Initiation of DNA synthesis by human thrombin: Relationships between receptor binding, enzymic activity, and stimulation of 86Rb + influx

✍ Scribed by Janet Stiernberg; Darrell H. Carney; John W. Fenton 2nd; Edward F. Lablle

• Publisher: John Wiley and Sons
• Year: 1984
• Tongue: English
• Weight: 804 KB
• Volume: 120
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041200305

✦ Synopsis

Stimulation of amiloride-sensitive sodium (Na+) influx and the subsequent activation of NA+, K+-ATPase by serum or growth factors have been implicated as early events leading to initiation of cell proliferation. We recently demonstrated that amiloride inhibits thrombin-initiated DNA synthesis not by inhibiting an early event occurring during the first 8 hr, but rather by inhibiting some later event 8 to 12 h r after thrombin addition. To further probe the relationship between stimulation of ion influx and initiation of cell proliferation, human a-thrombin was converted to y-thrombin, nitro-athrombin, and diisopropylphospho (DIP)-a-thrombin. These derivatives retain either the capacity to bind cell surface a-thrombin receptors or thrombin esterase activity, but they do not initiate DNA synthesis. At low concentrations of a-thrombin or the various thrombin derivatives, only a-thrombin stimulates sbRb' influx, suggesting a correlation between stimulation of influx and the ability of these derivatives to initiate DNA synthesis. Concentrations of a DIPa-thrombin that saturate the a-thrombin recptors (up to 2 & n l ) do not stimulate either the early or late influx of 86Rb+, indicating that DIP-a-thrombin binding alone is not sufficient to stimulate ion fluxes. High concentrations of either y-thrombin or nitro-a-thrombin, however, stimulate both early and late 86RB+uptake but do not initiate DNA synthesis. These results demonstrate that events leading to both the early and late stimulation of 86Rb+ influx by themselves are not sufficient to initiate cell proliferation. Thus, initiation may require a combination of events that can be independently regulated by different transmembrane signals.