Microtubule-associated proteins of HeLa cells: heat stability of the 200,000 mol wt HeLa MAPs and detection of the presence of MAP-2 in HeLa cell extracts and cycled microtubules.

Abstract

One of the major groups of microtubule-associated proteins (MAP) found associated with the microtubules isolated from HeLa [human cervical carcinoma] cells has a MW of just over 200,000. Previous work has demonstrated that these HeLa MAP are similar in several properties to MAP-2, 1 of the major MAP of mammalian neural microtubules, although the 2 types of proteins are immunologically distinct. The 200,000-MW HeLa MAP remained soluble after incubation in a boiling water bath and retain the ability to promote tubulin polymerization after this treatment, 2 unusual properties also shown by neural MAP-2. This property of heat stability has allowed the development of a simplified procedure for purification of the 200,000 HeLa MAP and has provided a means for detection of these proteins, even in crude cell extracts. A protein was detected in crude extracts of HeLa cells and in cycled HeLa microtubules which has been identified as MAP-2 on the basis of: comigration with calf brain MAP-2 on SDS PAGE [sodium dodecyl sulfate polyacrylamide gel electrophoresis]; presence in purified microtubules; heat stability; and reaction with 2 types of antibodies prepared against neural high MW-MAP. MAP-2, although present in HeLa cells, is at all stages of microtubule purification a relatively minor component in comparison to the 200,000 HeLa MAP.