Cytokinesis in Smooth Muscle

Abstract

Cytokinesis plays important roles in smooth muscle cell hyperplasia and hypertrophy. Since in proliferating cells the contractile machinery is of the non-muscle type we tested the hypothesis that one of the regulatory enzymes for cytokinesis, the 210 kDa molecular mass non-muscle type myosin light chain kinase (nmMLCK-210), is present at the cell’s contraction ring. Immunocytochemistry showed the presence of the enzyme in the inter-phase nucleus and suggested it may be a transcription factor; however cis-platin cross-linking studies of DNA to the enzyme did not substantiate this. At anaphase the enzyme migrated to the contraction ring zone of the dividing cell where we had demonstrated the presence of non-muscle myosin heavy chain, α-sm-actin and α-tubulin. Thus a complete contractile machinery existed at this site. As cytokinesis proceeds a mid-body structure develops which is made of a centromeric protein, CENP-F, that is initially bound to the kinetochore, but dissociates from it and migrates to the midbody or telophase disc zone. It is involved in the final stage of cytokinesis. We have obtained preliminary evidence to show that CENP-F is localized to the nucleus in smooth muscle. We conclude that the location of non-muscle myosin light chain kinase at the contraction ring suggests it plays a role in cytokinesis.