The roles of IGF-I and IGFBP-3 in the regulation of proximal tubule, and renal cell carcinoma cell proliferation.
BACKGROUND
Insulin-like growth factor I (IGF-I), a potent proximal tubule cell (PTC) mitogen, has been implicated in the progression of many human cancers. Our previous work on human renal tissues has suggested that IGF-I and several of its binding proteins (IGFBP-3 and -6) are up-regulated in clear cell renal cell carcinoma (RCC).


METHODS
To further elucidate the role of IGF-I and IGFBPs in RCC growth, immunohistochemistry, thymidine incorporation, and Western analysis were performed in primary cultures of normal PTC (priPTC) and clear-cell RCC (priRCC), as well as in SN12K1 cells (a cell line derived from metastatic RCC).


RESULTS
By immunohistochemistry, IGFBP-3 and IGF-I were prominently expressed in SN12K1 cells, and weakly expressed in priPTC and priRCC. Incubation with 100 ng/mL IGF-I significantly augmented DNA synthesis by priPTC (mean +/- SD 120.7%+/- 19.7% of controls, P < 0.05), priRCC (238.7%+/- 279.9% of controls, P < 0.01), and SN12K1(120.0%+/- 22.9% of controls, P < 0.05). Neutralizing antibodies to IGF-I and IGF-I receptor significantly suppressed SN12K1 growth (81.9%+/- 13.5% of control, P < 0.01 and 87.4%+/- 16.2% of control, P < 0.05, respectively). Removal of endogenous IGFBP-3 by an anti-IGFBP-3 increased SN12K1 DNA synthesis (243.9%+/- 35.3% of control, P < 0.001), which was partially abrogated by coincubation with exogenous IGFBP-3 (135.97%+/- 5.9% of controls, P < 0.001). Using Western analysis, IGFBP-3 expression was enhanced in IGF-I-stimulated SN12K1 cells exposed to exogenous IGF-I. Coincubation with anti-IGFBP-3 further enhanced IGF-I-induced DNA synthesis.


CONCLUSIONS
RCC cells express IGF-I and IGFBP-3, and are responsive to exogenous IGF-I stimulation. Moreover, in SN12K1 cells (derived from metastatic RCC), autocrine IGF-I and IGFBP-3 actions, respectively, stimulated and inhibited growth. These results suggest that IGF-I and IGFBP-3 may be potential candidates for therapeutic manipulation in patients with advanced RCC.
Cheung
Catherine W
CW
Department of Medicine and Department of Surgery, University of Queensland, Brisbane, Queensland, Australia.
Vesey
David A
DA
Nicol
David L
DL
Johnson
David W
DW
D000906:Antibodies / Q000494:pharmacology; D002292:Carcinoma, Renal Cell / Q000378:metabolism / Q000473:pathology* / Q000556:secondary; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism* / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism* / Q000494:pharmacology; D007680:Kidney Neoplasms / Q000378:metabolism / Q000473:pathology* / Q000556:secondary; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000378:metabolism*
D000906:Antibodies; D018972:Insulin-Like Growth Factor Binding Protein 3; D007334:Insulin-Like Growth Factor I; D004247:DNA