PHOSPHORYLATION AND ACCUMULATION OF TAU WITHOUT ANY CONCOMITANT INCREASE IN TUBULIN LEVELS IN CHINESE-HAMSTER OVARY CELLS STABLY TRANSFECTED WITH HUMAN TAU(441)

Eucaryotic expression vectors bearing a 1.4 kb cDNA encoding the 4 rep eat isoform of human tau, tau(441), in either the sense or anti-sense orientation with respect to a cytomegalovirus (CMV) promoter were cons tructed. The resulting constructs were used to transiently express tau in Chinese Hamster Ovary cells and to generate non-neuronal stable ce ll lines, Immunocytochemical studies of these cells show that tau is e xpressed in the sense but not the anti-sense or vector containing line s. Some of the cells expressing tau showed fine elongated processes wh ich were stained by tau antibodies, The general tau immunostaining pat tern appeared diffuse and punctuate, The expressed tau was seen both u nbound and bound to microtubules. In some cells labeling with antibodi es that specifically recognize hyperphosphorylation of tau was observe d. The size of this population increased with increasing numbers of ce ll passages, However, no increase in steady-state tubulin level was ob served following tau(441) expression, These studies show that tau can accumulate in the cells without a concomitant increase in tubulin.