Expression of Exon 1 and 6 of Indulin-like Growth Factor / 대한내분비학회지

ABSTRACT

Background: Goiter has been a common problem in the thyroid disease. The exact mechanism of goiter had not been clarified yet, but some goiters were increased with TSH(thyrotropin releasing hormone) dependent manner. TSH might be a major influencing factor for increasing size of goiter(goitrogen) and theres many cofactors those influenced to goiter size. One of the rnost prominent growth factor as a goitrogen is a IGF-I(insulin-like growth factor-I). IGF-I play a great role as a cofactor of goitrogen with TSH. This study, therefore, is aimed to investigate intracellular activation of IGF-I gene promoter in the surgical specimens of thyroid tumor. Methods: We used surgical specimen of various thyroid tissues from normal to malignant along its cell nature. Actually we used normal liver tissue as a IGF-I control tissue, normal thyroid, benign adenoma, and papillary thyroid cancer tissue with its malignat nature. We checked Mrna expression of whole IGF-I and IGF-I exon 6 by Northern blot method, and IGF-I, promoter 1 expression by RT-PCR-transcription method. Autoradiographied signals were analysed with densitometer. Results: We found whole IGF-I mRNAs were expressed with alternate splicing in exon 1, 2 and exon 4, 5 respectively. Striking events of IGF-I transcription were multiple tranascription initiatian in Pl and P2, and 3 sites for polyadenylation in exon 6. Four or more Mrna bands in Northern blot analysis of IGF-I(0.8, 1.4, 4.2, and 7.8kb) were noted. In low molecular weight IGF-I Mrna did not change their signal intensity with tissues, but exan 6(7.8kb) signals were significantly increased to its hepatic expression levels in malignant tissue. IGF-I, exon 1 expression by RT-PCR-T7 transcription was strikingly increased in thyroid cancer tissue, but exon 6 expression was not a great expession. Conclusion: One possible guess for this expression discrepancy of each exon may be originated from different Mrna degradation of each IGF-I signals. We need more preeise experiment for Mrna degradation speed of IGF-I.