Reduction of heat-shock protein-70 after prolonged treatment with retinoids: biological and clinical implications.
Heat shock proteins (HSPs) are a group of highly conserved polypeptides involved in cellular response to heat or other physical or chemical stresses. It has been recently reported that HSPs could play a role in cellular differentiation. In this study we have evaluated, by a cytofluorimetric method, the presence of HSP-70 in HL-60 cells during treatment with all-trans retinoic acid (ATRA), 9-cis retinoic acid (9-cis RA), and 13-cis retinoic acid (13-cis RA). After 1 and 3 days of incubation at 10(-7) M, HSP-70 did not show any variation compared to control; prolonging the exposure, together with the appearance of cellular differentiation along the granulocytic pathway and apoptosis, a progressive decrease of HSP-70 was observed that, after 8 days of treatment, was reduced by 40% with ATRA and by 28% with 9-cis RA compared to untreated samples, while only minimal changes were evident by incubating the cells with 13-cis RA. Reduction of HSP-70 was not associated with decreased protein synthesis, as demonstrated by [3H] leucine incorporation. Double labeling with propidium iodide showed a decrease in HSP-70 in all the phases of the cell cycle concomitant with a reduced percentage of cycling cells in ATRA-treated samples. Dot blot and Northern blot analysis demonstrated no change in HSP-70 mRNA after retinoid treatment, thus suggesting a post-transcriptional regulation of the phenomenon. This reduced production of HSP-70 caused by ATRA and by 9-cis RA, though to a lesser extent, could render the cells more sensitive to cytotoxic agents and could provide the rationale for the efficacy of ATRA + chemotherapy combinations.
Tosi
P
P
Institute of Hematology and Medical Oncology Seràgnoli, University of Bologna, Italy.
Visani
G
G
Ottaviani
E
E
Gibellini
D
D
Pellacani
A
A
Tura
S
S
D000077556:Alitretinoin; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D005434:Flow Cytometry; D006131:Growth Inhibitors; D018922:HL-60 Cells / Q000187:drug effects*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015474:Isotretinoin / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D012334:RNA, Neoplasm / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology*
D000970:Antineoplastic Agents; D006131:Growth Inhibitors; D018840:HSP70 Heat-Shock Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D000077556:Alitretinoin; D014212:Tretinoin; D015474:Isotretinoin