Cancer and pH Dynamics: Transcriptional Regulation, Proteostasis, and the Need for New Molecular Tools
, Ricardo Romero-Moreno 1,2,†, Keelan J. Trull 1,2,† and Katharine A. White 1,2,*Round 1
Reviewer 1 Report
This review cites multiple lines of evidence that perturbed pH homeostasis, specifically increased cytosolic pH, is a major early determinant of cancer progression. The authors point out the multiple levels at which the established increase in pHi in cancer cells can mechanistically drive adaptation and acquisition of characteristic cancer phenotypes. They also point out that these changes can be heterogeneous and dependent on microenvironment, and in the end discuss existing mechanisms for measuring and manipulating pH at the cellular and tissue level. Overall, the review is exceptionally well-written and clear. I have only minor suggestions for changes.
- The authors focus on cytosolic pH almost exclusively, except for a brief mention of the importance of lysosomes in proteolysis and inclusion of organelle-targeted pH sensors in the final section on tools. However, it might be worth some discussion of whether organelle pH homeostasis is also perturbed in cancer and how this could be important. For example, there is considerable data implicating V-ATPase activity in cancer. Some of this may come from acquisition of V-ATPase activity at the plasma membrane (NHE activity is really the only export mechanism highlighted here), but there may also be roles for V-ATPases at organelles such as the lysosomes. This deserves at least some mention.
- Section 4 on the relationship between transcript and protein abundance may be unnecessary. It has been recognized for a long time that there is not a direct relationship between transcript and protein levels in cancer or non-cancer cells, although it is true that people still misinterpret increased transcript levels as increased protein levels.
Author Response
See attached.
Reviewer 2 Report
The proposed article summarizes the effects of altered pHi, as a hallmark of cancer cells, on transcriptional regulation and proteostasis in tumorigenesis. The authors also provide an overview of the tools of pHi measurement techniques. The topic of the importance of increased pHi for cancer cell progression, metastasis and therapy resistance is very significant and scientifically sound and there is not too much literature summarizing the impact of pHi changes on different cellular processes that dramatically affect cancer cells behavior. However, the article needs minor revision, please, see below my questions and comments.
I think the general readership would benefit from a detailed description of the mechanisms by which altered pHi, resulting in changes of protonation of amino acids, affects protein conformation, activity, interactions, etc. Please also specify which amino acids are pH-sensitive.
The process of pHi alkalinization in cancer cells is a complex interplay of various proteins and different pH buffering systems which shouldn’t be limited to the activity of NHE1 (lines 100-101). Please describe shortly other mechanisms involved in this process (carbonic anhydrases, bicarbonate transporters, lactate transporters, etc.)
The message of the chapter ”Heterogeneity and pHi” is unclear. Please rewrite it and be more specific. Could you please explain the meaning of the following sentence ….” pHi may be a biomarker for more cryptic phenotypic heterogeneity markers”?
Ionic liquid (mentioned from line 324) represents a new interesting tool for pHi measurement so could you please expand this paragraph and provide more information?
I do not consider the sentence in lines 397-399 (”However, with the exception of a few superstars, targeted molecular therapeutics have not been able to overcome issues of tumor heterogeneity and clonal adaptation and selection”) appropriate for a scientific paper. It is more suitable to give specific examples of successful targeted molecular therapeutics to treat cancer diseases.
A message of some statements in the article is unclear, please could you rephrase/explain in more detail?
- lines 166-167: …. pH-sensitive cancer-associated phenotypes…
- lines 400-401: The work summarized in this review suggests the tantalizing possibility that tumor pHi may be a biomarker of more cryptic measures of tumor heterogeneity
- lines 418-421: …quantitative pHi measurements across cancer model systems could alone revolutionize the way clinicians think about therapeutic interventions targeting pHi-dependent cancer fitness advantages that result from the single-cell acquisition of phenotypic advantage, clonal expansion, and competition.
Regarding the existing possibilities of pHi measurement in vivo, as well as, targeting pHi in cancer patients, this statement is too strong towards the therapeutic intervention. Please, specify the therapeutic approach more precisely or rephrase.
Author Response
See attached.
