Grzelkowska K, Motyl T, Ostrowski J, Trzeciak L
Department of Animal Physiology, Veterinary Faculty, Warsaw Agricultural University, Poland.
Int J Hematol. 1995 Apr;61(3):147-56. doi: 10.1016/0925-5710(95)00360-5.
Orotic acid (OA), a known promoter of carcinogenesis, significantly stimulated proliferation of K 562 leukemic cells even at as high a concentration as 0.1 mM. This effect was accompanied by a significant increase of the activity of two key enzymes of the polyamine pathway, i.e. ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC). The induction of ODC activity was associated with increased expression of the ODC gene. The participation of ODC in early events evoked by OA in leukemic cells was confirmed by the decrease of the stimulatory effect of OA on cell proliferation in the presence of alpha-difluoromethylornithine (DFMO)--an irreversible inhibitor of ODC. The involvement of protein kinase C (PK-C) and cyclic nucleotide-dependent kinases in OA action on K 562 leukemic cells was demonstrated by a significant reduction of cell proliferation by addition of H-7 (1-(5-isoquinolinesulphonyl)-2-methylpiperazine). Since PK-C is involved both in induction of ODC activity and in membrane transport of polyamines, H-7 significantly inhibited the proliferation of K 562 leukemic cells even in the presence of OA and exogenous putrescine. The importance of extracellular sources of polyamines for leukemic cell growth was shown by supplementation of the incubation medium with putrescine. Exogenous putrescine significantly enhanced the concentration of spermidine and spermine within the cell and increased the number of cells. The effect of OA on natural killer (NK) cell cytotoxicity was also examined. Rat peripheral blood mononuclear cells were used as effector cells and K 562 cells as targets. OA, progressively with dose, significantly decreased specific lysis when targets were preincubated with it. On the other hand, pretreatment of PBMC effector cells with OA, regardless of the applied concentration, did not affect the amount of 51Cr released from lysed cells. OA as a promoter of carcinogenesis stimulates proliferation of leukemic cells and impairs their responsiveness to NK activity. ODC/polyamine system and PK-C appear to be involved in OA action on K 562 cells. The presented observations are important from a practical point of view, since an elevated blood concentration of OA resulting from the impaired kidney function in hematological proliferative diseases may accelerate their progression.
乳清酸（OA）是一种已知的致癌促进剂，即使在高达0.1 mM的浓度下，也能显著刺激K 562白血病细胞的增殖。这种作用伴随着多胺途径的两种关键酶，即鸟氨酸脱羧酶（ODC）和S-腺苷甲硫氨酸脱羧酶（SAMDC）活性的显著增加。ODC活性的诱导与ODC基因表达的增加有关。在存在α-二氟甲基鸟氨酸（DFMO）——一种ODC的不可逆抑制剂的情况下，OA对细胞增殖的刺激作用减弱，这证实了ODC参与了OA在白血病细胞中引发的早期事件。添加H-7（1-（5-异喹啉磺酰基）-2-甲基哌嗪）可显著降低细胞增殖，这证明了蛋白激酶C（PK-C）和环核苷酸依赖性激酶参与了OA对K 562白血病细胞的作用。由于PK-C既参与ODC活性的诱导，又参与多胺的膜转运，因此即使在存在OA和外源性腐胺的情况下，H-7也能显著抑制K 562白血病细胞的增殖。向孵育培养基中添加腐胺表明了多胺的细胞外来源对白血病细胞生长的重要性。外源性腐胺显著提高了细胞内亚精胺和精胺的浓度，并增加了细胞数量。还研究了OA对自然杀伤（NK）细胞细胞毒性的影响。以大鼠外周血单个核细胞作为效应细胞，K 562细胞作为靶细胞。当靶细胞预先与OA孵育时，OA随着剂量的增加显著降低特异性裂解。另一方面，无论应用何种浓度，用OA预处理PBMC效应细胞均不影响裂解细胞释放的51Cr量。OA作为一种致癌促进剂，刺激白血病细胞的增殖并损害它们对NK活性的反应性。ODC/多胺系统和PK-C似乎参与了OA对K 562细胞的作用。从实际角度来看，所呈现的观察结果很重要，因为血液系统增殖性疾病中肾功能受损导致血液中OA浓度升高可能会加速疾病进展。
