Ca²⁺‐dependent cell surface protein phosphorylation may be involved in the initiation of DNA synthesis

Abstract

Incubating T51B rat liver cells in Ca2+-deficient, serum-rich medium containing only 0.02 mM Ca2+ strikingly decreased the phosphorylation of several trypsin-removable cell surface proteins and arrested the cells in late G1 phase. Raising the Ca2+ concentration in the Ca2+-deficient medium from 0.02 mM to 0.5 mM or adding 80 nM TPA (12-O-tetradecanoyl-phorbol-13-acetate), a protein kinase C activator, stimulated the phosphorylation of a certain set of surface proteins within 5 min and the initiation of DNA replication within the next 2 hr. By contrast, incubation in the same Ca2+-deficient medium, which does not affect the proliferation of neoplastic T51B-261B cells, did not reduce the phosphorylation of cell surface proteins. These observations suggest that the stimulation of a Ca2+-dependent protein kinase (possibly protein kinase C) directly or indirectly phosphorylates certain cell surface proteins that might be part of the mechanism that triggers the Ca2+-dependent G1----S transition of normal cells. They also suggest that an alteration of this Ca2+-dependent protein kinase might be the reason for neoplastic cells being able to proliferate in the face of an external Ca2+ shortage that would stop the proliferation of normal cells.

Reinioside C, a triterpene saponin of Polygala aureocauda Dunn, exerts hypolipidemic effect on hyperlipidemic mice

“…These above findings suggested that reinioside C can partially abolish OxLDL action by inhibiting calcium influx into macrophages. As Ca 2+ also plays an essential role in cell proliferation and contractility (Kleine et al, 1986), it is suggested that Reinioside C can inhibit the proliferation of vascular smooth muscle cells mediated by the modification of Ca 2+ mobilization.…”

Electric fields stimulate DNA synthesis of mouse osteoblast‐like cells (MC3T3‐E1) by a mechanism involving calcium ions

“…Effect of electric stimulation on calcium uptake by MC3T3-El cells It is reported that changes in cellular levels of either calcium ions or cAMP are involved in the regulation of cell proliferation and differentiation (Whitfield et al, 1980, Kleine et al, 1986. To further examine the effect of electric stimulation on DNA synthesis, we investigated whether electric stimulation promotes calcium uptake into osteoblast-like MC3T3-El cells.…”

Leishmanial protein kinases phosphorylate components of the complement system.

“…..v field, 1987; Fishelson et al, 1989). The function of these extracellular enzymes is unknown, though it has been suggested that such enzymes might be involved in the initiation of DNA synthesis (Kleine et al, 1986) or evasion of complement lysis . Evasion of the complement cascade by Leishmania is an integral part of the parasite life-cycle.…”