Jin W, Huang E S, Bi W, Cote G J
Section of Endocrine Neoplasia and Hormonal Disorders, Department of Medical Specialties, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
J Biol Chem. 1999 Sep 24;274(39):28035-41. doi: 10.1074/jbc.274.39.28035.
The human fibroblast growth factor receptor-1 primary transcript is alternatively processed to produce receptor forms that vary in their affinity for fibroblast growth factor. The inclusion of a single exon (alpha) in normal brain glial cells produces a low affinity form of the receptor. Recognition of the alpha-exon is dysregulated during neoplastic transformation of glial cells to produce a high affinity receptor form. In this study, we have identified a second intronic repressor of RNA splicing located approximately 250 nucleotides upstream of the alpha-exon. Deletion or mutation of this sequence resulted in a significant increase in exon recognition in glioblastoma cells. This intronic repressor was found to share significant sequence homology with an intronic repressor element located downstream of the alpha-exon. The two repressor elements are functionally redundant in that they are capable of inhibiting alpha-exon recognition when positioned upstream or downstream of the exon. Finally, the elements were found to mediate enhanced exclusion of an unrelated exon, but only the repressors were placed flanking the exon. However, under these conditions, the cell-specific exon exclusion was no longer maintained. These results suggest that although the alpha-exon inclusion is actively repressed in glioblastomas, the absence of trans-activators appears to be key to the production of the high affinity form of fibroblast growth factor receptor-1 in glioblastomas.
人成纤维细胞生长因子受体-1初级转录本经过可变剪接，产生对成纤维细胞生长因子亲和力不同的受体形式。在正常脑胶质细胞中包含单个外显子（α）会产生低亲和力形式的受体。在胶质细胞向肿瘤转化过程中，α外显子的识别失调，从而产生高亲和力受体形式。在本研究中，我们鉴定出了一个位于α外显子上游约250个核苷酸处的RNA剪接的第二个内含子抑制因子。该序列的缺失或突变导致胶质母细胞瘤细胞中外显子识别显著增加。发现这个内含子抑制因子与位于α外显子下游的一个内含子抑制元件具有显著的序列同源性。这两个抑制元件在功能上是冗余的，因为当它们位于外显子的上游或下游时，都能够抑制α外显子的识别。最后，发现这些元件介导了一个不相关外显子的增强排除，但前提是只有抑制因子位于该外显子两侧。然而，在这些条件下，细胞特异性外显子排除不再维持。这些结果表明，虽然在胶质母细胞瘤中α外显子的包含被积极抑制，但反式激活因子的缺失似乎是胶质母细胞瘤中产生高亲和力形式的成纤维细胞生长因子受体-1的关键。
