Regulation of protein metabolism of human cells during and after acute hypoxia

Protein synthesis and protein degradation were measured in human NHIK 3025 cells cultured in vitro during and after an acute treatment of extreme hypoxia (less than 4 ppm O2). Furthermore, total protein content per cell was recorded and related to cell cycle phase by coincident measurement of DNA and protein using two-parametric flow cytometry. During hypoxia protein synthesis was reduced and protein degradation was increased, resulting in no net accumulation of protein. From the flow cytometric recordings, the amount of protein per cell was found to be constant, or perhaps in some of the cells slightly reduced, after a 3-h period of extreme hypoxia. Three h after reaeration protein degradation had returned to normal while protein synthesis was slightly above normal. The flow cytometric recordings showed that after reaeration the protein accumulation was particularly high in the subpopulation of cells which accumulated at the G1-S border during hypoxia and entered S phase as a partly synchronized subpopulation after reaeration. Since we know from our earlier studies that these cells are more resistant to hypoxia than cells in S phase we conclude that this high protein accumulation may be important in restoring a pool of proteins which initiate DNA synthesis and perhaps other proteins of importance to cell growth.