5 The activity of cyclin-dependent protein kinase p34cdc2 is regulated by phosphorylation. In this study, we show that the presence of phosphatase inhibitors can have major effects on the levels of phosphorylation and the activities of the kinase extracted from cells. The combination of okadaic acid and sodium vanadate was most effective in protecting p34cdc2 against cellular phosphatases. In the absence of these inhibitors, p34cdc2 was dephosphorylated with an altered activity, indicating that phosphatase activities remained high during extractions. In contrast to when both inhibitors were used, lower activity of the kinase was found when only sodium vanadate was used, whereas higher activity was found in the presence of okadaic acid. Other conventional phosphatase inhibitors such as NaP, NaRS03 and glycero12-phosphate, were not effective in preventing dephosphorylation from p34cdc2 in whole cell lysates.

The Cell Cycle

The Epstein-Barr virus transforming protein LMP1 engages signaling proteins for the tumor necrosis factor receptor family

The vacuolar (H+)-ATPases (or V-ATPases) function in the acidification of intracellular compartments in eukaryotic cells The V-ATPases are multisubunit complexes composed of two functional domains The peripheral V1 domain, a 500-kDa complex responsible for ATP hydrolysis, contains at least eight different subunits of molecular weight 70-13 (subunits A-H) The integral V0 domain, a 250-kDa complex, functions in proton translocation and contains at least five different subunits of molecular weight 100-17 (subunits a-d) Biochemical and genetic analysis has been used to identify subunits and residues involved in nucleotide binding and hydrolysis, proton translocation, and coupling of these activities Several mechanisms have been implicated in the regulation of vacuolar acidification in vivo, including control of pump density, regulation of assembly of V1 and V0 domains, disulfide bond formation, activator or inhibitor proteins, and regulation of counterion conductance Recent information concerning targeting and regulation of V-ATPases has also been obtained

Structure, function and regulation of the vacuolar (H+)-ATPase.

On the origin, evolution, and nature of programmed cell death: a timeline of
 four billion years

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On the origin, evolution, and nature of programmed cell death: a timeline of four billion years.

Role of connexin genes in growth control.

The major transforming protein of bovine papillomavirus type 1, E5, is mainly associated with endomembranes, specifically binding to a cellular protein of relative molecular mass 16,000 (16K). At the same time as transformation, E5 causes the phosphorylation of tyrosine residues in epidermal and platelet-derived growth factor receptors. We show here that the 16K protein associated with E5 is the 16K component of vacuolar ATPases. This protein is known to be an integral membrane protein in endosomes, bovine chromaffin granules, synaptic vesicles, fungal and plant vacuoles and clathrin-coated vesicles, as well as a component of gap-junction-like membrane complexes. Because proton pumps are critical for the function of cellular compartments that process growth-factor receptors, the interaction of E5 with the 16K protein could explain the pleiomorphic features of cells transformed by E5.

Malcolm E. Fmbow

Papers

Bovine papillomavirus E5 oncoprotein binds to the 16K component of vacuolar H(+)-ATPases.