Insulin-stimulated cell growth in insulin receptor substrate-1–deficient ZR-75-1 cells is mediated by a phosphatidylinositol-3-kinase–independent pathway

Abstract

In many human breast cancers and cultured cell lines, insulin receptor expression is elevated, and insulin, via its own insulin receptor, can stimulate cell growth. It has recently been demonstrated that the enzyme phosphatidylinositol-3-kinase (PI3-K) mediates various aspects of insulin receptor signaling including cell growth. In order to understand the mechanisms for insulin-stimulated cell growth in human breast cancer, we measured insulin-stimulable PI3-K activity in a non-transformed breast epithelial cell line, MCF-10A, and in two malignantly transformed cell lines, ZR-75-1 and MDA-MB157. All three cell lines express comparable amounts of insulin receptors whose tyrosine autophosphorylation is increased by insulin, and in these cell lines insulin stimulates growth. In MDA-MB157 and MCF-10A cells, insulin stimulated PI3-K activity three- to fourfold. In ZR-75-1 cells, however, insulin did not stimulate PI3-K activity. In ZR-75-1 cells PI3-K protein was present, and its activity was stimulated by epidermal growth factor, suggesting that there might be a defect in insulin receptor signaling upstream of PI3-K and downstream of the insulin receptor. Next, we studied insulin receptor substrate-1 (IRS-1), a major endogenous substrate for the insulin receptor which, when tyrosine is phosphorylated by the insulin receptor, interacts with and activates PI3-K. In ZR-75-1 cells, there were reduced levels of protein for IRS-1. In these cells, both Shc tyrosine phosphorylation and mitogen-activated protein kinase (MAP-K) activity were increased by the insulin receptor (indicating that the p21ras pathway may account for insulin-stimulated cell growth in ZR-75-1 cells). The PI3-K inhibitor LY294002 (50 microM) reduced insulin-stimulated growth in MCF-10A and MDA-MB157 cell lines, whereas it did not modify insulin effect on ZR-75-1 cell growth. The MAP-K/Erk (MEK) inhibitor PD98059 (50 microM) consistently reduced insulin-dependent growth in all three cell lines. Taken together, these data suggest that in breast cancer cells insulin may stimulate cell growth via PI3-K-dependent or-independent pathways.

Analysis of signaling pathways related to cell proliferation stimulated by insulin analogs in human mammary epithelial cell lines

“…However, out of seven mammary epithelial cell lines tested only MCF7 and MCF10A cells showed a clear proliferative response to insulin treatment (Table 1). ZR75-1 cells do not express IRS-1 (Gliozzo et al 1998) and BT474 show only small IRS-1 levels (Mayer et al 2008) which may explain the little or lack of growth response to insulin. However, other breast cancer lines tested, though clearly expressing IR, IGF-IR and IRS-1 (Mayer et al 2008), did not show growth response to insulin, IGF-I and insulin analogues.…”

The cellular and molecular mechanisms by which insulin influences breast cancer risk and progression

“…The ZR-75-1 cell line does express PI3K protein, which is functional as demonstrated by its response to EGF, but in experiments performed by Gliozzo et al (1998), insulin-induced mitosis was not associated with a change in PI3K activity nor blocked by a PI3K inhibitor; it was, however, accompanied by an increase in Shc tyrosine phosphorylation and MAPK activity and suppressed in the presence of an inhibitor of MAPK.…”

“…Gliozzo et al (1998) reported that cultured MDA-MB-157 cells, which do not express ER (Sawatsri et al (2001), showed a strong mitogenic response to exogenous insulin. This stimulation was suppressed by a pharmacological inhibitor of MAPK kinase, which phosphorylates and activates MAPK (Fig.…”

Possible importance of Cannabis sativa L. in regulation of insulin and IL-6R/MAO-A in cancer cell progression and migration of breast cancer patients with diabetes

“…15 Many human breast cancers overexpress the insulin receptor, and overexpression of these receptors can result in a transformed phenotype in human mammary epithelial cells.…”

“…Recent findings indicate that fasting insulin levels predict disease-free survival and overall survival of women with breast cancer who are receiving adjuvant therapy. 14,15 In most human oestrogenreceptor-and progesterone-receptor-positive breast cancer cell lines, like MCF-7, insulin stimulates cell growth via its own receptor; however, insulin, at concentrations as high as 100 nM, has no effect on cell growth in triple negative breast cancer cells line like MDA-MB231, meriting further studies in this context. 16 In contrast, insulin enhances the metabolic capacity of cancer cells by dual regulation of the glycolytic enzyme pyruvate kinase M2.…”