The therapeutic value of DNA-damaging antineoplastic agents is dependent upon their ability to induce tumor cell apoptosis while sparing most normal tissues. Here, we show that a component of the apoptotic response to these agents in several different types of tumor cells is the deamidation of two asparagines in the unstructured loop of Bcl-xL, and we demonstrate that deamidation of these asparagines imports susceptibility to apoptosis by disrupting the ability of Bcl-xL to block the proapoptotic activity of BH3 domain-only proteins. Conversely, Bcl-xL deamidation is actively suppressed in fibroblasts, and suppression of deamidation is an essential component of their resistance to DNA damage-induced apoptosis. Our results suggest that the regulation of Bcl-xL deamidation has a critical role in the tumor-specific activity of DNA-damaging antineoplastic agents.
In Deverman et al. (Cell 111, 51-62), we concluded that deamidation inactivates Bcl-x L . This conclusion was based partly on results obtained using Bcl-x L constructs in which asparagines 52 and 66 were replaced with aspartates to mimic deamidation. We reported that these constructs lacked the antiapoptotic and BIM-binding function of native Bcl-x L (Figure 4). However, during the course of subsequent studies, we discovered a previously undetected mutation in these constructs. When this secondary mutation was corrected and the resulting constructs were assessed as in Figure 4, we found that their antiapoptotic activity was similar to that of wild-type Bcl-x L and their BIMbinding activity was restored. However, we stand by our conclusion that deamidation results in the loss of cellular Bcl-x L activity. This is evidenced by our finding that replacement of asparagines 52 and 66 in Bcl-x L with alanines [Bcl-x L (N52A/N66A)] to block deamidation increases the antiapoptotic activity of Bcl-x L , which is stated as "data not shown" in our manuscript (second paragraph from the bottom of the righthand column on page 55). Thus, all of the other conclusions in the manuscript remain supported. We are currently pursuing studies to determine the precise mechanism by which deamidation results in the loss of cellular Bcl-x L activity.We sincerely apologize for the confusion we have caused.
Endoplasmic reticulum (ER) stress and disrupted proteostasis contribute to the pathogenesis of a variety of glomerular and tubular diseases. Thus, it is imperative to develop noninvasive biomarkers for detecting ER stress in podocytes or tubular cells in the incipient stage of disease, when a kidney biopsy is not yet clinically indicated. Mesencephalic astrocyte-derived neurotrophic factor (MANF) localizes to the ER lumen and is secreted in response to ER stress in several cell types. Here, using mouse models of human nephrotic syndrome caused by mutant laminin β2 protein-induced podocyte ER stress and AKI triggered by tunicamycin- or ischemia-reperfusion-induced tubular ER stress, we examined MANF as a potential urine biomarker for detecting ER stress in podocytes or renal tubular cells. ER stress upregulated MANF expression in podocytes and tubular cells. Notably, urinary MANF excretion concurrent with podocyte or tubular cell ER stress preceded clinical or histologic manifestations of the corresponding disease. Thus, MANF can potentially serve as a urine diagnostic or prognostic biomarker in ER stress-related kidney diseases to help stratify disease risk, predict disease progression, monitor treatment response, and identify subgroups of patients who can be treated with ER stress modulators in a highly targeted manner.
PURPOSE Urinary tract obstruction causes hydroureteronephrosis and requires surgical intervention to prevent the development of permanent renal injury. While many studies have focused on the development of renal injuries, here we examine the molecular mechanisms that promote renal recovery following the correction of obstruction. MATERIALS AND METHODS A reversible murine model of ureteral obstruction was used to examine the BMP-7 and TGF-β signaling pathways during renal recovery following obstruction-induced injury. Analysis was conducted using standard molecular techniques including RT-PCR, ELISA, immunoblotting, and co-immunoprecipitation. RESULTS We found that the upregulation of BMP-7 following the correction of obstruction inhibits TGF-β-dependent pro-fibrotic pathways that are central to the pathogenesis of renal injury. The inhibitory effects of BMP-7 are mediated, in part, by the activation of its downstream target proteins, Smad1, Smad5, and Smad8, which suppress the activity of TGF-β-dependent Smad proteins and, in turn, inhibit the expression of TGF-β-dependent genes. Finally, the activation of the BMP-7–Smad1/5/8 pathway during renal recovery promotes the restoration of renal architecture and resolution of fibrosis in the kidney following the correction of obstruction. CONCLUSIONS Together, these findings demonstrate that the BMP-7–Smad1/5/8 pathway promotes the repair of the kidney following obstruction-induced injury. Accordingly, the BMP-7 pathway represents an important therapeutic target to stimulate the innate repair mechanisms of the kidney during the treatment of obstruction-induced renal injuries.
SH-PTP2, a non-transmembrane-type protein-tyrosine phosphatase with two Src homology 2 domains, was previously shown to play a positive signaling role in the insulin-induced activation of Ras and mitogen-activated protein kinase. SH-PTP2 was shown to associate with a 115-kDa tyrosine-phosphorylated protein (pp115), as well as with insulin receptor substrate 1, in insulinstimulated Chinese hamster ovary cells that overexpress human insulin receptors (CHO-IR cells). In vivo and in vitro binding experiments revealed that SH-PTP2 bound to pp115 through one or both of its SH2 domains. The pp115 protein was partially purified from insulinstimulated CHO-IR cells that overexpress a catalytically inactive SH-PTP2 by a combination of immunoaffinity and lectin-affinity chromatography. A monoclonal antibody to pp115 was then generated by injecting the partially purified protein into mice. Experiments with this monoclonal antibody revealed that pp115 is a transmembrane protein with a domain exposed on the cell surface and that it binds to SH-PTP2 in response to insulin. The insulin receptor kinase appeared to phosphorylate pp115 on tyrosine residues both in vivo and in vitro. The extent of tyrosine phosphorylation of pp115 associated with SH-PTP2 was greatly increased in CHO-IR cells that overexpress catalytically inactive SH-PTP2 compared with that observed in CHO-IR cells overexpressing wild-type SH-PTP2. Furthermore, recombinant SH-PTP2 preferentially dephosphorylated pp115 in vitro, indicating that SH-PTP2 may catalyze the dephosphorylation of phosphotyrosine residues in pp115 after it binds to this protein. These results suggest that pp115 may act as a transmembrane anchor to which SH-PTP2 binds in response to insulin. Furthermore, pp115 may be a physiological substrate for both the insulin receptor kinase and SH-PTP2.
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