Abstract
With increasing size, multicellular prostate tumor spheroids develop regions of quiescent, multidrug-resistant cells expressing the cyclin-dependent kinase inhibitor p27(kip1). Treatment of small (diameter 60 +/- 20 micrometer) spheroids with 200 microM hydrogen peroxide (H(2)O(2)) resulted in cell cycle arrest owing to up-regulation of p27(kip1) and down-regulation of the transcription factor c-Fos. Incubation with 100 nM-1 microM H(2)O(2) led to up-regulation of c-Fos and enhanced tumor growth. Growth stimulation was inhibited by bisindolylmaleimide I, indicating a role for protein kinase C in the signaling cascade that involved the mitogen-activated protein kinase members MEK1,2, ERK1, -2, and c-Jun N-terminal kinase. Changes in Ca(2+) influx underlined the differential effects of H(2)O(2). Incubation with 200 microM H(2)O(2) released [Ca(2+)](i) from intracellular stores followed by prolonged Ca(2+) influx. Inhibition of influx by Ca(2+)-free media or Ni(2+), La(3+), Mn(2+) and SKF-96365 prevented the induction of quiescence and stimulated spheroid growth. Consequently, treatment with 200 microM H(2)O(2) in Ca(2+)-free media down-regulated p27(kip1) and increased Fos protein. ATP exerted effects comparably to those observed with H(2)O(2). Encoding growth stimulation by [Ca(2+)](i) release and induction of cell quiescence by prolonged Ca(2+) influx may provide a general mechanism for the control of tumor growth.
Highlights
The role of [Ca2ϩ]i fluctuations in the control of a variety of cell functions including contraction, differentiation, motility, secretion, and proliferation is well established [1]
We have recently shown that 100 nM H2O2 caused release of [Ca2ϩ]i from intracellular thapsigargin-sensitive stores of Du145 prostate cancer cells grown to the three-dimensional tissue of multicellular tumor spheroids [19]
In the present study treatment of multicellular spheroids with 200 M H2O2 resulted in tumor growth depression and up-regulation of the cyclin-dependent kinase inhibitor p27kip1. p27kip1 acts as a negative regulator of G1 progression [20] and has been suggested to be associated with intrinsic multidrug resistance in three-dimensional tumor tissues [21]
Summary
The role of [Ca2ϩ]i fluctuations in the control of a variety of cell functions including contraction, differentiation, motility, secretion, and proliferation is well established [1]. We have recently shown that 100 nM H2O2 caused release of [Ca2ϩ]i from intracellular thapsigargin-sensitive stores of Du145 prostate cancer cells grown to the three-dimensional tissue of multicellular tumor spheroids [19]. P27kip acts as a negative regulator of G1 progression [20] and has been suggested to be associated with intrinsic multidrug resistance in three-dimensional tumor tissues [21]. In the present study treatment of multicellular spheroids with 200 M H2O2 resulted in tumor growth depression and up-regulation of the cyclin-dependent kinase inhibitor p27kip. Under these experimental conditions Ca2ϩ release from intracellular stores was followed by a prolonged period of Ca2ϩ influx. On the other hand prolonged Ca2ϩ influx is mediating cell cycle arrest, which results in the depression of tumor growth
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
