Enhanced insulin signaling via Shc in human breast cancer.
Insulin is a mild mitogen and has been shown to potentiate mitogenic influence of other growth factors. Because hyperinsulinemia and/or overexpression of insulin receptors have been linked to development, progression, and outcome of breast cancer, we attempted to evaluate the mechanism of these associations. We have compared the expression of insulin receptors and the magnitude of insulin signaling in breast tumors and adjacent normal mammary tissue samples obtained from 20 patients. We observed that insulin binding more than doubled in the tumors as compared with the normal tissue (P <.01 by paired t test). Insulin signaling to Shc, judged by the magnitude of its phosphorylation, was also significantly enhanced in the tumors. In contrast, the phosphorylation of the insulin-receptor substrate-1 (IRS-1), Akt, and mitogen-activated protein (MAP) kinase were identical in the tumorous and normal mammary tissues. Finally, tumors displayed significantly increased amounts of farnesylated p21 Ras and geranylgeranylated Rho-A (P <.01), consistent with Shc-dependent activation of farnesyl (FTase) and geranylgeranyl transferases (GGTase) in the tumor tissue. We conclude that the mechanism of the mitogenic influence of insulin in breast cancer may include increased expression of insulin receptors, preferential hyperphosphorylation of Shc, and increased amounts of prenylated p21 Ras and Rho-A in tumor tissue as compared with adjacent normal mammary tissue.
Finlayson
Christina A
CA
Department of Surgery, University of Colorado Health Sciences Center, Denver, USA.
Chappell
James
J
Leitner
J Wayne
JW
Goalstone
Marc L
ML
Garrity
Maureen
M
Nawaz
Samia
S
Ciaraldi
Theodore P
TP
Draznin
Boris
B
D000328:Adult; D000368:Aged; D001940:Breast / Q000378:metabolism / Q000601:surgery; D001943:Breast Neoplasms / Q000503:physiopathology* / Q000601:surgery; D005260:Female; D006801:Humans; D007328:Insulin / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D008875:Middle Aged; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D051058:Oncogene Protein v-akt; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011446:Prospective Studies; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D011972:Receptor, Insulin / Q000502:physiology; D011960:Receptors, Estrogen / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism; D015682:Retroviridae Proteins, Oncogenic / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism; D018909:src Homology Domains / Q000502:physiology*
C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D015682:Retroviridae Proteins, Oncogenic; D011972:Receptor, Insulin; D051058:Oncogene Protein v-akt; D020928:Mitogen-Activated Protein Kinases; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras); D020742:rhoA GTP-Binding Protein