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마우스 폐암세포주에서 Insulin-like Growth Factor-I(IGF-I), IGF-I Receptor(IGF-IR) 및 IGF Binding Proteins(IGFBPs)의 역할

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 (The) role of Insulin-like Growth Factor I(IGF-I), IGF-I Receptor(IGF-IR), IG 
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[한글] 본 저자는 마우스 폐암세포주(3LL)에서 IGF-I, IGP-IR 및 IGFBPs이 세포증식(collular proliferation)과 세포사망(cell death)에 어떠한 역할을 하는지 알기 위해 본 실험을 수행하여 다음과 같은 결과를 얻었다. 3LL 마우스 폐암세포주에서 IGF-I과 IGF-IR mRNA가 발현되었고, IGF-I을 serum free media에 첨가시 세포증식이 증가되었다. IGF-lR의 활성화를 보기 위해 IGF-I을 첨가시 분자량 95 kDa의 IGF-IR β-subunit의 tyrosine kinase와 분자량 185 kDa의 insulin receptor substrate-I(IRS-I)의 인산화가 증가되었다. IGF-I이 adriamycin (ADR)에 의한 세포사망에 미치는 영향을 관찰하였을 때, 고농도 ADR(1 ㎍/㎖)에서는 세포사망 정도의 차이가 없었으나 저농도 ADR(0.1, 0.01 ㎍/㎖)에서는 세포사망이 억제되었다. 3LL 마우스 폐암세포주에서 IGFBP-4가 분비되었고, anti-IGFBP-4 antibody를 첨가 시 세포증식이 증가되었다. 따라서 분비된 IGFBP-4는 세포증식을 억제하는 기능을 가지고 있음을 간접적으로 알 수 있었다. 이상의 실험 결과로 마우스 폐암세포주(3LL)에서 IGF-I은 IGF-IR의 tyrosine kinase를 활성화시켜 세포증식을 증가시키는 유사분열물질(mitogen)로 작용하고, adriamycin에 의한 세포사망을 억제하는 생존인자(survival factor)로 작용함을 알 수 있었다. 또한 3LL 마우스 폐암세포주에서 분비된 IGFBP-4는 세포증식을 억제하는 기능을 가지고있다고 생각된다.
[영문] The importance of growth factors in the molecular mechanisms of cell transformation and tumor proliferation has been recently demonstrated. IGFs are polypeptides which are closely related in structure to insulin and stimulate cell growth in culture, perhaps by controlling the progression through Gl phase of the cell cycle. It has become apparent over the past few years that IGF-I is an important mitogen in many types of malignancies. Following binding of IGF-I to its receptor, signal transduction may occur through autophosphorylation of intracellular receptor domains and tyrosine phosphorylation of other substrates by the activated receptor kinase. Tumors also express many of the IGF binding proteins, which modulate IGF action. The purpose of this study was to evaluate the role of IGF system in mouse lung cancer cell (3LL). Northen analysis of the mRNA samples using the IGF-I and IGF-lR cDNA revealed IGF-I and IGF-IR mRNA message. The treatment of 3LL cell with IGF-I increased cellular proliferation in the serum free containing media. In this study, we used antiphosphotyrosine antibodies to identify phosphotyrosine-containing protein which occur during IGF-I stimulation of 3LL cell. IGF-I stimulated tyrosine phosphorylation of two proteins. One of them, with a molecular mass of 95 kDa, was the β-subunit of the IGF-IR. The other protein had an approximate molecular mass of 185 kDa, which originally identified as the insulin receptor substrate-I (IRS-I) that transmits important intracytoplasmic signals during ligand binding. The involvement of IGF-I in cell survival in the presence of anticancer drug was investigated. IGF-I inhibited cell death induced by adriamycin at the low concentration. To determine whether 3LL cells secrete IGFBPs, Western ligand blot of 3LL cell conditioned medium with 125**I-IGF-I demonstrated one single major band with estimated MΥ 24 kDa. This band was identified as IGFBP-4 with immunoblot analysis using antisera. The addition of anti-IGFBP-4 antibody to abrogate the effect of IGFBP-4 resulted in increased cellular proliferation suggesting that IGFBP-4 has cell growth inhibition. In conclusion, IGF-I is a mitogen through the phosphorylation of IGF-IR β-subunit and acts as a survival factor to inhibit cell death. IGFBP-4 has inhibitory function on cell growth. Therefore, these findings suggest that IGF-I, IGF-IR and IGFBP are involved in the cell proliferation and death related to cancer cell growth.
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