DIFFERENTIAL REGULATION OF NA,K-ATPASE ISOZYMES BY PROTEIN-KINASES AND ARACHIDONIC-ACID

While several studies have investigated the regulation of the Na,K-ATP ase consisting of the alpha 1 and beta 1 subunits, there is little evi dence that intracellular messengers influence the other Na pump isozym es. We studied the effect of different protein kinases and arachidonic acid on the rat Na,K-ATPase isoforms expressed in Sf-9 insect cells. Our results indicate that PKA, PKC, and PKG; are able to differentiall y modify the function of the Na,K-ATPase isozymes. While PKC activatio n leads to inhibition of all isozymes, PKA activation stimulates the a ctivity of the Na,K-ATPase alpha 3 beta 1 and decreases that of the al pha 1 beta 1 and alpha 2 beta 1 isozymes. In contrast, activation of P KG diminishes the activity of the alpha 1 beta 1 and alpha 3 beta 1 is ozymes, without altering that of alpha 2 beta 1. Treatment of cells wi th arachidonic acid reduced the activities of all the isozymes. The ch anges in the catalytic capabilities of the Na pump isozymes elicited b y PKA and PKC are reflected by changes in the molecular activity of th e Na,K-ATPases. One of the mechanisms by which PKA and PKC affect Na p ump isozyme activity is through direct phosphorylation of the alpha su bunit. In the insect cells, we found a PKA- and PKC-dependent phosphor ylation of the alpha 1, alpha 2 and alpha 3 polypeptides. In conclusio n, several intracellular messengers are able to modulate the function of the Na,K-ATPase isozymes and some of them in a specific fashion. Be cause the Na,K-ATPase isozymes have kinetic properties that are unique , this isozyme-specific regulation may be important in adapting Na pum p function to the requirements of each cell. (C) 1998 Academic Press.