Nuclear location of a diadenosine 5′,5′"-P1,P4-tetraphosphate (Ap4A) hydrolase in tomato cells grown in suspension cultures

Diadenosine 5',5'''-P-1,P-4-tetraphosphate (Ap(4)A) cleaving enzymes are assumed to regulate intracellular levels of Ap(4)A, a compound known to affect cell proliferation and stress responses. From plants an Ap(4)A hydrolase was recently purified using tomato cells grown in suspension. It was partially sequenced and a peptide antibody was prepared (Feussner et al., 1996). Using this polyclonal monospecific antibody, an abundant nuclear location of Ap(4)A hydrolase in 4-day-old cells of a tomato cell suspension culture is demonstrated here by means of immunocytochemical techniques using FITC (fluorescein-5-isothiocyanate) labeled secondary antibodies. The microscopic analysis of the occurrence of Ap(4)A hydrolase performed for different stages of the cell cycle visualized by parallel DAPI (4,6-diamidino-2-phenylindole) staining revealed that the protein accumulates within nuclei of cells in the interphase, but is absent in the nucleus as well as cytoplasm during all stages of mitosis. This first intracellular localization of an Ap(4)A degrading enzyme within the nucleus and its pattern of appearance during the cell cycle is discussed in relation to the suggested role of Ap(4)A in triggering DNA synthesis and cell proliferation.