Coppa A, Mincione G, Lazzereschi D, Ranieri A, Turco A, Lucignano B, Scarpa S, Ragano-Caracciolo M, Colletta G
Dipartimento di Medicina Sperimentale e Patologia, Università La Sapienza, Roma, Italy.
J Cell Physiol. 1997 Aug;172(2):200-8. doi: 10.1002/(SICI)1097-4652(199708)172:2<200::AID-JCP7>3.0.CO;2-S.
Transforming growth factor beta 1 (TGF beta 1) inhibits the growth of normal rat epithelial thyroid cells (FRTL-5 strain) by counteracting thyrotropin (TSH)-stimulated DNA synthesis and by slowing the cells in the G1 phase of the cell cycle. Here, we have studied two clones of FRTL-5 thyroid cell line transformed by the wild type (wt) v-k-ras oncogene (K.M.A1, K.M.A2) and one clone (A6) transformed by a temperature-sensitive (ts) v-k-ras mutant. Anchorage-dependent as well as anchorage-independent growth of these k-ras-transformed cells was not inhibited by TGF beta 1. TGF beta 1 resistance appeared to be dependent by a functional p21 k-ras, because A6 cell growth was partially inhibited at the nonpermissive temperature (39 degrees C). To determine the basis for TGF beta 1 resistance in k-ras-transformed thyroid cells, we looked for possible defects in the expression of type I (T beta R-I/ALK5) and type II TGF beta receptors (T beta R-II). Lower levels of type II receptors were present in all of the k-ras-transformed clones, as revealed by both Northern blot and cross-linking experiments. A partial reversion of the malignant phenotype of the wt k-ras-transformed clone was obtained in two clones isolated after transfection of the malignant thyroid cells (K.M.A1) with a T beta R-II expression vector. These two clones also showed restored levels of exogenous T beta R-II mRNA and protein, and both clones showed a partially reacquired sensitivity to TGF beta 1. Similarly, the reversion of the malignant phenotype of the A6 clone grown at the nonpermissive temperature was accompanied by a restored expression of the T beta R-II receptors. These data indicate that active k-ras oncogene can induce TGF beta 1 resistance in rat thyroid cells and suggest that one of the possible mechanisms of escape from TGF beta 1 growth control in k-ras-induced thyroid carcinogenesis involves a reduced expression of T beta R-II receptors.
转化生长因子β1（TGFβ1）通过抵消促甲状腺激素（TSH）刺激的DNA合成以及减缓细胞在细胞周期的G1期进程，来抑制正常大鼠甲状腺上皮细胞（FRTL - 5株）的生长。在此，我们研究了由野生型（wt）v - k - ras癌基因转化的FRTL - 5甲状腺细胞系的两个克隆（K.M.A1、K.M.A2）以及由温度敏感型（ts）v - k - ras突变体转化的一个克隆（A6）。这些k - ras转化细胞的贴壁依赖性和非贴壁依赖性生长均不受TGFβ1抑制。TGFβ1抗性似乎依赖于功能性p21 k - ras，因为A6细胞在非允许温度（39℃）下生长受到部分抑制。为了确定k - ras转化甲状腺细胞中TGFβ1抗性的基础，我们寻找了I型（TβR - I/ALK5）和II型TGFβ受体（TβR - II）表达中可能存在的缺陷。Northern印迹和交联实验均显示，所有k - ras转化克隆中II型受体水平较低。在用TβR - II表达载体转染恶性甲状腺细胞（K.M.A1）后分离得到的两个克隆中，wt k - ras转化克隆的恶性表型得到了部分逆转。这两个克隆还显示出外源性TβR - II mRNA和蛋白质水平恢复，并且两个克隆对TGFβ1的敏感性均部分恢复。同样，在非允许温度下生长的A6克隆的恶性表型逆转伴随着TβR - II受体表达的恢复。这些数据表明，活性k - ras癌基因可诱导大鼠甲状腺细胞产生TGFβ1抗性，并提示在k - ras诱导的甲状腺癌发生过程中，逃避TGFβ1生长控制的一种可能机制涉及TβR - II受体表达降低。
