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      Insulin-Like Growth Factor-1 Receptor Regulation in Activated Human T Lymphocytes

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          Objective: To investigate the kinetics of insulin-like growth factor-1 receptor (IGF-1R) expression in PHA-stimulated T lymphocytes. Methods: IGF-1R protein and mRNA were detected by flow cytometry and RT-PCR respectively, between 0 and 48 h after cell activation. Results: Few minutes after T lymphocytes were activated, internalization of the IGF-1R from the cell membrane was observed, achieving the lower level between 1 and 6 h and was accompanied by a reduction in its mRNA. This was followed by re-expression of IGF-1R on the cell surface and an increase in IGF-1R mRNA levels in the cytoplasm, reaching levels higher than those recorded initially after 48 h activation. Conclusion: This down- and up-regulation suggests that restoration of IGF-1R would be the result of receptor recycling and de novo synthesis and highlights its importance for T lymphocyte proliferation.

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          Insulin-like growth factor expression in human cancer cell lines.

          The insulin-like growth factors (IGFs), IGF-I and IGF-II, are potent mitogens for human lung and other epithelial cancer cell lines. Previous studies in defined medium lacking added IGF or insulin suggest that an IGF-related ligand can act as an autocrine growth factor for many cancer cell lines through action via the type I IGF receptor (IGF-R). Analysis of RNA isolated from human lung and breast cancer cell lines by reverse transcription of mRNA and polymerase chain reaction reveal that IGF-I and IGF-II mRNAs were co-expressed with IGF-R in the majority of cell lines. IGF-I mRNA was detected in 11/12 small cell lung cancer cell lines (SCLC), 13/14 nonsmall cell lung cancer (NSCLC) cell lines, and 1/2 breast cancer cell lines. IGF-II mRNA was detected in 8/10 SCLC, 11/12 NSCLC cell lines, and 2/2 breast lines. All cell lines expressed IGF-R. For analysis of IGF peptide secretion, cell lines were adapted to growth in serum/hormone-free culture medium (R0), and to avoid interference by IGF-binding proteins, secreted IGF peptides were isolated under acidic conditions and analyzed by Western blotting. Based upon measurement of the sensitivity of the anti-IGF antibodies for detection of recombinant human IGFs, IGF peptides accumulated in conditioned medium at greater than picomolar concentrations should have been readily detected. In three cell lines (two lung and one breast) secreted IGF immunoreactivity was detected as three molecular mass species of 23, 14, and 6 kDa. Isolation and NH2-terminal sequencing of each of these species definitively identified them as differentially processed forms of the IGF-II prohormone. Despite the high frequency of IGF-I gene expression detected by reverse transcription-polymerase chain reaction analysis, only one lung cancer cell line, NCI-N417d, was found that unequivocally secreted IGF-I peptide. This direct sequence determination unambiguously identifies IGF-II as the predominant IGF involved in the autocrine growth stimulation of human lung and breast epithelial tumor cell lines and supports a growing body of literature that implicates IGF-II/IGF-R autocrine loops as a common growth mechanism in epithelial carcinogenesis.

            Author and article information

            Horm Res Paediatr
            Hormone Research in Paediatrics
            S. Karger AG
            05 June 2003
            : 59
            : 6
            : 276-280
            aInstituto de Biología y Medicina Experimental CONICET, and bLaboratorio de Patología Sanatorio Mater Dei, Buenos Aires, Argentina
            70625 Horm Res 2003;59:276–280
            © 2003 S. Karger AG, Basel

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            Figures: 2, References: 11, Pages: 5
            Original Paper


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