Figure 13. Changes in OL cell cycle proteins in 4% O₂.

Whole cell lysates from OLs cultured at 21% O₂ or 4% O₂ in the presence of GFs, were analyzed by immunoblot analysis for phosphorylation state of cell cycle proteins Rb and cdc2, and for the negative regulator of cell cycle, p27^Kip1. Ribosomal S6 protein was used as a loading control. The approximate sizes for Rb, cdc-2, p27^Kip1 and ribosomal S6 protein are 110 kDa, 34 kDa, 27 kDa and 32 kDa, respectively. Representative Western blot from 3 different preparations shows an increase in phosphorylated forms of Rb and cdc-2, and total p27^Kip1 levels in hypoxia. (B) Densitometric analysis was done by normalizing protein levels to ribosomal S6 protein levels. The percent increase in the expression of cell cycle proteins is shown relative to levels in 21% O₂ (* p<0.05, ** p<0.01). Data shown are representative of three separate studies.