A systems biology dynamical model of mammalian G1 cell cycle progression.

The current dogma of G(1) cell-cycle progression relies on growth factor-induced increase of cyclin D:Cdk4/6 complex activity to partially inactivate pRb by phosphorylation and to sequester p27(Kip1)-triggering activation of cyclin E:Cdk2 complexes that further inactivate pRb. pRb oscillates between an active, hypophosphorylated form associated with E2F transcription factors in early G(1) phase and an inactive, hyperphosphorylated form in late G(1), S and G(2)/M phases. However, under constant growth factor stimulation, cells show constitutively active cyclin D:Cdk4/6 throughout the cell cycle and thereby exclude cyclin D:Cdk4/6 inactivation of pRb.

The influence of different InsP(3) receptor isoforms on Ca(2+) signaling in tracheal smooth muscle cells.

In airway myocytes, like in many cells, Ca(2+) signaling is controlled by inositol 1,4,5-trisphosphate (InsP(3)) via InsP(3) receptors (InsP(3)R) located in the sarco-endoplasmic reticulum. Three types of InsP(3)R exist, labeled Types 1, 2, and 3, which differ in their gating kinetics. We analyze a possible impact of the different gating kinetics of Type 1 and Type 3 InsP(3)R on the time course of cytosolic Ca(2+) concentration in tracheal smooth muscle cells upon agonist stimulation.