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Could tripelennamine target phosphatidylethanolamine?

Posted by eperlste on 15 Sep 2012 at 02:01 GMT

Nice study! (And thanks for citing my lab's 2010 GENETICS paper on sertraline).

My lab's experience with CADs is mostly with unconditional cytotoxicity, which your screen filtered out. Whenever we've looked at CAD response in deletion collections we've never seen such strong enrichment for autophagy genes. So that makes me wonder whether tripelennamine has greater selectivity for PE-enriched membranes. PE modification is the first step in classical autophagosome formation.


No competing interests declared.

RE: Could tripelennamine target phosphatidylethanolamine?

schlecht replied to eperlste on 24 Sep 2012 at 20:59 GMT

We performed our deletion pool experiment under starvation conditions (no external fermentable carbon sources or nitrogen sources added to the media). In this condition autophagy-related genes become essential. In rich media, however, these genes are not essential and would therefore not be observed in a deletion mutant screen. Could this be a possible explanation for the observed differences between your screens and ours?

At this point we don't know the precise underlying mechanism by which tripelennamine interferes with autophagy, nor do we know whether tripelennamine prefers to reside within certain types of membranes (for example PE-enriched membranes).

No competing interests declared.

RE: Could tripelennamine target phosphatidylethanolamine?

schlecht replied to eperlste on 25 Sep 2012 at 04:05 GMT

One challenge we encountered while writing the paper was to reconcile your observation (published in Rainey et al. and more recently in Chen et al.) that sertraline-treated yeast cells show an elevated number of undigested autophagosomes (presumably due to a stimulation in autophagic activities) and our claim that tripelennamine inhibits these processes. Of course both drugs may not act through the same molecular MOA. However, if we assume they did: do they diminish or increase autophagy?

You may have seen that there is a paper on the problem of measuring flux through the autophagy pathway published in the journal 'Autophagy' in April of this year (PMID: 22966490). We tried to think of ways to prove one or the other with a more direct autophagy assay, but eventually decided to publish the work as it was.

No competing interests declared.

RE: RE: Could tripelennamine target phosphatidylethanolamine?

eperlste replied to schlecht on 28 Sep 2012 at 13:47 GMT

Obviously not all cationic amphipaths are the same. What I found most interesting about your study is that you selected for conditional lethality, it just so happens your condition is a differentiated cell state. While I think all cationic amphipaths will accumulate in membrane, there must be specificity determinants of accumulation, especially at sub-micellar concentrations. My argument is that tripelennamine may selectively target PE-enriched membrane, which itself not a lethal accumulation, but because PE is an essential first step in committed autophagosome formation, tripelennamine accumulation could further sensitize autophagy-compromised mutants.

So I would still predict an autophagy induction in response to tripelennamine accumulation if you looked by EM, especially at sublethal doses. It may just be that autophagy compromised mutants cannot tolerate accumulation at high doses. Long story short: the autophagy response is complex w/r/t accumulation.

And I agree that most assays of autophagic flux suck, which is why I prefer static EM.

No competing interests declared.