl A
KA
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001798:Blood Proteins / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002461:Cell Line, Transformed; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology* / Q000187:drug effects; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism; D051547:Heme Oxygenase-1; D006427:Hemin / Q000633:toxicity*; D007687:Kidney Tubules, Proximal / Q000166:cytology*; D051381:Rats
D001798:Blood Proteins; C493958:Cdkn1a protein, rat; D016895:Culture Media, Serum-Free; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D006427:Hemin; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1