Tumor Suppressor SMAR1 Activates and Stabilizes p53 through Its Arginine-Serine-rich Motif
Authors: Archana Jalota
Lakshminarasimhan Pavithra
Samit Chattopadhyay
Kamini Singh
Ruchika Kaul-Ghanekar
Shahid Jameel
Journal: Journal of Biological Chemistry (2005)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: p53; SMAR1; post-translational modifications; protein kinase C; cell proliferation
Affiliations: National Center for Cell Science, Pune University Campus, Ganeshkhind, Pune 411007, India.

Abstract:  Various stresses and DNA-damaging agents trigger transcriptional activity of p53 by post-translational modifications, making it a global regulatory switch that controls cell proliferation and apoptosis. Earlier we have shown that the novel MAR-associated protein SMAR1 interacts with p53. Here we delineate the minimal domain of SMAR1 (the arginine-serine-rich domain) that is phosphorylated by protein kinase C family proteins and is responsible for p53 interaction, activation, and stabilization within the nucleus. SMAR1-mediated stabilization of p53 is brought about by inhibiting Mdm2-mediated degradation of p53. We also demonstrate that this arginine-serine (RS)-rich domain triggers the various cell cycle modulating proteins that decide cell fate. Furthermore, phenotypic knock-down experiments using small interfering RNA showed that SMAR1 is required for activation and nuclear retention of p53. The level of phosphorylated p53 was significantly increased in the thymus of SMAR1 transgenic mice, showing in vivo significance of SMAR1 expression. This is the first report that demonstrates the mechanism of action of the MAR-binding protein SMAR1 in modulating the activity of p53, often referred to as the "guardian of the genome." 

Retracted: No

PubPeer comments:
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 For Figure 5e and 5f, thank you for bringing this to our notice. It is known that MDM2 allows degradation of p53. So overexpression of MDM2 reduces levels of p53 (Fig. 5e). In figure 5f, the objective was to show SMAR1 overexpression prevents MDM2 mediated p53 degradation. Dose dependent overexpression of SMAR1 along with MDM2 resulted in p53 stabilization depicting protecting role of SMAR1. Since, Same concentration of MDM2 is used in both 5e and 5f, the presence of mdm2 panel for 5f is redundant. By mistake upper panel blot for MDM2 was put in panel 5f during image assembly. But the above error does not alter the final conclusion of the article that SMAR1 prevents p53 degradation. However, we shall inform this error to the journal. For Figure 10, we thank PubPeer for pointing out the mistake of HE stained histological section panels between SMAR1-WT and transgenic mice. Both the panels mentioned are internal controls of HE stained images to finally depict the higher expression of SMAR1 and phospho-p53 in transgenic mice using specific antibodies. The left HE stained panel for SMAR1 transgenic mice got inadvertently pasted during image assembly. For this, the overall inference of data is not affected considering that there is no gross change in the histological sections between WT and SMAR1 transgenic mice. We should have picked up the error ourselves. We have the original pictures of the HE stained sections of both types. We shall inform the journal and replace the HE stained section of transgenic mice. , 
 2019 Expression of Concern. http: www.jbc.org content 294 46 17708 The publisher of the Journal of Biological Chemistry is issuing an Expression of Concern to inform readers that credible concerns have been raised regarding some of the data and conclusions in the article listed above. The Journal of Biological Chemistry will provide additional information as it becomes available. , 
 Earlier Pubpeer raised two minor points in the Figures of the above manuscript. Since this paper was published about 15 years back, it is difficult to get the originals of photographs of H E stained sections of thymus of WT and SMAR1 transgenic mice. However, we have repeated the experiments and sending the uncropped images of the H E stained sections. We have also incorporated the same in the corrected Figure. We feel that since, these are very minor changes that does not change the ultimate conclusion of the paper, an erratum from JBC is expected. We have sent the minor corrections to be made and provided the necessary documents for the erratum. For Figure 5e and 5f, we have now prepared the correct figure and also answered the queries of the Pubpeer already (available online). It is known that MDM2 allows degradation of p53. So overexpression of MDM2 reduces levels of p53 (Fig. 5e). In figure 5f, the objective was to show SMAR1 overexpression prevents MDM2 mediated p53 degradation. Dose dependent overexpression of SMAR1 along with MDM2 resulted in p53 stabilization depicting protective role of SMAR1. Since, Same concentrations of MDM2 are used in both 5e and 5f, the presence of mdm2 panel for 5f is redundant. By mistake upper panel blot for MDM2 was put in panel 5f during image assembly. But the above error does not alter the final conclusion of the article that SMAR1 prevents p53 degradation. Accordingly, we are providing a revised one that has minor alteration in the labeling. For this the change in the Figure legend is not required. For Figure 10, there was a minor mistake in the H E stained histological section panel between SMAR1-WT and transgenic mice. Both the panels mentioned are internal controls of H E stained images to finally depict the higher expression of SMAR1 and phospho-p53 in transgenic mice using specific antibodies. The left H E stained control panel for both WT and SMAR1 transgenic mice got inadvertently pasted during image assembly. For this, the overall inference of data is not affected considering that there is no gross change in the histological sections between WT and SMAR1 transgenic mice. We should have picked up the error ourselves. We have repeated the experiment and incorporated the original pictures of the H E stained section of thymus from WT and SMAR1 transgenic mice. There were no gross changes in the cellularity or cellular morphology was observed. With these, we have requested the journal for an erratum with these minor changes in the new figures provided. ![file] , 
 2020 retraction. https: www.jbc.org content 295 10 3390 VOLUME 280 (2005) PAGES 16019u201316029 This article has been withdrawn by the authors. In Fig 2A, a portion of the image for 24 hrs Control was reused in hrs SMAR1 stable. The Mdm2 immunoblot in Fig. 5E was mislabeled in Fig. 5F. In Fig. 9E, image 3 was flipped vertically and reused as image 1. Also, a portion of image 5 was resized and reused in image 7. The H E staining in Fig. 10F was rotated in Fig. 10E. The authors state that they could not trace a few of the original images, so they repeated all the relevant experiments and they state that the results are the same as the published data. The authors thus stand by the overall conclusion of the study. ,