Enzymatic modification of Novikoff hepatoma lamins A and C

A significant increase in the molecular weights of lamin A and more so of lamin C was observed when isolated Novikoff hepatoma chromatin was incubated in the presence of Ca2+. This increase did not occur to any significant degree in similar preparations of normal rat liver nuclei. Although detectable in Coomassie Brilliant Blue stained gels, this increase to a higher molecular weight (by approximately 2000 Mr) was much more visible when the electrophoretically separated lamins were transferred to nitrocellulose sheets and stained (using peroxidase-antiperoxidase) with polyclonal antiserum to the three major lamin proteins. This modification could also be induced when whole Novikoff hepatoma cell lysates were incubated in the presence of calcium. Again, this change did not occur in normal rat liver cells treated in the same manner. Further analysis has provided evidence that this modification is most likely mediated by the transaminating activity of an intrinsic nuclear transglutaminase forming a cross-link between the affected lamins and an unknown low molecular weight (approximately equal to 2000 Mr) moiety.