J. Biol. Chem., Vol. 257, Issue 19, 11728-11733, Oct, 1982
Switching of beta- to alpha-tubulin phosphorylation in uterine smooth muscle of parturient rats
MK Joseph, MA Fernstrom and MS Soloff
Proteins from pregnant rat uterine myometrium, previously incubated in the
presence of (32P)orthophosphate, were analyzed by one- and two- dimensional
polyacrylamide gel electrophoresis and subsequent autoradiography.
Electrophoretic patterns of Coomassie blue-stained proteins in preterm and
labor myometria were indistinguishable. However, radioactivity incorporated
into tubulin in preterm myometrium was predominantly associated with the
beta-subunit, whereas in labor, the alpha-subunit was labeled. Endogenous
phosphorylated alpha- and beta-tubulins were clearly identified on
two-dimensional gel electrophoretograms by apparent molecular weights,
isoelectric points, co-migration with marker brain tubulin, and reactivity
to specific antitubulin antibodies. The antibodies were incubated with
nitrocellulose sheets onto which the myometrial proteins were
electrophoretically transferred from the two-dimensional gels. The
switching in phosphorylation of beta- to alpha-tubulin in the labor
myometrium appears to be a manifestation of estrogen action. The labor-
specific phosphorylation changes occurred in parallel with changes in serum
estradiol/progesterone ratios. Indeed, estrogen administered to
ovariectomized rats caused the appearance of phosphorylated alpha- tubulin,
and this effect was inhibited by progesterone. Although the significance of
tubulin phosphorylation is not currently understood, the switching in
phosphorylation from beta- to alpha-tubulin under estrogen domination may
help clarify the role of microtubule phosphorylation.
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