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The role of protein kinase C isoenzymes in the growth inhibition caused by bryostatin 1 in human A549 lung and MCF‐7 breast carcinoma cells
Author(s) -
Tanwell Caroline S,
Gescher Andreas,
Bradshaw Tracey D.,
Pettit George R.
Publication year - 1994
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.2910560420
Subject(s) - bryostatin 1 , protein kinase c , cytosol , mcf 7 , pkc alpha , biology , cell culture , microbiology and biotechnology , cell growth , 12 o tetradecanoylphorbol 13 acetate , isozyme , chemistry , biochemistry , kinase , cancer cell , enzyme , cancer , genetics , human breast , phorbol ester
Bryostatin I is a natural product currently under clinical evaluation as an antitumor agent. Like the tumor‐promoting phorbol ester 12‐O‐tetradecanoylphorbol‐13 ‐acetate (TPA) it activates protein kinase C (PKC). Bryostatin I inhibits the growth of the human‐derived A549 lung and MCF‐7 adenocarci‐noma cell lines, but much more weakly than TPA. The hypotheses were tested that differences between cell lines in their response to bryostatin I are related to cellular PKC isotype content, and that differences between TPA and bryostatin I in their effects on cell growth are associated with differential abilities to modulate specific PKC isoenzymes. PKC isozyme profiles were studied by Western‐blot analysis in the cytosol, particulate and nuclear fractions of A549 and MCF‐7 cells. PKCs‐α, −ϵ and −ζ were detected in both cell types with predominant location in the cytosol. Separation of cytosolic PKC isoenzymes in A549 cells by hydroxylapatite column chromatography and determination of PKC activity in fractions yielded a major peak which contained PKC‐α. Exposure of cells to bryostatin I or TPA for 30 min caused the redistribution of PKCs‐α and −ϵ from the cytosol to the particulate and nuclear fractions in a concentration‐dependent fashion. PKC −ϵ was completely down‐regulated by exposure to 10 nM bryostatin I for 18 hr or to TPA for 24 hr. Down‐regulation of PKC‐α was partial at 10 nM and complete at I μM of either agent. Bryostatin I inhibited incorporation of [ 3 H]‐labelled thymidine into cells only transiently, whereas TPA arrested growth for several days in A549 cells and irreversibly in MCF‐7 cells. A549 cells, in which PKC was depleted by exposure to phorbol ester for 9 weeks, were resistant towards bryostatin‐induced inhibition of DNA synthesis. The results suggest that the susceptibility of adenocarcinpma cells towards bryostatin‐induced growth delay are determined by cellular levels of PKCs‐α and/or −ϵ. However, differences between bryostatin I and TPA in their abilities to inhibit cell growth do not seem to be intrinsically related to differences in redistribution or down‐regulation of specific PKC isoenzymes.