Possible Role of the Multi Catalytic Proteinase (Proteasome) in Regulating of the Cell Cycle

Abstract

We have investigated the intracellular distribution of proteasomes (multi catalytic proteinase) during the somatic cell cycle and during differentiation. The granulosa cell system was chosen for investigating the spatial and temporal distribution pattern of proteasomes, since stable lines derived from primary cells have recently been established in our laboratory. Moreover, these lines can be stimulated to differentiate by substances that elevate they intracellular cAMP levels. We found a dramatic accumulation of proteasomes in metaphase and early anaphase, the stages at which cyclin A and B₁ are degraded. Moreover, only a low concentration of proteasomes could be observed in cells that were stimulated to differentiate. A preferential high concentration of proteasomes was clearly evident in close proximity to spindle microtubules in dividing cells, with significantly lower concentrations of proteasomes outside the spindle apparatus. in contrast, no spatial correlation was evident between proteasomal and microtubular localization in nondividing cells. The modulation of proteasome distribution in mitosis suggests that they play a regulatory role during the cell cycle.