Protein phosphorylation and dephosphorylation systems modulate many ce
llular activities and have recently been implicated in the in vitro tr
ansport of newly synthesized proteins. Here we show that polarized tra
nsport from the Golgi to the plasma membrane in intact MDCK cells is r
egulated by phosphorylation-dephosphorylation, Transport is inhibited
by the phosphatase inhibitor okadaic acid and is stimulated by the kin
ase inhibitor staurosporine. Stimulation of apical transport exceeds s
timulation of basolateral transport by up to 5-fold. We also find that
the G protein activator aluminum fluoride, which stimulates transport
to the surface at low fluoride concentrations as previously reported,
inhibits transport at higher concentrations. In the nonpolarized fibr
oblast cell line CV-1, neither staurosporine nor aluminum fluoride sti
mulates transport to the cell surface. Our results suggest that the ph
osphorylation-dephosphorylation system. Like the G protein, may be inv
olved in the specialized sorting process characteristic of polarized c
ells, We show some evidence that these two mechanisms of regulation ma
y act through common intermediates.