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Leptin, Insulin-Like Growth Factor-1, and Insulin-Like Growth Factor-2 Are Mitogens in Apc^Min/+ but not Apc^+/+ Colonic Epithelial Cell Lines

¹ Cancer Prevention Fellowship Program, Division of Cancer Prevention; ² Laboratory of Biosystems and Cancer, National Cancer Institute, Bethesda, Maryland; and ³ Departments of Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan

Requests for reprints: Jenifer I. Fenton, Cancer Prevention Fellowship Program, National Cancer Institute, Division of Cancer Prevention, 6130 Executive Boulevard, MSC 7361, Bethesda, MD 20892-7361. Phone: 517-285-0296. E-mail: imigjeni{at}msu.edu

The obese state is associated with elevated circulating levels of insulin, insulin-like growth factors (IGF), and leptin. Research is contradictory regarding the role of these elevated growth factors in colon cancer risk. We hypothesized that colonic epithelial cells that were Apc deficient (Apc^Min/+) but not those expressing wild-type Apc (Apc^+/+) would experience a hyperproliferative and antiapoptotic phenotype when exposed to these growth factors. This hypothesis was addressed using two nontumorigenic murine colonic epithelial cell lines with distinct Apc genotypes: Apc^+/+ YAMC cells and Apc^Min/+ IMCE cells. Cells were treated for 48 hours with various concentrations of leptin (0.001-50 ng/mL), IGF-1 (0.1-200 ng/mL), or IGF-2 (0.1-600 ng/mL). In YAMC cells, leptin caused a significant decrease in cell proliferation (P < 0.01) compared with controls due to induction of caspase activity and apoptosis. In contrast, in the IMCE cells, leptin induced a 75% increase in cell proliferation compared with controls (P < 0.0001). IGF-1 and IGF-2 also induced 50% greater proliferation in the IMCE cells (P < 0.001) compared with controls. Cotreatment of IMCE cells with leptin and either IGF-1 or IGF-2 induced greater proliferation than either growth factor alone (P < 0.0001). IMCE cell proliferation caused by leptin only treatment was associated with activation of p42/44 mitogen-activated protein kinase (MAPK), p38 MAPK, and nuclear factor-B nuclear translocation but not with MAPK kinase or Janus-activated kinase/signal transducers and activators of transcription activation. These data provide the first evidence that leptin may interact with IGFs to promote survival and expansion of colonic epithelial cells that were Apc deficient (Apc^Min/+) but not those expressing wild-type Apc (Apc^+/+).

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