Abstract 498 Endocrinology & Diabetes II Platform, Saturday, 5/1

Growth factors such as the insulin-like growth factors (IGFs), transforming growth factor-β (TGF-β) and related molecules have been demonstrated to be critical regulators of cell growth, proliferation, and apoptosis in many systems and may play a role in human fetal lung development and maturation. To study the role of the IGF axis in lung epithelial cells, we identified members of the IGF family and characterized effects of IGF-I, IGF binding protein-3 (IGFBP-3) and TGF-β on growth and differentiated function of the H441 human lung epithelial cell line of Clara cell origin. The effects of IGF-I, IGFBP-3 and TGF-β on surfactant protein A (SP-A) and IGFBP-3 expression and on cell growth are summarized in the table. Using reverse transcription-polymerase chain reaction (RT-PCR) technique and appropriate primers, we demonstrated gene expression of IGF-I, IGF-II, and IGFBP-2, 3-, -4 and -5 in H441 cells. We confirmed the presence of these peptides with appropriate immunoblots. Mean values as percentage of control; * p< 0.05 relative to baseline. ** not different from baseline, p< 0.05 relative to TGF-β alone or IgG.

Table 1 No caption available.
Full size table

Treatment with IGF-I for 3 days induced a 2-fold increase in cell growth (in both the presence and absence of serum) and in IGFBP-3 levels and markedly decreased SP-A production. IGFBP-3 inhibited cell growth with and without serum after 3 days exposure and decreased SP-A after 5 days exposure. Treatment with TGF-β resulted in a significant dose dependent increase in the level of IGFBP-3 expression with maximum 3-fold rise seen at 10 ng/ml. SP-A expression and cell growth were downregulated by TGF-β. To investigate the role IGFBP-3 may play in mediating TGF-β actions, we evaluated cell growth after 3 days and SP-A expression after 5 days exposure to TGF-β (10 ng/ml) and TGF-β + IGFBP-3 neutralizing antibodies. TGF-β effects on cell growth and SP-A expression were significantly blocked (p< 0.05) by neutralizing antibodies for IGFBP-3, but not by non-immune serum (IgG). These results show that TGF-β and IGF-related molecules influence H441 cell proliferation and phenotypic expression and that some effects of TGF-β may be mediated by IGFBP-3. Imbalance of the IGF axis or TGF-β could mediate alterations in epithelial cell growth and function during development or after injury.

Supported by NIH SCOR grant # 5P50HL56401