title: Temporal changes in the expression of protein phosphatase 1 and protein phosphatase 2A in proliferating and differentiating murine erythroleukaemia cells.
abstract: Rhythmic changes in the expression of protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A) were investigated during hexamethylene bisacetamide (HMBA) induced differentiation of murine erythroleukaemic (MEL) cells. Cell extracts were analysed by SDS-PAGE and western immunoblotting using specific antibodies. An immunospecific band of molecular mass 36 kDa (catalytic subunit) was detected for PP1. For PP2A, two immunospecific bands of 32 kDa (proteolytically cleaved catalytic subunit) and 36 kDa (catalytic subunit) were observed. Comparisons of proliferating and differentiating cells using only one time point showed no significant differences between mean values for the expression of the PP1 or PP2A enzyme proteins. This kind of analysis, implying that HMBA had little effect, proved misleading, as comparisons using multiple time points showed rhythmic patterns of protein expression which were modulated by the differentiating agent. The effects were complex affecting both the frequency and phasing of rhythms. The results add further support for the view that live cells are multi-oscillators and for the concept that differentiation depends on changes in temporal organization of complex autodynamic feedback loops and multiple interactions between control circuits performing in parallel. In particular, modulation of the dynamics of key proteins, such as PP1 and PP2A, may be a possible mechanism for controlling cellular function and reversing transformation in accordance with long standing theoretical and other experimental data.
authors.affiliation: Department of Molecular Medicine and Haematology, Medical School, University of the Witwatersrand, York Road, Parktown, Johannesburg, 2193, South Africa.
authors.forename: U M
authors.initials: UM
authors.lastname: Bodalina
authors.forename: K D
authors.initials: KD
authors.lastname: Hammond
authors.forename: D A
authors.initials: DA
authors.lastname: Gilbert
mesh_terms: D000081:Acetamides / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation; D015971:Gene Expression Regulation, Enzymologic; D004915:Leukemia, Erythroblastic, Acute / Q000201:enzymology; D051379:Mice; D010507:Periodicity; D010749:Phosphoprotein Phosphatases / Q000096:biosynthesis*; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D014407:Tumor Cells, Cultured
chemical_list: D000081:Acetamides; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; C014026:hexamethylene bisacetamide