Wade D R, Burkart M E
J Cell Physiol. 1978 Mar;94(3):265-73. doi: 10.1002/jcp.1040940304.
Incubation of cultured B-16 melanoma cells with 1-methyl-3-isobutyl xanthine (MIX) produced a sustained rise in intracellular adenosine 3',5'-cyclic monophosphate (cAMP) which preceded an increase in the specific activity of tyrosinase (EC 1.10.3.1). Cultures of two clones of melanoma cells, one having a mean population doubling time twice that of the other, showed density-dependent inhibition of growth. The tyrosinase activity of each line increased progressively during logarithmic growth, reaching maximal values shortly after the cultures achieved confluence. Intracellular cAMP levels fell during logarithmic growth, being minimal in confluent cultures. The stimulatory effects of MIX and confluence on tyrosinase activity were additive. Cells plated at high density had a lower tyrosinase activity than cells allowed to achieve a similar density by successive division from sparsely planted cultures although the intracellular cAMP levels of such cultures were not different. We support the observations of other investigators that agents which increase intracellular cAMP concentrations can both inhibit cell division and stimulate tyrosinase activity. There are, however, mechanisms for increasing tyrosinase activity and inhibiting cell division which are expressed as B-16 melanoma cells approach confluence and which are not mediated by an increase in intracellular cAMP concentrations.
用1-甲基-3-异丁基黄嘌呤（MIX）培养B-16黑色素瘤细胞，会使细胞内3',5'-环磷酸腺苷（cAMP）持续升高，这一升高先于酪氨酸酶（EC 1.10.3.1）比活性的增加。两种黑色素瘤细胞克隆培养物，其中一种的平均群体倍增时间是另一种的两倍，显示出密度依赖性生长抑制。在对数生长期，每条细胞系的酪氨酸酶活性逐渐增加，在培养物达到汇合后不久达到最大值。在对数生长期，细胞内cAMP水平下降，在汇合培养物中降至最低。MIX和汇合对酪氨酸酶活性的刺激作用是相加的。高密度接种的细胞比通过从稀疏接种的培养物中连续传代达到相似密度的细胞具有更低的酪氨酸酶活性，尽管这些培养物的细胞内cAMP水平没有差异。我们支持其他研究者的观察结果，即增加细胞内cAMP浓度的试剂既能抑制细胞分裂又能刺激酪氨酸酶活性。然而，随着B-16黑色素瘤细胞接近汇合，存在增加酪氨酸酶活性和抑制细胞分裂的机制，且这些机制不是由细胞内cAMP浓度的增加介导的。
