Numb Protects Human Renal Tubular Epithelial Cells From Bovine Serum Albumin‐Induced Apoptosis Through Antagonizing CHOP/PERK Pathway

Abstract

In recent studies, we found that Numb is involved in oxidative stress-induced apoptosis of renal proximal tubular cells; however, its function on ER stress-induced apoptosis in proteinuric kidney disease remains unknown. The objective of the present study is to explore the role of Numb in urinary albumin-induced apoptosis of human renal tubular epithelial cells (HKCs). In this study, we demonstrate that incubation of HKCs with bovine serum albumin (BSA) resulted in caspase three-dependent cell death. Numb expression was down-regulated by BSA in a time- and dose-dependent manner. Knockdown of Numb by siRNA sensitized HKCs to BSA-induced apoptosis, whereas overexpression of Numb protected HKCs from BSA-induced apoptosis. Moreover, BSA activated CHOP/PERK signaling pathway in a time- and dose-dependent manner as indicated by increased expression of CHOP, PERK, and P-PERK. Furthermore, knockdown of CHOP or PERK significantly attenuated the promoting effect of Numb on BSA-induced apoptosis, while overexpression of CHOP impaired the protective effect of Numb on BSA-induced apoptosis. Taken together, our findings demonstrate that Numb plays a protective role on BSA-induced apoptosis through inhibiting CHOP/PERK signaling pathway in human renal tubular epithelial cells. Therefore, the results from this study provides evidence that Numb is a new target of ER-associated apoptotic signaling networks and Numb may serve as a promising therapeutic target for proteinuric diseases.

Mammalian ECD Protein Is a Novel Negative Regulator of the PERK Arm of the Unfolded Protein Response

“…3F to I ). As activation of the PERK pathway promotes cell death in response to ER stress, primarily through CHOP-dependent expression of proapoptotic genes ( 24 – 32 ), and inhibition/attenuation of PERK signaling protects cells against stress-induced cell death ( 64 – 66 ), our results support the likelihood that ECD functions to modulate PERK pathway activity and promote cell survival during ER stress. Indeed, assessment of cellular survival in response to ER stress showed that reductions in ECD levels impaired cell survival in response to ER stress ( Fig.…”

“…The ER stress response is initially aimed at the survival of cells ( 62 ); however, severe ER stress shifts the response from a prosurvival to a proapoptotic response ( 23 , 31 ) through PERK-mediated induction of expression of CHOP, a transcription factor that enhances the expression of proapoptotic pathway genes ( 24 – 28 , 30 , 31 , 63 ). Several studies found that inhibition/attenuation of the PERK pathway protected cells against stress-induced cell death ( 64 – 67 ). Given our observation that ECD functions as a modulator of PERK signaling, we assessed if the level of ECD determines a differential survival versus apoptotic cell fate upon ER stress induction.…”

Rtn1a-Mediated Endoplasmic Reticulum Stress in Podocyte Injury and Diabetic Nephropathy

“…We have shown that overexpression of RTN1A increases PERK phosphorylation leading to CHOP expression in kidney cells, whereas knockdown of RTN1A prevented tunicamycin or albumin induced phosphorylation of PERK and activation of CHOP 16 . It is known that CHOP deletion can protect renal tubular epithelial cells from apoptosis through inhibition or PERK/CHOP pathway 37 . In vivo , CHOP deficiency decreases renal cell apoptosis in murine models of unilateral ureteral obstruction (UUO) or renal ischemia/reperfusion injury 38, 39 .…”

Numb contributes to renal fibrosis by promoting tubular epithelial cell cycle arrest at G2/M

“…Our present study demonstrates that Numb provokes G2/M arrest of proximal tubules via stabilizing p53 protein. We and others have reported that Numb inhibits puromycin aminonucleoside- and albumin-induced proximal tubular cells apoptosis [ 33 , 34 ]. Notably, Numb inhibited puromycin aminonucleoside-induced apoptosis through antagonizing Notch signaling but independent of p53 [ 33 ].…”