The alpha and beta subunits of the Na,K-ATPase can assemble at the plasma membrane into functional enzyme.

Abstract

Synthesis and assembly of most oligomeric plasma membrane proteins occurs in the ER. However, the role the ER plays in oligomerization is unknown. We have previously demonstrated that unassociated alpha and beta subunits of the Na,K-ATPase are targeted to the plasma membrane when individually expressed in baculovirus-infected Sf-9 cells. This unique property allows us to determine if assembly of these two polypeptides is restricted to the ER, or if it can also occur at the plasma membrane. To investigate the assembly of the Na,K-ATPase we have taken advantage of the ability of baculovirus-infected cells to fuse. Lowering the extracellular pH of the infected cells triggers an endogenously expressed viral protein to initiate plasma membrane fusion. When individual Sf-9 cells expressing either the Na,K-ATPase alpha or beta subunits are plated together and subjected to a mild acidic shock, they form large syncytia. In the newly continuous plasma membrane the separate alpha and beta polypeptides associate and assemble into functional Na,K-ATPase molecules. However, a hybrid ATPase molecule consisting of a Na,K-ATPase alpha subunit and a H,K-ATPase beta subunit, which efficiently assembles in the ER of coinfected cells, does not assemble at the plasma membrane of fused cells. When cells expressing the Na,K-ATPase alpha subunit are fused to cells coexpressing the Na,K-ATPase beta subunit and the H,K-ATPase beta subunit, the Na,K-ATPase alpha subunit selectively assembles with the Na,K-ATPase beta subunit. However, when cells are coinfected and expressing all three polypeptides, the Na,K-ATPase alpha subunit assembles with both beta subunits in the ER, in what appears to be a random fashion. These experiments demonstrate that assembly between some polypeptides is restricted to the ER, and suggests that the ability of the Na,K-ATPase alpha and beta subunits to leave the ER and assemble at the plasma membrane may represent a novel mechanism of regulation of activity.

Differential Na+–K+‐ATPase activity in rat lemniscal and non ‐ lemniscal auditory Thalami

“…For example, recent studies of exocrine gland cells using fractionation and phasepartitioning methods showed that upon physiological stimulation, pumps are being actively recruited to the basolateral plasma membrane from cytoplasmic structures (Mircheff et al 1989). Alternatively, subunits of Na¤-K¤-ATPase may assemble at the plasma membrane (DeTomaso, Blanco & Mercer, 1994). While the mechanism of differential Differential Na¤-K¤-ATPase expression J. Physiol.…”

Augmentation of lung liquid clearance via adenovirus-mediated transfer of a Na,K-ATPase beta1 subunit gene.

“…These agents have been reported to increase Na,KATPase function via a variety of mechanisms. Gene transfer has been used to study Na,K-ATPase expression and subunit interregulation in mammalian cell lines (34,(44)(45)(46)(47)(48)(49). Increased mRNA expression and altered protein profiles have been noted in these studies.…”

Pathways and control of connexin oligomerization

“…For example, targeting of coronavirus coat proteins [50] and Golgi resident enzymes [51] correlates with oligomerization in the Golgi apparatus. Remodeling and assembly of ion channels, such as ENaC and Na-K ATPases, can occur in late secretory compartments and at the plasma membrane [52][53][54]. Another class of proteins that oligomerize in the Golgi apparatus are tetraspanins, such as CD9, CD63, CD81 and CD151 [55].…”