Said T K, Medina D
Baylor College of Medicine, Department of Cell Biology, Houston, TX 77030, USA.
Carcinogenesis. 1995 Apr;16(4):923-30. doi: 10.1093/carcin/16.4.923.
Tyrosine phosphorylation status was investigated during mouse mammary tumor development using non-tumorigenic and tumorigenic hyperplastic outgrowth lines. These outgrowth lines were compared with normal mammary glands from pregnant mice and with their corresponding tumors. The levels of total tyrosine phosphorylation in proteins of hyperplastic and neoplastic tissues were 4.7- and 3.4-fold higher than in the normal gland respectively. These results indicate that increases in tyrosine phosphorylation occur in the earliest stages of neoplastic development and are not restricted to neoplastic cells per se. These results led to the identification of the specific proteins showing high levels of tyrosine phosphorylation. Of the eight molecular weight bands of proteins exhibiting detectable levels of tyrosine phosphorylation, the only proteins exhibiting consistently different degrees of phosphorylation between hyperplasias and tumors were of approximately 34 kDa. In a series of six different hyperplasias with tumorigenic potentials ranging from 0 to 93%, the extent of tyrosine phosphorylation of 34 kDa proteins correlated inversely with tumorigenic potential. The levels of p34cdc2 and p33cdk2 proteins were examined, using antibodies specific for the cdc2 and cdk2 proteins. The amounts of p34cdc2 and p33cdk2 proteins were low in non-tumorigenic (TM3 and TM2L) compared to tumorigenic hyperplasias and correlated inversely with tyrosine phosphorylation of 34 kDa proteins during tumor development. Thus in the non-tumorigenic hyperplasias (TM2L and TM3) the majority of p34cdc2 was phosphorylated on tyrosine, in contrast to the p34cdc2 in tumorigenic (TM2H) hyperplasias and tumors. Two-dimensional PAGE analysis of mammary tumor samples with antibodies specific to cdc2, cdk2 and phosphorylated tyrosine revealed one p34cdc2 form, two p33cdk2 isoforms and two phosphotyrosine isoforms of about 33-34 kDa. The results suggest that the high levels of tyrosine phosphorylation in cdc2 and cdk2 reflect the low tumorigenic potential of a subset of mammary preneoplastic hyperplasias. This interpretation is in accord with current concepts on the role of tyrosine phosphorylation in the regulation of the cyclin-dependent kinases.
利用非致瘤性和致瘤性增生性生长系，研究了小鼠乳腺肿瘤发生过程中的酪氨酸磷酸化状态。将这些生长系与妊娠小鼠的正常乳腺及其相应肿瘤进行比较。增生性和肿瘤性组织中蛋白质的总酪氨酸磷酸化水平分别比正常腺体高4.7倍和3.4倍。这些结果表明，酪氨酸磷酸化增加发生在肿瘤发生的最早阶段，且不仅限于肿瘤细胞本身。这些结果导致鉴定出显示高水平酪氨酸磷酸化的特定蛋白质。在显示可检测水平酪氨酸磷酸化的八个蛋白质分子量条带中，增生组织和肿瘤之间唯一显示出一致不同程度磷酸化的蛋白质约为34 kDa。在一系列六个具有0%至93%致瘤潜能的不同增生组织中，34 kDa蛋白质的酪氨酸磷酸化程度与致瘤潜能呈负相关。使用针对cdc2和cdk2蛋白质的特异性抗体检测p34cdc2和p33cdk2蛋白质的水平。与致瘤性增生组织相比，非致瘤性（TM3和TM2L）组织中p34cdc2和p33cdk2蛋白质的含量较低，并且在肿瘤发生过程中与34 kDa蛋白质的酪氨酸磷酸化呈负相关。因此，在非致瘤性增生组织（TM2L和TM3）中，大多数p34cdc2在酪氨酸上磷酸化，这与致瘤性（TM2H）增生组织和肿瘤中的p34cdc2相反。用针对cdc2、cdk2和磷酸化酪氨酸的特异性抗体对乳腺肿瘤样本进行二维聚丙烯酰胺凝胶电泳分析，发现一种p34cdc2形式、两种p33cdk2异构体和两种约33 - 34 kDa的磷酸酪氨酸异构体。结果表明，cdc2和cdk2中高水平的酪氨酸磷酸化反映了一部分乳腺肿瘤前增生组织的低致瘤潜能。这种解释与目前关于酪氨酸磷酸化在细胞周期蛋白依赖性激酶调节中的作用的概念一致。
