Abstract
Fibroblast growth factor (FGF)-2 is stored in the extracellular matrix (ECM). We hypothesized that FGF-2 is mobilized from the ECM and binds to receptors on the surface of FGF-2 responsive cells during thyroid enlargement. To test this hypothesis, we estimated levels of FGF-2 free from ECM in thyroids by comparing the efficiency of two methods for FGF-2 extraction (low salt and high salt). Because the high salt concentration (more than 1.5 M NaCl) is necessary to release FGF-2 from the normal ECM, FGF-2 extracted by low salt is indicative of ECM-free FGF-2. Human papillary thyroid carcinomas, normal part thyroid, and Graves' thyroid tissues were homogenized separately in an extraction buffer containing either 0 M NaCl (low salt) or 2.0 M NaCl (high salt), and the concentration of FGF-2 in the extracts was measured by enzyme-linked immunosorbent assay (ELISA). The yields of low and high salt extracts of immunoreactive (ir)FGF-2 from papillary carcinomas (low salt: 40.0 ± 7.5, high salt: 233 ± 53 ng/g tissue, mean ± SE) were significantly higher than those of normal thyroid tissues extracted by the corresponding salt concentration (low salt: 14.6 ± 1.8, high salt: 123 ± 12 ng/g tissue). On the other hand, the extractable irFGF-2 from Graves' thyroid tissues (low salt: 25.2 ± 2.5, high salt: 135 ± 24 ng/g tissue) were not significantly different from that of normal thyroid tissues. However, the ratio of the extractable irFGF from carcinomas and Graves' thyroids by low salt to that by high salt (0 M/2 M ratio = 0.206 ± 0.051, 0.209 ± 0.025) were significantly higher than that of normal thyroids (0.120 ± 0.014) (p < 0.05). These results suggest that intratissue ECM-free FGF-2 is increased in papillary thyroid carcinomas and Graves' thyroid tissues, and therefore a greater amount of FGF-2 may be available for stimulation of FGF-2 responsive cells.
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