Integrins are the primary receptors used by cells to interact with extracellular matrix. Various  <SUB>1</SUB> and  <SUB>4</SUB> integrin complexes were shown to be involved in the activation of a number of cell cyclin inhibitors.  The  <SUB>4 </SUB>integrin cytoplasmic domain<SUB> </SUB>was shown to be involved in the activation of p21 pathways of growth arrest and apoptosis.  In this study, the  <SUB>1 </SUB>integrin was blocked and cell were cultured on laminin as ECM, thus only the  <SUB>4 </SUB> integrins binds to the ECM.  This way we were able to study the mouse Clara cell cycle progression and death possible through the regulation of p21 in a controlled integrin-ECM binding environment using both wt and p21-/-mice. Upon beta-1 integrin blocking, an increase in apoptosis was observed in Clara cells from both wt and p21 ko mice at 72 and 120 h in culture, the apoptosis rate was higher (p&lt;0.05) in cells from wt mice compared to cells from p21 ko mice at 72 h and  a decrease (p&lt;0.05) in BrdU incorporation was observed in cells from wt mice at 24 and 72 h in culture and in cells from p21 ko mice at 24 h in culture.   Cytoplasmic PCNA expression was found to be higher (p&lt;0.05) in cells from both wt and p21 ko mice upon beta-1 integrin blocking at 120 h and the expression of nuclear PCNA expression significantly increased (p&lt;0.05).  In the absence of p21, there was an increase in cytoplasmic PCNA expression but not nuclear PCNA expression. The expression of PCNA increases in cells from both wt and p21 ko mice but p21 is essential for the nuclear PCNA localisation.