Stable and slow-turning-over microtubules characterize the processes of motile epithelial cells treated with scatter factor.

The turnover of microtubules was studied in the processes of PtK2 cells, after treatment with the cytokine scatter factor (SF), using micro-injected biotin-tubulin as a reporter of new microtubule growth. Cells treated with SF became dispersed and fibroblast-like in morphology, showing one or more elongated processes. These processes contained bundles of microtubules, a significant proportion of which did not turn over during incubation times of up to an hour. Short broken pieces of microtubule were frequently found in all parts of the cell, particularly after longer incubation times, suggesting that more-stable microtubules were cut into pieces, which were subsequently degraded. From about half an hour after injection small tangles of stable microtubules were found. Some of these were clearly within the cell bodies. Others were usually larger in size and seemingly located outside the injected cells. These were considered to have formed part of small 'feet' presumed to be broken off during the retraction of trailing processes. The microtubules within the processes were resistant to the effects of both microtubule-depolymerizing drugs and cold under conditions where the processes were maintained. When these microtubules disappeared as the result of longer drug treatment the processes were also lost although, rarely, short processes lacking microtubules were found. It is concluded that the stable microtubules have a major role in process maintenance, although one that is indirect rather than a structural relationship.