A sad (but brilliant) paper about autophagy

Over the past several decades I’ve accumulated a lot of notes on autophagy (> 125,000 characters).  It’s obviously important, but in a given cell or disease (cancer, neurodegeneration) whether it helps a cell die gracefully or is an executioner is far from clear.  Ditto for whether enhancing or inhibiting it in a given situation would be helpful (or hurtful).

A major reason for the lack of clarity despite all the work that’s been done can be found in the following excellent paper [ Cell vol. 177 pp.1682 – 1699 ’19 ].  Some 41 proteins are involved in autophagy in yeast and more in man.  Many are described as ATGnn (AuTophagy Gene nn).

Autophagy is a complicated business: forming a membrane, then engulfing various things, then forming a vacuole,  then fusing with the lysosome so that the engulfees are destroyed.

The problem with previous work is that if a protein was found to be important in autophagy, it was assumed to have that function and that function only.   The paper shows that core autophagy proteins are involved in (at least) 5 other processes (endocytosis, melanocyte formation, cytokinesis, LC3 assisted phagocytosis and translocation of vesicles from the Golgi to the endoplasmic reticulum).

Experiments deleting or  increasing a given ATGnn were assumed to produce their biological effects by affecting autophagy.

The names are unimportant.  Here is a diagram of 6 autophagy proteins forming a complex producing autophagy

1 2 3

4 5 6

So 2 binds to 1, 3 and 5

But in endocytosis

1 2 3

5

form an important complex

In cytokinesis the complex formed by

2 3

5

is important.

Well you get the idea.  Knocking out 2 has cellular effects on far more than autophagy.  So a lot of work has to be re-thought and probably repeated.

Notice that all 6 functions involve movement of membranes.  So just regard the 6 proteins as gears of different diameters which can form the guts of different machines as they combine with each other (and proteins specific to the other 5 processes mentioned) to move things around in the cell.