In vitro folate deficiency induces apoptosis by a p53, Fas (Apo-1, CD95) independent, bcl-2 related mechanism in phytohaemagglutinin-stimulated human peripheral blood lymphocytes.
In vitro folate deficiency is associated with S phase accumulation and apoptosis in various cell types. To investigate the role of p53 and two apoptosis-related molecules, bcl-2 and Fas antigen (Apo-1, CD95), in the mechanism whereby folate-deficient lymphocytes accumulate and undergo apoptosis in the S phase, normal human peripheral blood lymphocytes were cultured for 3-9 d in control medium or in specially ordered and formulated HAM's F-10 medium lacking folic acid, thymidine and hypoxanthine. Cells were stimulated with phytohaemagglutinin for the final 72 h prior to harvesting. The results indicate that p53 expression was downregulated in folate-deficient lymphocytes when compared with the control lymphocytes during the relevant period of S phase accumulation and apoptosis. In addition, folate deficiency was also found to downregulate IL-2, Fas antigen and bcl-2 expression, in terms of either mRNA or protein levels. The downregulation of Fas antigen suggests that folate deficiency-induced apoptosis probably does not occur via the Fas pathway. As IL-2 is a known inducer of bcl-2, and the downregulation of bcl-2 induces apoptosis, the downregulation of IL-2 and bcl-2 is suggested to play an important role in apoptosis. The complete rescue of folate-deficient lymphocytes from apoptosis was achieved by folic acid, thymidine or hypoxanthine alone or thymidine and hypoxanthine in combination. These results suggest that IL-2 depletion by folate deficiency in lymphocytes reduces the bcl-2 level, thereby triggering deoxynucleoside triphosphate pool imbalance and p53-independent apoptosis.
Lin
Hui-Li
HL
Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC.
Chen
Chung-Jern
CJ
Tsai
Wen-Chan
WC
Yen
Jeng-Hsien
JH
Liu
Hong-Wen
HW
D017209:Apoptosis / Q000187:drug effects; D002478:Cells, Cultured; D015536:Down-Regulation; D005492:Folic Acid / Q000378:metabolism / Q000494:pharmacology; D005494:Folic Acid Deficiency / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D019271:Hypoxanthine / Q000494:pharmacology; D007376:Interleukin-2 / Q000096:biosynthesis / Q000235:genetics; D008213:Lymphocyte Activation; D010835:Phytohemagglutinins / Q000276:immunology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D016196:S Phase; D013936:Thymidine / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism / Q000502:physiology; D019014:fas Receptor / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology
D007376:Interleukin-2; D010835:Phytohemagglutinins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D019014:fas Receptor; D019271:Hypoxanthine; D005492:Folic Acid; D013936:Thymidine