Blat C, Villaudy J, Delbé J, Troalen F, Golde A, Harel L
Institut de Recherches Scientifiques sur le Cancer, Paris, France.
Growth Factors. 1992;6(1):65-75. doi: 10.3109/08977199209008872.
From medium conditioned by 3T3 cells, we had previously purified an inhibitory factor of Mr 45 kDa which we termed IDF45 (inhibitory diffusible factor). The protein was able to 100% inhibit stimulation induced in CEF by 1% calf serum and to reversibly prevent cell growth. We then demonstrated that IDF45 was an IGF-binding protein. Our results suggested that IDF45 was a bifunctional molecule able to bind IGF and to inhibit DNA synthesis stimulated by this hormone, but also to inhibit stimulation of DNA synthesis induced by another growth factor in serum. Indeed, its N terminal amino acid sequence has great homology with that of IGFBP-3 and IDF45 is now proposed to be named IGFBP-3 (mouse IGF binding protein). Present results show that Ha-ras transfected 3T3 cells (EJ cells), like 3T3 cells, secrete a mIGFBP-3 molecule. In addition, transfected cells secrete a doublet of an IGF-binding protein (IGFBP-28) of Mr 28 kDa which is not secreted by untransformed 3T3 cells. IGFBP-28 has been purified and characterized in this work. Various results suggest that IGFBP-28 is not a degradation product of mIGFBP-3. Its N terminal amino acid sequence was different from that of mIGFBP-3. IGFBP-28 inhibited DNA synthesis stimulated by IGF-I, but much more IGFBP-28 protein than mIGFBP-3 was required to prevent this stimulation. In agreement with this result, IGFBP-28 has low affinity for IGF-I. In contrast, IGFBP-28 has high affinity for IGF-II. Like mIGFBP-3, IGFBP-28 was able to inhibit the stimulation induced by serum in CEF and to reversibly prevent growth, though with a specific activity lower than that of mIGFBP-3. It has also the capacity to inhibit stimulation of DNA synthesis induced by high molecular weight serum proteins depleted in IGF-I and II. In conclusion we have shown that transformation of 3T3 cells with Ha-ras induced the synthesis of a new IGF binding protein in medium conditioned by normal 3T3 cells. Our results suggest that IGFBP-28 like mIGFBP-3 is a bifunctional protein able to inhibit stimulation induced by IGF and by serum proteins different from IGFs.
我们先前已从3T3细胞条件培养基中纯化出一种分子量为45 kDa的抑制因子，我们将其命名为IDF45（抑制性扩散因子）。该蛋白能够100%抑制1%小牛血清诱导的CEF刺激，并可逆地阻止细胞生长。然后我们证明IDF45是一种IGF结合蛋白。我们的结果表明，IDF45是一种双功能分子，能够结合IGF并抑制该激素刺激的DNA合成，还能抑制血清中另一种生长因子诱导的DNA合成刺激。实际上，其N端氨基酸序列与IGFBP - 3的序列具有高度同源性，现在提议将IDF45命名为IGFBP - 3（小鼠IGF结合蛋白）。目前的结果表明，Ha - ras转染的3T3细胞（EJ细胞）与3T3细胞一样，分泌一种mIGFBP - 3分子。此外，转染细胞分泌一种分子量为28 kDa的IGF结合蛋白（IGFBP - 28）双峰，未转化的3T3细胞不分泌该蛋白。在这项工作中，IGFBP - 28已被纯化和鉴定。各种结果表明，IGFBP - 28不是mIGFBP - 3的降解产物。其N端氨基酸序列与mIGFBP - 3不同。IGFBP - 28抑制IGF - I刺激的DNA合成，但需要比mIGFBP - 3更多的IGFBP - 28蛋白才能阻止这种刺激。与此结果一致，IGFBP - 28对IGF - I的亲和力较低。相反，IGFBP - 28对IGF - II具有高亲和力。与mIGFBP - 3一样，IGFBP - 28能够抑制CEF中血清诱导的刺激并可逆地阻止生长，尽管其比活性低于mIGFBP - 3。它还具有抑制IGF - I和II耗尽的高分子量血清蛋白诱导的DNA合成刺激的能力。总之，我们已经表明，用Ha - ras转化3T3细胞会在正常3T3细胞条件培养基中诱导合成一种新的IGF结合蛋白。我们的结果表明，IGFBP - 28与mIGFBP - 3一样，是一种双功能蛋白，能够抑制IGF和不同于IGF的血清蛋白诱导的刺激。
