[The nature of the phosphorylation of retinoblastoma gene product in stable mouse and human cell lines].
The retinoblastoma gene product mediates the interaction between transcriptional factors and cyclin-kinase complexes, which perform a regulatory and effector function in the process of cell division. The activity of the retinoblastoma gene product is regulated by phosphorylation, which results in the appearance of additional protein molecules migrating in the region of 105--116 kDa during electrophoresis. Stereochemical analysis has established a direct correspondence between the extent of phosphorylation of the retinoblastoma gene product and its electrophoretic mobility. The results obtained permit an estimate of the phosphorylation of this protein in cells of different tissues by immunoblotting analysis of their lysates. The results of this study demonstrate that the degree of phosphorylation of retinoblastoma gene product in a series of stable cell lines increases as we go from monolayer to multilayer cultures, and further to cell cultures in suspension. Human cells produce more phosphorylated proteins compared to homologous mouse cells. The phosphorylation pattern of retinoblastoma gene product is probably tissue-specific. Much like mouse fibroblasts, HeLa cells may contain a hypophosphorylated protein with a molecular weight of 105 kDa. Phosphorylation of the retinoblastoma gene product in cells of embryonic mouse adenocarcinoma (line p19) changes in response to cloning or stimulation of differentiation by retinoic acid. The formation of all forms of retinoblastoma gene product, which pre-exist during asynchronous growth, is increased in the course of cloning. Differentiation is associated with the synthesis of an increased amount of hypophosphorylated protein. The results obtained lead to the hypothesis that even though the phosphorylation pattern of the retinoblastoma gene product is tissue-specific, it can show significant variation under the conditions of either cloning or differentiation and can be maintained for extended period of time at a new level that was not characteristic of the initial cell population.
Popov
B V
BV
Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia.
Kulakova
I A
IA
Popov
N B
NB
Frenkel'
Z M
ZM
D000818:Animals; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D004586:Electrophoresis; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D010766:Phosphorylation; D016160:Retinoblastoma Protein / Q000032:analysis / Q000378:metabolism*; D013045:Species Specificity
D016160:Retinoblastoma Protein