维甲酸对人肝癌细胞磷脂酰胆碱专一性磷脂酶D的作用

EFFECT OF RETINOIC ACIDS ON PHOSPHATIDYLCHOLINE SPECIFIC PHOSPHOLIPASE D IN 7721 HUMAN HEPATOCARCINOMA CELL LINE

为了解细胞信号转导与细胞分化间的关系,研究了诱导分化剂全反式视黄酸(ATRA)和13顺视黄酸(13 cis-RA)对7721人肝癌细胞中磷脂酰胆碱专一性磷脂酶D(PC-PLD)的影响。发现ATRA和13 cis-RA除能抑制7721细胞生长,并在形态上向正常方向分化外,分别在第2或第4天使膜结合性PC-PLD的比活力升高,用每瓶细胞的总活力计算,ATRA的作用在第2天也高于13 cis-RA,但13 cis-RA在第4天的效应却高于ATRA,说明13 cis-RA较ATRA的效应滞后。每天更换培养液的条件较不更换时细胞生长速度较快,且更能引起PC-PLD比活力的上升,提示新鲜培养液中可能存在促进生长和增强维甲酸升高PC-PLD的化合物。ATRA在第2天对PC-PLD比活力的作用高于第4天,可能由于第4天细胞增殖加快,细胞中蛋白质含量上升,以至使以蛋白含量计算的酶比活力下降。进一步研究维甲酸使膜结合性PC-PLD升高与蛋白激酶的关系,发现ATRA不论在第2天和第4天均使膜结合性和胞液中蛋白激酶C(PKC)和酪氨酸蛋白激酶(TPK)的比活力下降,说明ATRA使膜结合性PC-PLD活力的升高不是通过PKC 或TPK对PC-PLD的激活作用来实现,其机理有待进一步研究。对维甲酸引起PC-PLD升高的生物学意义作了讨论。

In order to elucidate the relation between cell signal transduction and cell differentiation, the effect of two differentiation inducers-all trans-retinoic acid (ATRA) and 13 cis-retinoic acid (13 cis-RA) on the specific activities (nmol/hr·mg protein) of phosphatidyl choline specific phospholipase D (PC-PLD) in 7721 human hepatocarcinoma cell line was studied. It was found that ATRA and 13 cis-RA increased the specific activities of membrane bound PC-PLD on 2nd and 4th day of cell culture respectively. If the PC-PLD activities were calculated as activity per bottle cells, the effect of ATRA on the 2 nd day was also higher than that of 13 cis-RA. while the reverse was true on the 4 th day. revealing a postponed effect of 13 cis-RA as compared with ATRA. The increase of PC-PLD was higher when the culture medium was refreshed every day than that when the medium was unrefreshed. suggesting that a factor might be existed in the fresh medium which could enhance the stimulating effect of retinoic acids on PC-PLD. The effect of ATRA on PC-PLD specific activity were higher on 2 nd day than that on 4 th day. owing to the accelerated proliferation of the cells on 4 th day. leading to the increase of protein contents and decrease of the enzyme specific activity calculated on the base of protein contents. Whereas, the effect of 13 cis-RA on PC-PLD specific (?) were higher on 4th day than that on 2 nd day. because the increase of enzyme activity was higher than the increase of protein contents on 4 th day. The relation between the elevation of PC-PLD and protein kinases was further studied and discovered that ATRA decreased both the specific activities of membrane bound and cytosolic protein kinase C (PKC) as well as tyrosine protein kinase (TPK) either in 2 nd or 4 th day of cell culture, which indicated that the increasing effect of ATRA on membrane bound PC-PLD was not resulted from the stimulating effect of PKC and TPK on PC-PLD. and its mechanism remains to be further investigated.