In tissue culture systems, p21 and p27 inhibit cyclindependent kinase (CDK) activity and cell cycle progression in response to numerous stimuli, but little is known about their involvement in cell growth in vivo. We examined the modulation of CDK activity by these proteins after 70% partial hepatectomy (PH), an in vivo model of synchronous hepatocyte cell cycle progression. After PH in BALB/c mice, p21 was induced during the prereplicative (G1) phase and was maximally expressed after peak hepatocyte DNA synthesis. p27 was present in quiescent liver and was minimally induced after PH. p21 and p27 immunoprecipitated with CDK2, CDK4, and cyclin D1 in the regenerating liver. The activity of CDK2-, CDK4-and cyclin D1-associated kinases was upregulated after PH, and maximal activity of these enzyme complexes corresponded to peak DNA synthesis. Immunodepletion experiments suggested that p27 plays a role in downregulating CDK2 activity before and after peak DNA synthesis. Compared to cogenic wild-type mice, p217/7 mice demonstrated evidence of markedly accelerated hepatocyte progression through G1 phase after PH: DNA synthesis, upregulation of cyclin A and PCNA, induction of cyclin D1-and CDK2-associated kinase activity, and appearance of a phosphorylated retinoblastoma protein (Rb) species occurred earlier in the p217/7 mice. These results suggest that p21 and p27 modulate CDK activity in the regenerating liver, and that p21 regulates the rate of progression through G1 phase of the cell cycle in vivo.

Despite a growing organ shortage in the United States, many deceased donor kidneys removed for transplantation are discarded. Kidney biopsy findings often play a role in these discards, although it is not clear whether biopsies reliably inform acceptance decisions. Therefore, we carried out a systematic review of the medical literature on the utility of both procurement and implantation biopsies for predicting posttransplant outcomes. Between January 1, 1994 and July 1, 2014, 47 studies were published in the English language literature that examined the association between pretransplant donor biopsy findings from 50 or more donors (with more than half being from deceased donors) and either posttransplant graft failure, delayed graft function, or graft function. In general, study quality was poor. All were retrospective or did not indicate if they were prospective. Results were heterogeneous, with authors as often as not concluding that biopsy results did not predict posttransplant outcomes. The percent glomerular sclerosis was most often examined, and failed to predict graft failure in 7 of 14 studies. Of 15 semiquantitative scoring systems proposed, none consistently predicted posttransplant outcomes across studies. Routine use of biopsies to help determine whether or not to transplant a kidney should be reexamined.

Background and objectives There is a shortage of kidneys for transplant, and many patients on the deceased donor kidney transplant waiting list would likely benefit from kidneys that are currently being discarded. In the United States, the most common reason given for discarding kidneys retrieved for transplant is procurement biopsy results. This study aimed to compare biopsy results from discarded kidneys with discard attributed to biopsy findings, with biopsy results from comparable kidneys that were successfully transplanted.Design, setting, participants, & measurements In this retrospective, observational, case-control study, biopsy reports were examined from 83 kidneys discarded in 2010 due to biopsy findings (cases), 83 contralateral transplanted kidneys from the same donor (contralateral controls), and 83 deceased donors randomly matched to cases by donor risk profile (randomly matched controls). A second procurement biopsy was obtained in 64 of 332 kidneys (19.3%).Results The quality of biopsy reports was low, with amounts of tubular atrophy, interstitial inflammation, arteriolar hyalinosis, and acute tubular necrosis often not indicated; 69% were wedge biopsies and 94% used frozen tissue. The correlation between first and second procurement biopsies was poor; only 25% of the variability (R 2 ) in glomerulosclerosis was explained by biopsies being from the same kidney. The percentages of glomerulosclerosis overlapped substantially between cases, contralateral controls, and randomly matched controls: 17.1%615.3%, 9.0%66.6%, and 5.0%65.9%, respectively. Of all biopsy findings, only glomerulosclerosis.20% was independently correlated with discard (cases versus contralateral controls; odds ratio, 15.09; 95% confidence interval, 2.47 to 92.41; P=0.003), suggesting that only this biopsy result was used in acceptance decisions. One-year graft survival was 79.5% and 90.7% in contralateral and randomly matched controls, respectively, versus 91.6% among all deceased donor transplants in the Scientific Registry of Transplant Recipients.Conclusions Routine use of biopsies could lead to unnecessary kidney discards.

The p21 protein is a universal inhibitor of cyclindependent kinases and of cell-cycle progression and is involved in numerous growth-inhibitory pathways in cell culture systems. Recent studies suggest that p21 regulates hepatocyte cell cycle progression in models of liver regeneration. The present study was designed to investigate the possible involvement of p21 in the control of hepatocyte proliferation in human liver diseases. To examine that, the expression of p21 in clinical liver biopsy specimens was determined by immunohistochemistry. This was correlated with hepatocyte Ki-67 immunostaining (a marker of hepatocyte proliferation in vivo) as well as histologic features. Little p21 or Ki-67 expression was detected in normal human liver or in specimens of nonalcoholic steatohepatitis. In patients with alcoholic hepatitis, increased expression of p21, but not of Ki-67, was observed. In specimens with chronic hepatitis C, hepatocyte p21 expression was significantly correlated with Ki-67 immunostaining, as well as with the degree of inflammation and fibrosis. These results indicate that hepatocyte p21 expression is upregulated in response to hepatic injury and correlates with histologic markers of proliferation and disease activity. This study provides evidence that p21 plays a role in the regulation of hepatocyte proliferation in human liver diseases. (HEPATOLOGY 1998;28:738-743.) Cell proliferation is controlled by protein kinase complexes consisting of cyclins and cyclin-dependent kinases (CDKs) which regulate distinct phases of the cell cycle. Extracellular signals control cell-cycle progression by influencing the activity of cyclin/CDK kinase complexes; the dysregulation of these complexes contributes to the development of neoplasia.

Cdk2 was once believed to play an essential role in cell cycle progression, but cdk2-/- mice have minimal phenotypic abnormalities. In this study, we examined the role of cdk2 in hepatocyte proliferation, centrosome duplication and survival. Cdk2-/- hepatocytes underwent mitosis and had normal centrosome content after mitogen stimulation. Unlike wild-type cells, cdk2-/- liver cells failed to undergo centrosome overduplication in response to ectopic cyclin D1 expression. After mitogen stimulation in culture or partial hepatectomy in vivo, cdk2-/- hepatocytes demonstrated diminished proliferation. Cyclin D1 is a key mediator of cell cycle progression in hepatocytes, and transient expression of this protein is sufficient to promote robust proliferation of these cells in vivo. In cdk2-/- mice and animals treated with the cdk2 inhibitor seliciclib, cyclin D1 failed to induce hepatocyte cell cycle progression. Surprisingly, cdk2 ablation or inhibition led to massive hepatocyte and animal death following cyclin D1 transfection. In a transgenic model of chronic hepatic cyclin D1 expression, seliciclib induced hepatocyte injury and animal death, suggesting that cdk2 is required for survival of cyclin D1-expressing cells even in the absence of substantial proliferation. In conclusion, our studies demonstrate that cdk2 plays a role in liver regeneration. Furthermore, it is essential for centrosome overduplication, proliferation and survival of hepatocytes that aberrantly express cyclin D1 in vivo. These studies suggest that cdk2 may warrant further investigation as a target for therapy of liver tumors with constitutive cyclin D1 expression.