ABSTRACT
The role if insulin-like growth factor binding protein-2 (IGFBP-2) in mediating chemoresistance in breast cancer cells has been demonstrated, but the mechanism of action is unclear. This study aimed to further investigate the role of IGFBP-2 in the DNA damage response induced by etoposide in MCF-7, T47D (ER+ve), and MDA-MB-231 (ER-ve) breast cancer cell lines. In the presence or absence of etoposide, IGFBP-2 was silenced using siRNA in the ER-positive cell lines, or exogenous IGFBP-2 was added to the ER-negative MDA-MB-231 cells. Cell number and death were assessed using trypan blue dye exclusion assay, changes in abundance of proteins were monitored using Western blotting of whole cell lysates, and localization and abundance were determined using immunofluorescence and cell fractionation. Results from ER-positive cell lines demonstrated that upon exposure to etoposide, loss of IGFBP-2 enhanced cell death, and this was associated with a reduction in P-DNA-PKcs and an increase in γH2AX. Conversely, with ER-negative cells, the addition of IGFBP-2 in the presence of etoposide resulted in cell survival, an increase in P-DNA-PKcs, and a reduction in γH2AX. In summary, IGFBP-2 is a survival factor for breast cancer cells that is associated with enhancement of the DNA repair mechanism.
ABSTRACT
This minireview is a brief overview examining the roles of insulin-like growth factors (IGFs) and the PI3K/Akt pathway in two apparently unconnected diseases: Alzheimer's dementia and cancer. For both, increased age is a major risk factor, and, in accord with the global rise in average life expectancy, their prevalence is also increasing. Cancer, however, involves excessive cell proliferation and metastasis, whereas Alzheimer's disease (AD) involves cell death and tissue destruction. The apparent "inverse" nature of these disease states is examined here, but also some important commonalities in terms of the PI3K/Akt pathway, glucose utilization and cell deregulation/death. The focus here is on four key molecules associated with this pathway; notably, the insulin receptor substrate 1 (IRS-1), cellular tumor antigen p53 (p53), peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) and low-density lipoprotein receptor-related protein-1 (LRP1), all previously identified as potential therapeutic targets for both diseases. The insulin-resistant state, commonly reported in AD brain, results in neuronal glucose deprivation, due to a dampening down of the PI3K/Akt pathway, including overactivity of the mammalian target of rapamycin 1 (mTORC1) complex, hyperphosphorylation of p53 and neuronal death. This contrasts with cancer, where there is overstimulation of the PI3K/Akt pathway and the suppression of mTORC1 and p53, enabling abundant energy and unrestrained cell proliferation. Although these disease states appear to be diametrically opposed, the same key molecules are controlling pathology and, with differential targeting of therapeutics, may yet provide a beneficial outcome for both.
