Tumours with PI3K activation are resistant to dietary restriction
Authors: David M Sabatini
Nada Y Kalaany
Journal: Nature (2009)
Discipline: Multidisciplinary
Keywords: Dietary restriction; tumours; cancer cell lines; xenografts; PI3K pathway
Affiliations: Whitehead Institute for Biomedical Research, Nine Cambridge Center, Cambridge, Massachusetts 02142, USA.

Abstract:  Dietary restriction delays the incidence and decreases the growth of various types of tumours, but the mechanisms underlying the sensitivity of tumours to food restriction remain unknown. Here we show that certain human cancer cell lines, when grown as tumour xenografts in mice, are highly sensitive to the anti-growth effects of dietary restriction, whereas others are resistant. Cancer cells that form dietary-restriction-resistant tumours carry mutations that cause constitutive activation of the phosphatidylinositol-3-kinase (PI3K) pathway and in culture proliferate in the absence of insulin or insulin-like growth factor 1. Substitution of an activated mutant allele of PI3K with wild-type PI3K in otherwise isogenic cancer cells, or the restoration of PTEN expression in a PTEN-null cancer cell line, is sufficient to convert a dietary-restriction-resistant tumour into one that is dietary-restriction-sensitive. Dietary restriction does not affect a PTEN-null mouse model of prostate cancer, but it significantly decreases tumour burden in a mouse model of lung cancer lacking constitutive PI3K signalling. Thus, the PI3K pathway is an important determinant of the sensitivity of tumours to dietary restriction, and activating mutations in the pathway may influence the response of cancers to dietary restriction-mimetic therapies. 

Retracted: No

PubPeer comments:
 Fig. 3a more similar than expected. Could the authors check?  , 
 Thank you for noting this error and apologies for the confusion. I am the first author of the paper and now at Boston Children s Hospital, Harvard Medical School. In Fig. 3a of this Article, the western blot on the top right corner (P-S473 Akt, DLD-WT, 24h) was mistakenly placed as a duplicate of the blot on its left (1h), during the submission of reformatted figure panels. This error does not impact the conclusions of the paper. Nevertheless, we will contact the Nature Editorial Office to let them know about this mistake and its correction. The corrected panel is shown below.  , 
 Can author show the original uncropped images to support their claim  This error does not impact the conclusions of the paper ? , 
 #3 Can you provide a concrete explanation of how uncropped images would affect the conclusions? Can you identify a conclusion in the paper that has been impacted by the mistake and or its correction? , 
 i) It s a little weird that the  1h P-S473 Akt blot (WT) blot has a background color that is different when you compare all others blots. Showing the uncropped images would definitely clear any issue. ii) Also, the authors might agree that this new blot suggests a slight difference in the understanding of this particular result. Article: *** Consistent with their genetic statuses, DLD-mut, but not DLD-WT cells, maintained high levels of phospho-S473 Akt after serum withdrawal for 1 or 24 h *** I agree that the removal of serum has a clear effect in decreasing phospho-akt levels in 1 hour in the WT condition but not in DLD-mutant. However, the interpretation for24h is trickier. In the new provided blot for WT-DLD, the phospho-Akt levels are already very reduced even in the presence of the serum. So, in 24 hours, the effect of the removal of serum in decreasing phospho-Akt leveles seems to be very similar in both DLD-WT and DLD-mut. , 
 #5 #4 Thank you for your comments and discussion. Below is my response, and I am happy to discuss further. Sincerely, Nada Kalaany. My apologies for this unintentional error. Having looked back into our paper submission files, I found that the error occurred post-review of the first and second submission (post-revisions), when we were re-formatting the figure panels; this is when we were asked to submit higher resolution figures and to remove some panels out of the Main figures and place them into Supplementary Info. In all prior manuscript versions, as well as my poster and oral Powerpoint presentations, the correct Fig. 3a panel was shown and discussed. i) Below please find the scanned p-S473 Akt blot for DLD-WT cells in the presence or absence of serum (without and with cropping). The first 4 lanes represent DLD-WT - + serum for 1 hour, followed by DLD-WT - + serum for 24 hours. The rest of the sample lanes are unrelated to this experiment. This western blot was completed on June 04, 2008. The scan was cut between the serum conditions in this figure panel, because for DLD-Mut cells, the order of sample loading was not the same as that for DLD-WT. ii) This comment points rightfully at a significant decrease in p-Akt following the incubation of DLD-WT cells with 10% serum for 24 hours, compared to a 1 hour incubation. Given that cancer cells use deplete some nutrients over time (as they grow and divide) and given that growth factors present in the serum become less potent upon longer incubation (as compared to freshly added serum), this result would be expected. We have indeed consistently observed a decrease in p-Akt in cancer cells incubated for longer periods of time in the same medium serum, compared to shorter incubation times. This is why incubating cells with refreshed medium serum for the same amount of time is key when assaying for u201cbasalu201d serum growth factor signaling. As for DLD-Mut cells, they display a decrease in p-Akt, only upon 24 hour (not 1 hour) incubation in the absence of serum. However, it is noteworthy that Akt phosphorylation remains significantly higher in the DLD-Mut, when compared to DLD-WT cells, independent of serum levels. This is supported by the article published in 2005 in Cancer Cell (Samuels et al.), where the Velculescu and Vogelstein labs first described the generation of the isogenic DLD-WT and DLD-Mut cells, which only genetically differ in the PIK3CA allele that they carry: WT or activated Mut (E545K), respectively. We obtained the DLD cells from their labs. Below, please find a screen shot from Figure 4A of their paper (see right panel for DLD cells), demonstrating that whether cultured under 0.5% or 10% serum conditions, DLD-Mut cells maintain significantly higher p-Akt levels than DLD-WT cells.    , 
 This article has a correction note (Author Correction) https: www.nature.com articles s41586-020-2215-y  In Fig. 3a of this Article, the western blot at the top right (P-S473 Akt, DLD-WT, 24 h) was a duplicate of the blot on the left (1 h). This error does not affect the conclusions of the paper. The corrected panel is shown as Fig. 1 of this Amendment, together with the incorrect published panel, for transparency to readers. See Supplementary Information to this Amendment for the raw data for the corrected Fig. 3. The original Article has not been corrected. ,