Cell shape and increased free cytosolic calcium [Ca2+]i induced by growth factors.
Growth factors stimulate DNA synthesis of neoplastic cells but not of non-neoplastic cells in suspension cultures. Similarly, growth ceases in dense monolayers of non-neoplastic cells, while crowded neoplastic cells continue to grow. The mechanism of these important phenotypic changes is unknown; the block in growth stimulation could occur in early events of signal transduction at the plasma membrane or in a late step in the final steps of gene activation and induction of DNA synthesis. One particular early intracellular event, [Ca2+]i increases, is in fact necessary for the induction of DNA synthesis in attached non-neoplastic Balb/c 3T3 cells stimulated by platelet-derived growth factor (PDGF). We therefore used digital image analysis of intracellular Fura-2 fluorescence to determine whether PDGF can stimulate [Ca2+]i transients in suspension or in dense monolayer cultures of Balb/c 3T3 cells. In dense cells (greater than 8 x 10(4) cells/cm2) the basal [Ca2+]i and [Ca2+]i response to PDGF stimulation were both lower than those in sparser, more spread cells. PDGF also did not release internal stores of Ca2+ or produce Ca2+ influx in completely suspended cells. Remarkably, attachment alone, with minimal cell spreading, was enough to reinitiate the entire early signalling mechanism stimulated by PDGF. Thus, a block in PDGF-induced [Ca2+]i increases may contribute to the inability of PDGF to stimulate DNA synthesis in suspended non-neoplastic cells. This early block in signal transduction must be abrogated in neoplastic cells growing in suspension and dense monolayer cultures.
Tucker
R W
RW
Johns Hopkins Oncology Center, Baltimore, Maryland.
Meade-Cobun
K
K
Ferris
D
D
D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D002452:Cell Count; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism*; D004247:DNA / Q000096:biosynthesis; D005347:Fibroblasts; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D007091:Image Processing, Computer-Assisted; D015759:Ionomycin; D051379:Mice; D008856:Microscopy, Fluorescence; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*
D001572:Benzofurans; D005456:Fluorescent Dyes; D010982:Platelet-Derived Growth Factor; D015759:Ionomycin; D004247:DNA; D002118:Calcium; D016257:Fura-2